Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/18/2007
Publication Date: 11/2/2007
Citation: Kendall, D.C., Gaines, A.M., Kerr, B.J., Allee, G.L. 2007. True ileal digestible trypotophan to lysine ratios in 90 to 125 kg barrows. Journal of Animal Science. 85:3004-3012. Interpretive Summary: As the building blocks of protein, both amino acid intake and the relationship between amino acids (i.e., tryptophan:lysine) are important dietary factors in optimizing growth performance and carcass lean deposition in pigs. Furthermore, improving the balance of dietary amino acids has a positive environmental impact because excessive amino acid intake leads to increased nitrogen excretion. This research demonstrated that the optimal ratio of true ileal digestible tryptophan:lysine was between 0.145 and 0.170 for barrows fed low crude protein, corn-soybean meal based diets from 90 to 125 kg body weight. This information is important for nutritionists at universities, feed companies, and swine production facilities who are responsible for formulating diets that optimize animal performance while minimizing nitrogen losses into the environment.
Technical Abstract: Three experiments were conducted to determine the optimal true ileal digestible (TID) tryptophen:lysime (Trp:Lys) ratio for 90 to 125 kg barrows. Basal diets contained 0.55% TID Lys and were either corn (Exp. 1) or corn-soybean meal (Exp. 2 and 3) based diets supplemented with crystalline amino acid (AA). In addition, each experiment contained a corn-soybean meal control diet. Trial size progressively increased with pigs housed in 2 (n = 82), 7 (n = 210), or 20 to 22 (n = 759) pigs per pen for each successive experiment. In Exp. 1, a 6 point titration was formulated to contain TID Trp:Lys ratios of 0.109, 0.145, 0.182, 0.218, 0.254, and 0.290. For the 28 d period, there was a quadratic improvement in gain to feed ratio (G:F) (P = 0.05) and average daily gain (ADG) (P = 0.08) with increasing TID Trp:Lys, characterized by an improvement in performance from pigs fed the basal diet to those consuming diets with a 0.145 TID Trp:Lys, with a plateau thereafter. Pigs fed the control diet had less increase in backfat depth than the average of pigs fed the titration diets (1.30 vs. 4.09 mm, respectively; P = 0.02), but pork quality was unaffected by dietary treatment. Pigs in Exp. 2 were fed four incremental additions of L-Trp equating to TID Trp:Lys ratios of 0.130, 0.165, 0.200, and 0.235. Average daily gain and average daily feed intake (ADFI) increased in a linear fashion with increasing TID Trp:Lys for the 29 d trial (P < 0.01), with quadratic improvements noted in d 29 body weight (BW) (P = 0.06) and G:F (P = 0.05). Pigs fed a TID Trp:Lys ratio of 0.165 diet had greater d 29 BW, ADG, G:F, and lower plasma urea N levels than pigs fed the basal diet (P < 0.05), but were similar to pigs fed TID Trp:Lys ratios of 0.200 and 0.235 for all criterion measured. In Exp. 3, TID Trp:Lys ratios of 0.13, 0.15, 0.17, 0.19, and 0.21 were evaluated. The response to increasing TID Trp:Lys was limited to a quadratic (P < 0.10) improvement in G:F with increasing TID Trp:Lys ratios. Maximum G:F was noted at a TID Trp:Lys ratio of 0.17. No relationship was noted between TID Trp:Lys and carcass characteristics. These experiments demonstrate that the minimum TID Trp:Lys ratio for pigs from 90 to 125 kg is at least 0.145, but not greater than 0.17.