Abstract:
Animal Production in Australia Vol. 15 THE EFFECT OF INITIAL FAT RESERVES OF GILTS ON THEIR SUBSEQUENT REPRODUCTIVE PERFORMANCE R.H. KING*, G.V. CLEARY**, N. MAUGHAN+ and C. POWER** The combined effects of genetic change and earlier mating mean that gilts now start their breeding lives with less body reserves than l0-20 years ago (Brooks 1982). The effects of body reserves of gilts on subsequent reproductive efficiency in the breeding herd were assessed by relating the amount of backfat at selection to subsequent reproductive efficiency. Data were collected from the records of 200 gilts which had been selected for the breeding herd between July 1980 and November 1981 in an intensive piggery housing approximately 500 sows and their progeny. Live weight and backfat depth ({C+K1/2; where C is 4.5 cm, and K is 8 cm from the midline at the level of the last rib) of gilts were recorded at selection. The age, live weight and backfat depth (means + SE) of gilts at selection were 1.77 k 0.8 days, 82.5 2 0.6 kg and 14.3 t 0.2 mm respectively. The subsequent reproductive performance of these gilts up until March 1983 was recorded and is summarised in Table 1. TABLE 1 Reproductive parameters and partial correlation coefficients (corrected for live weight at selection) between these parameters and backfat depth of gilts at selection The number of litters produced was positively correlated (P < 0.01) to backfat depth at selection, whilst there was a negative correlation between farrowing interval and backfat depth (Table 1). Chapman et al. (1978) reported that gilts which were older at first farrowing tended to have shorter farrowing intervals and were retained in the breeding herd longer than gilts which farrowed at an earlier age. Presumably the older gilts were heavier and had greater body reserves at first farrowing. In our study the relative differences in fat depths of gilts at selection would likely be maintained until the first farrowing since all gilts were on the same feeding regime after selection. The results of our study suggest that gilts which entered the breeding herd with larger fat reserves were retained in the herd longer and had a shorter farrowing interval than gilts with less fat reserves. 702