Influence of age at first estrus, body weight, and average daily gain of replacement gilts on their subsequent reproductive performance as sows

The present study investigated the influence of age at first estrus, body weight, and average daily gain (ADG) of the replacement gilts on their subsequent reproductive performance as sows. In total, 4243 Landrace×Yorkshire F1 crossbred replacement gilts were included. They were classified according to age at first estrus, body weight at entering the breeding unit, and ADG. Reproductive performance data, including age at first insemination, age at first farrowing, the number of total piglets born per litter (TB), the number of piglets born alive per litter (BA), farrowing rate, age and parity at removal, and reasons for removal were collected for 3 years. The gilts exhibited first standing estrus, entered the breeding house, and was first mated at 202.6±17.7, 230.3±15.0 and 236.5±17.5 days of age, respectively. On average, body weight and ADG of the gilts were 139.1±6.0 kg and 601.7±38.2 g/day, respectively. The gilts mated at ≤224 days of age were younger at first estrus (200.8 vs. 206.0 days, P<0.001) and had higher ADG (627.0 vs. 587.6 g/day, P<0.001) than those mated at >224 days of age. Gilts with a body weight >150 kg at entering the breeding unit had a larger TB in the second parity than those with a body weight of 136-140 kg (P=0.050). Gilts with ADG of 601-650 g/day had a larger TB in the second parity than those with ADG of 551-600 g/day (P=0.012). The sows that were culled at parity 0 or 1 exhibited first estrus at 204.4±0.7 days of age, while those culled at parity ≥5 exhibited first estrus at 198.9±2.1 days of age (P=0.015). It could be concluded that age at first estrus, body weight, and ADG of the replacement gilts significantly influenced their subsequent reproductive performance as sows.