The effect of standardized ileal digestible isoleucine:lysine in diets containing 20% dried distillers grains with solubles on finishing pig performance and carcass characteristics

In order to determine the standardized ileal digestible (SID) Ile:Lys requirement in finishing diets containing 20% DDGS, a 56-d study was conducted utilizing 2,268 pigs (DNA 600 x Topigs Norsvin 70, initially 82.3 kg). A total of six dietary treatments were fed, including a standard corn-soybean meal (SBM) diet and five diets containing 20% DDGS with SID Ile:Lys ratios of 55%, 60%, 65%, 70%, and 75%. Dietary treatments were assigned to pens, incompletely balancing for previous treatment, with each treatment being replicated 14 times. Pair-wise comparisons were used to evaluate the impact of dietary treatment on performance and carcass traits, whereas single degree of freedom orthogonal polynomials were used to evaluate dose response of SID Ile:Lys in 20% DDGS diets. Increasing the SID Ile:Lys ratio in diets containing 20% DDGS did not impact pig growth performance criteria in a quadratic or linear fashion (P = 0.18). However, increasing the SID Ile:Lys ratio in 20% DDGS diets resulted in decreased back fat (BF; Quadratic, P = 0.01), increased loin depth (Quadratic, P = 0.03), and tended to increase percent lean (Quadratic, P = 0.07) with optimal carcass parameters occurring when 65% SID Ile:Lys was supplied in 20% DDGS diets. Pigs fed the corn-SBM diet had a similar final body weight (BW; P = 0.26) and cumulative average daily gain (ADG; P = 0.12) compared to pigs fed a 20% DDGS diet containing 70% SID Ile:Lys ratio and 3% greater cumulative average daily feed intake (ADFI) compared to pigs receiving diets with SID Ile:Lys ratios of 65% and 75% (P = 0.01). In conclusion, these results suggest that when feeding 20% DDGS in late finishing swine diets, a SID Ile:Lys ratio of 70% should be utilized when attempting to achieve similar overall growth performance relative to a corn-SBM diet. Lay Summary The use of corn by-products, such as dried distillers grains with solubles (DDGS), from the ethanol industry in swine rations is a common practice when economical. However, the inclusion of these by-products can potentially impact the nutrient requirements of pigs. It is important to understand how one should adjust diets to meet these changes in nutrient requirements and to minimize the reduction in growth performance. Previous research has indicated that the excess of a specific amino acid, leucine, can negatively impact the performance of pigs through the increased breakdown of other amino acids, more specifically valine and isoleucine. This increased breakdown of valine and isoleucine can result in inadequate amounts being available for protein deposition and, therefore, reduce growth performance. In the present study, late finishing pigs fed a diet containing 20% DDGS required a ratio of 70% between the amino acids isoleucine and lysine, on a digestible basis, to perform similarly to pigs receiving a standard corn soybean meal diet. Further research is necessary to more accurately define the optimal dietary isoleucine level for finishing pigs when fed 20% DDGS.

Automated summary

The study determined that a 70% SID Ile:Lys ratio should be utilized in finishing diets containing 20% DDGS to achieve similar growth performance to a corn-SBM diet.