Effects of selection for lower backfat, and increased levels of dietary amino acids to digestible energy on growth performance, carcass merit and meat quality in boars, gilts, and barrows

Two experiments were conducted, using a total of 288 crossbred boars, gilts and barrows from the progeny of two Yorkshire sow lines, one kept as control, and the other selected for lower backfat thickness and increased growth rate for six generations. The lysine to DE (g MJ−1) levels used during grower (20 to 60 kg) and finisher (60 to 105 kg) periods, respectively, in the three diets (14.2 MJ DE kg−1) were: 1) 0.53 and 0.42 with no other supplemental amino acids except lysine, 2) 0.69 and 0.57 with supplemental threonine and methionine at a ratio of 0.65 and 0.30 to dietary lysine and 3) 0.85 and 0.72 with supplemental threonine and methionine at similar ratios as in diet 2. Feeding diets 2 and 3 increased (P < 0.05) the ADG and feed conversion efficiency of all pigs in both experiments, and this response was mainly during the grower period. Feeding diet 3 improved the growth rate more than diet 2 only in boars and gilts but not barrows. It also increased the feed conversion efficiency in exp. 2. The increased feed conversion efficiency response was higher in select than control line pigs, and in boars. Feeding diets 2 and 3 also improved the carcass merit but reduced the meat quality with an increased firmness and reduced marbling, juiciness, and flavour. The overall results indicated that an average daily intake of approximately 17 g of lysine (0.74 g MJ−1 DE), 11 g of threonine and 5 g of methionine during the grower period and 25 g lysine (0.62 g MJ−1 DE), 18 g threonine and 8 g methionine during finisher period optimized the growth performance, lean growth rate and carcass merit. This response tended to be higher in select than control line, and in boars and gilts than barrows. Key words: Lysine, amino acids, energy, growth, carcass, pigs