title: Induced lactation in pubertal heifers: efficacy, response to bovine somatotropin, and profitability.
abstract: Heifer rearing represents one of the largest costs of commercial dairying because these animals do not begin to produce milk until approximately 2 yr of age. The objectives of this study were to characterize milk production, growth, reproduction, and herd life after induced lactation in healthy 15-mo-old heifers. We further wanted to quantify their lactation response to bovine somatotropin (bST), and compare survival rate and profitability of heifers induced into lactation to that of heifers reared using traditional methods. Holstein heifers (n = 32) were induced into lactation by administration of estradiol-17β (0.075 mg/kg of body weight per d) and progesterone (0.25 mg/kg of body weight per d) for 7 d. Milking began on experimental d 18. Heifers were paired based on milk production, and one in each pair was assigned randomly to bST or control treatment groups; treatments began on 25 ± 7 d of lactation, and milk production was compared for 70 d. Heifers treated with bST produced 14.7% more milk than did controls. After the 70-d comparison period, all heifers received bST for the remainder of their lactations. Throughout the induced lactation, heifers gained 0.69 kg/d, averaged 1.8 services/pregnancy, and 27 heifers calved for a second lactation. For the herd life and economic analyses, heifers induced into lactation were compared with similarly aged heifers in the same herd reared by traditional management methods. The animals induced into lactation had a 62.7% chance of remaining in the herd as long as the peer cohorts, but both groups had similar productive lifespans. Net present value for an induced animal ($2,459) was not different from that of a traditionally raised peer ($3,137). In summary, heifers hormonally induced into lactation with estrogen and progesterone were healthy, grew normally, had a mean daily milk production of 18 kg with normal composition, and had good reproductive performance. Based upon the assumptions and prevailing financial environment of this experiment, hormonally induced lactation of 15-mo-old heifers, as a routine management tool, was not more profitable than traditional management practices.
authors.affiliation: Department of Dairy and Animal Science, The Pennsylvania State University, University Park, PA 16802, USA. ALM106@psu.edu
authors.forename: A L
authors.initials: AL
authors.lastname: Macrina
authors.forename: P R
authors.initials: PR
authors.lastname: Tozer
authors.forename: R S
authors.initials: RS
authors.lastname: Kensinger
mesh_terms: D000367:Age Factors; D000818:Animals; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D003612:Dairying / Q000191:economics / Q000379:methods; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007774:Lactation / Q000187:drug effects*; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D012098:Reproduction / Q000502:physiology; D015996:Survival Rate
chemical_list: D013006:Growth Hormone