Determination of the Post-Partum Time when the Pituitary-Ovarian Axis of the Suckler Zebu Cow (<em>Bos indicus</em>) is Sensitive to Synthetic GnRH

Abstract

In order to determine the time of puerperium when the pituitary- ovarian axis of the suckler zebu cow (Bos indicus) is functional, a single dose of 100 μg synthetic GnRH was injected intramuscularly in 60 suckler zebu cows divided into six groups. The animals were treated 7, 10, 15, 20, 25 and 30 days after parturition. Ten milliliters of milk were sampled from each animal as follows: before GnRH injection (A: 1st sample range), on days 5, 6, 7, 8 (B: 2nd sample range) and 20, 21, 22, 23, 24 (C: 3rd sample range) after GnRH injection. In each group, samples obtained before GnRH injection were used as control. Overall, 600 milk samples were used to determine progesterone concentrations by radioimmunoassay. Among the animals treated with GnRH 15 days after parturition, 60% responded to the treatment with a mean progesterone concentration of 2.67 ± 1.89 nmol/L. This response increased along with the length of the post-partum period. Thirty days after calving, all animals responded well to the treatment (mean progesterone concentration: 4.09 ± 1.09 nmol/L) and presented a significant reduction (p < 0.05) in the interval from calving to conception compared to animals treated on days 7 and 10 after calving. This study shows that, as early as 15 days post-partum, the pituitary-ovarian axis of suckler zebu cows is sensitive to exogenous GnRH and that such treatment may improve reproductive performances.

Keywords

• Bos indicus
• GnRH
• Hypophyse
• Ovaire
• Période périnatale
• Progestérone