ASSOCIATION OF THE INBREEDING COEFFICIENT ON MILK, PROTEIN, AND FAT PRODUCTION IN THE FIRST LACTATION OF HOLSTEIN COWS

Inbreeding increases homozygosity, favoring the expression of deleterious recessive alleles and resulting in the phenomenon of inbreeding depression, which can compromise the productive and reproductive performance of animals. The objective of this study was to estimate the inbreeding coefficients of Holstein cows from genealogical records and evaluate their association with the 305 d milk yield (MY305), 305 d fat yield (FY305), and 305 d protein yield (PY305) of the first lactation. The data analyzed belong to an agricultural company in the southeastern region of Brazil. The pedigree file contained information on 7,561 animals born between 1911 and 2023, of which 763 founders were identified, in addition to 790 bulls and 4,953 cows with progeny, covering 16 generations. Within this relationship matrix, 5,307 animals are inbred, with an average inbreeding coefficient (F) of 2.26% and a maximum of 28%. The F value of each animal was used as a linear covariate in the statistical model, including the contemporary group effect (year and month of birth), age class at calving, and additive genetic and residual random effects. In this analysis, the first lactations of 2,228 cows were used, with averages of 10,383 ± 1,291 kg, 369 ± 87 kg, and 312 ± 63 kg for MY305, FY305, and PY305, respectively. The estimated heritabilities for MY305, FY305, and PY305 were 0.17 ± 0.05, 0.19 ± 0.04, and 0.12 ± 0.01, respectively. The F effect prediction solution described a decrease in MY305, FY305, and PY305 of 33.96, 95.81, and 21.6 kg for each 1% increase in F. These results show the importance of monitoring inbreeding and directing animal mating, given that inbreeding depression leads to economic losses.