Genetic components of heat stress in finishing pigs: Development of a heat load function

Abstract

The objective of this study was to quantify the effect of heat stress during the life of a pig on its final weight, as a first step toward a genetic evaluation for heat tolerance. Data included carcass weights of 23,556 crossbred pigs [Duroc x (Landrace x Large White)] raised on 2 farms in North Carolina and slaughtered from May 2005 through December 2006. Weather data were available from a nearby weather station. Lifetime of a pig was assumed to be partitioned into 2 periods. During an initial period, the effect of heat stress was assumed to be negligible or compensated for later. During the second period ending in slaughtering, the ADG was assumed to be affected linearly by heat load. Weekly heat load was calculated as degrees of average temperature-humidity index in excess of a threshold (18 degrees C). The total heat load (H) was the sum of weekly heat loads during the second period. During the months of January to May H was 0; H reached a peak in September. The final BW during the peak of heat stress decreased about 6 kg compared with BW during months of non-heat stress. Weekly and monthly averages of carcass weight generally moved similarly to H. However, there were large fluctuations unrelated to H; the fluctuations were different on the 2 farms. The model included the effects of farm-year of slaughter, sex, age at slaughter, and H, where age at slaughter and H were linear regressions. In analyses, the threshold was varied from 16 to 20 degrees C, and the second period was varied from 8 to 16 wk. The greatest R(2) (10.4%) was at the threshold of temperature-humidity index = 18 degrees C for a period of 10 wk. Varying the threshold and the length of time reduced R(2) less than 1%. Least squares means of year-month and year-week of carcass weight were calculated using a model with the fixed effects farm-year-month or farm-year-week of slaughter, sex, and age at slaughter (linear covariate), and the random effect of birth litter. Changes in BW of finisher pigs due to heat stress can be quantified by H during the last 10 wk of the life of the pig.

Adaptation to climate change – exploring the potential of locally adapted breeds

“…High thermal resistance has a physiological cost in terms of lower performance in non-stressed environments (Williams et al, 2008). The capacity to tolerate elevated temperatures has declined with increasing metabolic heat production related to high milk yield in dairy cattle, and growth rates and leanness in pigs or poultry (Zumbach et al, 2008;Dikmen and Hansen, 2009;Gauly et al, 2013).…”

“…High thermal resistance has a physiological cost in terms of lower performance in non-stressed environments (Williams et al, 2008). The capacity to tolerate elevated temperatures has declined with increasing metabolic heat production related to high milk yield in dairy cattle, and growth rates and leanness in pigs or poultry (Zumbach et al, 2008;Dikmen and Hansen, 2009;Gauly et al, 2013).Beyond thermoregulation, rumen physiology, the ability to walk and reach scarce feed resources, to intake water and rehydrate, to compensate for low feed quality by selecting high-quality diets from different plant components or species, or to respond with increased night-time grazing to high afternoon temperatures, or even genetic aspects of diet selection play a role in adaptation to climate change (Hall, 2004;Gauly et al, 2013). Breeds are known to differ with regard to their ability to survive, grow and reproduce in the presence of poor seasonal nutrition as well as parasites and diseases; they vary in their ability to mobilize body resources to cope with periodic underfeeding and cease reproduction at different levels of BW loss.…”

Adaptation to hot climate and strategies to alleviate heat stress in livestock production

“…This approach was first developed in dairy cattle by Ravagnolo et al (2000), who estimated genetic parameters for resistance to heat stress indirectly by regressing phenotypic performance on a THI value calculated from data coming from public weather stations. A similar work was performed in finishing pigs using a heat load index calculated for the 10 weeks before slaughter (Zumbach et al, 2008). In both studies, heritabilities for performance traits (milk production or carcass weight at slaughter) were found to increase as a function of THI.…”

The impact of evaporative cooling on the thermoregulation and sensible heat loss of sows during farrowing

“…These differences suggest that the genetic selection on sow heat stress tolerance may be possible (ZUMBACH et al, 2008;BLOEMHOF et al, 2012 andMADZIMURE et al, 2012).…”