Isoleucine requirement of pigs weighing 8 to 18 kg fed blood cell–free diets1

Abstract

The aim of the present study was to determine the minimum requirement of Ile in young pigs, enabling feeding of balanced low-CP diets. Most previous studies have used experimental diets that included blood cells, which are particularly high in Leu and known to antagonize the use of Ile. One week after weaning at d 28, 100 crossbred female pigs weighing 7.9 ± 0.7 kg were allocated to 1 of 5 dietary treatments. Diets were formulated to contain 1.15 g standardized ileal digestible (SID) Lys/MJ NE and were free of blood cells. The SID Ile was 0.42, 0.47, 0.53, 0.58, and 0.62 relative to Lys. The other indispensable AA were supplied according to requirements. Representative samples from the 5 diets were analyzed in 4 replicates at 3 different laboratories. The pigs were fed ad libitum and individually housed in 7 identical rooms during a 21-d period. At d 0, 7, 14, and 21, the pigs were weighed, and feed intake was determined. At d 15, blood samples were collected from the jugular vein to determine the plasma urea and free AA content. There were differences among the 3 laboratories in the analyzed content of several AA, and also Ile and Lys showed a large variation within the diets, which may cause variation in published requirement estimates. The concentration of Ile in plasma increased linearly (P < 0.01), and Lys in plasma decreased linearly (P = 0.02) with increasing SID Ile:Lys. A tendency for a linear decrease in plasma concentration was found for Thr (P = 0.10). Both ADFI and ADG were reduced when Ile was supplied above the Ile requirement estimate. Quadratic regression curves on ADFI, ADG, and G:F all showed the maximum at 0.52 SID Ile:Lys. Modeling with 2-sloped quadratic broken-line curves showed the maximum at 0.50, 0.53, and 0.54 SID Ile:Lys for ADFI, ADG, and G:F, respectively. In conclusion, the average estimation of requirement in this dose-response study using blood cell-free diets was 0.52 SID Ile:Lys during a 21-d experimental period from 8 kg BW.

The optimum ratio of standardized ileal digestible isoleucine to lysine for 8–15kg pigs

“…Thus, the results of the current study are in agreement with the recent studies on SID Ile:Lys requirements using blood free diets and suggesting a range between 0.50 and 0.54 SID Ile:Lys for the optimum animal performance (Wiltafsky et al, 2009;Gloaguen et al, 2013;Nørgaard et al, 2013). It should be noticed that the upper 95% confidence limits in the current study were up to 0.61 SID Ile:Lys.…”

“…The impaired animal performance at high Ile intake, which is also reported by Nørgaard et al (2013) and Wiltafsky et al (2009), could be derived from the interaction among BCAA. As it has been shown previously (Wiltafsky et al, 2010), excess Leu causes more degradation of Ile.…”

“…There are only few studies that estimate the Ile requirement in cereal-based diets without using blood cells (Barea et al, 2009;Nørgaard et al, 2013). A meta-analysis on literature on Ile requirement was carried out by Van Milgen et al (2012).…”

“…A recent study by Nørgaard et al (2013) estimated the optimum level of SID Ile:Lys at 0.52, 0.52, and 0.52 for ADFI, ADG, and G:F, respectively using a quadratic regression model, and 0.50, 0.53, and 0.54 SID Ile:Lys for maximum ADFI, ADG, and G:F, respectively using quadratic broken-line model.…”

The optimum ratio of standardized ileal digestible leucine to lysine for 8 to 12 kg female pigs1

“…In comparison to Leu, Val and Ile are reported to have less or no effect on the regulation of the BCKDH complex activity (Cynober and Harris, 2006;Wiltafsky et al, 2009). The results of recently published works from our group showed that Ile may also have a regulatory effect on BCAA catabolism, as an Ile excess decreases performance and plasma Leu concentration (Soumeh et al, 2014, Nørgaard et al, 2013.…”