Influence of body condition and bovine somatotropin on estrous behavior, reproductive performance, and concentrations of serum somatotropin and plasma fatty acids in postpartum Brahman-influenced cows

¹ Department of Animal Science, University of Arkansas, Fayetteville 72701
² USDA-ARS, Dale Bumpers Small Farms Research Center, Booneville, AR 72927
³ Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003

^* To whom correspondence should be addressed. E-mail: mlooper{at}spa.ars.usda.gov.

	Abstract

Ninety-nine, multiparous Brahman-influenced (1/4 to 3/8 Brahman) cows were managed to achieve low (BCS = 4.3 ± 0.1; n = 50) or moderate (BCS = 6.1 ± 0.1; n = 49) body condition (BC) to determine the influence of bovine somatotropin (bST) on estrous characteristics, reproductive performance, and concentrations of serum GH and plasma NEFA. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg, s.c.) on d -35, -21, and -7 before initiation of the breeding season. On d -7, all cows received an intravaginal controlled internal drug-releasing (CIDR) device. On d 0 (initiation of 70-d breeding season), CIDR were removed and cows received prostaglandin F₂ (PGF₂). Blood samples were collected from the caudal vein of cows at each bST treatment and d -28 and 0. Estrous behavior was monitored by radiotelemetry during the first 30 d of the breeding season. Growth hormone was increased (P < 0.05) in low and moderate BC cows treated with bST. Percentage of cows detected in estrus during the first 30 d of the breeding season was decreased (P = 0.05) for low BC (64%) compared with moderate BC (82%) cows. Interval to first estrus tended (P = 0.07) to be shorter in low BC-bST-treated cows (3.7 ± 1.9 d) than moderate BC-bST-treated cows (9.6 ± 1.8 d). During the first 30 d of the breeding season, cows in low BC had decreased (P = 0.02) number of mounts received and increased (P = 0.001) quiescence between mounts compared with cows in moderate BC. Number of mounts received was reduced (P = 0.04) in bST-treated cows. More (P < 0.05) cows treated with bST became pregnant during the first 3 d of breeding season compared with non-bST treated cows. Cumulative first-service conception rate tended (P = 0.07) to be greater for bST-low BC cows than non-bST treated cows in either low or moderate BC. On d 0, NEFA were greater (P < 0.05) in bST-treated vs. non-bST treated cows. Low BC as well as bST reduced intensity of behavioral estrus in postpartum Brahman-influenced cows. However, bST increased first-service conception during the first 30 d of breeding and pregnancy rates during the first 3 d of breeding in postpartum Brahman-influenced cows.

Key Words: beef cows, body condition, conception rate, estrous behavior, somatotropin

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