Effect of Seasons on Physiological Responses in Sahiwal and Crossbred Cows

Background: Growing demand for improving milk production and rising temperatures due to global warming has increased the thermal load on dairy animals. Physiological parameters such as respiration rate and body temperature mainly determine the adaptability of animals to climate stress. During genetic adaptation, Bos indicus cattle have acquired thermo tolerant genes and when exposed to heat stress conditions, the Bos indicus cattle have lower respiration rates and rectal temperatures than Bos taurus animals. The present study was aimed to study the effect of seasons on the physiological responses in Sahiwal and crossbred cows. Methods: A total of 50 crossbred cows maintained at Military Dairy Farm, Secunderabad and 50 Sahiwal cows maintained at Livestock Farm Complex, College of Veterinary Science, Rajendranagar, PVNRTVU were utilized for the present investigation. The study was conducted during summer (THI= 83.71 +/- 0.01), rainy (THI= 71.37 +/- 0.01) and winter (THI= 66.69 +/- 0.01) seasons. Changes in respiration rate (RR), rectal temperature (RT) and heat tolerance coefficient (HTC) were observed in different seasons in Sahiwal and crossbred cows. Result: RR (breaths/min) in Sahiwal cows during summer, rainy and winter were 28.56 +/- 0.38, 23.38 +/- 0.38 and 20.54 +/- 0.38 respectively whereas RR (breaths/min) in crossbred cows were 44.58 +/- 0.38, 25.94 +/- 0.38 and 21.90 +/- 0.38 respectively. In Sahiwal cows RT (degrees C) during summer, rainy and winter were 38.52 +/- 0.03, 38.23 +/- 0.03 and 38.13 +/- 0.03 respectively whereas RT (degrees C) in crossbred cows were 39.22 +/- 0.02, 38.72 +/- 0.03 and 37.80 +/- 0.03 respectively. The magnitude of increase in RR, RT and HTC were found to be higher during summer compared to other seasons in both Sahiwal and crossbred cows. It was observed that Sahiwal cows are less sensitive to heat stress and are better able to regulate their body temperature than crossbred cows when environmental temperature increases during summer. The HTC values were lower in Sahiwal cows in all the seasons studied indicating better thermo tolerance when compared to the crossbred cows.