Some environmental factors and variance components affecting birth and weaning weight in holstein calves

This study utilized data from 926 calves born between 2019 and 2023 in a private enterprise located in the Ilgın district of Konya province, where 61 bulls and 595 Holstein-Friesian cows were reared under intensive production conditions. This study aimed to identify environmental factors affecting the birth weight and weaning weight of calves and to estimate the corresponding variance components. Accurate identification of environmental factors and reliable estimation of genetic parameters, particularly heritability, is crucial for determining optimal selection and breeding strategies in livestock genetic improvement programs. Variance components for birth and weaning weights were estimated using the WOMBAT software within the framework of the Single-Trait Animal Model. Based on the estimated components, genetic parameters such as heritability and repeatability were calculated, and breeding values for individuals were predicted using the Best Linear Unbiased Prediction (BLUP) method. The overall mean birth and weaning weights for Holstein-Friesian calves were determined as 37.51±0.35 kg and 89.22±0.97 kg, respectively. Birth weight was significantly influenced (P < 0.01) by type of birth, dam age, sex, year, and season of birth. Weaning weight was significantly affected by season and type of birth (P < 0.05), as well as by sex, dam age, and birth weight (P < 0.01). Although year-to-year differences in weaning weight were observed, these differences were not statistically significant (P>0.05). Four different models were employed to estimate variance components and genetic parameters for birth and weaning weights. In Model I, the additive genetic variance (σ²ₐ), environmental variance (σ²ₑ), and phenotypic variance (σ²ₚ) were estimated as 7.9791, 11.751, and 19.730, respectively. Model II included maternal genetic variance (σ²ₘ) in addition to Model I components. In Model III, maternal permanent environmental variance (σ²ₚₑ) was added. Model IV incorporated all variance components and yielded estimates of σ²ₐ = 4.2900, σ²ₘ = 0.54180, σ²ₚₑ = 2.0420, σ²ₑ = 12.261, and σ²ₚ = 19.134. The highest direct heritability estimate (h_a^2= 0.404±0.095) was obtained in Model I, while the highest repeatability (r = 0.362) was found in Model III. In terms of birth weight breeding value accuracy, Model I yielded the highest accuracy scores for calves (EBVc: 62.69), sires (EBVS: 50.82), and dams (EBVD: 41.38). However, Model IV demonstrated greater potential for identifying a larger number of animals. For weaning weight, Model III stood out with the highest accuracy levels (BuBV: 75.07, SiBV: 70.66, DaBV: 51.51), whereas Model I offered acceptable accuracy with a higher percentage of animals evaluated. Despite Model IV's potential to highlight more animals, its accuracy remained below expectations. Model II, although showing high percentages for calf breeding values, exhibited reduced accuracy in general. In conclusion, for selection based on birth weight, breeding values estimated using Model I for calves and dams, and Model IV for sires, are recommended. For weaning weight, Model III is preferable for all animal categories. These findings suggest that both birth and weaning weights in Holstein-Friesian calves can be effectively utilized in genetic improvement programs and that the use of appropriate models can enhance the reliability of breeding value estimations, thereby accelerating genetic progress within the population.