Abstract：
Up to now, little has been known about backfat thickness (BFT) in dairy cattle. The objective of this study was to investigate the lactation curve and genetic parameters for BFT as well as its relationship with body condition score (BCS) and milk yield (MKG). For this purpose, a dataset was analysed including phenotypic observations of 1929 German Holstein cows for BFT, BCS and MKG recorded on a single research dairy farm between September 2005 and December 2022. Additionally, pedigree and genomic information was available. Lactation curves were predicted and genetic parameters were estimated for all traits in first to third lactation using univariate random regression models. For BCS, lactation curves had nadirs at 94 DIM, 101 DIM and 107 DIM in first, second and third lactation. By contrast, trajectories of BFT showed lowest values later in lactation at 129 DIM, 117 DIM and 120 DIM in lactation numbers 1 to 3, respectively. Although lactation curves of BCS and BFT had similar shapes, the traits showed distinct sequence of curves for lactation number 2 and 3. Cows in third lactation had highest BCS, whereas highest BFT values were found for second parity animals. Average heritabilities were 0.315 ± 0.052, 0.297 ± 0.048 and 0.332 ± 0.061 for BCS in lactation number 1 to 3, respectively. Compared to that, BFT had considerably higher heritability in all lactation numbers with estimates ranging between 0.357 ± 0.028 and 0.424 ± 0.034. Pearson correlation coefficients between estimated breeding values for the 3 traits were negative between MKG with both BCS (r = -0.245 to -0.322) and BFT (r = -0.163 to -0.301). Correlation between traits BCS and BFT was positive and consistently high (r = 0.719 to 0.738). Overall, the results of this study suggest that BFT and BCS show genetic differences in dairy cattle, which might be due to differences in depletion and accumulation of body reserves measured by BFT and BCS. Therefore, routine recording of BFT on practical dairy farms could provide valuable information beyond BCS measurements and might be useful, for example, to better assess the nutritional status of cows.
摘要：
到目前为止,对奶牛的背脂肪厚度(BFT)知之甚少。这项研究的目的是研究BFT的泌乳曲线和遗传参数及其与身体状况评分（BCS）和产奶量（MKG）的关系。为此,分析了一个数据集，包括1929年德国荷斯坦奶牛的BFT表型观察，BCS和MKG记录在2005年9月至2022年12月之间的一个研究奶牛场。此外,谱系和基因组信息可用。使用单变量随机回归模型预测泌乳曲线，并估算第一至第三泌乳中所有性状的遗传参数。对于BCS，泌乳曲线的最低点为94DIM，101DIM和107DIM在第一，第二次和第三次哺乳。相比之下,BFT的轨迹在129DIM的哺乳期后期显示最低值，泌乳编号1至3分别为117DIM和120DIM。尽管BCS和BFT的泌乳曲线具有相似的形状，性状表现出不同的2号和3号泌乳曲线序列。第三哺乳期奶牛的BCS最高，而第二胎次动物的BFT值最高。泌乳编号1至3的BCS的平均遗传率分别为0.315±0.052、0.297±0.048和0.332±0.061。相比之下,BFT在所有泌乳数量中的遗传力都高得多，估计值在0.357±0.028和0.424±0.034之间。在具有BCS（r=-0.245至-0.322）和BFT（r=-0.163至-0.301）的MKG之间，3个性状的估计育种值之间的Pearson相关系数为负。性状BCS和BFT之间的相关性呈正相关，并且一直很高（r=0.719至0.738）。总的来说,这项研究的结果表明，BFT和BCS在奶牛中显示出遗传差异，这可能是由于BFT和BCS测量的身体储备的消耗和积累的差异。因此,BFT在实际奶牛场的常规记录可以提供BCS测量之外的有价值的信息，并且可能有用，例如,更好地评估奶牛的营养状况。
