Seasonal Effects on Body Temperature, Thyroid Function, Blood Glucose and Milk Production in Lactating and Dry Holstein Cows in Semi-Arid Environment PDF

Keywords

body temperature, thyroid function, blood glucose, milk, cows

Abstract

Effects of summer and winter season were studied in two groups of 15 non-pregnant Holstein cows. Each group included 5 dry cows, 5 high-yielders and 5 average-yielders. The rise in air temperature and temperature-humidity index (THI) during summer compared with winter caused a significant (p< 0.01) rise in rectal temperature (RT) and respiratory rate (RR) of lactating cows compared with the early morning, and in the high-yielders compared with the average-yielders. Diurnal rhythms in RT and RR were found in winter but not in summer. Productivity status was found to exert greater effect on plasma thyroid hormone levels than did the season. Regardless of season effect, thyroxine (T4) and triiodothyronine (T3) concentrations were significantly (p<0.01) lower in lactating cows than in dry cows. In summer, dry cows had higher T4:T3 ratio and blood glucose concentration compared with winter season, meanwhile the lactating cows showed an opposite trend. Among the two lactating groups, T3 level was significantly (p< 0.01) reduced in the high-yielding cows only during the winter season. The decline in the milk yield of the high producing cows for each unit rises in THI, air temperature and RT were 0.92, 0.15 and 3 kg/day, respectively.