Effect of biostimulation on uterine involution, early ovarian activity and first postpartum estrous cycle in beef cows

The objective was to determine the effect of biostimulation (bull-exposure) on uterine involution (UI), plasma progesterone concentration (P₄), size of largest follicle (LF), number of follicles larger than 5mm (F≥5), presence of fluid in uterine lumen (PF), presence of luteal tissue (LT), and length of the first estrous cycle postpartum (LEC). Ninety Angus cows with calves were allocated by parity and body frame into three groups (30 per group) 1 week postpartum. Two groups were exposed to bulls (BE) and one non-exposed group (NE) served as a control. Data were collected during weekly sessions of palpation per rectum, ultrasonography and bleeding on a subgroup of 30 cows (10 cows per group) for 6 weeks, and permanent surveillance of estrus with HeatWatch® on all 90 cows. There were no significant differences between BE and NE cows for UI (17.1±1.1 days versus 20.1±1.6 days), LF (9.5±1.7mm versus 11.0±2.4mm), F≥5 (1.20±0.3 versus 1.47±0.09), and PF. However, LT was detected in more BE than NE cows (13 versus 2; P<0.001). Overall differences in P₄ were found between BE and NE cows with detected LT (2.00±0.3ng/ml versus 1.05±0.4ng/ml, respectively; P<0.05). More BE cows resumed reproductive cyclicity with estrous cycles normal in length compared with NE cows (16/30, 53%; 16/30, 53%; and 8/30, 26.6%, for the two BE groups and the NE group, respectively; P<0.01). In conclusion, BE hastened luteal function but did not affect uterine involution. © 2003 Elsevier Inc. All rights reserved.