RELATIONSHIPS BETWEEN PUBERTY AND PRODUCTION TRAITS IN THE GILT .1. AGE AT PUBERTY

The main object of this study was to investigate the relationships between age at puberty and production traits in Swedish Yorkshire gilts. Another object was to analyse the age distribution at puberty. The study included 547 gilts from a selection experiment for lean tissue growth rate on two different protein lines. The gilts were penned indoors in groups of six gilts. Oestrus was checked twice daily from 160 to 260 days of age in the presence of a boar and blood samples for progesterone were taken regularly. Puberty was defined as the first ovulation, judged by progesterone levels. A total of 481 gilts reached puberty during the experimental period. Backfat thickness at 90 kg liveweight was negatively correlated with age at puberty whereas backfat thickness recorded at puberty had no influence on puberty attainment. When the gilts from each protein line were studied separately, the same negative relationship between backfat thickness at 90 kg and age at puberty was found. The growth rate (25-90 kg liveweight) was negatively correlated with age at puberty. This correlation was only found in gilts on the high protein line. The age distribution at puberty in the present analysis did not differ significantly from the normal distribution.