-_ _ _~_ _ _ Diets were formulated using sugar, soya-bean meal and free amino acids to contain 0 , 1 4 8 g lysine/MJ digestible energy (DE) and offered at three times maintenance to male and female pigs from 20 to 45 kg live weight. Growth responses and retentions of protein, fat, energy and lysine were assessed.Increasing the dietary lysine concentration resulted in significant (P < 0401) linear and curvilinear increases in growth rates and decreases in food conversion ratios. There was only a small effect of lysine concentration on total energy retention, but a substantial effect on the partitioning of energy deposition, with increases in the rate of protein deposition and decreases in fat retention. There was no difference in the efficiency of protein deposition between male and female pigs but males responded more to higher lysine concentrations than females (estimated 0.93 and 0.74 g lysine/MJ DE for males and females respectively). Lysine concentration in the protein deposited by the pigs increased linearly and curvilinearly (P < 0.01) from 5.8 to 6.6 g lysine/l6 g N with increasing dietary lysine concentration.There was a linear and quadratic response (P < 0.001) in retention of ileal digestible lysine, with the minimum retention of 0.16 occurring at 0.1 g lysine/MJ DE and increasing to a maximum retention of 073 a t a dietary concentration of 0.47 g lysine/MJ DE. The efficiency of lysine retained/ileal digestible lysine intake was 0.86 and the endogenous lysine loss was estimated a t 0.94 g/d.
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;
Two experiments were conducted to determine the utilization of ileal digestible lysine by pigs. In the first, the apparent ileal digestibility of amino acids in cottonseed meal, meat-and-bone meal and soya-bean meal was determined in pigs fitted with 'T'-shaped cannulas. In the second experiment, three lysinedeficient diets were formulated to 0.36 g ileal digestible lysine/MJ digestible energy (DE), with lysine contributed from the three protein concentrates as the only source of lysine in sugar-based diets. An additional three diets were formulated with supplements of lysine to verify that lysine was limiting in the first three diets. The growth performance and retention of lysine by pigs given the six diets over the 20-45 kg growth phase were then determined. The apparent ileal digestibility of lysine in the three protein concentrates (proportion of total) was : cottonseed meal 0.74, meat-and-bone meal 0.78, soyabean meal 0.89. Growth rates (g/d) of the pigs given the three diets formulated to 0.36 g ileal digestible lysine/MJ DE were significantly different (P < 0001): cottonseed meal 377, meat-and-bone meal 492, soya-bean meal 541. The response of pigs to the addition of lysine confirmed that lysine was limiting in these diets. Crude protein (nitrogen x 6.25) deposited by the pigs was significantly higher (P < 0.001) for those given soya-bean meal (77 g/d), relative to meat-and-bone meal (66 g/d) and cottonseed meal (38 g/d). The proportion of ileal digestible lysine retained by pigs given the three protein concentrates was: cottonseed meal 0.36, meat-and-bone meal 0.60, soya-bean meal 0.75. The results indicate that values for the ileal digestibility of lysine in protein concentrates are unsuitable in dietary formulations as the assay does not reflect the proportion of lysine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the lysine is absorbed in a form(s) that is (are) inefficiently utilized. Interest has centred on the use of the ileal digestibility assay to estimate amino acid availability. This assay has the advantage 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 that can be utilized by the pig. With weaner pigs, Leibholz (1985) reported that the retention of apparently absorbed lysine at the terminal ileum was 0.860.94 for five diets containing different protein sources, and suggested that the apparent digestibility of lysine could be used to predict lysine availability.However, in a previous study (Batterham et al. 1990a), there was close agreement between ileal digestibility and lysine availability in soya-bean meal (0.89, 0.90 respectively) but not for cottonseed meal (0.58-0.72 ileal digestibility, 0.274-30 lysine availability). Formulating diets containing cottonseed or soya-bean meals on an available lysine basis
The ileal digestibility of tryptophan for growing pigs was determined for cottonseed, meat-and-bone and soya-bean meals. Tryptophan in the food and digesta was measured by two analytical procedures (NaOH hydrolysis and colorimetric estimation (method 1) and LiOH hydrolysis and HPLC determination (method 2)). The results were respectively: cottonseed meal 0.46, 0.81 ; meat-and-bone meal 0.55, 0.65; soya-bean meal 0.74,0.90. In the first experiment the values for method 1 were shown to be inapplicable to pigs. In a second experiment three tryptophan-deficient diets (005 g ileal digestible tryptophan/MJ digestible energy (DE)) were formulated using values from method 2 for cottonseed meal, meat-and-bone meal plus L-tryptophan and soya-bean meal respectively as the only sources of tryptophan in the diets. This experiment was terminated after 28 d as overall growth performance of the pigs was very low. A third experiment was conducted in a similar manner to Expt 2 except that the diets were formulated to 0.065 g ileal digestible tryptophan/MJ DE and growth responses and tryptophan retention were assessed over the 20-45 kg growth phase. Growth rates (g/d) of the pigs given the three diets were significantly different (P < 0.01): cottonseed meal 393, meat-and-bone meal plus L-tryptophan 531, soya-bean meal 437 (SED 39.0). Tryptophan retention (as a proportion of ileal digestible tryptophan intake) was significantly different (P < 0.05) : cottonseed meal 0.51, meat-and-bone meal plus L-tryptophan 0.49, soya-bean meal 0.41. These results indicate (1) that the colorimetric technique for assessing tryptophan was inapplicable and (2) that ileal digestible values for tryptophan were not suitable for formulating diets containing heat-processed proteins, possibly due to absorption of some of the tryptophan in a form that was non-utilizable, and/or to underestimation of total tryptophan in the protein concentrates. Tryptophan: Ileal digestibility: PigsThe ileal digestibility of amino acids is commonly used to estimate the availability of amino acids for the growing pig. However, values for the ileal digestibility of lysine, threonine and methionine have been shown to be unsuitable for formulating diets in certain heatprocessed protein concentrates, as a considerable portion of these amino acids appear to be absorbed in a form(s) that is (are) inefficiently utilized (Batterham et al. 1990a(Batterham et al. , 1993 Beech et al. 1991). It appears that ileal digestibility values for these amino acids overestimate availability in heat-processed meals.As a number of amino acids are affected, it is possible that chemical reactions occur between amino acids within a protein molecule rather than specific Maillard reactions between lysine and carbonyl groups of reducing sugars. As such, other amino acids in addition to threonine and methionine may also be affected.
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