Growth performance and adipose tissue deposition in barrows fed n-methyl-D,L-aspartate

We previously reported that broilers fed n-methyl-D,L-aspartate (NMA) exhibited enhanced feed conversion efficiency and decreased percentage of fat in carcasses. In this experiment, growth performance and backfat thickness were evaluated in barrows fed NMA. Poland China x Yorkshire barrows weighing 68.8 +/- 1.7 kg (mean +/- SE) were allowed ad libitum access to feed containing NMA at levels of either 0 (n = 7), 100 (n = 6), 200 (n = 8), or 300 (n = 8) mg/kg for 36 d. Barrows were slaughtered at 99.5 +/- 2.3 kg BW. There was no effect (P > 0.1) of NMA on ADG or feed consumption. Gain:feed ratio decreased (P < 0.03) in a linear fashion with increasing level of NMA. There was a cubic effect (P < 0.05) of NMA treatment on first-rib backfat thickness. In response to graded levels of NMA, backfat thickness at the 10th rib (P < 0.08) and last rib (P < 0.03) increased in a linear fashion. The NMA had no effect (P > 0.1) on backfat thickness measured at the lumbar vertebra or longissimus muscle area measured at the 10th rib interface. The percentage of lean in the carcass decreased in a linear fashion (P < 0.05) in response to increasing levels of NMA in the diet. In summary, NMA had an overall negative effect on growth performance and carcass yield characteristics in barrows. The dichotomous effects of NMA on feed efficiency and body composition in poultry and swine warrants further scrutiny.