[Seasonal variations in creole heifer cyclicity: effect of growth, age and emotivity]

The ovarian and estrous activities in creole heifers have been studied in Guadeloupe in a tropical environment. We carried out two experiments. In the first one, all the heifers from the research station's herd were blood-sampled twice every 2 months at a 10-day interval to determine their ovarian activity. The observations were ranked in order of ascending live weight, and the percentage of heifers showing ovarian activity was calculated for consecutive 10-kg increments in live weight from 115 to 275 kg. The percentage showing ovarian activity (Y) was subjected to probit transformation and related to live weight (X); probit Y = 12.4 log10 X - 23.7. The equation for observations ranked in order of ascending age and the percentage of heifers showing ovarian activity calculated for age increments over 2 consecutive months was: probit Y = 7.06 log10 X - 3.9. Furthermore, the percentage of cyclic heifers in the herd varied from 40 p. 100 in September 1979 to 0 p. 100 in July 1980 and then to 30 p. 100 in September 1980. The percentage of cyclic heifers at a given period of observation was highly correlated with the mean daily increase in body weight (r = 0.86). In the second experiment, 12 heifers with a high feed level were blood-sampled weekly and checked for estrous daily with an androgenized female with a chin ball mating harness. The mean duration of a "normal cycle" (interval between two estruses: more than 15 but less than 31 days) was 21 days. There was no variation of ovarian activity with the month of the year, but the incidence of silent ovulation was high (23.7 p. 100). The seasonal variation of this percentage is shown. Female emotivity was also an important factor: emotional heifers had a higher percentage of silent ovulations than unemotional heifers (27 vs 17 p. 100) and a smaller mean daily gain (180 vs 280 g).