The influence of dietary concentration of amino acids on protein and energy utilization in growing rats and piglets 1. fortification with lysine and methionine
Eggum, B.O.; Chwalibog, A.; Nielsen, H.E.; Danielsen, V.
Zeitschrift fuer Tierphysiologie Tierernaehrung und Futtermittelkunde 53(3-4): 113-123
Four diets with decreasing protein concentration from 27.3-15.0% were prepared from natural food sources. All diets were balanced with respect to lysine and methionine. The protein concentration was adjusted by replacing soybean meal with maize and wheat. Dietary protein value was tested in balance experiments with rats and piglets (8-20 kg) and in a separate growth trial with piglets. The balance experiments with pigs included both N- and energy balances while only N balances and digestible energy were measured in the rat experiments. Tested at a constant protein concentration with rats, the biological value varied considerably from diet to diet. This was primarily due to the fortification with lysine and methionine. Digestibility of both protein and energy was very much the same for all diets determined with rats as well as pigs. In the balance experiments with pigs it could be seen that daily N retained decreased from 15.7 to 6.8 g when dietary protein concentration was lowered from 27.3 to 15.0%. This in spite of the diets were balanced with respect to lysine and methionine. Results from pigs fed Diets 2 and 3 were intermediate. Results from the growth trial supported the values obtained in the balance studies with significanlty lower values for daily gain as dietary protein concentration decreased. Frequency of diarrhea was lower in pigs fed diets low in protein. The results from energy metabolism showed that retained protein energy was significantly different between all diets decreasing from Diet 1 to 4. Retained energy was highest in pigs fed Diet 3, having 18.4% protein, but these pigs had also the highest values for retained fat energy. Heat energy in percent of metabolizable energy was slightly > 50% for pigs on all diets. Consequently, retained energy in percent of metabolizable energy was < 50%. When comparing the amino acid pattern of the present diets with values given for requirements, it is assumed that other amino acids than lysine and methionine become limiting factors when the protein concentration of a traditional diet for piglets (8-20 kg) is < 27% of dry matter.