Effects of exposure to an estrual female on the attainment of puberty in gilts

Abstract

A total of 304 prepubertal gilts were randomly allocated to 4 treatment groups across 10 replications for a 50 d treatment period beginning at 170 d of age. The 4 treatment groups consisted of: 1) Gilts that were continuously exposed to one of a group of older, ovariectomized females that had been treated with 2 mg/ml estradiol benzoate to stimulate estrus (SE); 2) Gilts that were continuously exposed to an older, anestrous, ovariectomized female (OVX); 3) Gilts that were exposed to a mature boar for 15 min/d (BE); 4) Gilts that were isolated from any direct physical contact with other pigs (C). A gilt was considered to have attained puberty when she exhibited a standing reflex when mounted by the boar (BE group only) or to pressure applied manually to the back or had plasma progesterone concentrations > 2 ng/ml for 2 consecutive weeks. Data were analyzed as a randomized complete block design with treatment and replication in the model. A higher percentage of gilts attained puberty in the BE group than in the 3 other groups (52 vs 26, 30 and 32%, BE vs SE, OVX and C, respectively; P = 0.002). Gilts exposed to an estrual female or a mature boar attained puberty sooner after treatment was initiated than gilts in other treatment groups (12.6 and 17.8 vs 26.7 and 24.1 d, SE and BE vs OVX and C, respectively; P = 0.0003). Of the gilts attaining puberty during the experimental period, the highest percentage of gilts exhibited estrus within 10 d of treatment in the SE group (55.0 vs 26.1, 37.8 and 16.7%, BE vs SE, OVX and C, respectively; P = 0.05). Age at puberty was also lower SE or BE than OVX or C groups (176.3 and 181.0 vs 189.4 and 188.1 d, respectively; P = 0.0001). Weight at puberty was unaffected by treatment. These results suggest that exposure to an estrual female was effective in stimulating peripubertal females to express estrus, thus reducing the age at puberty. Boar exposure had a stimulatory effect not only at the initiation of exposure but throughout the experimental period, resulting in a higher percentage of gilts attaining puberty.