Evidence for an annual reproductive rhythm independent of food availability in male creole goats in subtropical northern Mexico

The aim of this study was to determine if there is a seasonal pattern of se xual activity dependent on food availability in male Creole goats in subtro pical Mexico. The study was conducted in the Laguna Region in the State of Coahuila, Mexico (26 degrees N). Male Creole goats (n=8) were kept in a she d, fed alfalfa ad libitum and given 200 g of concentrate daily throughout t he study. Live weight and testicular weight were determined every 2 wk. Sex ual behavior and sperm production were determined monthly. Blood samples we re obtained weekly to determine testosterone plasma concentrations. All var iables were subjected to sinusoidal modeling procedures and showed importan t seasonal variations (P<0.0001) with different phase angles for body weigh t, testicular weight and testosterone plasma concentrations. The nadir of l ive weight occurred in November and the peak in May. The lowest testicular weight (90 g) and testosterone plasma concentrations (0.1 ng/mL) were obser ved in January and February, respectively, while the peaks were observed in July and August (145 g and 10 ng/mL, respectively). Ejaculation latency al so varied during the study, being low between May and November (96 sec) and reaching a peak in April (183 sec) Minimum number of spermatozoa per ejacu late occurred between February and April (1.4 x 10(9) cells/ejaculate) whil e the maximum number was observed between May and September (2.8 x 10(9) sp ermatozoa/ejaculate). Progressive sperm motility was low between January an d April (3.04 on average) and high between May and November (about 3.55 on average). The percentage of live spermatozoa diminished between January and April (68% in April) and then increased to values around 80% between May a nd November. These results lead us to conclude that male Creole goats in No rthern Mexico, fed constantly throughout the year, exhibit seasonality in t heir reproductive activity. Intense sexual activity occurred between May an d December. (C) 1999 by Elsevier Science Inc.