Estimation of genotype by temperature-humidity index interactions on milk production and udder health traits in Montbeliarde cows

Table 2 Difference between averages of adjusted performances recorded at the optimal temperature-humidity index (THI) and averages of adjusted performances recorded under the strongest heat stress conditions (THI ≥ 70) and slopes above optimal THI (per unit of additional THI)

	MY	FC	PC	FY	PY	SCS
Optimal THI
L1	50–55	≤ 35	≤ 35	≤ 50	45–55	≤ 45
L2	50–55	≤ 35	≤ 35	≤ 50	45–55	≤ 45
Average absolute differences between performances recorded at optimal THI and at THI ≥ 70
L1	− 1.49 kg/d	− 3.82‰	− 3.04‰	− 100.4 g/d	− 92.9 g/d	+ 0.25
L2	− 1.86 kg/d	− 4.00‰	− 3.23‰	− 107.8 g/d	− 112.5 g/d	+ 0.11
Average relative differences between performances recorded at optimal THI and at THI ≥ 70 (% overall mean)
L1	− 7.0	− 9.9	− 9.1	− 12.4	− 13.2	+ 10.3
L2	− 7.4	− 10.3	− 9.6	− 11.5	− 13.8	+ 4.8
Average slopes above optimal THI
L1	− 0.07 kg/d	− 0.11‰	− 0.09‰	− 5.02 g/d	− 4.64 g/d	+ 0.010
L2	− 0.09 kg/d	− 0.11‰	− 0.09‰	− 5.39 g/d	− 5.63 g/d	+ 0.004

MY milk yield, FY fat yield, PY protein yield, FC fat content, PY protein content, SCS somatic cell score, L1 = first lactation, L2 second lactation

ISSN: 1297-9686