aDepartamento de Ciencias Médico, Veterinarias Universidad Autónoma Agraria Antonio Narro Periférico Raúl López Sánchez y Carretera, a Santa Fe CP. 27054. Torreón, Coahuila, Mexico.
bDepartamento de Producción AnimalUnidad Regional de Zonas Áridas Universidad AutónomaChapingo Km 40 Carretera Gómez Palacio-Jiménez. Bermejillo, Durango, Mexico.
To determine whether the administration of two low doses of recombinant bovine somatotropin (bST, 250 mg each) improves conception rate in Holstein cows when using a protocol of estrus synchronization 266 multiparous, postpartum first service Holstein cows were used. Control cows (CON; n=158) were injected with placebo and bST cows (TRT; n=108) received two doses of 250 mg of bST on d 56 and 67±2 d (at the time of AI). Insulin-like growth factor-I plasma concentration was higher in TRT cows (d 58; P<0.01 and d 62; P<0.05) and conception rate was also higher in TRT cows (P<0.05). Days to estrus in TRT cows were shorter (62.2±0.8 vs 74.1±0.9; P<0.01). Milk production was higher in TRT cows (58 to 63 d; P<0.05). The results indicated beneficial effect of bST given in two divided doses in respect of conception rate, insulinlike growth factor-I plasma concentration and days to estrus in postpartum lactating dairy cows.
Bovine somatotropin, conception rate, insulin-like growth factor-I, estrus synchronization, onset of estrus
