Climatic effects on productive traits in livestock

Abstract

Each species, breed or animal category has its own thermal zone of comfort outside of which it experiences heat stress in the attempt to maintain homeothermy, so that less energy is available for production processes. Cold represents less of a problem than heat. Heat stress (HS) can negatively affect the number of spermatozoa and motile cells per ejaculate, impair oocyte growth, conception rates, embryo development, increase embryo mortality or reduce growth of the foetus during pregnancy. Heat stress also reduces dry matter intake, average daily weight gain and carcass weight and composition. In dairy cows, HS lowers the energy and protective value of colostrum, results in a lower milk yield and percentage of milk fat, protein, and lactose and causes changes in the proportions of protein fractions, fatty acid composition and rheological behaviour of milk. Sheep and goat milk production is similarly affected. In poultry, egg production, egg weight, shell weight and shell thickness are considerably worsened under high temperature conditions; egg breakage also increases. Areas of investigation are suggested to alleviate the negative effects of climatic constraints in livestock production systems.