Effect of adaptation and heat stress on reproductive performances of fat-tail Awassi rams in eastern Mediterranean

الملخص EN

The Awassi fat-tail sheep is desired in the middle east and Sahara for its hardiness and resistance.

in this region, the adaptability of Awassi rams to elevated heat stress is controversial.

the objective of this study was to assess the effect of ambient or testicular 43 ºC heat on semen characteristics.

12 Awassi rams of 1.2 to 2 years were allowed an initial adaptation period (P0), followed by two experimental phases (P1 and P2), each including a period of heat stress (HS1 and HS2) followed by a period of recovery from heat stress (R1 and R2).

heat stress conditions were considered when ambient temperature (Group 2) or testicular environment (Group 3) reached 42 to 44 ºC.

Control animals (Group 1) were exposed to ambient environmental conditions.

temperature-humidity index (THI) as a relationship of ambient temperature, wet and dry humidity effect along with respiration and pulse rate, body temperature and live body weight (BW) were measured weekly as adaptation parameters.

reproductive parameters assessed included scrotum circumference and testicular volume measured twice per heat stress period, whereas semen volume, density concentration and motility were measured twice weekly.

data were analyzed using the mixed procedure of SAS under a time series analysis model, with treatment and time nested within period as main effects, and treatment by time within period as interaction terms.

treatment means were separated using fisher protected LSD.

results showed a THI of 25.7 during the rest periods (R1 and R2), 30 during HS1 and 28 during HS2.

BW decreased with ambient stress, whereas respiration rate increased during heat stress periods (HS1 and HS2).

testes volume decreased with both ambient and testicular heat stress, whereas testicular circumference was not affected by these conditions.

semen concentration decreased whereas semen volume increased with ambient but not testicular heat stress.

spermatozoa abnormalities increased in R1 following heat stress (HS1) mainly in the acrosomal and mid piece regions, but not the tail.

Progressive motility was decreased immediately during heat stress periods, but recovered in the rest period.

Awassi rams show a potential for heat stress adaptability where the effect of a 1st period of heat stress observed by a decrease in semen characteristics is thereafter dissipated during subsequent heat stress events.