Effect of GnRH dose on occurrence of short oestrous cycles and LH response in cyclic dairy heifers.
Reprod Domest Anim
; 44(4): 647-52, 2009 Aug.
Article
em En
| MEDLINE
| ID: mdl-18673332
ABSTRACT
Prostaglandin F(2 alpha) (PGF(2 alpha)) and GnRH treatments given 24 h apart have been shown to result in short oestrous cycles (8-12 days) in some cows and heifers. The differences in responses may depend on the dose of GnRH. Therefore, the effect of the dose of GnRH on occurrence of short cycles and LH response was studied here. Oestrus was induced with dexcloprostenol (0.15 mg) in two groups of Ayrshire heifers. A second luteolysis was induced similarly on day 7 after ovulation; 24 h after PGF(2 alpha) treatment, the heifers were administered either a high (0.5 mg, n = 15, group T500) or low (0.1 mg, n = 10, group T100) dose of gonadorelin. Blood samples for progesterone analyses were collected daily from the second PGF(2 alpha) administration to the second ovulation after the PGF(2 alpha) injection. Beginning 24 h after the GnRH treatment, ovaries were examined by transrectal ultrasonography every 6 h until ovulation, and daily between day 4 and the next ovulation. Five heifers from both groups were sampled for LH analyses via a jugular catheter every 30 min from 1 h before to 6 h after the GnRH administration. Short oestrous cycles were detected in 7 of 10 cases in group T100 and in 12 of 15 cases in group T500. No significant differences in LH responses were detected between the groups. In group T500, the rise in LH concentration tended to be somewhat slower than in group T100. The dose of GnRH (0.1 vs 0.5 mg) did not affect the occurrence of short oestrous cycles and LH response.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Bovinos
/
Hormônio Luteinizante
/
Hormônio Liberador de Gonadotropina
/
Ciclo Estral
Tipo de estudo:
Diagnostic_studies
Limite:
Animals
Idioma:
En
Revista:
Reprod Domest Anim
Assunto da revista:
MEDICINA REPRODUTIVA
/
MEDICINA VETERINARIA
Ano de publicação:
2009
Tipo de documento:
Article
País de afiliação:
Finlândia