INDUCED LACTATION IN DAIRY HEIFERS: EFFECTS OF BOVINE SOMATOTROPIN, TIME OF BOVINE SOMATOTROPIN ADMINISTRATION, AGE AT INDUCTION, AND DEXAMETHASONE ADMINISTRATION
Open Access
- Author:
- Macrina, Ann Lynne
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 16, 2010
- Committee Members:
- Terry D Etherton, Dissertation Advisor/Co-Advisor
Terry D Etherton, Committee Chair/Co-Chair
Daniel M Kniffen, Committee Chair/Co-Chair
Joy Lee Pate, Committee Member
Michael O'connor, Committee Member
Lester C Griel Jr., Committee Member - Keywords:
- dairy heifers
somatotropin
economics
dairy cattle
induced lactation
milk composition - Abstract:
- Heifer rearing represents a large cost component of commercial dairying because these animals do not produce milk until approximately two years of age. Inducing heifers into lactation at a younger age would reduce this non-productive time. The objectives of this research were to characterize milk production, growth, reproduction, and herd life after induced lactation in healthy 15-month old heifers; to quantify the lactation response to bovine somatotropin (bST), and compare survival rate and profitability of induced heifers to conventionally raised heifers; to evaluate whether starting bST treatment during lactation induction would improve milk production; and to determine if dexamethasone administration at the onset of milking and age at lactation induction would affect milk production. Holstein heifers were induced into lactation by daily administration of estradiol-17β (0.075 mg/kg body weight [BW]) and progesterone (0.25 mg/kg BW) for 7 days. Milking began on day 18. Heifers treated with bST (500 mg dose every 14 days) between 25 and 95 days in milk (DIM) produced 14.7% more milk than controls. Induced heifers gained 0.69 kg/d, averaged 1.8 services/pregnancy, and 27 heifers calved subsequently. Induced animals had a 62.7% chance of remaining in the herd as long as conventionally raised heifers, however both groups had similar productive lifespans. Net present value for an induced animal ($2459) was not different from that of a traditionally raised peer ($3137). When bST administration began on experimental day 1 with the induction treatment, mean daily milk yield for bST-treated heifers was 36% higher than for controls. Milk production remained higher in bST-treated heifers (15.5%) through 305 DIM even though control animals began bST treatment at 54 DIM. The data suggest that heifers treated with bST during the induction phase had more mammary secretory tissue than controls. Dexamethasone administration (10 mg) on days 1 and 2 of lactation increased initial milk production through 15 DIM, but this did not persist through 305 DIM. Milk yield was 8.6% higher in heifers induced into lactation at 18 months compared to those induced at 14 months of age. This may be due to higher feed intake capacity, greater mammary epithelium, or both.