Genetic and non-genetic features of female gender determination in Friesian calves as replacements under Egyptian farm conditions

This study aimed to address the genetic and environmental features that affect the calf’s sex in dairy farms, which favors female birth for extra milk production and efficient replacements. A total of 4913 calves' records from 1047 Friesian cows collected at Sakha dairy farm between 1975 and 2020 were analyzed to estimate genetic parameters and various environmental effects on calf gender, including year and season of mating, first calving year, gestation length, parity, service period, and number of services per conception. Variance components, heritabilities, and repeatability values were estimated using the THRGIBBS1F90 program based on Gibbs sampling. The results showed highly significant effects of the season (P < 0.001) and year of mating, gestation length (P < 0.01), and the others (P < 0.05) on calf gender. For female birth, direct (h2a), sire (h2s), and dam (h2m) heritability and repeatability estimates are 0.13- 0.16, around 0.12, 0.09, and 0.15-0.18, respectively. Short gestational length, few services per conception, plus first and fifth parties were the main predictors of female births. Moderate estimates of female birth and sire heritability demonstrate that genetic manipulation can change additive genetic variability.  With only 0.15-0.18% confidence, the moderate repeatability estimates of female birth indicated that previous calf sex can influence calf gender in subsequent pregnancies.  By manipulating some management techniques in addition to genetic parameters in dairy cows before mating, it is possible to change the gender proportion of fresh births to a preferred value.