Impact of some micronutrients on the quantity and quality of colostrum and milk produced during the transition period of dairy cows under heat stress conditions.

Heat stress in most parts of the world has a negative effect on the performance of dairy cows and reduces milk production in dairy cows. Supplementation of cows with micronutrients (minerals and vitamins), especially in the close up period, can have benefits in reducing the negative effects of heat stress and improve the yield of cows during the next lactation period. This study was conducted to investigate the effect of some nutrients on the physiological and performance processes of dairy cows in heat stress.

In this research, 24 multiparous dairy cows were used in the transition period. The cows were randomly divided into 2 groups of 12 and each group was assigned to a test treatment. Treatments include control group: only from the common diet and without nutritious additives and the second group, which in addition to the common diet, received a micronutrients for 21 days before parturition. After parturition, each of the control and treatment groups were again subdivided into two groups of 6, so that in each group, they were either fed with diets without micronutrients or enriched with micronutrients until 21 days after parturition.The supplement containing a micronutrient of the close up period, including micronutrients of selenium, copper, zinc, chromium, beta carotene, vitamin E, magnesium, ascorbic acid and niacin and the micronutrient supplementation of the freshly period in addition to the micronutrient above, contained sodium and potassium. The average temperature- humidity index was during the text period of 74 and cows were heat stress. The conditions of maintenance and management of nutrition and environment were the same for all the animals during the whole experiment period. Weight variations, feed intake and rectal temperature were determined each week 4 hours after feed intake in two consecutive days. The weight of the newborn calves, the weight of the placenta and the amount of colostrum produced during the first three milking was recorded.

The amount of dry matter intake during close up was higher in the micronutrient intake group than the control group, and in the last week of pregnancy there was a significant difference between them (P<0/05). Although weight gain during the close up was not affected by treatment, more weight gain was observed in the group receiving micronutrients. The numbers of pregnant days in cows receiving micronutrients were longer than the control group. The birth weight of calves in cows receiving micronutrients was higher than the control group. colostrum was also more produced in this group. Calves weaning weight was not affected by treatments. Feed intake during the lactating period was affected in the first week of lactation and receiving micronutrients transition period treatment in the third week had the highest feed intake, which in parallel with this week the milk production of this group was higher than other groups and its difference with other treatments was significant(P<0/05). Milk composition were not affected by treatments (P>0/05).

This experiment showed that heat stress can have a negative effect on the performance of dairy cows during the transition period and the use of micronutrients in this period can have beneficial effects on the repair of heat stress in dairy cows.