Rabbits' productive, reproductive and physiological performance traits as affected by heat stress: a review

Rabbits are very susceptible to heat stress, since they have few functional sweat glands and have difficulty in eliminating excess body heat, when the environmental temperature is high. Exposure of growing and adult male and female rabbits to < 30 THI (temperature-humidity index) units as severe heat stress during summer, adversely affects their growth and reproductive traits and reduces the resistance to diseases. In female rabbits, conception rate, embryonic development, litter size, litter weight and milk production decrease and age at puberty and pre- and postweaning mortality increase by exposure to heat stress. In males, testosterone concentration, spermatogenesis, temporary sterility, sexual desire, ejaculate volume, motility, sperm concentration and total number of spermatozoa in an ejaculate decrease and sperm abnormalities and dead sperm increase by exposure to the same factor. The drastic changes that occur in rabbits' biological functions are depression in feed intake and feed efficiency and utilization, disturbances in metabolism of water, protein, energy and mineral balances, enzymatic reactions, hormonal secretions and blood metabolites. When exposure to THI 30 or more, rabbits can no longer regulate internal temperature and heat prostration sets in. (C) 2002 Elsevier Science B.V. All rights reserved.