SERUM LH, FSH, ESTRADIOL-17-BETA AND PROGESTERONE PROFILES OF NATIVE AND CROSSBRED GOATS IN A TROPICAL SEMIARID ZONE OF VENEZUELA DURING THE ESTROUS-CYCLE

The patterns of serum luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone and estradiol-17 beta during the estrous cycle of six crossbred (Alpine X Nubian X Native) and six native goats showing a 21 day estrous cycle in a semiarid zone of Venezuela are presented. In the crossbred goats, FSH had two significant peaks on Days 19 and 0 (33 +/- 8.6 ng ml(-1) and 25 +/- 6 ng ml(-1), respectively); in contrast, native goats only had one significant peak on the day of estrus (22 +/- 2 ng ml(-1)), with the increase beginning on Day 17. During the follicular phase of crossbred goats, estradiol-17 beta and LH increased to 28 +/- 6 pg ml(-1) and 23 +/- 6.9 ng ml(-1), respectively, on Day 0. Prior to Day 0, LH increased to 10.0 +/- 4.9 ng ml(-1) on Day 18, decreasing to 1.5 ng ml(-1) on Day 19, while estradiol-17 beta was increasing. This relationship between estradiol-17 beta and LH was not found to exist in native does, which presented a LH peak on Day 0 (30 +/- 8 ng ml(-1) and 35 +/- 10 ng ml(-1) in first and second estrus, respectively). LH basal levels were notably higher in native does. The highest concentrations of progesterone (10 and 12 ng ml(-1)) were detected on Days 12 and 15 in crossbred and native females, respectively. In conclusion, the relationship between estradiol-17 beta and gonadotropins during the follicular phase in crossbred goats suggests negative and positive feedback effects on both LH and FSH. Serum concentrations of LH were higher in native than in crossbred goats, whereas concentrations of FSH were higher in crossbred does. Thus, genetic factors need to be taken into account when comparing blood levels of gonadotropins in goats raised in tropical semiarid zones.