Document Type : Research Paper
Authors
1 Master’s Degree Graduate, University of Birjand, Iran
2 Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran
Abstract
Objective: There are a few research considering the relationship between birth weight (BW) of Holstein cows and their productive and reproductive traits. As matter of fact, BW is expected to be associated with some of productive and reproductive traits. Based on this, the objective of this research was to conduct a genetic analysis of BW and its association with some future productive and reproductive traits of Holstein cows in Isfahan province.
Methods: A total of 51,427 records from dairy cows in 82 herds of Isfahan province collected during the calving years from 2001 to 2023 were used. The traits under consideration were BW, 305-day milk yield (MY), 305-day fat yield (FY), 305-day protein yield (PY), days to first service (DFS), days open (DO), number of services per conception (NSPC), and age at first calving (AFC). Genetic analysis was performed using a series of bivariate animal models. Fixed effects of herd, calving year, calving season, and age at first calving, along with the random additive genetic effect were included in the model. The model was fitted to the data using DMU software.
Results: Mean BW (± standard deviation) of female calves was 39.05 ± 4.52 kg. The mean values for MY, FY, and PY traits were 11432 ± 1731, 324.09 ± 90.63, and 301.26 ± 68.74 kg, respectively. The mean values for reproductive traits, including DO, DFS, AFC, and NSPC were 122.8 ± 45.35, 68.55 ± 21.09, 726 ± 59.19 day, and 1.64 ± 0.95, respectively. Heritability estimates for BW female calves, MY, FY, and PY were 0.24, 0.26, 0.36, and 0.39, respectively while the estimates for AFC, NSPC, DFS , and DO were 0.15, 0.08, 0.08, 0.02, and 0.02, respectively. Phenotypic and genetic correlations between the BW of calves and their future productive and reproductive traits were generally low. Phenotypic and genetic trends for BW were -0.26 ± 0.03 kg per year and 0.024 ± 0.005 kg per year, respectively, which were statistically significant (P < 0.01). The findings of the present research indicated that one kilogram increase in BW of Holstein calves is connected to an increase of 33.77 kg, 0.79 kg, and 0.814 kg for MY, FT, and PY, respectively. Additionally, DFS, DO, AFC, and NSPC in the first lactation period increased by 0.151, 0.115, 0.992 day, and 0.155, respectively.
Conclusion: The results of this research revealed that any increase in BW is expected to lead an increment of productive and reproductive traits in dairy cows. The positive genetic trend for BW indicates that BW genetically increased over the time of period suggesting that this trait has been successfully been selected directly or indirectly in the herds. With respect to the moderate heritability estimate of BW, it could be concluded that rapid change of BW could influence productive and reproductive traits. Therefore, a multiple trait selection index is needed to be developed and applied for having a balanced breeding programs in terms of economic traits.
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