Spearman's rank correlations between breeding values in extreme THI levels were greater than 0.80 for all traits considering all animals, only cows and only bulls. However, the greatest variations may have been the result of the limitations of Legendre polynomials at the extreme points of the curve, and the pattern of heritabilities curves was approximately constant for the evaluated traits. For PUFA and C18:0, heritabilities were approximately constant (0.13 to 0.14 and 0.15, respectively). For PP, heritabilities (0.26 to 0.39) presented larger values in intermediate THI. The best fit order for MY, PP and C18:0 was the third, whereas the second for all other traits. Legendre orthogonal polynomials from second to seventh order were tested.
Measurements of milk yield (MY), somatic cell score (SCS), percentage of fat (FP), protein (PP), lactose (LP), casein (CP) and percentage of palmitic (C16:0), stearic (C18:0), oleic (C18:1), total saturated (SFA), unsaturated (UFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids in milk from 5,224 Holstein cows were evaluated as a function of a temperature and humidity index (THI).