Assessment of a balance of dietary amino acids required to maximise protein utilisation in the growing pig (20–80 kg liveweight)

Abstract

Reservations about the interpretation of 3 recent empirical estimates of the ideal amino acid balance for the growing pig prompted this study. A basal diet was formulated, in which enzymatically hydrolysed casein supplemented with synthetic amino acids was the sole protein source. The balance of essential amino acids in the diet was close to the mean of the 3 published estimates. Eight entire male pigs of 28 kg initial liveweight were confined in metabolism crates, and fed the basal diet for 20 days. They were then fed a protein-free diet for a further 8 days. The basal diet was fed at a level (based on body weight} calculated to allow a body protein deposition rate of 100 gfday. The protein-free diet was fed at a level which ensured an equivalent intake of all nutrients (except protein) to that of the basal diet. Mean daily excretion of urinary urea nitrogen (N) over 6-day collection periods was 93 and 19 mgfkg 075 for pigs fed the basal diet and the protein-free diet respectively. If it is assumed that the difference between these values was attributable to deamination of amino acids from the basal diet, the efficiency of dietary protein utilisation was 0.940. Taking into consideration the difficulties encountered in accurate measurement of irreducible minimum urinary urea nitrogen excretion, it was concluded that the amino acid pattern of the basal diet was close to an ideal balance.

Effect on pig performance of decreasing amino acid levels in practical grower diets of equal lysine content

“…Based on a determined apparent ileal digestibility of dietary crude protein of 0.80 and a determined chemical score of 0.73, and assuming a maintenance nitrogen requirement for the growing pig of 0.17 g N/WO.75 (kg) per day (Moughan & Smith 1984), it can be shown that for a 20 kg pig fed Diet 4 (mid-range in the present series) 90 g of ideal protein per day would have been available for growth. Corresponding values for pigs of 50 and 80 kg liveweight were 189 and 224 gfday respectively.…”

“…However, the amino acid balance of Diet 2 was generous compared to the recommended balance of ARC (1981) and that of Moughan & Smith (1984) ( Table 5). Although the ARC (1981) amino acid balance was assumed to be "optimal for growing pigs of all ages though not for sows", whereas the latter balance was deemed to be ideal for growing pigs over the liveweight range 20-80 kg this may not necessarily be so.…”

“…Recent recommendations of essential amino acid requirements relative to lysine for the growing pig (Agricultural Research Council (ARC) 1981;Moughan & Smith 1984) are generally much lower than earlier ones (ARC 1967). Despite this there is little evidence that dietary levels of essential amino acids may be reduced from the earlier recommendations without adversely affecting performance.…”

“…The amino acid levels in the initial grower diet were generous compared to the estimates of the ARC (1981) and Moughan & Smith (1984).…”

“…Amino acid analysis, which did not include cystine and tryptophan, was performed by ion exchange chromatography of duplicate acid hydrolysates using a Beckman 119 B.L. amino acid auto-analyser (Moughan & Smith 1984).…”