Effect of additional cobalt, copper, manganese, and zinc on reproduction and milk yield of lactating dairy cows receiving bovine somatotropin

The objective of this study was to determine whether organically complexed Co, Cu, Mn, and Zn would improve the reproductive performance and milk and milk component production in lactating dairy cows that began receiving bovi ne somatotropin in the ninth week of lactation. Holstein(n = 50) and Jersey (n = 10) cows were blocked by breed, lactation number, and incidence of ret ained fetal membranes. Two diets assigned within blocks and fed from partur ition until 154 d of lactation were control or control supplemented daily w ith 26 mg of Co as Co glucoheptonate, 125 mg of Cu as Cu-Lys, 199 mg of Mn as Mn-Met, and 359 mg of Zn as Zn-Met. Cows were fitted with electronic pre ssure-sensing devices in the second week of lactation for detection of estr us. Ovarian structures were determined via transrectal ultrasonography at 7 -d intervals from parturition until observation of the first corpus luteum. Blood samples were taken at 7-d intervals and analyzed for plasma concentr ations of progesterone, insulin, and urea nitrogen. Onset of luteal activit y was identified by progesterone concentrations greater than or equal to 1 ng/ml. Retained fetal membranes increased days to first estrus (detected vi a electronic estrous detection), first luteal activity, and first corpus lu teum in control cows but not in supplemented cows. Days to first observed e strus were greater for control cows than for supplemented cows. Days to fir st service, days open, days from first service to conception, services per conception, milk yield, milk components, and somatic cell counts were simil ar for control and supplemented cows. Supplementation with complexed trace minerals effectively reduced days to first estrus.