Abstract：
The aims of this study were to estimate the genetic parameters for fat-to-protein ratio (F:P) within the first 90 days of lactation and to examine their genetic associations with daily milk yield (MY), somatic cell score (SCS), and calving interval between the first and second calving (IFSC) and between the second and third calving (ISTC) during the first three lactations of Holstein cows. We utilized 200,626 production-related data officially recorded from 77,436 cows milked two or three times a day from 2012 to 2022, sourced from the Holstein Cattle Breeders Association of Paraná State, Brazil. The (co)variance components were estimated using animal models, adopting the restricted maximum likelihood (REML) method with single-trait analysis (for heritability and repeatability) and two-trait analysis (for genetic and phenotypic correlations), per lactation. Regardless of lactation number, heritability estimates were relatively low, ranging from 0.08 ± 0.005 to 0.10 ± 0.003 for F:P; 0.08 ± 0.01 to 0.18 ± 0.005 for MY; 0.04 ± 0.01 to 0.07 ± 0.004 for SCS; and 0.03 ± 0.01 for both IFSC and ISTC. Repeatability estimates within the same lactation were low for F:P (ranging from 0.17 ± 0.002 to 0.19 ± 0.03), high for MY (between 0.50 ± 0.003 and 0.53 ± 0.002), and moderate to high for SCS (between 0.39 ± 0.003 and 0.44 ± 0.004). Genetic correlations between F:P and MY ranged from -0.26 ± 0.03 to -0.15 ± 0.02; F:P and SCS, from -0.06 ± 0.03 to -0.03 ± 0.08; F:P and IFSC, 0.31 ± 0.01; F:P and ISTC, 0.20 ± 0.01; MY and IFSC, 0.24 ± 0.05; and MY and ISTC, 0.13 ± 0.08. The fat-to-protein ratio during early lactation showed low genetic variability, regardless of lactation number. Furthermore, it was genetically correlated with MY, IFSC, and ISTC, although there is an antagonistic and unfavorable correlation between traits that can limit genetic progress.
摘要：
这项研究的目的是估计泌乳前90天内脂肪与蛋白质比率（F：P）的遗传参数，并检查其与每日产奶量（MY）的遗传关联。体细胞评分（SCS），在荷斯坦奶牛的前三个泌乳期间，第一次和第二次产奶（IFSC）之间以及第二次和第三次产奶（ISTC）之间的产奶间隔。我们利用了从2012年到2022年每天两次或三次挤奶的77,436头奶牛中正式记录的200,626个生产相关数据，这些数据来自巴拉那州的荷斯坦牛育种者协会。巴西。使用动物模型估计(协)方差分量，采用限制性最大似然（REML）方法进行单性状分析（用于遗传和可重复性）和双性状分析（用于遗传和表型相关性），每次哺乳。不管哺乳次数如何，遗传力估计相对较低，F：P为0.08±0.005至0.10±0.003；MY为0.08±0.01至0.18±0.005；SCS为0.04±0.01至0.07±0.004；IFSC和ISTC均为0.03±0.01。对于F：P，相同泌乳内的可重复性估计值较低（范围从0.17±0.002到0.19±0.03），MY的高（在0.50±0.003和0.53±0.002之间），SCS中至高（在0.39±0.003和0.44±0.004之间）。F：P和MY之间的遗传相关性范围为-0.26±0.03至-0.15±0.02；F：P和SCS，从-0.06±0.03到-0.03±0.08；F：P和IFSC，0.31±0.01；F：P和ISTC，0.20±0.01；MY和IFSC，0.24±0.05；MY和ISTC，0.13±0.08。泌乳早期的脂肪与蛋白质比率显示出较低的遗传变异性，无论哺乳数量。此外，它与我的基因相关，IFSC,ISTC,尽管性状之间存在拮抗和不利的相关性，可以限制遗传进展。
