Seasonal changes in productive and reproductive performance in holstein dairy cows synchronized for estrus with the ovsynch protocol under subtropical conditions

الملخص EN

This study aimed to evaluate the effects of heat stress on productive and reproductive performances in Holstein dairy cows during summer compared to winter seasons.

During each seasons, temperature– humidity index (THI), rectal temperature, and respiration rate were recorded for 105 days.

Daily milk yield (Kg/day) was recorded for 5 consecutive months each season.

Serum cholesterol, glucose, urea and progesterone (P4) concentrations were determined around the times of inseminations.

Conception rate to first insemination (CR/AI), overall pregnancy rate, number of services per conception (NSPC) and number of days open (DO) were determined each season.

Values of THI, rectal temperatures and respiration rate were greater in summer than winter.

Daily milk yield was greater (P<0.05) in winter months compared to summer.

Serum glucose and urea concentrations were greater in summer than winter during the dry period and at the times of GnRH and PGF injections.

However, cholesterol was greater in winter during GnRH and PGF injection times.

Serum P4 concentrations were not affected by GnRH treatment in summer, whereas GnRH injection increased P4 concentration during winter season.

More winter cows conceived to first AI and required less number of services per conception and had fewer days open compared to summer cows