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Influence of dietary isoleucine:lysine ratio on the optimal tryptophan:lysine ratio for weanling pigs

Isoleucine:lysine ratio does not influence the response to increasing tryptophan:lysine ration in 5,9- to 10,9-kg pigs.

Tuesday 5 March 2013 (5 years 4 months 14 days ago)

It was hypothesized that the isoluecine level in the diet may influence the response to dietary tryptophan. A marginal isoleucine level may limit the response to tryptophan, so this experiment was conducted to determine whether the dietary standardized ileal digestible (SID) isoleucine:lysine ratio influenced the response to increasing SID tryptophan:lysine ratios in 5.9- to 10.9-kg pigs. A total of 475 nursery pigs (initially 6.08 kg and 5 d postweaning) were used in the all-in, all-out nursery. Each treatment had 8 replications with 4 or 5 pigs per pen, with equal numbers of barrows and gilts within block and across treatments. Pens were allotted to 1 of 12 treatments in a randomized complete block design. Treatments were arranged as a 2 x 6 factorial with main effects of 2 SID isoleucine:lysine ratios (52 and 60% of lysine) and 6 SID tryptophan:lysine ratios (14.7, 16.6, 18.5, 20.4, 22.3, and 24.0% of lysine). Treatment diets were fed for 14 d, and then a common diet was fed from d 14 to 21. Overall, no interactions (P > 0.27) were observed between SID isoleucine:lysine and SID tryptophan:lysine ratios. For the main effect of SID isoleucine:lysine ratio, no differences (P > 0.21) were observed in growth performance between pigs fed the 52 or 60% SID isoleucine:lysine ratio. Increasing the SID tryptophan:lysine ratio also had no effect (P > 0.30) on growth performance.

In conclusion, dietary SID isoleucine:lysine ratio did not influence the response to increasing SID tryptophan:lysine ratios in 5.9- to 10.9-kg pigs. The results also suggested that the SID isoleucine:lysine ratio is not greater than 52% for pigs fed diets that do not contain blood products.

S Nitikanchana, AL Chipman, MD Tokach, SS Dritz, J Usry, JF Patience. 2011. Influence of dietary isoleucine:lysine ratio on the optimal tryptophan:lysine ratio for 13 to 24-lb pigs. Kansas State University Swine Day, 145-154.

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