Effect of exogenous bovine growth hormone and ovariectomy on prepubertal mammary growth, serum hormones and acute in-vitro proliferative response of mammary explants from Holstein heifers

Sixteen prepubertal Holstein Friesian heifers were used to study the effect of long-term administration of bovine GH (bGH) on mammary development in intact and ovariectomized heifers. Eight heifers were ovariectomized at 2-5 months of age. Four intact and four ovariectomized heifers received subcutaneous injection of bGH (15 mg/day) for 15 weeks starting at 176±3 days of age (147±3 kg body weight), while the remaining eight heifers received an equal volume of excipient. Blood samples were collected weekly from 2 months of age. Heifers were slaughtered on the day after the last injection of bGH or excipient. Mammary gland development was quantified by dissection, chemical analysis and computer tomographic scanning