PROTEIN AND AMINO ACID LEVELS AND SEQUENCE IN SWINE DIETS: EFFECTS ON GAIN, FEED CONVERSION, AND CARCASS CHARACTERISTICS

Two experiments with a total of 176 pigs were conducted to assess the effects of dietary protein level and amino acid balance on performance of starting, growing, and finishing pigs and carcass quality at market weight. Diets offered in the three stages of growth contained 20, 17, or 14% protein, 14% protein + 0.2% L-lysine HCl (L), or 14% protein + L + 0.1% DL-methionine (M). Feed intake, average daily gain, and feed conversion were inferior in the starting period for pigs fed the 14% protein diet, with less effect as the pigs aged. A compensatory feed conversion effect in later growth stages was observed in pigs fed 14% protein diets throughout. However, age to market averaged 2–3 weeks longer for pigs fed the 14% protein sequence throughout compared with other treatments. L or L plus M supplements improved feed intake, rate of gain, and feed conversion, with less effect as the pigs aged. The sequences of 20, 17, 14; 20, 14, 14; or 17, 17, 17% protein resulted in an average overall daily gain of 0.70 kg. Digestible energy and nitrogen coefficients were not influenced by diet, breed, or sex. In experiment 1, treatment had no effect on carcass measurements but in experiment 2, loin area was reduced in pigs fed 14% protein diets throughout and was improved with amino acid supplements. Although gilts generally had lower feed intakes and slower gains than barrows, they had equal feed conversion and superior carcasses. Hampshire × Yorkshire pigs gained more slowly but had superior carcasses in comparison with Landrace × Yorkshire pigs in experiment 2. The experiments demonstrate that there is considerable flexibility allowable in levels and sequence of protein that may be fed during starting, growing, and finishing periods to allow similar performance of market pigs.