Protein, lysine and feed intake level effects on pig growth

Abstract

SummaryA total of 512 pigs were given from 50 lb live weight one of 16 diets (four lysine levels at each of 12, 14, 16 and 18% protein), at one of four levels of intake. They were killed at 100, 150, 200 or 250 lb live weight and the carcasses jointed in a standard manner and right sides dissected into lean meat, fat, skin and bone.Mean percentage proportion of shoulder, middle and ham joints in the dressed sides at the four weights was 36·3, 36·4 and 27·3; 35·4, 37·9 and 26·7; 34·5, 39·6 and 25·9; and 33·8, 40·7 and 25·5, respectively. Mean percentage lean meat at the four live weights was 61·5, 59·9, 56·7 and 54·2 and the mean percentage fat was 20·7, 24·4, 29·4 and 32·8.Carcass quality was influenced significantly by dietary treatment and sex. Increasing the level of protein in the diet up to 16, 16, 14–16 and 14%, respectively, for the four live weight groups gave a significant increase in carcass leanness. Increasing the level of lysine in the diet did not have a very marked effect on carcass composition, while increasing feed intake to the highest level produced fatter carcasses at all weights. Carcasses of males were fatter and with a lower proportion of ham than those of females. Interactions involving dietary treatments and sex were described.Chemical composition of the m. longissimus dorsi was not altered markedly by dietary treatment or sex but dry matter and intramuscular fat content rose with increasing weight. Protein content of the dry matter remained fairly constant at all weights, while colour and shear value rose with increasing weight but were not significantly influenced by dietary treatment or sex.The pH values of the m. multifidus dorsi just after slaughter or on the day following were not markedly affected by dietary treatment, sex or weight.