Meta-analysis of the response of growing pigs to the isoleucine concentration in the diet

Abstract

The efficiency of nitrogen utilization will be highest when the amino acid (AA) supply approaches the requirement of the animal. With the availability of different crystalline AA, it is theoretically possible to formulate low-protein diets for growing pigs in which seven AA are co-limiting for performance. In such a diet, the concentration of Lys, Met, Met 1 Cys, Thr, Trp and Val and a seventh AA would exactly match the requirement. To determine the extent to which low-protein diets can be used, it is important to have reliable information about the requirements for these AA. Isoleucine is often considered the seventh-limiting AA in diets for growing pigs; however, information about the Ile requirement is limited and sometimes conflicting. The purpose of this study was to carry out a meta-analysis of the available literature information to determine the Ile requirement in growing pigs. A total of 46 Ile dose-response experiments were identified that used at least four concentrations of Ile in the diet. Because of differences in experimental design, both the Ile concentration and the response criteria were standardized. In 13 dose-response experiments, there was no indication of a response to an increasing Ile concentration. For the other 33 experiments, a response to the increasing Ile concentration was observed and the Ile requirement estimates ranged from 53% to 114% of that of the National Research Council (1998). An Ile concentration below the requirement resulted in important reductions in both feed intake and growth. A 10% reduction in the Ile concentration (below the requirement) resulted in a 15% reduction in feed intake and a 21% reduction in daily gain. The use of blood products in the diet was the main factor determining whether a response to the Ile concentration was observed or not. Blood meal and blood cells are protein sources with a very low Ile concentration, but with high or very high concentrations of Leu, Val, Phe and His. Some of these AA compete with Ile for catabolic pathways or transport across the blood-brain barrier, thereby potentially increasing the requirement for Ile. In diets without blood products, the Ile requirement appears to be lower than the currently recommended requirement. On the basis of the outcome of this study, we recommend a Ile : Lys requirement ratio of at least 50% on a standardized ileal digestible basis.

Standardized ileal digestible (SID) isoleucine requirement of barrows (15- to 30- kg) fed low crude protein diets

“…In the same way, Barea et al (2009), upon evaluating SID Ile levels (0.50 to 0.58%) for barrows and gilts from 11 to 23 kg, observed no effects on performance, reporting that the optimum SID Ile was the lowest evaluated level (0.50%). In the same way, Van Milgen et al (2012), using a meta-analysis procedure, reported that 13 doseresponse experiments (a total of 46) demonstrated no evidence (P>0.25) for, at least, a linear response in ADFI or ADG as a function of an increasing Ile concentration in the diet, suggesting that different factors may have contributed to the lack of response, and explaining that other AA besides Ile and Lys may have limited the growth performance in seven experiments, although the extent of this limitation was modest.…”

“…The efficiency of nitrogen utilization will be highest when the amino acid supply approaches the requirement of the animal ( VAN MILGEN et al, 2012). However, nitrogen efficiency for weight gain (NEWG) only showed a tendency toward a linear increase (P = 0.091) as the SID Ile was supplied in the diets (Table 4).…”

Response of piglets to the standardized ileal digestible isoleucine, histidine and leucine supply in cereal–soybean meal-based diets

“…Using literature data, van Milgen et al (2012) reported that there was no strong ADFI and ADG response to Ile supplementation when diets do not contain blood cells. These authors recommended that diets should provide at least 50% SID Ile : Lys.…”

Amino acid requirement of growing and finishing pigs

“…Blood meal and blood cells are protein sources with a very low isoleucine concentration, but with high or very high concentrations of leucine, valine, phenylalanine and histidine. Some of these AA, in particular leucine, compete with isoleucine for catabolic pathways or transport across the blood-brain barrier (Van Milgen et al, 2012). Excess leucine in the diet increases branch chain keto acid dehydrogenase levels which lead to catabolism of all branch chain AA.…”