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 h ormone (FSH), progesterone and estradiol-17 beta during the estrous cy cle of six crossbred (Alpine X Nubian X Native) and six native goats s howing a 21 day estrous cycle in a semiarid zone of Venezuela are pres ented. In the crossbred goats, FSH had two significant peaks on Days 1 9 and 0 (33 +/- 8.6 ng ml(-1) and 25 +/- 6 ng ml(-1), respectively); i n contrast, native goats only had one significant peak on the day of e strus (22 +/- 2 ng ml(-1)), with the increase beginning on Day 17. Dur ing 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 wa s 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 estr us, 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, respectiv ely. In conclusion, the relationship between estradiol-17 beta and gon adotropins during the follicular phase in crossbred goats suggests neg ative and positive feedback effects on both LH and FSH. Serum concentr ations of LH were higher in native than in crossbred goats, whereas co ncentrations of FSH were higher in crossbred does. Thus, genetic facto rs need to be taken into account when comparing blood levels of gonado tropins in goats raised in tropical semiarid zones.