Seasonal variations in characteristics of estrous cycles in pubertal Brahman heifers.

摘要: A group of pubertal Brahman heifers (n = 16) was monitored from October through March to investigate the seasonal changes in estrous cyclicity. The had a mean age 16.7 +/- 0.3 mo at initiation experiment. They were kept on pasture with vasectomized marker bulls. Supplemental feed meet NRC requirements provided. Estrus occurrence checked once day and blood samples taken weekly by tail venipuncture that been estrus 7 14 d earlier. Samples processed yield serum assayed for progesterone radioimmunoassay. high proportion (88%) abnormalities such as without formation functional corpus luteum (CL) or anestrus, distribution two follows: 0 0, November 50 25, December 50, January February 18 31 7%, respectively. Mean concentrations during luteal phase differed month: 4.26, 1.50, 3.25, 2.27, 2.65 3.70 ng/ml October, November, December, January, March, respectively (P<0.001). Heifers went into anestrus lower than regular cycles throughout study period (1.35 vs 2.22 ng/ml; P<0.0005). months shortest daylengths (December January) highest incidence anestrus. Transitional periods (November February) seemed occur before after During this transitional CL detected. Serum all abnormal cycles.