Influence of energy and protein concentration in the diet on the performance of growing pigs 3. Response to differences in levels of both energy and protein

Abstract

SUMMARYOne hundred and twenty eight gilts by Landrace sires out of Large White × Landrace females were allocated on the basis of litter relation-ship and initial weight to 16 treatments involving the individual feeding of four dietary protein levels (approximately 15%, 18%, 21% and 24% CP) at each of four energy levels (2830, 3100, 3375 and 3585 kcal DE/kg air-dry feed). Amino acid balance (as% of total CP) was maintained relatively constant, using synthetic lysine and methionine where necessary. Growth performance was measured over a live-weight range of 23 kg to 59 kg, at which latter weight the pigs were slaughtered for carcass evaluation by dissection of the middle ‘joint’ from a half carcass. Linear carcass measure-ments were also taken. There was a significant energy × protein interaction only for killing-out percentage; for all other measures the main effects could be assessed independently. Increase in dietary energy value gave linear increase in growth rate (GR) and improve-ment in efficiency of feed conversion (EFC), accompanied by linear decrease in lean percentage and increase in fat percentage. Increase in dietary protein level gave an increase in GR and improvement in EFC with the first increment (from 15% to 18% CP), but depressions in both these characteristics with the final increment (from 21% to 24% CP). Lean percentage increased and fat percentage decreased with the first protein increment, with no further significant changes. Calculation of daily rates of tissue deposition indicated that maximum rate and efficiency of fat-free carcass gain could be attained with the second lowest energy and protein levels tested (i.e. 3106 kcal DE/kg and 18·2% CP).