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Growth -promoting agents to reduce climatic stress in feedlot cattle
Two feedlot trials conducted at the University of Nebraska-Lincoln and one metabolism trial in a climate controlled room at the University of Queensland-Gatton were used to determine the effects of growth promoting agents (TRT) and changes in climatic conditions on physiological and behavioral characteristics. In feedlot trials, feeding melengesterol acetate (MGA) to heifers when an estrogenic/androgenic combination (ET) implant was used resulted in a synergistic effect on DMI in the summer and not in the winter. Heifers were more efficient for gain: feed in the summer when compared to the winter. Quality grades were improved when MGA was fed to ET treated heifers. Serum IGF-I, plasma triiodynthine and thyroxin were elevated in the winter compared to the summer as a result of greater DMI in the winter. The more aggressive the growth promoting strategy resulted in increased levels of serum IGF-I. Also, plasma urea nitrogen was lowest for heifers treated with ET and ET plus MGA. Maximum tympanic temperature (TT) was greatest under heat stress and minimum TT was lowest under heat stress. Heifers fed MGA had the lowest maximum TT under heat stress. Under cold stress, heifers treated with estrogen showed less signs of shivering when compared to other TRT. Rectal temperatures were the highest in animals implanted with an estrogen. Heat production was elevated when a TRT was utilized. In summary, MGA provided some heat stress alleviation in feedlot trials and estrogenic implants tended to raise body temperature. ^
Biology, Animal Physiology|Agriculture, Animal Culture and Nutrition
Kreikemeier, Wanda Mae, "Growth -promoting agents to reduce climatic stress in feedlot cattle" (2003). ETD collection for University of Nebraska - Lincoln. AAI3092565.