Required dietary zinc concentrations for dry and prefresh cows were reduced from 40 parts per million (ppm) by the NRC in 1989 to 22 to 30 ppm in 2001, depending upon age and dry matter intake. However, Tennessee researchers found that feeding an additional 800 milligrams of zinc to late gestation cows, which were already receiving a diet containing 102 ppm zinc, resulted in improved fertility and health postcalving. Cows fed additional zinc prepartum had fewer days to first estrus and less udder edema when they were fed diets high in iron, while tending to have fewer days to first service.
New research with other species has found that feeding high levels of zinc to pregnant animals or injecting zinc into eggs resulted in improved gut development and health of offspring. Canadian researchers found that feeding sows an additional 250 ppm zinc from zinc amino acid complex during the last trimester of pregnancy resulted in improved intestinal development of pigs. Intestinal defenses of pigs against pathogens also appeared to have been improved. Sows fed the additional 250 ppm of zinc from a zinc amino acid complex had 2.1 more live pigs than sows fed the control diet.
Results of these studies indicate that increasing zinc supply to pregnant animals has the potential to improve gut health and development of offspring, Mike Socha, research nutritionist with Zinpro Corp., told audience members at the California Animal Nutrition Conference in May.
More research is needed to determine whether calves and cows would benefit from feeding more than the NRC 2001 requirements for zinc during the late gestation period. Socha currently recommends feeding diets containing 75 to 85 ppm zinc during the dry period. Socha discusses more research on trace mineral supplementation in his paper here.