Estimation of genetic and phenotypic parameters for body condition score, milk yield and milk composition, and factors affecting related traits during the first 150 days of lactation in Holstein cows

This study aimed to estimate the genetic and phenotypic parameters for BCS, milk yield and its composition in Holstein cows. The data were collected in the first 150 days in milk (DIM) of 317 Holstein cows calved between 2017 and 2018 raised at a private dairy cattle farm located in Kirsehir of Turkey. In this study, parity and DIM were included as fixed factors in the model. The cows were grouped according to their BCS: low (BCS <= 2.50), moderate (BCS=2.75-3.00) and high (BCS >= 3.25). The results showed that effects of parity and DIM on BCS, test-day milk yield (TDMY), solids-non-fat (SNF), protein content (PC), lactose (LACT), fat yield (FY) and protein yield (PY) were significantly important (P<0.05), whereas fat content (FC) was not. The highest TDMY, FY and PY were determined in cows with low BCS. FC, SNF, PC and LACT were the highest in cows with high BCS compared to those with low BCS and moderate BCS. The estimated heritability were 0.188, 0.301, 0.184, 0.197, 0.194, 0.223, 0.196 and 0.342 for BCS, TDMY, FC, SNF, PC, LACT, FY and PY, respectively. Repeatability for these traits was estimated to vary from 0.257 to 0.521. Genetic correlations between BCS and milk yield traits were generally low and ranged from -0.175 to 0.191. Low to moderate phenotypic correlations were also observed between BCS and milk yield traits (-0.234 to 0.217). Despite estimated low heritability and correlations during the early lactation period in our study, these results showed that cows with lower BCS had higher milk yield and lower milk contents, and selection programs including BCS will lead to slight improvements of milk yield traits in Holstein cows.