EXOGENOUS PGF(2)ALPHA ENHANCED GNRH-INDUCED LH-RELEASE IN POSTPARTUM COWS

Citation
Rd. Randel et al., EXOGENOUS PGF(2)ALPHA ENHANCED GNRH-INDUCED LH-RELEASE IN POSTPARTUM COWS, Theriogenology, 45(3), 1996, pp. 643-654
Citations number
37
Categorie Soggetti
Veterinary Sciences
Journal title
ISSN journal
0093691X
Volume
45
Issue
3
Year of publication
1996
Pages
643 - 654
Database
ISI
SICI code
0093-691X(1996)45:3<643:EPEGLI>2.0.ZU;2-W
Abstract
This study evaluated the effect of exogenous PGF(2) alpha on circulati ng LH concentrations in postpartum multiparous (n = 32) and primiparou s (n = 46) Brahman cows. The cows were randomly allotted within parity and calving date to receive 0, 1, 2 or 3 mg im PGF(2) alpha (alfapros tol)/100 kg body weight (BW), with or without GnRH on Day 30 after cal ving. Blood samples were collected at weekly intervals from calving th rough treatment. Serum progesterone concentrations were determined usi ng RIA procedures to assure that only anestrous cows were treated. Ste rile marker bulls were maintained with cows on Coastal bermudagrass pa stures until the first estrus was detected. Multiparous cows had a sho rter (P < 0.05) interval from calving to estrus than did primiparous c ows. Serum LH was affected by time (P < 0.0001), PGF(2) alpha dose (P < 0.0002), GnRH (P < 0.0001), parity by PGF(2) alpha dose (P < 0.0003) , PGF(2) alpha dose by GnRH (P < 0.0009), parity by GnRH (P < 0.0008), and by parity by PGF(2) alpha dose by GnRH (P < 0.0005). Multiparous cows not receiving GnRH had higher mean serum LH (P < 0.02), LH peak p ulse height (P < 0.03), and area under the LH release curve (P < 0.03) compared with primiparous cows. The number of LH pulses/6 h was great er (P < 0.06) in multiparous than primiparous cows, and was greater (P < 0.02) in multiparous cows receiving 3 mg/100 kg BW than in cows rec eiving 2 mg/100 kg BW, but not in the controls or in cows receiving 1 mg/100 kg BW. Exogenous GnRH resulted in increased (P < 0.0001) serum LH concentrations in all cows, and LH was enhanced (P < 0.0009) by sim ultaneous treatment with PGF(2) alpha. Primiparous cows had a greater response (P < 0.0005) to PGF(2) alpha and GnRH compared with multiparo us cows. Pituitary release of LH in response to GnRH was enhanced by s imultaneous exposure to PGF(2) alpha in Day 30 postpartum cows.