Abstract:
Valine (Val) is considered to be the fifth-limiting amino acid in a maize–soyabean meal diet
for pigs. Excess leucine (Leu) levels often occur in commercial diets, which may attenuate
the effect of Val deficiency because of an increased oxidation of Val. The objective of the
present experiment was to determine the effect of increasing concentrations of Leu on the
response of young piglets to dietary Val. In all, 75 Large White×Landrace entire male pigs, 44
days of age and with a mean starting weight of 13.5 kg, were used. Three of these were
sacrificed at the start to determine their mean initial chemical composition. A summit feed
first limiting in Val was serially diluted with a non-protein diluent to produce a series of five
digestible Val concentrations of 11.9, 10.1, 8.3, 6.6 and 4.8 g/kg, with a sixth treatment
being added to test that the feeds were limiting in Val. Three identical Val series, each with
six levels of Val, were supplemented with increasing amounts of Leu (23, 45 and 67 g/kg),
thus 18 treatments in total. All pigs were killed at the end of the trial after 18 days for
analysis of water, protein, lipid and ash in the carcass. The levels of Val and Leu and their
interaction significantly influenced all the measurements taken in the trial. Daily gain in
liveweight, water and protein, and feed conversion efficiency all increased with dietary Val
content, whereas feed intake decreased as both Val and Leu contents increased. The
deleterious effect of increased Leu on feed intake and growth was more marked at lower
levels of Val. Supplementing the feed with the lowest Val content with additional Val largely
overcame the effect of excess Leu. The efficiency of utilisation of Val for protein growth was
unaffected by the level of Leu in the feed, the primary response to excess Leu being a
reduction in feed intake. An intake of around 9 g Val/day yielded maximal protein growth
during the period from 44 to 62 days of age in pigs of the genotype used in this trial.
