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Extended abstract
Introduction (and purpose): The genetic potential of the animal can play an important role in controlling the reduction in milk production, reproductive performance and udder health of the herd in stressful weather conditions. Therefore, the purpose of this study is to investigate the effect of heat stress on milk production, reproduction and SCS traits of Iranian Holstein dairy cows.
Materials and methods: Genetic parameters that considered heat stress tolerance were estimated for milk production, udder health and reproductive traits, including open days and calving interval to the first insemination. The data including 145,731 test day records of Holstein cows from the first lactation in 323 herds of Iran breeding center were collected between 2008 and 2018. The records of the test day were integrated with daily temperature-humidity index (THI) values based on weather records of meteorological stations, and genetic parameters were estimated with the use of animal model and random regression.
Results: The results showed that production and performance traits with increasing THI (THI>72) had phenotypic and genetic reduction, while the level of SCS increased with increasing THI. In addition, the traits of milk production and reproduction had the highest genetic slope ratio, which indicates that they are more affected by heat stress at high levels of THI. Since this trait is known to reflect the mobilization of body reserves, the use of its changes in hot conditions can be a very cost-effective biomarker for heat stress in dairy cows that expresses the balance between consumption and motility in hot conditions, it highlights the need to include the additive genetic effect in the heat resistance evaluation model. On the other hand, a positive genetic correlation for SCS was identified between neutral and heat stress, hence the continued selection for lower SCS is a favorable selection response for SCS will yield under thermal stress.Conclusion: The optimal THI index for Iranian Holstein cows was below 72 for productive, reproductive and udder health traits. Disturbance in various reproductive functions due to heat stress can lead to low conception rate in the first insemination and as a result increase the calving interval and open days to especially during the warm season.
Introduction (and purpose): The genetic potential of the animal can play an important role in controlling the reduction in milk production, reproductive performance and udder health of the herd in stressful weather conditions. Therefore, the purpose of this study is to investigate the effect of heat stress on milk production, reproduction and SCS traits of Iranian Holstein dairy cows.
Materials and methods: Genetic parameters that considered heat stress tolerance were estimated for milk production, udder health and reproductive traits, including open days and calving interval to the first insemination. The data including 145,731 test day records of Holstein cows from the first lactation in 323 herds of Iran breeding center were collected between 2008 and 2018. The records of the test day were integrated with daily temperature-humidity index (THI) values based on weather records of meteorological stations, and genetic parameters were estimated with the use of animal model and random regression.
Results: The results showed that production and performance traits with increasing THI (THI>72) had phenotypic and genetic reduction, while the level of SCS increased with increasing THI. In addition, the traits of milk production and reproduction had the highest genetic slope ratio, which indicates that they are more affected by heat stress at high levels of THI. Since this trait is known to reflect the mobilization of body reserves, the use of its changes in hot conditions can be a very cost-effective biomarker for heat stress in dairy cows that expresses the balance between consumption and motility in hot conditions, it highlights the need to include the additive genetic effect in the heat resistance evaluation model. On the other hand, a positive genetic correlation for SCS was identified between neutral and heat stress, hence the continued selection for lower SCS is a favorable selection response for SCS will yield under thermal stress.Conclusion: The optimal THI index for Iranian Holstein cows was below 72 for productive, reproductive and udder health traits. Disturbance in various reproductive functions due to heat stress can lead to low conception rate in the first insemination and as a result increase the calving interval and open days to especially during the warm season.
Type of Study: Research |
Subject:
ژنتیک و اصلاح نژاد دام
Received: 2023/09/2 | Accepted: 2023/10/30
Received: 2023/09/2 | Accepted: 2023/10/30
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