Publications > Animal Science > 2002 > Volume 74 Part 3 > View abstract

Animal Science Abstract

Response of beef heifers and non-suckling beef cows to different oestrous synchronization protocols

D. Cavestany^1,A, N. Negrin², R. Negrin² and J. F. Groth³

^AE-mail: cavestan@inia.org.uy

¹Instituto Nacional de Investigaciones Agropecuarias, INIA La Estanzuela, 70000 Colonia, Uruguay
²Private veterinarians, Uruguay
³Veterinarian and farm manager, Brazil and Uruguay

Abstract

The objective was to evaluate different oestrous synchronization schemes in beef cattle under range conditions. In experiment 1, 202 heifers averaging 26 months of age were assigned randomly to three treatments: (a) GnRH-PG. (no. = 44) day 0 (D0): injection of GnRH; D7: injection of PGF₂a; D0 to D25 oestrous detection (OD) and artificial insemination (AI); (b) OD-PG. (no. = 45) D0 to D4; OD + AI; D5: injection of PGF₂a; D5 to D25 OD + AI; and (c)Ovsynch. (no. = 113) D0: injection of GnRH; D7 : injection of PGF₂a; D9: injection of GnRH and 16 h later AI at fixed time. In experiment 2, 318 non-suckling cows were assigned randomly to three treatments : (a) GnRH-PG. (no. = 106) D0: injection of GnRH; D7: injection of PGF2a; D0 to D25 OD + AI; (b) GnRH-MAP-PG. (no. = 106) D0: injection of a GnRH analogue and insertion of an intravaginal sponge impregnated with 250 mg of medroxyprogesterone acetate; D7: injection of PGF₂a and sponge withdrawal; D0 to D25 OD + AI; (c) controls. (no. = 106) OD and AI. The experimental period lasted 25 days and, with exception of the Ovsynch treatment, oestrous detection was carried out twice a day (a.m./p.m.) and inseminations performed 12 h later. The pregnancy rates assessed by ultrasonography 30 days after AI were: experiment 1: (a) 30•0%; (b) 28•6% and (c) 62•3% (P < 0•05); experiment 2: (a) 60•2%; (b) 57•8% and (c) 45•5% (P < 0•05). It is concluded that in heifers and non-suckling cows, oestrous synchronization treatments result in higher pregnancy rates. In non-suckling cows, the addition of a progestagen did not improve the response.

Keywords: beef cattle, GnRH, oestrus, prostaglandins

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