A note on the effects of health environment on heterosis for growth rate in pigs

Abstract

Heterosis for growth rate in pigs is usually expressed, and reviews of European and North American studies have been given by Sellier (1976) and Johnson (1981). Kennedy and Moxley (1980) observed heterosis of 0·044 to 0·067 for weight at 154 days and attributed some of the crossbred advantage to heterosis for resistance to atrophic rhinitis. Similarly, McGuirk, Bourke and Manwaring (1978) attributed some of the heterosis for growth rate in sheep to heterosis for resistance to pneumonia. Although little attention has been paid to interactions between heterosis and health environment, Barlow (1981) concluded from an extensive review of studies involving farm and laboratory animals that heterosis is environment dependent and is enhanced by increased stress. Sellier (1976) commented that it would be useful to examine the degree of heterosis with ‘specific pathogen free’ pigs raised in a healthy environment, and this study examined heterosis for days to 90 kg in Yorkshire × Landrace pigs under three different environments with respect to health conditions.