Interaction and imbalance between indispensable amino acids in young piglets.

Lowering protein level in diets for piglets urge to have knowledge on the piglet's requirements for essential amino acids (AA) and their interactions. The present studies aimed to determine the interaction between the dietary level of valine (Val) and tryptophan (Trp) and the effect of AA imbalance at two levels of dietary Val on the growth performance of post-weaning piglets. In Experiment 1 (duration 4 weeks), the effects of supplementation of free l-Val (1.0 g/kg) and/or l-Trp (0.5 g/kg) in a low-CP diet (CP 17.7%), marginal in Trp and Val, was studied in a 2×2 factorial design and using an additional reference treatment (CP 19.5%). In Experiment 2 (duration 5 weeks), the influence of a stepwise increase in excess supply of isoleucine (Ile), histidine (His) and leucine (Leu), up to 10, 10% and 30% relative to their requirement values respectively, was evaluated at 60% or 70% standardized ileal digestible (SID) Val relative to SID lysine, using a 3×2 factorial design. In Experiment 1, over the whole experimental period, feed intake (FI) was affected by dietary Trp level (P<0.05) and feed conversion ratio (FCR) by both the level of Trp and Val in the diet (both P<0.05). Increasing Trp level increased FI and decreased FCR while increasing dietary Val level reduced FI and increased FCR. For BW gain (BWG), there was an interaction between dietary level of Trp and Val (P<0.05). Valine supplementation decreased BWG using a diet marginal in Trp, whereas it increased BWG when using a Trp sufficient diet. Piglets fed the low-CP diet with adequate levels of Val and Trp showed at least same performance compared to piglets fed the high CP reference diet. In Experiment 2, increasing dietary Val improved FI and BWG (P<0.001) and tended to improve FCR. Dietary AA excess for Ile, His and Leu reduced FI and BWG (P<0.05) and only affected FCR (P<0.01) in the 1st week of the study. Dietary level of Val and AA excess did not show interactive effects, except for FCR over the final 2 weeks of the study (P<0.05). In conclusion, an interaction exists between dietary supply of Val and Trp on the zootechnical performance of post-weaning piglets and dietary AA excess for Ile, Leu and His, reduces growth performance of piglets in low-protein diets, independent of the dietary level of Val.

Effects of surplus dietary L-tryptophan on stress, immunology, behavior, and nitrogen retention in endotoxemic pigs.

The possible beneficial effects of surplus dietary Trp (+5 g of Trp/kg of diet) on factors related to stress, immunology, behavior, and N retention were investigated in postweaning piglets (approximately 15 kg of BW) challenged for 10 d with intravenous bacterial lipopolysaccharide (from Escherichia coli). Two diets fed restrictively (732 kJ of NE/kg of BW(0.75)/d) were compared, 1) a basal diet (apparent ileal digestible Trp = 1.9 g/kg; the recommended amount of Trp to warrant near-optimal growth in nonendotoxemic piglets), and 2) a Trp-enriched basal diet (+5 g of free l-Trp/kg), with 8 individually housed piglets per diet. Pooled salivary cortisol, but not plasma cortisol sampled at euthanasia, showed a tendency (P = 0.07) toward reduced concentrations in the Trp group (1.1 vs. 1.4 ng/mL; pooled SE = 0.1 ng/mL). Plasma C-reactive protein was reduced (P = 0.04) in the Trp group (0.9 vs. 5.0 mg/L; pooled SE = 1.3 mg/L), but haptoglobin, IL-6, tumor necrosis factor α, and lipopolysaccharide-induced fever were similar between the 2 dietary treatments. Physical activity related to approaching a human showed a tendency (P = 0.08) toward increased latency time in the Trp group (101 vs. 60 s; pooled SE = 16 s), but the times spent standing, sitting, and lying were similar between dietary treatments. The ADFI, ADG (346 vs. 302 g/d; pooled SE = 14 g/d; P = 0.11), body N retention (11.6 vs. 11.0 g/d; pooled SE = 0.2 g/d; P = 0.18), and G:F (0.55 vs. 0.49; pooled SE = 0.03; P = 0.17) were not different between the groups fed Trp and the basal diet. In conclusion, surplus dietary Trp had limited effects on stress, immunology, behavior, and N retention in a pig model of systemic endotoxemia.

Phytase inclusion in pig diets improves zinc status but its effect on copper availability is inconsistent.

Complexation of dietary phytate with cations is a major cause of reduced bioavailability of Zn and possibly Cu in pig diets. We conducted 2 studies with 2 treatments in young growing pigs (8 to 40 kg) to estimate potential contributions of phytase to availability and supply of Zn and Cu, respectively. Each treatment comprised 10 pens with 8 pigs each as experimental units. In Exp. 1, 500 phytase units (FTU)/kg of microbial phytase (Natuphos 5000G; BASF) was added to a diet containing 15 mg Zn from ZnSO(4) and 160 mg/kg Cu from CuSO(4) in addition to Cu and Zn from feed ingredients. In Exp. 2, 500 FTU/kg was added to a diet containing 45 mg Zn from ZnSO(4) without added CuSO(4). Feces were collected to determine nutrient digestibility, blood was collected, and pigs were killed to determine Cu and Zn in the liver. In both experiments, phytase inclusion increased (P < 0.001) Zn digestibility by on average 10% units, serum Zn level (P < 0.001) by 0.4 mg/L, and liver Zn content (P < 0.001) by 129 mg/kg DM. In Exp. 1 phytase increased (P = 0.03) Cu digestibility by 6% units but reduced (P = 0.04) liver Cu content by 35 mg/kg DM. In Exp. 2 phytase reduced (P < 0.001) Cu digestibility by 16% units without affecting liver Cu content. Results indicate that the effect of phytase on Cu availability depends on dietary Cu and Zn content and the response variable studied. In conclusion, the consistent effects of phytase on indices of Zn status allow a reduction of Zn inclusion in phytase-supplemented diets.

The effect of diet composition on tryptophan requirement of young piglets.

The aim of the study was to evaluate the requirement for Trp in relation to diet composition in piglets in the period after weaning (BW range of 9 to 24 kg). Two Trp-deficient [relative to the Dutch (CVB, 1996) and NRC (NRC, 1998) requirement values for piglets of 10 to 20 kg of BW] basal diets were formulated: one based on corn and soybean meal and a second one based on wheat, barley, soybean meal, peas, and whey powder [10.0 g/kg of apparent ileal digestible (AID) Lys; 1.4 g/kg of AID Trp; 1.5 g/kg of standardized ileal digestible (SID) Trp]. Both basal diets were supplemented with 0.3, 0.6, and 0.9 g of l-Trp per kg of diet to obtain diets with 1.7, 2.0, and 2.3 g of AID Trp per kg (1.8, 2.1, and 2.4 g of SID Trp per kg), respectively. Each of the 8 treatments was evaluated in 8 replicates (pens with 8 male or female piglets). Average daily feed intake, ADG, and G:F were measured as response criteria. Over the 28-d experimental period, ADG and G:F were greater for the treatments on the wheat/barley diet compared with those on the corn/soybean meal and were increased by the level of Trp in the diet (P < 0.05). Average daily feed intake was only increased by the level of Trp supplementation (P < 0.05). Increasing the Trp level increased ADFI for the corn/soybean meal diet up to 2.3 g of AID Trp per kg (2.4 g of SID Trp per kg) and up to 2.0 g of AID Trp per kg (2.1 g of SID Trp per kg) in the wheat/barley diet (P < 0.05). For both diet types supplementation of free l-Trp increased the G:F up to 1.7 g of AID Trp per kg (1.8 g of SID Trp per kg). Nonlinear regression analysis of the response curves for ADFI using an exponential model for estimating a requirement value for Trp (defined as the Trp level resulting in 95% of the maximum response) revealed a requirement estimate of 2.3 g of AID Trp per kg for the corn/soybean meal-based diet and 2.1 g of AID Trp per kg for the wheat/barley-based diet, equivalent to 2.4 and 2.2 g of SID Trp per kg of diet, respectively. For ADG, a requirement estimate of 2.1 g of AID Trp per kg for both types of diets was derived, equivalent to 2.2 g of SID Trp per kg of diet. The Trp requirement for young piglets seems to be greater than indicated by some commonly used recommendations and does not seem largely dependent on diet ingredient composition.

Effect of graded doses and a high dose of microbial phytase on the digestibility of various minerals in weaner pigs.

An experiment with 224 weaner pigs (initial BW of 7.8 kg) was conducted to determine the effect of dose of dietary phytase supplementation on apparent fecal digestibility of minerals (P, Ca, Mg, Na, K, and Cu) and on performance. Four blocks, each with 8 pens of 7 pigs, were formed. Eight dietary treatments were applied to each block in the 43-d experiment: supplementation of 0 (basal diet), 100, 250, 500, 750, 1,500, or 15,000 phytase units (FTU) or of 1.5 g of digestible P (dP; monocalcium phosphate; positive control) per kilogram of feed. The basal diet, with corn, barley, soybean meal, and sunflower seed meal as the main components, contained 1.2 g of dP per kilogram of feed. Fresh fecal grab samples were collected in wk 4 and 5 of the experiment. Average daily feed intake, ADG, G:F, and digestibility of all of the minerals increased (P < 0.001) with increasing phytase dose. Digestibility of P increased from 34% in the basal diet to a maximum of 84% in the diet supplemented with 15,000 FTU, generating 1.76 g of dP per kilogram of feed. At this level, 85% of the phytate phosphorus was digested, compared with 15% in the basal diet. Compared with the basal diet, digestibility of the monovalent minerals increased maximally at 15,000 FTU, from 81 to 92% (Na) and from 76 to 86% (K). In conclusion, phytase supplementation up to a level of 15,000 FTU/kg of a dP-deficient diet improved performance of weaner pigs and digestibility of minerals, including monovalent minerals. Up to 85% of the phytate-P was digested. Thus, dietary phytase supplementation beyond present day standards (500 FTU/kg) could further improve mineral use and consequently reduce mineral output to the environment.