Nazari Mohammad Ali, Ghavi Hossein-Zadeh Navid, Shadparvar Abdol Ahad, Kianzad Davood
Department of Animal Science, Faculty of Agricultural Sciences, University of Guilan, Rasht, Iran.
Animal Breeding Center and Promotion of Animal Products, Karaj, Iran.
Front Genet. 2021 Mar 8;12:633017. doi: 10.3389/fgene.2021.633017. eCollection 2021.
This study aimed to estimate heritabilities and genetic trends for different persistency measures for milk fat yield and their genetic correlations with 270-day milk yield in Iranian buffaloes. The records of test-day milk fat yield belonging to the first three lactations of buffaloes within 523 herds consisting of 43,818 records were got from the Animal Breeding Center and Promotion of Animal Products of Iran from 1996 to 2012. To fit the lactation curves based on a random regression test-day model, different orders of Legendre polynomial (LP) functions were selected. Three persistency measures were altered according to the specific condition of the lactation curve in buffaloes: (1) The average of estimated breeding values (EBVs) for test day fat yield from day 226 to day 270 as a deviation from the average of EBVs from day 44 to day 62 (PM), (2) A summation of contribution for each day from day 53 to day 247 as a deviation from day 248 (PM), and (3) The difference between EBVs for day 257 and day 80 (PM). The estimates of heritability for PM, PM, and PM ranged from 0.20 to 0.48, from 0.36 to 0.47, and from 0.19 to 0.35 over the first three lactations, respectively. The estimate of genetic trends for different persistency measures of milk fat yield was not significant over the lactations (.05). Genetic correlation estimates between various measures of persistency were generally high over the first three lactations. Also, genetic correlations estimates between persistency measures and 270-day milk yield were mostly low and varied from 0.00 to 0.24 (between PM and 270-day milk yield), from -0.19 to 0.13 (between PM and 270-day milk yield), and from -0.02 to 0.00 (between PM and 270-day milk yield) over the first three lactations, respectively. Persistency measures that showed low genetic correlations with milk fat yield were considered the most suitable measures in selection schemes. Besides, medium to high heritability estimates for different persistency measures for milk fat yield indicated that relevant genetic variations detected for these characters could be regarded in outlining later genetic improvement programs of Iranian buffaloes.
本研究旨在估计伊朗水牛乳脂肪产量不同持续性指标的遗传力和遗传趋势，以及它们与270天产奶量的遗传相关性。从伊朗动物育种中心和动物产品推广部门获取了1996年至2012年期间523个牛群中43818条记录的水牛前三个泌乳期的测定日乳脂肪产量记录。为了基于随机回归测定日模型拟合泌乳曲线，选择了不同阶数的勒让德多项式（LP）函数。根据水牛泌乳曲线的具体情况改变了三种持续性指标：（1）测定日226天至270天的脂肪产量估计育种值（EBV）的平均值，相对于44天至62天EBV平均值的偏差（PM）；（2）从第53天到第247天每天相对于第248天的贡献总和（PM）；（3）第257天和第80天的EBV之差（PM）。在头三个泌乳期，PM、PM和PM的遗传力估计值分别为0.20至0.48、0.36至0.47和0.19至0.35。在整个泌乳期，乳脂肪产量不同持续性指标的遗传趋势估计不显著（P>0.05）。在前三个泌乳期，各种持续性指标之间的遗传相关性估计值总体较高。此外，持续性指标与270天产奶量之间的遗传相关性估计大多较低，分别为0.00至0.24（PM与270天产奶量之间）、-0.19至0.13（PM与270天产奶量之间）和-0.02至0.00（PM与270天产奶量之间）。与乳脂肪产量遗传相关性较低的持续性指标被认为是选择方案中最合适的指标。此外，乳脂肪产量不同持续性指标的遗传力估计值为中到高，这表明在制定伊朗水牛未来的遗传改良计划时，可以考虑为这些性状检测到的相关遗传变异。
