Inbreeding depression and environmental effect on milk traits of the Murciano-Granadina goat breed

Abstract

The extent of inbreeding as well as environmental factors such as parity order, age at kidding and contemporary group (herd-year-season) was evaluated for their effects on the total production of milk, fat, protein and dry extract in Murciano-Granadina goats in Spain. The pedigrees of 11,926 females were traced to calculate the inbreeding coefficient for each animal. The lactations of these 22,832 females were analysed, standardised to 210 days of lactation, and information on the whole milk, fat, protein and dry extract production was recorded. The least squares method was used, and fixed effects in the model included parity order, the age of goat at kidding and contemporary group, and the inbreeding rate as a continuous variable, considering linear and quadratic effects. Based on this model, only 1.18% of the animals presented inbreeding, and the average population was of low magnitude (0.24%). However, among inbred animals, the average was considered high (20.31%). The total average of milk, fat, protein and dry extract production is within the range considered normal for the breed. The variables of parity order, the age of goat at kidding and contemporary group, exerted a statistically significant influence on the milk production and composition traits. Inbreeding had a quadratic effect on total milk production with a minimum point at 10.59% of inbreeding. Inbreeding had a positive linear correlation with total fat and dry extract yield. There was no statistically significant effect of inbreeding on total protein production. In general, the inbreeding levels in the Murciano-Granadina goat population did not negatively affect milk traits in the evaluated period.