Improvement of fertility in post-partum beef cows by treatment with PMSG and progestagen.

Abstract

Many studies have shown that suckling beef cows have an extended anoestrous period after parturition (Wiltbank & Cook, 1958; Foote & Hunter, 1964; Chupin, Pelot, Alonso de Miguel & Thimonier, 1976). The interval from parturition to first oestrus has been shown to be prolonged by low-energy intake before or after parturition (Wiltbank, 1970) and also by suckling (Oxenreider 1968; Graves, Lauderdale, Hauser & Casida, 1968; Wiltbank, 1970). Fertility following artificial insemination of nursing beef cows is lower than in non-nursing cows and in the former the fertility level increases with the interval from parturition (Graves et al., 1968). The use of exogenous steroids to induce oestrus in suckling cows has generally resulted in a decrease of the post-partum interval to oestrus but fertility levels have been low (Ulberg & Lindley, 1960; Foote, Weeth & Hunter, 1960; Foote & Hunter, 1964; Smith & Vincent, 1972). In cyclic animals, normal fertility has been obtained after administration of progestagen for oestrous cycle control (Wiltbank & Kasson, 1968; Wishart & Young, 1974; Roche, 1974; Sreenan & Mulvehill, 1975). Using progestagens, Sreenan & Mulvehill (1974) reported a calving rate of 48% in suckling beef cows following a fixed-time insemination. Stimulation of follicular growth following the use of PMSG has been reported to result in a higher oestrous response and improved degree of synchronization in heifers when administered in combination with a short-term oestrous synchronization treatment (Thimonier, Pelot & Chupin, 1976).