Effect of Heat Stress on the Productive and Reproductive Performances of Crossbred Dairy Cattle at Chattogram

Abstract

Cattle among the other livestock species found in Bangladesh are the most versatile component in consideration to existing integrated agricultural farming system. Chattogram is one of the most dairy developed districts of Bangladesh in the aspect of commercial dairy farming. The present study intended to determine the effect of heat stress on productive and reproductive performances of the dairy cattle of Chattogram at different farming conditions. In context of this objective, three commercial dairy farms (denoted as farm A, B, C) from Chattogram were selected considering differences in housing conditions and availability of crossbred genotypes. From the selected farms 27 cows (3 from each genotype of same lactation, from each farm) of different genotypes, grouped as G1 (HF50%×L25%), G2 (HF75%×L25%), G3 (HF50%×S50%) were picked to determine the productive performances. Along with these all dairy cows of mentioned genotypes from selected farms (n=173) were observed during the experimental period for determining the reproductive performances. During the experimental period from December, 2018 to June, 2019 the highest average temperature humidity index (THI) were 66.22±5.55, 69.82±5.83, 72.80±5.42, 76.43±2.89, 78.93±1.75, 80.29±2.06 and 83.58±2.77 in December, January, February, March, April, May and June, respectively obtained from Farm C compared to farm A and B. The differences of THI between three farms were significant (p<0.05). The highest rectal temperature (RT) was 39.36±0.05°C observed in genotype G2 during June and the lowest was 38.5± 0.11°C observed in genotype G1 during December. The differences of RT in three groups were significant (p<0.05). Highest average milk yield was 18.88±0.58 L/day/cow in case of genotype G2 during January and the lowest was 9.11±0.12 L/day/cow in genotype G1 during June. The differences of milk production among different genotypes in different months were significant (p<0.05). In case of milk composition (Fat, protein) highest average percentage were obtained during cooler month and the lowest during month with low THI. As compared to G1 and G3 genotypes milk production and composition of G2 genotype had more negative impact by increased THI. For all genotypes group, the highest conception rate (62.5, 61.53 and 57.14% in G1, G2 and G3 genotype, respectively) was recorded in the month of December whereas the lowest rate (50, 30, and 42.12 in G1, G2 and G3 genotype, respectively) was observed in the month of June. The mean days open in selected groups were higher during cooler months and lower during hotter months of the trial. The highest CBW was 35.75±1.06 kg during January in genotype G2 and which was declined upto 17.5% during May when THI exceeds thermoneutral zone. Incidence of abortion, dystocia and retained placenta were higher 66.66%, 40% and 42.85%, respectively during the month with high THI due to heat stress condition of the pregnant cows. From the result it can be concluded that housing system plays an important role in THI of the stanchion barn, that increased THI clearly affect the productive and reproductive performances of crossbred dairy cows. Cows with higher temperate blood percentage in the study are more prone to heat stress.