Control of oestrus in gilts I. Management-induced puberty

Abstract The occurrence of the first ovulation was observed in 559 crossbred gilts from one breeding stock by oestrus detection using a boar, and by a circulating progesterone assay. Five hundred gilts (89.4%) presented oestrus at an average age of 173 days, whereas 40 (7.2%) presented ovulation without overt oestrous behaviour. Transport stress, associated with a change in environment and presentation to the male, induced oestrus in 363 (72.6%) gilts within 7 days. Neither the age at transport nor the season influenced the induction of puberty. However, significant differences appeared between sires (from 51 to 73.5% of oestrus within 7 days).