Use of bovine somatotropin in lactating dairy cows receiving timed artificial insemination.
Objectives of the research were to examine the effect of bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol and to test a resynchronization system with two consecutive synchronized services. Lactating Holstein cows (n = 403) were assigned to the following treatments: bST treatment (500 mg) was initiated at 63 +/- 3 d postpartum concomitantly with initiation of the timed artificial insemination protocol or bST treatment was initiated at 105 +/- 3 d postpartum. At 63 +/- 3 d postpartum, all cows received GnRH (100 microg), an injection of PGF2alpha (25 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were reinseminated at detected estrus or resynchronized with a GnRH injection at 20 d after insemination. At 27 d after insemination, cows were examined for pregnancy. Resynchronized cows diagnosed nonpregnant received an injection of PGF2alpha and were inseminated at detected estrus or received an injection of GnRH at 48 h after PGF2alpha and inseminated 16 to 20 h later. Cows pregnant at d 27 were reexamined for pregnancy at 45 d after insemination. First-service pregnancy rates at d 45 were increased in cows not resynchronized that initiated bST treatment at 63 +/- 3 d postpartum, compared with cows initiating bST treatment at 105 +/- 3 d postpartum (37.7 +/- 5.8% and 22.1 +/- 4.2%, respectively), but the effect of bST treatment was not observed when cows were resynchronized (25.6 +/- 4.3% and 25.8 +/- 5.5%, respectively). Thus, bST increased pregnancy rates to a timed artificial insemination protocol.
Moreira
F
F
Department of Dairy and Poultry Sciences, University of Florida, Gainesville 32611, USA.
Risco
C A
CA
Pires
M F
MF
Ambrose
J D
JD
Drost
M
M
Thatcher
W W
WW
D000704:Analysis of Variance; D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage; D005260:Female; D005298:Fertility / Q000187:drug effects*; D005300:Fertility Agents, Female / Q000008:administration & dosage; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D013006:Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000502:physiology / Q000662:veterinary*; D007774:Lactation; D011247:Pregnancy; D018873:Pregnancy Rate; D011258:Pregnancy Tests / Q000662:veterinary; D011374:Progesterone / Q000097:blood; D013997:Time Factors; D016216:Ultrasonography, Prenatal / Q000662:veterinary
D005300:Fertility Agents, Female; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D013006:Growth Hormone; D015237:Dinoprost