The effect of oestrous cycle number, at constant age, on gilt reproduction in a dynamic service system

Previous studies examining the effect of age on gilt reproduction have generally failed to discriminate between chronological (i.e. days) and physiological age (i.e. number of oestrous cycles experienced) and the importance of each factor remains unclear in the pig. The present investigation tested the hypothesis that the physiological age at which gilts are bred in a dynamic service system (DSS) affects their reproductive behaviour and performance. A hundred and ninety gilts were randomly allocated between two treatments. They were introduced into the service pens of a DSS to be bred at the same age (215 days) but either at second (2H; no. = 96) or third (3H; no. = 94) postpubertal heat period. The sexual behaviour of half of them was continuously recorded over a 13-week period and reproductive data from all the gilts were collected. Gilts of 2H treatment were significantly heavier at entry into the service pens (123 v. 119 kg; P 0·05). It is concluded that the reproductive behaviour and performance of gilts that had experienced either two or three oestrous cycles prior to mating at a constant age does not differ significantly in a DSS. More studies are needed in order to clarify the possible interactive influence of repeated and frequent services, which are common in a DSS, on gilt reproduction.