Genetic effects of heat stress on milk yield of Thai Holstein crossbreds

Abstract

The threshold for heat stress on milk yield of Holstein crossbreds under climatic conditions in Thailand was investigated, and genetic effects of heat stress on milk yield were estimated. Data included 400,738 test-day milk yield records for the first 3 parities from 25,609 Thai crossbred Holsteins between 1990 and 2008. Mean test-day milk yield ranged from 12.6 kg for cows with <87.5% Holstein genetics to 14.4 kg for cows with ≥93.7% Holstein genetics. Daily temperature and humidity data from 26 provincial weather stations were used to calculate a temperature-humidity index (THI). Test-day milk yield varied little with THI for first parity except above a THI of 82 for cows with ≥93.7% Holstein genetics. For third parity, test-day milk yield started to decline after a THI of 74 for cows with ≥87.5% Holstein genetics and declined more rapidly after a THI of 82. A repeatability test-day model with parities as correlated traits was used to estimate heat stress parameters; fixed effects included herd-test month-test year and breed groups, days in milk, calving age, and parity; random effects included 2 additive genetic effects, regular and heat stress, and 2 permanent environment, regular and heat stress. The threshold for effect of heat stress on test-day milk yield was set to a THI of 80. All variance component estimates increased with parity; the largest increases were found for effects associated with heat stress. In particular, genetic variance associated with heat stress quadrupled from first to third parity, whereas permanent environmental variance only doubled. However, permanent environmental variance for heat stress was at least 10 times larger than genetic variance. Genetic correlations among parities for additive effects without heat stress considered ranged from 0.88 to 0.96. Genetic correlations among parities for additive effects of heat stress ranged from 0.08 to 0.22, and genetic correlations between effects regular and heat stress effects ranged from -0.21 to -0.33 for individual parities. Effect of heat stress on Thai Holstein crossbreds increased greatly with parity and was especially large after a THI of 80 for cows with a high percentage of Holstein genetics (≥93.7%). Individual sensitivity to heat stress was more environmental than genetic for Thai Holstein crossbreds.

Heat stress and ACTH administration on cortisol and insulin-like growth factor I (IGF-I) levels in lactating Holstein cows

“…These results are in agreement with other studies that have reported CORT decrease some days after heat stress imposition (Collier et al 2008;Boonkum et al 2011). The total amount of CORT released during the present study confirmed that CORT was significantly higher during heat stress than comfort and ACTH tests; this indicated that heat stress is a potent stressor.…”

Somatic Cells Count and Its Genetic Association with Milk Yield in Dairy Cattle Raised under Thai Tropical Environmental Conditions

“…These results implied that upgrading dairy cows to H under these Thai environmental conditions was favorable for milk production but unfavorable in terms of mastitis resistance and health status. Among Thai H crossbreds, cows with high H fraction were found to have higher levels of heat stress especially cows with more than 93.7% H fraction (Boonkum et al, 2011). In order to achieve or maintain high levels of milk production under Thai tropical environmental conditions, H cows and cows with high H fractions would need more intensive care and management (feeding, housing, milking, health care) than cows with lower H fractions (Koonawootrittriron et al, 2009; Boonkum et al, 2011).…”

Genetic relationships of fertility traits with test‐day milk yield and fat‐to‐protein ratio in tropical smallholder dairy farms

“…Most of the dairy cows are crossbred from Bos indicus , such as Sahiwal, Brahman and Thai Native cattle upgraded by HF (Boonkum et al . ). Currently, the majority of the dairy population has >75% HF blood.…”