Assessment of body and scrotal thermoregulation and semen quality of hair sheep rams throughout the year in a tropical environment

摘要

The present study was carried out to assess the capacity of Morada Nova (MON) and Santa Ines (SIN) hair sheep breeds to maintain homeothermy and its relation with semen quality in a tropical climate. Sixteen rams (MON = 7 and SIN = 9) were assessed for 12 months. During summer and spring, the Temperature-Humidity Index values surpassed the level indicative of thermal stress, and sweating, respiratory and heart rates increased (P & .05). Those responses allowed animals to dissipate heat, maintain rectal temperature in the physiological range and efficiently avoid thermal stress. Scrotal temperatures rose during summer and spring, but, unlike what occurs in wool breeds of sheep, the thermal gradient between poles of testis increased, which shows efficient compensatory scrotal thermoregulation in both breeds herein studied. Semen quality parameters remained within normal ranges. The high correlation observed between rectal and spermatic funicle temperature gradients with sperm membrane integrity (r = 0.62; P & .05) confirmed the importance of systemic and gonadal thermoregulation for the production of ejaculates with highest possible proportion of viable spermatozoa. Thus, MON and SIN rams can be considered resilient to tropical climate since they efficiently perform the thermolysis to face thermal challenges with no negative impact on semen quality throughout the year. Those adaptability characteristics are highly desirable in the genotypes proposed for use in production systems in tropical environments.