Genetic Component of Heat Stress in Dairy Cattle, Parameter Estimation

Abstract

Our data included 119,205 first-parity, test-day records from 15,002 Holsteins in 134 Georgia farms with temperature and humidity data from 21 weather stations throughout Georgia. The test-day model included the effects of herd test date, days-in-milk (DIM) classes, age, milking frequency, general additive effect, random regression on the heat-humidity index for heat-tolerance additive effect, general permanent environment, and the random regression on the heat-humidity index for a permanent environment. The general effects, which corresponded to effects in the current repeatability models, were assumed to be correlated with the heat-tolerance effects. Variance components were estimated by REML. For heat-humidity indices below 72, heritability for milk was 0.17, and additive variance of heat tolerance was 0. For a heat-humidity index of 86 (which would correspond to temperatures of 36 degrees C at 50% humidity), the additive variance of heat tolerance was as high as for general effect, and the genetic correlation between the two effects was -0.36. Results for fat and protein were similar. Current selection for production reduces heat tolerance. Joint selection for heat tolerance and production is possible.

Late reproductive senescence in a rabbit line hyper selected for reproductive longevity, and its association with body reserves

“…Also, in a genotype by environmental interaction experiment, an increased environmental sensitivity was observed when selecting for high production, i.e. selection for high milk production in dairy cows increased sensitivity to ambient temperatures [22]. Furthermore, in pig populations it has been observed that populations selected for leanness and reduced intake are more sensitive to environmental stressors than some higher feed intake US genetic populations [28].…”

Developing breeding schemes to assist mitigation of greenhouse gas emissions

“…Examples include selection for heat tolerance (e.g. Ravagnolo and Misztal, 2000), selection for hardiness traits (could be introduced for other breeds through crossing or by breed substitution) and selection for efficiency/sustainability of production levels in future systems (change in dietary regimes). Genotype by environment interaction may also become important in adaptation to climate change, especially if changes are extreme or for breeds already being used at the limit of their adaptation 'envelope', so that animals are suitable for the new production systems needed to adapt to climate change (e.g.…”

Climatic effects in Central Europe on the frequency of medical treatments of dairy cows

“…Accordingly, thresholds of heat stress vary between the different indices (Bohmanova et al, 2007). Brü gemann et al (2010) concluded that the THI of the NRC (1971) is more suitable than the index proposed by Ravagnolo and Misztal (2000) for the environmental conditions found in the studied region of Lower Saxony, Germany. The threshold of THI 5 60 was identified for the various regions characterized as a coastal region, a pasture-based region and a region of intensive crop production.…”