Effect of birth weight on the feed conversion ratio of growing-finishing pigs

Influence of birth weight on feed conversion ratio (FCR) was evaluated from three batches, representing 41 crossbred (LWxPP)x(LWxLd) litters, complete or not. Over the post-weaning and fattening periods, mixing of litters was restricted as far as possible with respect to space allowance, and group size. Over the fattening period, pigs were studied in pens of 13 animals each, equipped with electronic feed dispensers, that recorded individual daily feed intake. Within each batch, pigs were slaughtered in two groups, even when they were not heavy enough with regard to the French grading and payment system. At the end of the fattening period, 322 data were available both on growth performance and individual feed intake. Birth weight was categorized into six classes by steps of 200 g; the first one concerned piglets weighing less than 1.0 kg (P1.8). Data were submitted to a variance analysis with sex (S), birth weight class (P), batch (B) and SxP interaction as main effects. Over the fattening period, the higher the birth weight was, the higher feed intake and average daily gain were, whereas FCR was not affected by P. The conclusion was similar when a restricted growth period was considered (i.e., below 105 kg) in order to get free from the slaughter weight differences among P. The non significant effect of birth weight on FCR was consistent with the non significant effect on the carcass leanness at slaughter.