TABLE 4.
Examples of genetic parameters used for measuring heat tolerance in dairy cattle.
| Genetic models | Traits | Genetic parameters | Genetic values | Country | References |
|---|---|---|---|---|---|
| Random regression, reaction norm, Bivariate animal models | Milk production, fertility, calving age, calving season, udder health | Heritability, repeatability, breeding values, and genetic correlations | σ2 a = 0.08–0.22; rg = −0.24 to −0.56, h2 a = 0.13–0.28, h2 thi = 0.09–0.37; rg˃80; R = 0.021–0.411; h2 = 0.13–073; h2 = 0.111–0.176 | Belgium, Brazil, Iran, Italy, South Korea, Thailand | Boonkum et al. (2011), Bernabucci et al. (2014), Hammami et al. (2015), Rahbar et al. (2016), Santana et al. (2017), Lee et al. (2019) |
| Random regression models | Test day milk yield | Heritability, genetic and phenotypic correlations | h2 = 0.15–0.21 | Brazil | Negri et al. (2021) |
σ2 a = genetic correlations among parities for additive effects of heat stress (Thailand), h2 = heritability; rg = genetic correlations, h2 a = general effect heritability, h2 thi = heat stress heritability (Italy); rg = Estimates of genetic correlations within traits between cold and hot environment; R = Repeatability of fertility traits for first service to insemination outcome (Iran); h2 = Estimates of heritabilities within milk production traits at different THI, thresholds in first, second and third lactation stages (Brazil); h2 = heritability estimates of milk yield ranged from 0.111 t0 0.176 (average 0.128). It decreased slightly as THI, increased, and began to increase at THI, of 79 (South Korea).