The nutritive value of separated milk for pigs: II. The effects of different amounts on performance to 90 kg live weight

Comparison of protein concentrations in diets given unchanged to pigs from 18 to 93 kg live weight

In the national pig progeny test stations one diet is given up to about 55 kg live weight and another, with less protein, is given from then until slaughter. These diets were compared with four ‘single’ diets, similar in digestible-energy content, but containing either 15·6, 17·4, 18·7 or 22·1% crude protein, and each given unchanged from 18 to 93 kg live weight. There were twenty groups of one castrate and one gilt on each treatment.

Pigs given the lowest protein levels had the poorest growth rates and feed conversion efficiency up to 57 kg live weight, but the best from 57 to 93 kg. Hence there were no differences in overall feed efficiency, and overall growth rate was only slightly less with the lowest protein level than with other treatments.

Carcass leanness rose with protein level in the ‘single’ diets over the range 15·6·18·7% crude protein, but a further increase to 22·1% reduced leanness.

Pigs given the progeny test diets had carcasses intermediate in composition to those of pigs on the ‘single’ diets with 17·4% and 18·7% protein.

Responses to variations in dietary energy intakes by growing pigs 3. Effect of level of intake of diets of differing protein and fat content on the performance of growing pigs

Three diets were given separately, each at four levels of digestible energy (DE) intake, to gilts, castrates and boars growing from 21 to 92 kg live weight. The energy levels were those suggested by the Agricultural Research Council, compared with a 5% increase or 10% or 20% decreases in daily allowance. One diet (ME 18) had 3·0 Meal DE/kg and 18·2% crude protein; the other two (HE 16 and HE 19) had 3·26 Meal DE/kg and 16·1% or 19·3% crude protein.

They were given unchanged throughout the experiment. Responses to change in daily DE intake were not affected by sex or diet, except in shoulder fat thickness. Feed eaten per kg gain did not vary by more than 4% over the intake levels investigated, and no difference was significant. On average, each reduction in daily intake below the ARC+5% allowance led to an increase of 1·2 percentage units of carcass lean and a decrease of 1·3 percentage units of carcass fat.

In comparison with HE 16, the higher protein diet HE 19 gave improved feed conversion efficiency and growth rate, particularly in gilts. It did not cause significant changes in carcass measurements. In comparison with ME 18, HE 19 gave more efficient conversion of DE to weight gain, and faster growth.

Boars required less feed per kg gain and had faster growth rates and leaner carcasses than gilts, which were superior to castrates. There was a high incidence of unpleasant odour in fat from boars, but some was also detected in that from gilts and castrates.

Influence of energy and protein concentration in the diet on the performance of growing pigs 1. Response to protein intake on a high-energy diet

Sixty gilts by Landrace sires out of Large White × Landrace females were allocated on the basis of litter relationship and initial weight to six treatments involving the individual feeding of six dietary protein levels, 15·5%, 17·4%, 20·2%, 22·3%, 25·3% and 27·3% crude protein (CP), at a common energy level of approximately 3500 kcal/kg DE, from 23 to 59 kg live weight. Amino acid balance was maintained relatively constant with synthetic lysine, methionine and tryptophan. There were significant increases in growth rate and efficiency of feed conversion from the 15·5% to the 17·4% CP diets and significant reductions in both from the 25·3 % to the 27·3 % CP diets. Carcass lean by dissection increased linearly (r = 0·976) and fat decreased linearly (r = −0·992) with dietary protein increment over the full range studied. As best growth performance and maximum lean content were attained at different dietary CP levels, a combined measure of daily lean deposition was calculated; this indicated that maximum rate of lean growth and efficiency of feed conversion to lean were reached on the 22·3% CP level. In terms of efficiency of utilization of nutrients, maximum retentions of both DE and DCP in the edible part of the carcass appeared to be attained on the two lowest dietary protein levels.

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

One 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).