The influence of dietary concentration of amino acids on protein and energy utilization in growing rats and piglets 2. fortification with lysine methionine and threonine
Eggum, B.O.; Chwalibog, A.; Nielsen, H.E.; Danielsen, V.
Zeitschrift fuer Tierphysiologie Tierernaehrung und Futtermittelkunde 53(3-4): 124-133
Four diets with decreasing protein concentration from 25.4, 22.4, 19.2 to 15.8% in DM [dry matter] were prepared from natural food sourcesa. All diets were balanced with respect to lysine, methionine and threonine. The protein concentration was adjusted by replacing soybean meal with maize and wheat. Dietary protein value was tested in balance experiments with growing rats and piglets and 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 fortification with lysine, methionine and threonine. Digestibility of both protein as well as energy was the same for all diets and at the same level for both rats and pigs. In the balance experiments with pigs it could be seen that daily N deposition decreased from 14.4 to 8.0 g when dietary protein concentration was lowered from 25.4 to 15.8% in DM. This in spite of the diets were balanced with respect to lysine, methionine and threonine. Results from pigs fed Diets 2 and 3 were slightly lower than in pigs fed Diet 1. The growth trial supported the values obtained in the N-balance study with the lowest daily gain in pigs given Diets 3 and 4. Frequency of diarrhea was lower in pigs fed diets low in protein. The results from energy metabolism showed that retained protein energy was lowest in pigs given Diet 4 with only slight differences between pigs fed on the other diets. Retained energy was not significantly different between pigs on the 4 diets but retained fat energy was significantly higher in pigs on Diet 4. Heat energy in percent of metabolizable energy was close to 50% for all diets with the highest value for pigs on Diet 1. Retained energy in percent of metabolizable energy was lowest (46.9%) in pigs given Diet 1, highest in protein. The protein quality of Diet 3 was superior to the quality of the other diets for both growing rats and piglets. A protein concentration of 19.2% in DM is probably too low to lead to maximal protein synthesis in fast growing piglets of 9-19 kg body wt.