Asher A, Shabtay A, Haim A, Aharoni Y, Miron J, Adin G, Tamir A, Arieli A, Halachmi I, Moallem U, Orlov A, Brosh A
Newe-Ya'ar Research Center, Beef Cattle Section, Department of Ruminant Science, Institute of Animal Science, Agricultural Research Organization, PO Box 1021, Ramat Yishay 30-09500, Israel; Israeli Center for Interdisciplinary Research in Chronobiology, University of Haifa, Haifa 31905, Israel.
Newe-Ya'ar Research Center, Beef Cattle Section, Department of Ruminant Science, Institute of Animal Science, Agricultural Research Organization, PO Box 1021, Ramat Yishay 30-09500, Israel.
J Dairy Sci. 2014 Jul;97(7):4340-53. doi: 10.3168/jds.2013-7265. Epub 2014 May 2.
Thirty-five lactating dairy cows throughout weeks of lactation (WOL) 16 to 30 were used to determine optimal time needed for reliable measurement of performance variables, and to classify the cows into high-, medium-, and low-efficiency groups. Individual performance variables [body weight (BW), dry matter intake (DMI), and milk production] were measured daily with a computerized monitoring system. Body condition was visually scored weekly and used to calculate retained or depleted body energy as a result of fat content change (REF). Milk composition was analyzed weekly. Body weight, DMI, and total recovered energy (RE), which represents energy in milk production plus REF, were summarized weekly. Efficiency was calculated as RE/DMI and as residual feed intake (RFI; i.e., the difference between actual and expected DMI), which was calculated from multiple linear regression of DMI dependence on BW(0.75) and RE. Unexpectedly, it was found that BW did not affect DMI and RE/DMI. Changes and relative changes in phenotypic coefficient of variation and correlations among data from shortened tests ranging from 1 wk (WOL 16) to a sequence of 15-wk tests were used to determine optimal test period durations for 5 traits: BW, DMI, RE, RE/DMI, and RFI. Traits were fitted into a mixed model with repeated measures. For each week, the traits were summarized as a sequence of cumulative data, starting from WOL 16 and cumulated over periods that increased in 1-wk steps up to WOL 16 to 29. Weekly cumulations were compared with those for entire test period (WOL 16 to 30). Consistency of each cow's efficiency classification as high, medium, or low was tested by the total-agreement procedure; the kappa index P-value was used. Throughout WOL 16 to 30, the effects of increasing test period duration on between-animal coefficient of variation differed with respect to the various performance variables and RE/DMI: it tended to change with respect to BW, did not change with respect to DMI, and decreased with respect to RE and RE/DMI. In conclusion, compared with a 15-wk study, a 2-wk study can classify RFI and RE/DMI to 3 efficiency levels, with an individual correlation coefficient of 0.6. When the study was carried out over 3 wk or more, the lowest significant index of the classification was P<0.004, the lowest individual correlation coefficient was 0.65, and its lowest significance was P<0.01. The current study indicated that the insignificant effect of the BW of dairy lactating cows on their DMI should be validated in more studies.
选用35头处于泌乳期第16至30周的泌乳奶牛，以确定可靠测量生产性能变量所需的最佳时间，并将奶牛分为高效、中等效率和低效组。使用计算机化监测系统每日测量个体生产性能变量[体重（BW）、干物质摄入量（DMI）和产奶量]。每周对体况进行视觉评分，并用于计算由于脂肪含量变化（REF）导致的体能量保留或消耗情况。每周分析牛奶成分。每周汇总体重、DMI和总恢复能量（RE），RE代表产奶能量加上REF。效率计算为RE/DMI和残余采食量（RFI；即实际DMI与预期DMI之间的差值），RFI通过DMI对BW(0.75)和RE的多元线性回归计算得出。出乎意料的是，发现BW不影响DMI和RE/DMI。使用从1周（泌乳期第16周）到一系列15周测试的缩短测试数据的表型变异系数的变化和相对变化以及数据之间的相关性，来确定5个性状（BW、DMI、RE、RE/DMI和RFI）的最佳测试期持续时间。将性状拟合到具有重复测量的混合模型中。对于每周，性状汇总为一系列累积数据，从泌乳期第16周开始，以1周为步长累积增加，直至泌乳期第16至29周。将每周累积值与整个测试期（泌乳期第16至30周）的累积值进行比较。通过完全一致程序测试每头奶牛高效、中等或低效效率分类的一致性；使用kappa指数P值。在整个泌乳期第16至30周，增加测试期持续时间对动物间变异系数的影响因不同生产性能变量和RE/DMI而异：对于BW，其有变化趋势；对于DMI，无变化；对于RE和RE/DMI，其降低。总之，与15周的研究相比，2周的研究可以将RFI和RE/DMI分类为3个效率水平，个体相关系数为0.6。当研究进行3周或更长时间时，分类的最低显著指数为P<0.004，最低个体相关系数为0.65，其最低显著性为P<0.01。当前研究表明，奶牛体重对其DMI无显著影响这一结果应在更多研究中得到验证。
