IMPACT OF HEAT STESS EXPOSURE ON SOME REPRODUCTIVE AND PHYSIOLOGICAL TRAITS OF RABBIT DOES

Abstract

SUMMARY Effect of heat stress throught the first and second parities of NZW doe rabbits on some reproductive and physiological traits was evaluated. Fourty four parturitons (22 in each parity) were used in this study. Parturitions in each parity were divided into two main groups, each group of 11 ones. The first group was maintained at 21.9±0.9 °С and 46.1±2.7 RH % (20.8 THI, comfort conditions) and served as a control (C) group. The second one was exposed for about 8 h. to cyclic ambient temperature of 37.1±0.5 °С and 44.8±2.2 RH % (33.2 THI, severe heat stress conditions) from 13:00 to 21:00. Then, the temperature was lowered to the temperature in the rabbitry of control group from 21:00 to 13:00. Results obtained showed that high temperature cuased a significant increase (P<0.05 or 0.01) in respiration rate; rectal and skin temperature values (126.8 breaths/min., 39.6 and 38.5 ˚C, resp.) as compared with those maintained under comfort conditions (112.0, 38.5 and 38.2, resp.). Number of services per conception was increased while litter size significantly decreased (P<0.05 or 0.01) for heat stressed does compared with those of does kept in comfort conditions. Gestation period was not significantly affected by ambient temperature treatment. Number of services per conception of does at second parity were higher (P<0.01) than those at first one. Heat stressed does showed an acute decrease (- 24 to - 29 %) in milk yield compared to does reared in comfort conditions. High ambient temperature significantly decreased (P<0.01) hemoglobin concentration, red and white blood cell counts compared with those of does maintained under comfort conditions. Interaction effects between ambeint temperature and parity order on the studied parameters were mostly insignificant, however, differences among interaction groups were significant (P<0.05) only for number of services per conception and gestation period. Does at the second parity, which maintained in hot temperature had the highest value of number services per conception, while those of the first parity in comfort conditions were the lowest one. Most of the studied traits were correlated significantly by a valuable magnitude, especially the thermo-respiratory traits that negatively correlated with litter size and blood hematological traits and positively correlated with number of services per conception, while each of litter size and milk yield were positively correlated with blood hematological traits. Histological features showed that heat stress had a deleterious effect on the histological statues of ovaries and uteruses of rabbit does. These results indicate that high ambient temperature was of bad effects on most of the reproductive and physiological traits of rabbit does. Consequently, rabbit breeders must use the available methods to alleviate the heat stress on their animals during periods of hot conditions, particullary during summer months in Egypt.