U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



Published in Journal of Animal Science (1980) 50:2, 293-297


Concentrations of prolactin were measured in serum from three groups of Rambouillet ewes for 8 weeks to determine whether changes in prolactin concentrations were important during the transition from anestrus to seasonal breeding. Group I (control ewes) was maintained under conditions of natural daylength;group II (short-day ewes) was exposed abruptly on the longest day of the year to artificially shortened daylengths (8 hr light and 16 hr darkness); group III (CB 154 ewes) was maintained similar to control ewes except each ewe received twice daily im injections of 2-bromo-α-ergocryptine (CB 154). A fertile ram was kept with each group of ewes. Average serum prolactin remained above 200 ng/ml in control ewes throughout the 8-week study; however, short-day ewes had reduced (P<.05) serum prolactin and CB 154 ewes had low to nondetectable serum prolactin. Despite these differences, average interval to first estrus for the three groups of ewes was similar (control ewes, 25.2 ± 3.0; short-day ewes, 23.5 ± 2.9; CB 154 ewes, 26.4 ± 4.3 days). Short-day and CB 154 treatments did have an apparent effect on interval to conception. Of those ewes that lambed, short daylengths advanced (P<.O1) the average date of conception by 7.7 days in relation to that of controls, whereas CB 154 treatment delayed (P<.O1) the average date of conception by 8.4 days. All ewes exposed to short daylengths conceived at first estrus suggesting that this treatment may facilitate multiple lambing programs in Rambouillet flocks. In conclusion, high serum prolactin associated with anestrus is not a deterrent to the resumption of estrus and breeding activity in Rambouillet ewes and exposure to artificial lighting conditions may improve the reproductive performance of the breeding flock.