Lactation and reproductive performance of high producing dairy cows given sustained-release multi-trace element/vitamin ruminal bolus under heat stress condition

The aim of the study was evaluation the effect of sustained-release multi-trace element/vitamin bolus on blood metabolite and performance of Holstein dairy cows reared under heat stress conditions. Maximum temperature humidity index (THI) was 77.7 during the trial. Fifty multiparious cows were randomly allocated to two experimental groups: 1-bolus supplemented cows (Treatment), and 2-no bolus (Control). Each bolus contained minerals (16.2 g Cu, 0.251 g Se, 0.236 g Co, 0.497 g I, 8.28 g Mn and 13.32 g Zn) and vitamins (545.6×103 IU of vitamin A, 109.1×106 IU of vitamin D3 and 1092 IU of vitamin E). Results showed that cows supplemented with bolus tended to have higher milk yield (P=0.07), milk fat (P=0.03), protein (P<0.001), and solid non fat (SNF) (P<0.001) percentage compared to control. Bolus supplementation decreased the milk linear somatic cell count (SCC) score (P=0.01). Cows administered bolus tended to have lower plasma non-esterified fatty acids (NEFA) in the postpartum period (P=0.09). Days open (calving to conception) was shortened in response to bolus supplementation (P=0.02). Cumulative pregnancy at fifth artificial insemination was significantly increased in response to treatment (P=0.01). It was concluded that supplementation trace elements and vitamins above National Research Council (NRC) recommendation using a sustained release source had positive effects on reproductive and lactation performance of high producing dairy cows kept under heat stress condition.