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

Previous studies examining the effect of age on gilt reproduction have gene rally failed to discriminate between chronological (i.e. days) and physiolo gical age (i.e. number of oestrous cycles experienced) and the importance o f each factor remains unclear in the pig. The present investigation tested the hypothesis that the physiological age at which gilts are bred in a dyna mic service system (DSS) affects their reproductive behavior and performanc e. A hundred and ninety gilts were randomly allocated between tow treatment s. They were introduced int the service pens of a DSS to be bred at the sam e 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 contin uously recorded over a 13-week period and reproductive data from all the gi lts were collected. Gilts of 2H treatment were significantly heavier at ent ry into the service pens (123 v. 119 kg; P<0.05) than 3H gilts, but there w as no significant difference in their backfat thickness. Treatment failed t o affect the quality and frequency of mating attempts (MAs) gilts received or oestrus duration. Conception rate to first oestrus in the DSS (82%) was not affected by treatment. Litter size and number of piglets born alive was similar for 3H and 2H gilts (12.0 v 11.7, s.e.d. 0.40 and 11.5 v. 11.0, s. e.d. 0.4 respectively; all P>0.05). It is concluded that the reproductive b ehaviour and performance of gilts that had experienced either two or three oestrous cycles prior to mating at a constant age does not differ significa ntly in a DSS. More studies are needed in order to clarify the possible int eractive influence of repeated and frequent services, which are common in a DSS, on gilt reproduction.