Genetic and Environmental Sources of Variation for Lactation Milk Yield in Kilis Goats
Abstract
The Kilis goat is one of the most important indigenous dairy goat breeds in Türkiye and plays a significant role in milk production systems of the southeastern region. Despite its economic importance, information regarding genetic parameters for milk production traits remains limited. Therefore, the present study aimed to estimate variance components and genetic parameters for lactation milk yield in Kilis goats using a repeatability animal model. A total of 3,655 lactation milk yield records collected from 1,698 does and a pedigree comprising 1,815 animals were analyzed using the restricted maximum likelihood (REML) method implemented in WOMBAT software. Herd-year subclasses were included as fixed effects, while additive genetic and permanent environmental effects were fitted as random effects. The mean lactation milk yield was 402.23±84.02 kg. The estimated additive genetic, permanent environmental, residual, and phenotypic variances were 733.09±250.29, 0.01±264.20, 6298.76±187.39, and 7031.86±167.08 kg², respectively. Heritability for lactation milk yield was estimated as 0.10±0.03, indicating that additive genetic effects accounted for approximately 10.4% of the total phenotypic variation. The permanent environmental ratio was estimated to be negligible (0.00±0.00), resulting in a repeatability estimate equal to the heritability estimate (r=0.10). The results revealed that environmental and management factors constituted the major sources of variation in lactation milk yield, while a measurable but relatively low additive genetic component was present. These findings suggest that genetic improvement of milk yield in Kilis goats is possible through selection, although substantial gains will also require improvements in management practices and recording systems. The study provides baseline genetic parameters that may support the development of sustainable dairy-oriented breeding programs for the Kilis goat breed.