Effects of low protein diets on lean genotype pigs – growth, feed/ N-intake and fat indicators

Abstract

The EU nitrate directive and the increasing cost of protein sources are leading farmers to reduce the nitrogen content in livestock feed. UK pig production often employs high protein ration to ensure high growth rate and low fat deposition. The aim was to compare the performances of pigs of a lean genotype fed with a conventional (C) or 2 low protein (LP) diets, lysine supplemented (LP1) or not (LP2). 64 animals on each diet were reared from 40 to 115 kg and fed ad-libitum. Liveweights (LW) and feed intake (FI) were recorded and after slaughter backfat (P2 site) thickness was measured and samples of longissimus muscle were analysed for total fatty acids. Pen-based data were analysed examining diet and batch as main factors. There were no significant diet effects on FI. Pigs on LP2 had a lower average daily weight gain (ADG) and higher feed conversion ratio (FCR) than C or LP1 from 60 kg onwards. Between diet strategies there were no significant differences in backfat thickness, but body fat deposition was higher in the LP2 group, followed by the LP1, and C the lowest. Results confirm that the LP1 strategy allows growth performance similar to the C diet but with 11% higher intramuscular fat (IMF). Pigs on LP2 diet show an increased body fat and IMF, although subcutaneous fat thickness was little affected. LP1 results indicate that reduced nitrogen intake (C vs. LP1 by 11 to 15%) can be achieved without compromising the growth performance, however feed conversion is significantly poorer (−6%) compared to the C diet probably due to amino acids (AA) deficiencies.