Resumen

ROSETE-FERNANDEZ, Jorge V; VILLA-GODOY, Alejandro  y  VILLAGOMEZ-AMEZCUA-MANJARREZ, Eugenio. Effect of Naloxone over the secretion of the Luteinizing Hormone on double purpose cows with double milking and suckling. Rev Colom Cienc Pecua [online]. 2007, vol.20, n.1, pp.9-15. ISSN 0120-0690.

This study determined the effect of zero, one and three intramuscular injection of naloxone (NX, 500mg) on 30 postpartum day for 1 hour intervals over the release of the luteinizing hormone in dual purpose cows in anestrous (¾ Europe x ¼ Zebu) cows (n =18). The cows grazed on African Star grass (Cynodon plectostachyus) and native grass (Axonopus and Paspalum spp) and ate daily 5 kg of balanced food (16% crude protein). The cows were mechanically milked twice a day and after that their calves were allowed to suck for 30 minutes. A blood sample was collected every two days, from the delivery until 30 days postpartum for the quantification of progesterone (P) by RIA. In this blood anestrous was indicated by P< 1 ng/ml. On day 30 postpartum blood samples were drawn every 15 min during 3 hours: one hour after each naloxone injection or saline solution and Luteinising Hormone (LH) was measured by RIA. The response variables were mean (MLH) and basal concentration (BLH), number (PN), amplitude (PA) and pulse duration (PD) of LH. The statistic analysis was divided plot; principal plot was the treatment and secondary plot was the samples period. There were not effects (p>0.05) of treatment, samples period and its interactions on response variables. In double purpose cows with double milking and suckling naloxona did not affect the LH secretion at 30 day pospartum

Palabras clave : anestrus; double purpose cows; LH; naloxone.

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