A comparison of the availability and ileal digestibility of lysine in cottonseed and soya-bean meals for grower/finisher pigs

Abstract

The availability of lysine and the ileal digestibility of amino acids in three cottonseed meals and a soyabean meal for growerlfinisher pigs were determined. The usefulness of the availability estimates for formulating diets was assessed. The availability of lysine, as assessed with a slope-ratio assay, was (proportion of total): cottonseed meal no. 1, 0.27; no. 2, 0.30; no. 3, 0.29; soya-bean meal, 0.90. Ileal digestibility of lysine in the meals (proportion of total) was: cottonseed meal no. 1,0.58; no. 2,068; no. 3,0.72; soya-bean meal, 089. Pigs given diets formulated to the same available lysine concentration grew at similar rates and retained the same amount of lysine in the carcasses. The results indicate that, for meals of high availability (soya-bean meal), reduced ileal digestibility appears to be the main reason for reduced availability. However, in meals of low availability (cottonseed meal), reduced ileal digestibility only accounts for part of the reduced availability. Thus, the ileal digestibility of lysine is not a reliable indicator of lysine availability.Lysine: Ileal digestibility : Availability : Cottonseed meal: Soya-bean meal: Pigs Previous work (Batterham et al. 1979, 1984) indicated that the availability of lysine in cottonseed meal, as assessed by slope-ratio assays, was low for pigs (0.394.43). This was in contrast to soya-bean meal, where lysine availability was high (0.84-0.98). The low lysine availability in cottonseed meal is presumably due to the processing conditions used in the extraction of oil and inactivation of the toxin, gossypol. It is necessary to formulate diets on an available lysine basis to take into account the large difference in availability for growing pigs that occurs between the different protein concentrates.Slope-ratio assays are time-consuming and expensive to conduct and interest has centred on the use of the ileal digestibility assay to estimate amino acid availability. This assay also has the advantage over slope-ratio assays in that the digestibility of all amino acids can be assessed at the same time and only small numbers of pigs are required per assay. The assumption is made that, if an amino acid is not recovered at the terminal ileum, then it has been absorbed in a form suitable for utilization. This assumption is not strictly correct, as amino acids can be absorbed in forms that are not efficiently utilized (e.g. 6-N-propionyl-L-lysine in rats (Bjarnason & Carpenter, 1969)). Thus, ileal digestibility can overestimate availability.Despite the interest in these assays, there have been few studies of the relationship between ileal digestibility and lysine availability. In comparative studies with one sample of lupin (Lupinus aZbus)-seed meal, the ileal digestibility of lysine for finisher pigs (0.86;

Availability and Utilization of Amino Acids for Growing Pigs

“…The values for lysine availability from a cottonseed (0.30) and a soya-bean (0.90) meal were used to formulate diets of equal available lysine content (Batterham et al 1990b). In addition, the values for lysine availability were used to correct the estimated availability of other essential amino acids.…”

“…In a comparative study of ileal digestibility and availability of lysine, Batterham et al (1990b) reported that the values were similar for soyabean meal, but for three cottonseed meals ileal digestibility values were considerably higher than availabilities (Table 3). Subsequent testing of the values for lysine availability confirmed their applicability in dietary formulations (see Table 2).…”

Development of a novel bioassay for determining the available lysine contents of foods and feedstuffs

“…For severely processed protein sources, the slope-ratio assay gives superior information to the traditional ileal digestibility assay and considerable work has been conducted to compare these two assays. Batterham et al 48 showed that ileal digestible lysine determined using traditional amino acid analysis overestimated the available lysine content of cottonseed meal but not high-quality soyabean meal when fed to growing pigs. Furthermore, ileal digestible lysine also overestimated bioavailable lysine determined using the slope-ratio assay for heated field peas when fed to pigs 49 .…”

“…However, the failing of these assays is that they do not take into account the possibility that the digestion and absorption of unmodified lysine in a food protein may be less than 100 %. This is an important consideration since the amino acid (including reactive lysine) digestibility of processed foods or feedstuffs is often far from complete 29,32,48,64,89 . Moughan et al 46 using a heated glucose -casein mixture clearly demonstrated that considerable amounts of dietary reactive lysine were not absorbed from the small intestine of the growing pig ( Table 1).…”

“…True ileal lysine digestibility is an accurate measure of lysine availability when applied to unheated or minimally processed protein sources 48 . However, it is not accurate when applied to processed protein sources that have sustained lysine damage, since total lysine digestibility is being determined rather than reactive lysine digestibility.…”