Document Type : Research Paper

Authors

• Hossein Khoshroo ¹
• Hossein Naeemipour ²
• Seyed Homayon Farhangfar ³
• Hadi Sarir ⁴

¹ Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran. E-mail: h.khoshroo48@gmail.com

² Corresponding Author, Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran. E-mail: hnaeimipour@birjand.ac.ir

³ Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran. E-mail: hfarhangfar@birjand.ac.ir

⁴ Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran. E-mail: saririh@birjand.ac.ir

Abstract

Objective: Birth weight is expected to be correlated with future productive and reproductive traits. Several studies have examined the association between birth weight (BW) of Holstein cows and their productive and reproductive traits. In fact, BW is expected to be associated with some of productive and reproductive traits. The main objective of this research was to conduct a genetic analysis of BW and to evaluate its association with some future productive and reproductive traits of Holstein cows in Isfahan province.
Method: A dataset of 51,427 records of dairy cows in 82 herds of Isfahan province during the calving years from 2001 to 2023 was used in this research. The considered traits 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 (± SD) 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 of female calves, MY, FY, and PY were 0.24, 0.26, 0.36, and 0.39, respectively while the heritability estimates for AFC, NSPC, DFS , and DO were 0.15, 0.08, 0.08, 0.02, and 0.02, respectively. Overall, BW of calves had low phenotypic and genetic correlations with their future productive and reproductive traits. Phenotypic and genetic trends for BW were found to be -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 was associated with 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: Current research findings showed that BW gain in female calves is predicted to improve productive and reproductive traits in dairy cows. The positive genetic trend for BW suggests that BW genetically increased over the time of period, which implies that this trait has been selected directly or indirectly over the time of period. The moderate heritability estimate of BW suggests that rapid genetic change of BW could affect economically important traits, and hence, a multiple trait selection index is required to design a balanced breeding program for the economic traits.

Keywords

• Birth weight
• Bivariate animal model
• Fertility
• Milk production
• Replacement heifer