Maintenance Energy Requirements of Double-Muscled Belgian Blue Beef Cows
Identifieur interne : 000026 ( Pmc/Corpus ); précédent : 000025; suivant : 000027Maintenance Energy Requirements of Double-Muscled Belgian Blue Beef Cows
Auteurs : Leo O. Fiems ; Johan L. De Boever ; José M. Vanacker ; Sam De CampeneereSource :
- Animals : an Open Access Journal from MDPI [ 2076-2615 ] ; 2015.
Abstract
Double-muscled Belgian Blue animals are extremely lean, characterized by a deviant muscle fiber type with more fast-glycolytic fibers, compared to non-double-muscled animals. This fiber type may result in lower maintenance energy requirements. On the other hand, lean meat animals mostly have a higher rate of protein turnover, which requires more energy for maintenance. Therefore, maintenance requirements of Belgian Blue cows were investigated based on a zero body weight gain. This technique showed that maintenance energy requirements of double-muscled Belgian Blue beef cows were close to the mean requirements of cows of other beef genotypes.
Sixty non-pregnant, non-lactating double-muscled Belgian Blue (DMBB) cows were used to estimate the energy required to maintain body weight (BW). They were fed one of three energy levels for 112 or 140 days, corresponding to approximately 100%, 80% or 70% of their total energy requirements. The relationship between daily energy intake and BW and daily BW change was developed using regression analysis. Maintenance energy requirements were estimated from the regression equation by setting BW gain to zero. Metabolizable and net energy for maintenance amounted to 0.569 ± 0.001 and 0.332 ± 0.001 MJ per kg BW0.75/d, respectively. Maintenance energy requirements were not dependent on energy level (
Url:
DOI: 10.3390/ani5010089
PubMed: 26479139
PubMed Central: 4494341
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Maintenance Energy Requirements of Double-Muscled Belgian Blue Beef Cows</title><author><name sortKey="Fiems, Leo O" sort="Fiems, Leo O" uniqKey="Fiems L" first="Leo O." last="Fiems">Leo O. Fiems</name></author><author><name sortKey="De Boever, Johan L" sort="De Boever, Johan L" uniqKey="De Boever J" first="Johan L." last="De Boever">Johan L. De Boever</name></author><author><name sortKey="Vanacker, Jose M" sort="Vanacker, Jose M" uniqKey="Vanacker J" first="José M." last="Vanacker">José M. Vanacker</name></author><author><name sortKey="De Campeneere, Sam" sort="De Campeneere, Sam" uniqKey="De Campeneere S" first="Sam" last="De Campeneere">Sam De Campeneere</name></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">26479139</idno><idno type="pmc">4494341</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4494341</idno><idno type="RBID">PMC:4494341</idno><idno type="doi">10.3390/ani5010089</idno><date when="2015">2015</date><idno type="wicri:Area/Pmc/Corpus">000026</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Maintenance Energy Requirements of Double-Muscled Belgian Blue Beef Cows</title><author><name sortKey="Fiems, Leo O" sort="Fiems, Leo O" uniqKey="Fiems L" first="Leo O." last="Fiems">Leo O. Fiems</name></author><author><name sortKey="De Boever, Johan L" sort="De Boever, Johan L" uniqKey="De Boever J" first="Johan L." last="De Boever">Johan L. De Boever</name></author><author><name sortKey="Vanacker, Jose M" sort="Vanacker, Jose M" uniqKey="Vanacker J" first="José M." last="Vanacker">José M. Vanacker</name></author><author><name sortKey="De Campeneere, Sam" sort="De Campeneere, Sam" uniqKey="De Campeneere S" first="Sam" last="De Campeneere">Sam De Campeneere</name></author></analytic><series><title level="j">Animals : an Open Access Journal from MDPI</title><idno type="eISSN">2076-2615</idno><imprint><date when="2015">2015</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><sec><title>Simple Summary</title><p>Double-muscled Belgian Blue animals are extremely lean, characterized by a deviant muscle fiber type with more fast-glycolytic fibers, compared to non-double-muscled animals. This fiber type may result in lower maintenance energy requirements. On the other hand, lean meat animals mostly have a higher rate of protein turnover, which requires more energy for maintenance. Therefore, maintenance requirements of Belgian Blue cows were investigated based on a zero body weight gain. This technique showed that maintenance energy requirements of double-muscled Belgian Blue beef cows were close to the mean requirements of cows of other beef genotypes.</p></sec><sec><title>Abstract</title><p>Sixty non-pregnant, non-lactating double-muscled Belgian Blue (DMBB) cows were used to estimate the energy required to maintain body weight (BW). They were fed one of three energy levels for 112 or 140 days, corresponding to approximately 100%, 80% or 70% of their total energy requirements. The relationship between daily energy intake and BW and daily BW change was developed using regression analysis. Maintenance energy requirements were estimated from the regression equation by setting BW gain to zero. Metabolizable and net energy for maintenance amounted to 0.569 ± 0.001 and 0.332 ± 0.001 MJ per kg BW<sup>0.75</sup>/d, respectively. Maintenance energy requirements were not dependent on energy level (<italic>p</italic> > 0.10). Parity affected maintenance energy requirements (<italic>p</italic> < 0.001), although the small numerical differences between parities may hardly be nutritionally relevant. Maintenance energy requirements of DMBB beef cows were close to the mean energy requirements of other beef genotypes reported in the literature.</p></sec></div></front><back><div1 type="bibliography"><listBibl><biblStruct><analytic><author><name sortKey="Godfray, H C J" uniqKey="Godfray H">H.C.J. Godfray</name></author><author><name sortKey="Beddington, J R" uniqKey="Beddington J">J.R. Beddington</name></author><author><name sortKey="Crute, I R" uniqKey="Crute I">I.R. Crute</name></author><author><name sortKey="Haddad, L" uniqKey="Haddad L">L. 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<front><journal-meta><journal-id journal-id-type="nlm-ta">Animals (Basel)</journal-id><journal-id journal-id-type="iso-abbrev">Animals (Basel)</journal-id><journal-id journal-id-type="publisher-id">animals</journal-id><journal-title-group><journal-title>Animals : an Open Access Journal from MDPI</journal-title></journal-title-group><issn pub-type="epub">2076-2615</issn><publisher><publisher-name>MDPI</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">26479139</article-id><article-id pub-id-type="pmc">4494341</article-id><article-id pub-id-type="doi">10.3390/ani5010089</article-id><article-id pub-id-type="publisher-id">animals-05-00089</article-id><article-categories><subj-group subj-group-type="heading"><subject>Article</subject></subj-group></article-categories><title-group><article-title>Maintenance Energy Requirements of Double-Muscled Belgian Blue Beef Cows</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Fiems</surname><given-names>Leo O.</given-names></name><xref rid="c1-animals-05-00089" ref-type="corresp">*</xref></contrib><contrib contrib-type="author"><name><surname>De Boever</surname><given-names>Johan L.</given-names></name></contrib><contrib contrib-type="author"><name><surname>Vanacker</surname><given-names>José M.</given-names></name></contrib><contrib contrib-type="author"><name><surname>De Campeneere</surname><given-names>Sam</given-names></name></contrib></contrib-group><contrib-group><contrib contrib-type="editor"><name><surname>Phillips</surname><given-names>Clive J. C.</given-names></name><role>Academic Editor</role></contrib></contrib-group><aff id="af1-animals-05-00089">ILVO—Animal Sciences Unit, Scheldeweg 68, B-9090 Melle, Belgium; E-Mails:<email>johan.deboever@ilvo.vlaanderen.be</email> (J.L.D.B.);<email>jose.vanacker@ilvo.vlaanderen.be</email> (J.M.V.);<email>sam.decampeneere@ilvo.vlaanderen.be</email> (S.D.C.)</aff><author-notes><corresp id="c1-animals-05-00089"><label>*</label>Author to whom correspondence should be addressed; E-Mail: <email>leo.fiems@ilvo.vlaanderen.be</email>; Tel.: +32-9-2722600; Fax: +32-9-2722601.</corresp></author-notes><pub-date pub-type="epub"><day>13</day><month>2</month><year>2015</year></pub-date><pub-date pub-type="collection"><month>3</month><year>2015</year></pub-date><volume>5</volume><issue>1</issue><fpage>89</fpage><lpage>100</lpage><history><date date-type="received"><day>03</day><month>12</month><year>2014</year></date><date date-type="accepted"><day>05</day><month>2</month><year>2015</year></date></history><permissions><copyright-statement>© 2015 by the authors; licensee MDPI, Basel, Switzerland.</copyright-statement><copyright-year>2015</copyright-year><license><license-p><pmc-comment>CREATIVE COMMONS</pmc-comment>This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (<ext-link ext-link-type="uri" xlink:href="http://creativecommons.org/licenses/by/4.0/">http://creativecommons.org/licenses/by/4.0/</ext-link>).</license-p></license></permissions><abstract><sec><title>Simple Summary</title><p>Double-muscled Belgian Blue animals are extremely lean, characterized by a deviant muscle fiber type with more fast-glycolytic fibers, compared to non-double-muscled animals. This fiber type may result in lower maintenance energy requirements. On the other hand, lean meat animals mostly have a higher rate of protein turnover, which requires more energy for maintenance. Therefore, maintenance requirements of Belgian Blue cows were investigated based on a zero body weight gain. This technique showed that maintenance energy requirements of double-muscled Belgian Blue beef cows were close to the mean requirements of cows of other beef genotypes.</p></sec><sec><title>Abstract</title><p>Sixty non-pregnant, non-lactating double-muscled Belgian Blue (DMBB) cows were used to estimate the energy required to maintain body weight (BW). They were fed one of three energy levels for 112 or 140 days, corresponding to approximately 100%, 80% or 70% of their total energy requirements. The relationship between daily energy intake and BW and daily BW change was developed using regression analysis. Maintenance energy requirements were estimated from the regression equation by setting BW gain to zero. Metabolizable and net energy for maintenance amounted to 0.569 ± 0.001 and 0.332 ± 0.001 MJ per kg BW<sup>0.75</sup>/d, respectively. Maintenance energy requirements were not dependent on energy level (<italic>p</italic> > 0.10). Parity affected maintenance energy requirements (<italic>p</italic> < 0.001), although the small numerical differences between parities may hardly be nutritionally relevant. Maintenance energy requirements of DMBB beef cows were close to the mean energy requirements of other beef genotypes reported in the literature.</p></sec></abstract><kwd-group><kwd>double-muscled</kwd><kwd>beef cows</kwd><kwd>energy</kwd><kwd>maintenance requirement</kwd></kwd-group></article-meta></front><body><sec><title>1. Introduction</title><p>Improving the efficiency of energy utilization is of paramount importance from several points of view. First, a higher efficiency means a reduction of feed costs for livestock production. This may result in an increased income for the farmer. Furthermore, a higher efficiency also means that nutrients are better utilized by the animal, resulting in a lower excretion into the environment and lower costs for manure management. Feeding an increasing world population up to 9 billion people [<xref rid="B1-animals-05-00089" ref-type="bibr">1</xref>], or more, also means that the competition between feed and food will increase in the future. Nowadays, a substantial part of livestock is fed on grain and other plants that could be used as human food. So, an efficient animal nutrition is a key factor to reduce the environmental load from animal production and the competition with human food. Furthermore, land use for feed production may also interact with land use for bio-fuel production.</p><p>Double-muscled Belgian Blue (DMBB) animals originated from the dual-purpose Belgian Blue cattle breed. Due to an intensive selection, there was a transition from halfway the fifties to the end of the sixties of the previous century to animals with a larger muscular development [<xref rid="B2-animals-05-00089" ref-type="bibr">2</xref>]. In 1973 the Belgian Blue breed was divided into a double-muscled strain and a dual-purpose strain, each with a separate herd book. The DMBB breed is the most important breed for beef production in Belgium, and it is often used for crossbreeding abroad [<xref rid="B3-animals-05-00089" ref-type="bibr">3</xref>,<xref rid="B4-animals-05-00089" ref-type="bibr">4</xref>], because of its excellent carcass quality [<xref rid="B2-animals-05-00089" ref-type="bibr">2</xref>]. Derno <italic>et al.</italic> [<xref rid="B5-animals-05-00089" ref-type="bibr">5</xref>] reported a variation in energy requirements for maintenance of 10% to 30% because of genetic differences, so that it is not excluded that DMBB and non-DMBB animals have divergent requirements. Hanset <italic>et al.</italic> [<xref rid="B6-animals-05-00089" ref-type="bibr">6</xref>] reported 8% lower maintenance energy requirements for DMBB bulls compared to non-DMBB bulls. However, Vermorel <italic>et al.</italic> [<xref rid="B7-animals-05-00089" ref-type="bibr">7</xref>] found no significant difference in energy expenditure between 10-month old DMBB and non-DMBB bulls. Similar energy requirements for maintenance of double-muscled and non-double-muscled beef steers were obtained when they were scaled to adult and current protein masses [<xref rid="B8-animals-05-00089" ref-type="bibr">8</xref>]. Initially, most nutrient requirements of this young DMBB breed were unknown. In the mean time, energy and protein requirements for growing-finishing beef bulls have been derived [<xref rid="B9-animals-05-00089" ref-type="bibr">9</xref>], but maintenance requirements of DMBB cows are lacking.</p><p>The aim of the present experiments was to investigate the energy requirements for maintenance of DMBB beef cows. Maintenance energy requirements can be defined as the daily energy intake that will balance heat production, resulting in no loss or gain of body energy reserves [<xref rid="B10-animals-05-00089" ref-type="bibr">10</xref>].</p></sec><sec><title>2. Materials and Methods</title><sec><title>2.1. Animals and Management</title><p>Two experiments were conducted, starting in early autumn, and involving 20 and 40 DMBB cows, respectively. Initial age, body weight (BW) and body condition score (BCS), determined as described by Agabriel <italic>et al.</italic> [<xref rid="B11-animals-05-00089" ref-type="bibr">11</xref>], amounted to (mean ± SD) 1319 ± 511 and 1356 ± 512 days, 621 ± 81 and 636 ± 102 kg, and 1.68 ± 0.44 and 2.24 ± 0.50, respectively. Initial age and BW did not differ between experiments (<italic>p</italic> > 0.10), whereas BCS was lower in Exp. 1 than in Exp. 2 (1.7 <italic>vs.</italic> 2.2; <italic>p</italic> < 0.001). Three energy levels (EL) were studied during a restriction period of 112 (Exp. 1) or 140 (Exp. 2) days, respectively: 100% (EL100; Exp. 1 and 2), 70% (EL70; Exp. 1) or 80% (EL80; Exp. 2) of total energy requirements, according the energy evaluation system described by Van Es [<xref rid="B12-animals-05-00089" ref-type="bibr">12</xref>]. Cows were grazing on pasture in similar conditions before the start of both experiments, with grass as the sole component of the diet. They were adapted to confinement and diet during the week prior to the start of the experiments. Within each experiment cows were divided into similar treatment groups based on initial BW, age, BCS and parity, and assigned to one of the energy levels. Protein requirements [<xref rid="B13-animals-05-00089" ref-type="bibr">13</xref>] were always fulfilled. Diets consisted of an appropriate amount of maize silage, individually calculated per animal to realize the programmed EL, supplemented with 0.5 kg per day of a vitamin-mineral premix and urea. Urea was individually fed and top-dressed over the maize silage. The daily amount of urea was calculated so that dietary rumen degradable protein balance (OEB; [<xref rid="B13-animals-05-00089" ref-type="bibr">13</xref>]) was close to 0 g/day. The premix was offered once daily at 1000 h, whereas maize silage and urea were administered in two equal meals at 1000 and 1600 h. Drinking water was always freely available in both experiments.</p><p>Cows were confined in uninsulated tie stalls and bedded on sawdust. Monthly outdoor temperature from September to January averaged 14.9, 11.1, 6.8, 3.9 and 3.3 °C, respectively. Cows were weighed in the morning before feeding on two subsequent days at the start and the end of the experiments. BCS was also determined at the start and the end of the experiments. Rectal temperature (RT) was manually measured with a digital thermometer (MT1831, Microlife AG, Widnau, Switzerland) for cows involved in Exp. 2 (EL100 and EL80) at 0800 (T1), 1100 (T2), 1400 (T3) and 1700 h (T4) on 3 days: during the adaptation period on day 2 prior to the start of the experiment (D1), and on days 69 (D2) and 139 (D3). Animals involved in Exp. 1 were part of a larger study [<xref rid="B14-animals-05-00089" ref-type="bibr">14</xref>].</p><p>This research was compliant with regulations of the Ethical Committee of the Institute for Agricultural and Fisheries Research (ILVO; approval number 110/2009).</p></sec><sec sec-type="methods"><title>2.2. Analytical Procedures</title><p>Feeds were sampled every four weeks and chemical composition was determined on a pooled sample of each feed. Moisture was determined by drying at 103 °C [<xref rid="B15-animals-05-00089" ref-type="bibr">15</xref>]. Crude ash was obtained by incineration at 550 °C [<xref rid="B16-animals-05-00089" ref-type="bibr">16</xref>]. Crude protein (N × 6.25) was determined by the Kjeldahl method [<xref rid="B17-animals-05-00089" ref-type="bibr">17</xref>]. Crude fat was extracted with petroleum ether [<xref rid="B18-animals-05-00089" ref-type="bibr">18</xref>]. Neutral detergent fiber (NDF) was analyzed with an Ankom 200 Fiber Analyzer (Ankom Technology, Macedon, NY, USA), using α-amylase and sodium sulphite and expressed on ash-free base [<xref rid="B19-animals-05-00089" ref-type="bibr">19</xref>]. <italic>In vitro</italic> organic matter digestibility was determined using cellulase, to estimate metabolizable energy (ME) and net energy (NE) values as described by De Boever <italic>et al.</italic> [<xref rid="B20-animals-05-00089" ref-type="bibr">20</xref>]. Mean composition, <italic>in vitro</italic> organic matter digestibility and nutritive values of the feeds are shown in <xref ref-type="table" rid="animals-05-00089-t001">Table 1</xref>.</p><table-wrap id="animals-05-00089-t001" position="float"><object-id pub-id-type="pii">animals-05-00089-t001_Table 1</object-id><label>Table 1</label><caption><p>Chemical composition and nutritive value of the feeds.</p></caption><table frame="hsides" rules="groups"><thead><tr><th rowspan="2" align="center" valign="middle" colspan="1"></th><th style="border-bottom:solid thin" colspan="2" align="center" valign="middle" rowspan="1">Premix</th><th style="border-bottom:solid thin" colspan="2" align="center" valign="middle" rowspan="1">Maize Silage</th></tr><tr><th align="center" valign="middle" rowspan="1" colspan="1">Exp. 1</th><th align="center" valign="middle" rowspan="1" colspan="1">Exp. 2</th><th align="center" valign="middle" rowspan="1" colspan="1">Exp. 1</th><th align="center" valign="middle" rowspan="1" colspan="1">Exp. 2</th></tr></thead><tbody><tr style="border-bottom:solid thin"><td align="center" valign="top" rowspan="1" colspan="1">Dry matter (DM; g/kg)</td><td align="center" valign="top" rowspan="1" colspan="1">882</td><td align="center" valign="top" rowspan="1" colspan="1">891</td><td align="center" valign="top" rowspan="1" colspan="1">343</td><td align="center" valign="top" rowspan="1" colspan="1">351</td></tr><tr><td style="border-bottom:solid thin" colspan="5" align="center" valign="top" rowspan="1">Composition of DM (g/kg)</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crude protein</td><td align="center" valign="top" rowspan="1" colspan="1">100</td><td align="center" valign="top" rowspan="1" colspan="1">102</td><td align="center" valign="top" rowspan="1" colspan="1">68</td><td align="center" valign="top" rowspan="1" colspan="1">72</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crude fat</td><td align="center" valign="top" rowspan="1" colspan="1">16</td><td align="center" valign="top" rowspan="1" colspan="1">21</td><td align="center" valign="top" rowspan="1" colspan="1">33</td><td align="center" valign="top" rowspan="1" colspan="1">30</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crude ash</td><td align="center" valign="top" rowspan="1" colspan="1">394</td><td align="center" valign="top" rowspan="1" colspan="1">383</td><td align="center" valign="top" rowspan="1" colspan="1">39</td><td align="center" valign="top" rowspan="1" colspan="1">42</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">NDF</td><td align="center" valign="top" rowspan="1" colspan="1">189</td><td align="center" valign="top" rowspan="1" colspan="1">157</td><td align="center" valign="top" rowspan="1" colspan="1">387</td><td align="center" valign="top" rowspan="1" colspan="1">394</td></tr><tr style="border-bottom:solid thin"><td align="center" valign="top" rowspan="1" colspan="1"><italic>In vitro</italic> organic matter digestibility (%)</td><td align="center" valign="top" rowspan="1" colspan="1">84.4</td><td align="center" valign="top" rowspan="1" colspan="1">85.1</td><td align="center" valign="top" rowspan="1" colspan="1">73.1</td><td align="center" valign="top" rowspan="1" colspan="1">69.7</td></tr><tr><td style="border-bottom:solid thin" colspan="5" align="center" valign="top" rowspan="1">Nutritive value per kg DM</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Metabolizable energy <sup>1</sup> (MJ)</td><td align="center" valign="top" rowspan="1" colspan="1">4.83</td><td align="center" valign="top" rowspan="1" colspan="1">5.27</td><td align="center" valign="top" rowspan="1" colspan="1">11.20</td><td align="center" valign="top" rowspan="1" colspan="1">10.85</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Net energy lactation <sup>1</sup> (MJ)</td><td align="center" valign="top" rowspan="1" colspan="1">2.51</td><td align="center" valign="top" rowspan="1" colspan="1">2.82</td><td align="center" valign="top" rowspan="1" colspan="1">6.50</td><td align="center" valign="top" rowspan="1" colspan="1">6.23</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">DVE <sup>1</sup> (g)</td><td align="center" valign="top" rowspan="1" colspan="1">30</td><td align="center" valign="top" rowspan="1" colspan="1">30</td><td align="center" valign="top" rowspan="1" colspan="1">47</td><td align="center" valign="top" rowspan="1" colspan="1">45</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">OEB <sup>1</sup> (g)</td><td align="center" valign="top" rowspan="1" colspan="1">18</td><td align="center" valign="top" rowspan="1" colspan="1">20</td><td align="center" valign="top" rowspan="1" colspan="1">−35</td><td align="center" valign="top" rowspan="1" colspan="1">−30</td></tr></tbody></table><table-wrap-foot><fn><p><sup>1</sup> Metabolizable and net energy were estimated as described by De Boever <italic>et al.</italic> [<xref rid="B20-animals-05-00089" ref-type="bibr">20</xref>]; DVE: truly absorbed protein in the small intestine; OEB: rumen degradable protein balance as described by Tamminga <italic>et al.</italic> [<xref rid="B13-animals-05-00089" ref-type="bibr">13</xref>].</p></fn></table-wrap-foot></table-wrap></sec><sec><title>2.3. Statistical Analysis</title><p>Animal performances were analyzed using EL and experiment as fixed effects with initial age of the cows as covariate. Rectal temperature (Exp. 2, EL100 and EL80) was analyzed using a design with EL (<italic>n</italic> = 2), day of RT measurement (<italic>n</italic> = 3) and time of the day of RT measurement (<italic>n</italic> = 4) as fixed effects, with day and time of RT measurement as repeated measures.</p><p>Metabolizable energy (ME) and NE intakes without correction for initial age of cows were regressed against BW, BW change and initial BCS. Maintenance requirements for ME (MEm) and NE (NEm) were estimated from the regression equation by setting BW gain to zero, using regression analysis. Effect of EL and parity on MEm and NEm requirements were analyzed using an analysis of variance. Absolute MEm and NEm requirements of DMBB cows were compared with energy requirements of beef cows reported in the literature, using an analysis of variance. Furthermore, absolute MEm and NEm requirements from literature data were expressed as a percentage of the mean MEm and NEm requirements of DMBB cows, respectively. Pooled literature data and data from DMBB cows were compared, using an analysis of variance. Statistical analyses were performed using Statsoft Statistica software [<xref rid="B21-animals-05-00089" ref-type="bibr">21</xref>].</p><p>Results are presented as least squares means. Treatment effects are presented as significant when <italic>p</italic> ≤ 0.05, and trends are identified at 0.05 < <italic>p</italic> ≤ 0.10.</p></sec></sec><sec><title>3. Results and Discussion</title><sec><title>3.1. Effect of Energy Level on Animal Performance</title><p>Animal performance was not affected by experiment (<italic>p</italic> > 0.10). Therefore, only the effect of EL on BW and BCS, and energy intake is shown in <xref ref-type="table" rid="animals-05-00089-t002">Table 2</xref>. Increasing the level of feed restriction resulted in a decrease of BW and BCS (<italic>p</italic> < 0.001) and an increased daily BW loss (<italic>p</italic> < 0.001). By design, there was a decrease in daily intake of DM, ME and NE (<italic>p</italic> < 0.001), resulting in a lower daily intake of DM, ME and NE per kg BW<sup>0.75</sup> (<italic>p</italic> < 0.001).</p><table-wrap id="animals-05-00089-t002" position="float"><object-id pub-id-type="pii">animals-05-00089-t002_Table 2</object-id><label>Table 2</label><caption><p>Effect of energy level on body weight and condition, energy intake and body temperature.</p></caption><table frame="hsides" rules="groups"><thead><tr><th rowspan="2" align="center" valign="middle" colspan="1">Item <sup>1</sup></th><th style="border-bottom:solid thin" colspan="3" align="center" valign="middle" rowspan="1">Energy Level (%)</th><th rowspan="2" align="center" valign="middle" colspan="1">SEM <sup>2</sup></th><th rowspan="2" align="center" valign="middle" colspan="1"><italic>p</italic>-Value</th></tr><tr><th align="center" valign="middle" rowspan="1" colspan="1">100</th><th align="center" valign="middle" rowspan="1" colspan="1">80</th><th align="center" valign="middle" rowspan="1" colspan="1">70</th></tr></thead><tbody><tr><td align="center" valign="top" rowspan="1" colspan="1">Number of cows</td><td align="center" valign="top" rowspan="1" colspan="1">30</td><td align="center" valign="top" rowspan="1" colspan="1">20</td><td align="center" valign="top" rowspan="1" colspan="1">10</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="6" align="center" valign="top" rowspan="1">Body weight (kg)</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Initial weight</td><td align="center" valign="top" rowspan="1" colspan="1">631</td><td align="center" valign="top" rowspan="1" colspan="1">631</td><td align="center" valign="top" rowspan="1" colspan="1">624</td><td align="center" valign="top" rowspan="1" colspan="1">6.5</td><td align="center" valign="top" rowspan="1" colspan="1">0.954</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Final weight</td><td align="center" valign="top" rowspan="1" colspan="1">622 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">586 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">556 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">6.2</td><td align="center" valign="top" rowspan="1" colspan="1">0.002</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Daily gain</td><td align="center" valign="top" rowspan="1" colspan="1">−0.07 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">−0.33 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">−0.60 <sup>c</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.015</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="6" align="center" valign="top" rowspan="1">Body condition score</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Initial BCS</td><td align="center" valign="top" rowspan="1" colspan="1">1.9</td><td align="center" valign="top" rowspan="1" colspan="1">1.9</td><td align="center" valign="top" rowspan="1" colspan="1">2.1</td><td align="center" valign="top" rowspan="1" colspan="1">0.05</td><td align="center" valign="top" rowspan="1" colspan="1">0.835</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Final BCS</td><td align="center" valign="top" rowspan="1" colspan="1">2.0 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">1.6 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">1.2 <sup>c</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.04</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="6" align="center" valign="top" rowspan="1">Dry matter intake</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">kg/day</td><td align="center" valign="top" rowspan="1" colspan="1">6.8 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">5.4 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">4.8 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.10</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">g/BW<sup>0.75</sup>/day</td><td align="center" valign="top" rowspan="1" colspan="1">54.5 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">44.5 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">40.4 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.85</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="6" align="center" valign="top" rowspan="1">ME intake</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">MJ/day</td><td align="center" valign="top" rowspan="1" colspan="1">70.6 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">52.9 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">49.2 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.52</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">MJ/BW<sup>0.75</sup>/day</td><td align="center" valign="top" rowspan="1" colspan="1">0.55 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.45 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.40 <sup>c</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.003</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="6" align="center" valign="top" rowspan="1">NE intake</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">MJ/day</td><td align="center" valign="top" rowspan="1" colspan="1">40.9 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">32.5 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">28.4 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.55</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">MJ/BW<sup>0.75</sup>/day</td><td align="center" valign="top" rowspan="1" colspan="1">0.33 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.27 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.24 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.005</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Body temperature (°C)</td><td align="center" valign="top" rowspan="1" colspan="1">38.3</td><td align="center" valign="top" rowspan="1" colspan="1">38.3</td><td align="center" valign="top" rowspan="1" colspan="1">10</td><td align="center" valign="top" rowspan="1" colspan="1">0.10</td><td align="center" valign="top" rowspan="1" colspan="1">0.938</td></tr></tbody></table><table-wrap-foot><fn><p><sup>1</sup> BCS: body condition score; ME: metabolizable energy; NE: net energy; <sup>2</sup> SEM: standard error of the mean. <sup>a</sup>, <sup>b</sup>, <sup>c</sup> values within rows with different superscripts differ significantly (<italic>p</italic> < 0.05).</p></fn></table-wrap-foot></table-wrap><p>It has been assumed that beef cows can efficiently mobilize and restore body reserve tissues, when feed restriction is followed by an abundant feed supply [<xref rid="B22-animals-05-00089" ref-type="bibr">22</xref>,<xref rid="B23-animals-05-00089" ref-type="bibr">23</xref>]. The effect of an energy restriction on performance of DMBB cows has been reported previously [<xref rid="B24-animals-05-00089" ref-type="bibr">24</xref>].</p><p>The metabolism of nutrients generates heat, which contributes to temperature homeostasis. Body temperature of DMBB cows was similar for EL100 and EL80 (<italic>p</italic> > 0.10). However, RT was significantly affected by day (<italic>p</italic> = 0.012) and time of RT measurement (<italic>p</italic> < 0.001), with an interaction between day and time of RT measurement (<italic>p</italic> < 0.001). Temperatures at the start (D1, 38.5 °C) and halfway through the experiment (D2, 38.4 °C) were not different, but RT at D1 was higher compared to RT at D3 (38.1 °C, <italic>p</italic> = 0.010), whereas RT at D2 tended to be higher compared to RT at D3 (<italic>p</italic> = 0.091). Rectal temperatures at T1 (38.1 °C) were lower (<italic>p</italic> < 0.001) than RT measured at T2 (38.4 °C), T3 (38.5 °C) and T4 (38.5 °C), whereas RT at T2, T3 and T4 did not differ (<italic>p</italic> > 0. 10). Mader <italic>et al.</italic> [<xref rid="B25-animals-05-00089" ref-type="bibr">25</xref>] fed Hereford steers <italic>ad lib</italic> or at 90% of <italic>ad lib</italic> intake and found a lower RT (<italic>p</italic> < 0.05) at 0800 and 1600 h and for the entire 4-d test period for steers fed at the lower intake level. Feed deprivation for eight days in sheep and goats also resulted in a lower RT compared to the lowest RT recorded during the baseline period [<xref rid="B26-animals-05-00089" ref-type="bibr">26</xref>]. All in all, RT of DMBB cows was within the normal range for beef cattle [<xref rid="B27-animals-05-00089" ref-type="bibr">27</xref>]. The daily variation in RT in the current experiment is in accordance with the circadian rhythm [<xref rid="B28-animals-05-00089" ref-type="bibr">28</xref>]. The significant decrease of RT towards the end of the experiment may be an effective strategy to save energy, when feed availability is restricted (EL100 as well as EL80).</p></sec><sec><title>3.2. Energy Requirements for Maintenance</title><p>BCS did not exert a significant contribution to energy intake in this study. Therefore, BCS was omitted from the statistical analysis. Maintenance requirements of DMBB cows were neither affected by BCS. This is not in accordance with results of Birnie <italic>et al.</italic> [<xref rid="B29-animals-05-00089" ref-type="bibr">29</xref>], who found that fasting heat production was significantly higher for dairy cows with a low BCS. Furthermore, the higher fasting heat production of thin cows [<xref rid="B29-animals-05-00089" ref-type="bibr">29</xref>] agrees with the higher maintenance requirements of thinner cows [<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>]. DMBB cows are characterized by their leanness, while fat cows had a BCS, which was more than 3 times the BCS of the thin cows in the experiment of Birnie <italic>et al.</italic> [<xref rid="B29-animals-05-00089" ref-type="bibr">29</xref>].</p><p>Regressing daily intake of ME and NE (MJ/kg BW<sup>0.75</sup>/d) on BW and daily BW change (kg/d) resulted in a significant relationship:
<disp-formula>ME = 19.227 + 0.0828 BW + 38.911 BW change; <italic>R</italic><sup>2</sup> = 0.764, <italic>p</italic> < 0.001; RSD = 5.45 <break></break>NE = 10.573 + 0.0493 BW + 21.292 BW change; <italic>R</italic><sup>2</sup> = 0.579, <italic>p</italic> < 0.001; RSD = 4.72
</disp-formula></p><p>Setting BW change to zero resulted in MEm and NEm (±SE) of 0.569 ± 0.001 and 0.332 ± 0.001 MJ per kg BW<sup>0.75</sup>, respectively. Maintenance requirements per kg BW<sup>0.75</sup> of 0.332 MJ for DMBB cows in the current experiment were 35% lower than 0.507 MJ reported for DMBB bulls [<xref rid="B9-animals-05-00089" ref-type="bibr">9</xref>]. Cows fed EL100, EL80 or EL70 showed similar MEm (<italic>p</italic> = 0. 784) and NEm (<italic>p</italic> = 0.369) requirements (<xref ref-type="table" rid="animals-05-00089-t003">Table 3</xref>), indicating that maintenance requirements were not affected by plane of nutrition in the present study. However, Birkelo <italic>et al.</italic> [<xref rid="B31-animals-05-00089" ref-type="bibr">31</xref>] found that an increased plane of nutrition in Hereford steers increased fasting heat production and maintenance energy requirements. Fox <italic>et al.</italic> [<xref rid="B32-animals-05-00089" ref-type="bibr">32</xref>] reported that maintenance requirements may also be affected by previous plane of nutrition. Agnew and Yan [<xref rid="B33-animals-05-00089" ref-type="bibr">33</xref>] concluded that it seems unlikely that fasting greatly influences heat production. These authors mentioned that fasting after a long period of restricted nutrition can induce metabolic disorders, such as hypoglycaemia. However, similar blood glucose concentrations at the end of Exp. 1 have been reported previously [<xref rid="B14-animals-05-00089" ref-type="bibr">14</xref>].</p><p>Maintenance ME requirements were slightly but significantly higher for primiparous cows compared to older cows (<italic>p</italic> < 0.001), whereas NEm was slightly but significantly lower for second-calf cows compared to other parities (<italic>p</italic> < 0.001). Although the results were statistically significant, due to a small variance, the difference is small (<1%) and may hardly be nutritionally relevant. The effect of parity on maintenance energy requirements of beef cows is scarcely reported in the literature. However, this result is in line with an increasing body fat content in DMBB cows with advancing maturity [<xref rid="B34-animals-05-00089" ref-type="bibr">34</xref>] and the fact that maintenance energy requirements are lower for adipose tissue than for lean tissue [<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>].</p><table-wrap id="animals-05-00089-t003" position="float"><object-id pub-id-type="pii">animals-05-00089-t003_Table 3</object-id><label>Table 3</label><caption><p>Effect of energy level and parity on energy requirement for maintenance (MJ/kg BW<sup>0.75</sup>).</p></caption><table frame="hsides" rules="groups"><thead><tr><th align="center" valign="middle" rowspan="1" colspan="1"></th><th align="center" valign="middle" rowspan="1" colspan="1">Metabolizable Energy</th><th align="center" valign="middle" rowspan="1" colspan="1">Net Energy</th></tr></thead><tbody><tr><td style="border-bottom:solid thin" colspan="3" align="center" valign="top" rowspan="1">Energy level (%)</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">100</td><td align="center" valign="top" rowspan="1" colspan="1">0.569</td><td align="center" valign="top" rowspan="1" colspan="1">0.332</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">80</td><td align="center" valign="top" rowspan="1" colspan="1">0.569</td><td align="center" valign="top" rowspan="1" colspan="1">0.332</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">70</td><td align="center" valign="top" rowspan="1" colspan="1">0.569</td><td align="center" valign="top" rowspan="1" colspan="1">0.331</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1"><italic>p</italic>-value</td><td align="center" valign="top" rowspan="1" colspan="1">0.784</td><td align="center" valign="top" rowspan="1" colspan="1">0.369</td></tr><tr><td style="border-bottom:solid thin; border-top:solid thin" colspan="3" align="center" valign="top" rowspan="1">Parity</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">1</td><td align="center" valign="top" rowspan="1" colspan="1">0.571 <sup>a</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.332 <sup>a</sup></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">2</td><td align="center" valign="top" rowspan="1" colspan="1">0.568 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.331 <sup>b</sup></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">3 and more</td><td align="center" valign="top" rowspan="1" colspan="1">0.568 <sup>b</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.332 <sup>a</sup></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1"><italic>p</italic>-value</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td><td align="center" valign="top" rowspan="1" colspan="1"><0.001</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">All data</td><td align="center" valign="top" rowspan="1" colspan="1">0.569</td><td align="center" valign="top" rowspan="1" colspan="1">0.332</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">SEM <sup>1</sup></td><td align="center" valign="top" rowspan="1" colspan="1">0.0002</td><td align="center" valign="top" rowspan="1" colspan="1">0.0001</td></tr></tbody></table><table-wrap-foot><fn><p><sup>1</sup> SEM: standard error of the mean; <sup>a</sup>, <sup>b</sup> values within columns with different superscripts differ significantly (<italic>p</italic> < 0.05).</p></fn></table-wrap-foot></table-wrap><table-wrap id="animals-05-00089-t004" position="float"><object-id pub-id-type="pii">animals-05-00089-t004_Table 4</object-id><label>Table 4</label><caption><p>Comparison of metabolizable (MEm) or net energy (NEm) requirements (MJ/kg BW<sup>0.75</sup>) for maintenance of beef cows of different genotypes.</p></caption><table frame="hsides" rules="groups"><thead><tr><th align="center" valign="middle" rowspan="1" colspan="1">Genotype</th><th align="center" valign="middle" rowspan="1" colspan="1">MEm</th><th align="center" valign="middle" rowspan="1" colspan="1">Reference</th><th align="center" valign="middle" rowspan="1" colspan="1">Genotype</th><th align="center" valign="middle" rowspan="1" colspan="1">NEm</th><th align="center" valign="middle" rowspan="1" colspan="1">Reference</th></tr></thead><tbody><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus-Hereford crossbreds</td><td align="center" valign="top" rowspan="1" colspan="1">0.534</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1">Angus</td><td align="center" valign="top" rowspan="1" colspan="1">0.304</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B42-animals-05-00089" ref-type="bibr">42</xref>]</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus-Hereford crossbreds</td><td align="center" valign="top" rowspan="1" colspan="1">0.544</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B35-animals-05-00089" ref-type="bibr">35</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1">Not specified</td><td align="center" valign="top" rowspan="1" colspan="1">0.322</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B43-animals-05-00089" ref-type="bibr">43</xref>]</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Charolais crossbreds</td><td align="center" valign="top" rowspan="1" colspan="1">0.565</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B35-animals-05-00089" ref-type="bibr">35</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1">Angus, Exp. 1</td><td align="center" valign="top" rowspan="1" colspan="1">0.373</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B44-animals-05-00089" ref-type="bibr">44</xref>]</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Simmental crossbreds</td><td align="center" valign="top" rowspan="1" colspan="1">0.699</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B35-animals-05-00089" ref-type="bibr">35</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1">Angus, Exp. 2</td><td align="center" valign="top" rowspan="1" colspan="1">0.389</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B44-animals-05-00089" ref-type="bibr">44</xref>]</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus</td><td align="center" valign="top" rowspan="1" colspan="1">0.418</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B36-animals-05-00089" ref-type="bibr">36</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1">Angus, Exp. 3</td><td align="center" valign="top" rowspan="1" colspan="1">0.378</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B44-animals-05-00089" ref-type="bibr">44</xref>]</td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Hereford</td><td align="center" valign="top" rowspan="1" colspan="1">0.452</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B36-animals-05-00089" ref-type="bibr">36</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus</td><td align="center" valign="top" rowspan="1" colspan="1">0.656</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B37-animals-05-00089" ref-type="bibr">37</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crossbreds, low milk yield</td><td align="center" valign="top" rowspan="1" colspan="1">0.556</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B38-animals-05-00089" ref-type="bibr">38</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crossbreds, moderate milk yield</td><td align="center" valign="top" rowspan="1" colspan="1">0.636</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B38-animals-05-00089" ref-type="bibr">38</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Crossbreds, low milk yield</td><td align="center" valign="top" rowspan="1" colspan="1">0.615</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B38-animals-05-00089" ref-type="bibr">38</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus</td><td align="center" valign="top" rowspan="1" colspan="1">0.433</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B39-animals-05-00089" ref-type="bibr">39</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Simmental</td><td align="center" valign="top" rowspan="1" colspan="1">0.517</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B39-animals-05-00089" ref-type="bibr">39</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Charolais</td><td align="center" valign="top" rowspan="1" colspan="1">0.490</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B40-animals-05-00089" ref-type="bibr">40</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Angus-Hereford crossbreds</td><td align="center" valign="top" rowspan="1" colspan="1">0.503</td><td align="center" valign="top" rowspan="1" colspan="1">[<xref rid="B41-animals-05-00089" ref-type="bibr">41</xref>]</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">Mean (<italic>n</italic> = 14)</td><td align="center" valign="top" rowspan="1" colspan="1">0.544</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1">Mean (<italic>n</italic> = 5)</td><td align="center" valign="top" rowspan="1" colspan="1">0.353</td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">SEM</td><td align="center" valign="top" rowspan="1" colspan="1">0.023</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1">SEM</td><td align="center" valign="top" rowspan="1" colspan="1">0.017</td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr><tr><td align="center" valign="top" rowspan="1" colspan="1">DMBB (current experiment)</td><td align="center" valign="top" rowspan="1" colspan="1">0.569</td><td align="center" valign="top" rowspan="1" colspan="1"></td><td align="center" valign="top" rowspan="1" colspan="1">DMBB</td><td align="center" valign="top" rowspan="1" colspan="1">0.332</td><td align="center" valign="top" rowspan="1" colspan="1"></td></tr></tbody></table></table-wrap><p>The present study revealed that MEm and NEm requirements of DMBB cows were within the range of maintenance requirements reported in the literature for beef cows with other genotypes (<xref ref-type="table" rid="animals-05-00089-t004">Table 4</xref>). Maintenance requirements reported by Thompson <italic>et al.</italic> [<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>], Ferrell and Jenkins [<xref rid="B35-animals-05-00089" ref-type="bibr">35</xref>], Montaño-Bermudez <italic>et al.</italic> [<xref rid="B38-animals-05-00089" ref-type="bibr">38</xref>], Laurenz <italic>et al.</italic> [<xref rid="B39-animals-05-00089" ref-type="bibr">39</xref>], Buskirk <italic>et al.</italic> [<xref rid="B42-animals-05-00089" ref-type="bibr">42</xref>] and NRC [<xref rid="B43-animals-05-00089" ref-type="bibr">43</xref>] differed from DMBB cows by less than 10%, whereas results from other experiments were divergent from our findings by more than 10%. <xref ref-type="table" rid="animals-05-00089-t004">Table 4</xref> shows a range in MEm from 0.418 to 0.699 MJ/kg BW<sup>0.75</sup>, the latter being 68% higher than the lowest value. This variation is nearly the double of the variation of 10% to 30% due to genetic differences, reported by Derno <italic>et al.</italic> [<xref rid="B5-animals-05-00089" ref-type="bibr">5</xref>]. It may be clear that a wide range of animal factors, such as genotype, and environmental factors can influence maintenance energy expenditure [<xref rid="B32-animals-05-00089" ref-type="bibr">32</xref>]. Even the technique to determine maintenance requirements is variable: zero BW change [<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>,<xref rid="B35-animals-05-00089" ref-type="bibr">35</xref>,<xref rid="B36-animals-05-00089" ref-type="bibr">36</xref>,<xref rid="B37-animals-05-00089" ref-type="bibr">37</xref>,<xref rid="B38-animals-05-00089" ref-type="bibr">38</xref>,<xref rid="B44-animals-05-00089" ref-type="bibr">44</xref>], zero energy retention [<xref rid="B39-animals-05-00089" ref-type="bibr">39</xref>], calorimetry chamber [<xref rid="B40-animals-05-00089" ref-type="bibr">40</xref>] or respiration chamber [<xref rid="B41-animals-05-00089" ref-type="bibr">41</xref>]. Furthermore, extra activity for walking may increase maintenance energy requirements. Locomotion was restricted in our experiments because cows were confined in tie stalls, but maintenance energy requirements on pasture can be increased by 25%–50% [<xref rid="B45-animals-05-00089" ref-type="bibr">45</xref>].</p><p>Mean MEm and NEm requirements of DMBB cows amounted to 105% and 94% of the mean MEm or NEm requirements of other genotypes, respectively. Maintenance ME requirements of DMBB cows were higher than those reported in the literature (<italic>p</italic> = 0.021), whereas NEm requirements of DMBB cows were lower (<italic>p</italic> < 0.001). Pooling literature data (<xref ref-type="table" rid="animals-05-00089-t004">Table 4</xref>; <italic>n</italic> = 19) with individual results of DMBB cows showed that requirements were 1.5% higher for DMBB cows (<italic>p</italic> > 0.10). Both approaches demonstrate that maintenance energy requirements of DMBB cows are within the range reported in the literature for beef cows.</p><p>Double-muscled cattle are characterized by more fast-glycolytic fibers than non-double-muscled animals [<xref rid="B2-animals-05-00089" ref-type="bibr">2</xref>]. Protein turnover of glycolytic fibers is lower than in oxidative fibers [<xref rid="B46-animals-05-00089" ref-type="bibr">46</xref>]. Protein turnover may contribute to about 15% of energy expenditure [<xref rid="B47-animals-05-00089" ref-type="bibr">47</xref>], so that maintenance energy requirements of DMBB cows may be lower than in other genotypes. Furthermore, double-muscled cattle have smaller organs [<xref rid="B2-animals-05-00089" ref-type="bibr">2</xref>], and in general, the mass of organs is highly correlated with energy expenditure [<xref rid="B48-animals-05-00089" ref-type="bibr">48</xref>]. This is another argument to assume lower maintenance energy requirements for double-muscled cattle. Hanset <italic>et al.</italic> [<xref rid="B6-animals-05-00089" ref-type="bibr">6</xref>] reported 8% lower maintenance energy requirements of DMBB bulls in comparison with those of non-DMBB bulls, but it is not clear if the difference was significant. Maintenance energy requirements of DMBB cows are very similar to the mean requirements of other beef genotypes (<xref ref-type="table" rid="animals-05-00089-t004">Table 4</xref>). The reducing effect due to a lower protein turnover may be counterbalanced by the higher muscle mass in DMBB animals, and the fact that lean tissue is relatively more metabolically active than fat tissue [<xref rid="B30-animals-05-00089" ref-type="bibr">30</xref>,<xref rid="B49-animals-05-00089" ref-type="bibr">49</xref>]. The similar requirements of DMBB cows and cows of other breeds is in accordance with the findings of Vermorel <italic>et al.</italic> [<xref rid="B7-animals-05-00089" ref-type="bibr">7</xref>], who found no significant difference in energy expenditure between 10-month old DMBB and non-DMBB bulls. Thornton <italic>et al.</italic> [<xref rid="B50-animals-05-00089" ref-type="bibr">50</xref>] found that Red Angus steers, sired by bulls with a lower MEm, had more type I myofibers in the biceps femoris muscles than steers sired by bulls with a higher MEm. Furthermore, steers sired by bulls with a higher MEm resulted in more type IIb fibers compared to steers sired by bulls with a lower MEm. Consequently, the contrasting results of Bergen [<xref rid="B46-animals-05-00089" ref-type="bibr">46</xref>] and Thornton <italic>et al.</italic> [<xref rid="B50-animals-05-00089" ref-type="bibr">50</xref>] showed that the effect of myofiber type on maintenance energy requirements is not equivocal.</p></sec></sec><sec><title>4. Conclusions</title><p>Maintenance energy requirement of DMBB beef cows correspond to the mean requirements of other beef genotypes. Feeding level did not affect maintenance requirements, whereas there was a significant effect of parity. However, the small numerical differences between parities may hardly be nutritionally relevant.</p></sec></body><back><ack><title>Acknowledgments</title><p>The authors greatly acknowledge Piet Van Laere, Kristien Le Noir and Elke De Smet for their skilled technical assistance.</p></ack><notes><title>Author Contributions</title><p>Leo Fiems conceived the study, analyzed the data and wrote the paper. Johan De Boever and José Vanacker were responsible for feed analysis and determination of the nutritive value of the feeds. 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