Effect of temperature-humidity index on the evolution of trade-offs between fertility and production in dairy cattle

Abstract

Background: In the current context of climate change, livestock production faces many challenges to improve the sustainability of systems. Dairy farming, in particular, must find ways to select animals that will be able to achieve sufficient overall production while maintaining their reproductive ability in environments with increasing temperatures. With future forecasted climate conditions in mind, this study used data from Holstein and Montbeliarde dairy cattle to: (1) estimate the genetic-by-temperature-humidity index (THI) interactions for female fertility, and (2) evaluate the production-fertility trade-off with increasing values of THI.

Results: Two-trait random regression models were fitted for conception rate (fertility) and test-day protein yield (production). For fertility, genetic correlations between different THI values were generally above 0.75, suggesting weak genotype-by-THI interactions for conception rate in both breeds. However, the genetic correlations between the conception rate breeding values at the current average THI (THI = 50, corresponding to a 24-h average temperature of 8 °C at 50% relative humidity) and their slopes (i.e., potential reranking) for heat stress scenarios (THI > 70), were different for each breed. For Montbeliarde, this correlation tended to be positive (i.e., overall the best reproducers are less affected by heat stress), whereas for Holstein it was approximately zero. Finally, our results indicated a weak antagonism between production and fertility, although for Montbeliarde this antagonism intensified with increasing THI.

Conclusions: Within the range of weather conditions studied, increasing temperatures are not expected to exacerbate the fertility-production trade-off. However, our results indicated that the animals with the best breeding values for production today will be the most affected by temperature increases, both in terms of fertility and production. Nonetheless, these animals should remain among the most productive ones during heat waves. For Montbeliarde, the current selection program for fertility seems to be adequate for ensuring the adaptation of fertility traits to temperature increases, without adverse effects on production. Such a conclusion cannot be drawn for Holstein. In the future, the incorporation of a heat tolerance index into dairy cattle breeding programs would be valuable to promote the selection of animals adapted to future climate conditions.

Fig. 1

Average effect of average temperature-humidity indices (THIf) on conception rate. Results are given in number of points of success of the insemination compared to the effect at THIf = 50, for the two breeds, Holstein (HOL, in blue) and Montbeliarde (MON, in brown)

Fig. 2

Distribution of average temperature-humidity indices (THI) associated with performance records. Results are given as a percentage of the total records, within-trait and within-breed records. THI values used for the production trait (i.e., protein yield = THIp) are shown with a dashed line and THI values used for the fertility trait (i.e., conception rate = THIf) are shown with a solid line

Fig. 3

Trajectories of estimates of additive genetic variance for a conception rate (CR) and b protein yield (PY) with changing temperature-humidity index (THI) in Holstein (HOL) and Montbeliarde (MON) breeds. THIp THI for protein yield, THIf THI for conception rate

Fig. 4

Trajectories of estimates of permanent environmental variances for protein yield (PY) with changing temperature-humidity index (THI) in Holstein (HOL) and Montbeliarde (MON) cows. THIp THI for protein yield, THIf  THI for conception rate

Fig. 5

Trajectories of estimates of residual variance for a conception rate (CR) and b protein yield (PY) with changing temperature-humidity index (THI) in Holstein (HOL) and Montbeliarde (MON) cows. THIp THI for protein yield, THIf  THI for conception rate

Fig. 6

Smoothed trajectories of estimates of heritability for a conception rate (CR) and b protein yield (PY) with changing temperature-humidity index (THI) in Holstein (HOL) and Montbeliarde (MON) cows. THIp THI for protein yield, THIf  THI for conception rate

Fig. 7

Estimates of within-trait genetic correlations at different values of temperature-humidity index (THI) for conception rate (CR, left-hand graphs) and protein yield (PY, right-hand graphs) in Holstein (HOL, top graphs) and Montbeliarde (MON, bottom graphs). White contour lines separate genetic correlation classes differing by 0.05. THIp THI for protein yield, THIf  THI for conception rate

Fig. 8

Estimates of genetic correlations between conception rate and protein yield at a given temperature-humidity index (THIf = THIp) in Holstein (HOL) and Montbeliarde (MON) cows

Fig. 9

Estimates of genetic correlations between conception rate and protein yield with changing levels of temperature-humidity index for fertility (THIf) and for five levels of temperature-humidity index for production (THIp). Results are given for Holstein (HOL, left) and Montbeliarde (MON, right)