title: Effects of standardized ileal digestible tryptophan: lysine ratio on growth performance of nursery pigs.
abstract: Two experiments were conducted to estimate the standardized ileal digestible (SID) Trp:Lys ratio requirement for growth performance of nursery pigs. Experimental diets were formulated to ensure that lysine was the second limiting AA throughout the experiments. In Exp. 1 (6 to 10 kg BW), 255 nursery pigs (PIC 327 × 1050, initially 6.3 ± 0.15 kg, mean ± SD) arranged in pens of 6 or 7 pigs were blocked by pen weight and assigned to experimental diets (7 pens/diet) consisting of SID Trp:Lys ratios of 14.7%, 16.5%, 18.4%, 20.3%, 22.1%, and 24.0% for 14 d with 1.30% SID Lys. In Exp. 2 (11 to 20 kg BW), 1,088 pigs (PIC 337 × 1050, initially 11.2 kg ± 1.35 BW, mean ± SD) arranged in pens of 24 to 27 pigs were blocked by average pig weight and assigned to experimental diets (6 pens/diet) consisting of SID Trp:Lys ratios of 14.5%, 16.5%, 18.0%, 19.5%, 21.0%, 22.5%, and 24.5% for 21 d with 30% dried distillers grains with solubles and 0.97% SID Lys. Each experiment was analyzed using general linear mixed models with heterogeneous residual variances. Competing heteroskedastic models included broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP). For each response, the best-fitting model was selected using Bayesian information criterion. In Exp. 1 (6 to 10 kg BW), increasing SID Trp:Lys ratio linearly increased ( 0.05) ADG and G:F. For ADG, the best-fitting model was a QP in which the maximum ADG was estimated at 23.9% (95% confidence interval [CI]: [<14.7%, >24.0%]) SID Trp:Lys ratio. For G:F, the best-fitting model was a BLL in which the maximum G:F was estimated at 20.4% (95% CI: [14.3%, 26.5%]) SID Trp:Lys. In Exp. 2 (11 to 20 kg BW), increasing SID Trp:Lys ratio increased ( 0.05) ADG and G:F in a quadratic manner. For ADG, the best-fitting model was a QP in which the maximum ADG was estimated at 21.2% (95% CI: [20.5%, 21.9%]) SID Trp:Lys. For G:F, BLL and BLQ models had comparable fit and estimated SID Trp:Lys requirements at 16.6% (95% CI: [16.0%, 17.3%]) and 17.1% (95% CI: [16.6%, 17.7%]), respectively. In conclusion, the estimated SID Trp:Lys requirement in Exp. 1 ranged from 20.4% for maximum G:F to 23.9% for maximum ADG, whereas in Exp. 2 it ranged from 16.6% for maximum G:F to 21.2% for maximum ADG. These results suggest that standard recommendations may underestimate the SID Trp:Lys requirement for nursery pigs from 11 to 20 kg BW.
authors.forename: M A D
authors.initials: MA
authors.lastname: Gonçalves
authors.forename: S
authors.initials: S
authors.lastname: Nitikanchana
authors.forename: M D
authors.initials: MD
authors.lastname: Tokach
authors.forename: S S
authors.initials: SS
authors.lastname: Dritz
authors.forename: N M
authors.initials: NM
authors.lastname: Bello
authors.forename: R D
authors.initials: RD
authors.lastname: Goodband
authors.forename: K J
authors.initials: KJ
authors.lastname: Touchette
authors.forename: J L
authors.initials: JL
authors.lastname: Usry
authors.forename: J M
authors.initials: JM
authors.lastname: DeRouchey
authors.forename: J C
authors.initials: JC
authors.lastname: Woodworth
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology; D000818:Animals; D001499:Bayes Theorem; D001835:Body Weight; D004032:Diet / Q000662:veterinary; D005260:Female; D007082:Ileum / Q000502:physiology*; D008239:Lysine / Q000737:chemistry* / Q000378:metabolism; D008297:Male; D013552:Swine / Q000254:growth & development* / Q000502:physiology; D014364:Tryptophan / Q000737:chemistry* / Q000502:physiology
chemical_list: D014364:Tryptophan; D008239:Lysine