Physiology and Endocrinology: Synchronization of Estrus in Cattle

McKenzie’s laboratory (U. MO; 1930s) described the estrous cycle of domestic animals. Brownell (Cornell; 1936) reported AI and bull bred pregnancy rates were similar. Between 1938 (first, EJ Perry, NJ) and 1940, 54 AI organizations in 21 states were formed. Ulberg, Christian and Casida (1951) controlled time of ovulation in cows with progesterone (P) injected daily. Trimberger and Hansel (1955) controlled time of ovulation in cows with P injected daily but conception rate was reduced. Zimbelman (1963) reported the dose-response for MAP in cattle, leading to the first orally active progestogen to synchronize estrus in cattle. Participants at the Brook Lodge Ovarian Regulatory Mechanisms Conference (1965) reviewed P for cattle estrus synchronization; discussions launched discovery and development of prostaglandins (PGF2alpha) for regressing corpora lutea (CL) in cattle. Laboratories led by Thorburn, Niswender, Scaramuzzi, Henricks and Hansel (1969-1972) reported profiles of reproductive hormones, data crucial to development of successful breeding management programs. Rowson et al., Lauderdale, and Liehr et al. (each 1972) reported PGF2alpha to be luteolytic in cattle. Lauderdale (1974) reported PGF2alpha estrus synchronization programs and AI, including AI at a specifically designated day and time (TAI). Hansel and Fortune (1978) reported use of GnRH plus PGF2alpha enhanced estrus synchronization and pregnancy rate over PGF2alpha alone in cattle. The Ginther laboratory pioneered and developed transrectal ultrasonography (1982-1998), leading to characterization of follicular waves in cattle (Fortune et al. and Ginther et al., each 1988). Harms, Wiltbank and Randel (1984) reported pulsatile release of LH in cattle, leading to management of follicular waves with GnRH. Knowledge of the estrous cycle of cattle, including follicular waves, and commercially available progestogen, PGF2alpha and GnRH products led to development of multiple cattle breeding management programs by numerous ASAS members. TAI pregnancy rates of 60%-70% are achieved routinely under commercial cattle breeding management programs using PGF2alpha, GnRH and progestogen products.