title: Diminishing returns in weight, nitrogen, and lysine gain of pigs fed six levels of lysine from three supplemental sources.
abstract: Diminishing returns responses to increments of lysine intake were evaluated in 82 crossbred barrows (10.2 +/- SE = .31 kg) fed one of six concentrations of lysine expressed as 55, 80, 90, 100, 115, or 140% of a concentration (10.9 g/kg of diet) that supported maximum weight gain. Supplemental lysine was provided from either soybean meal (SBM), SBM+synthetic lysine (SBM + L), or SBM+corn gluten meal (SBM + CGM) additions to a basal diet consisting of corn, minerals, and vitamins. A logistic equation was used to describe weight (kilograms/day), nitrogen (grams/day) and lysine (grams/day) gain as a function of lysine intake from each diet. The parameter Rmax, asymptotic maximum response at infinite intake, was shared for SBM and SBM+L (.70 +/- .02, 17.6 +/- .4 and 7.6 +/- .5, respectively) but was different (P < .05) for SBM + CGM (.62 +/- .02, 15.7 +/- .4 and 6.4 +/- .4, respectively) diets. A plateau in weight gain response was observed at approximately 100% of our estimate of the lysine requirement (9.8 g/kg, based on analyzed values), but nitrogen and lysine gain responses did not approach a plateau until 120 or 145% of the requirement. No differences were detected among pigs fed the SBM and SBM+L sources; however, the efficiency of lysine use by pigs fed the SBM+CGM diet was lower. Maximum marginal efficiency (dr/dI) occurred at 45, 40, and 35% of Rmax for weight, nitrogen, and lysine gain, respectively. The maximum marginal efficiency of lysine gain was 81% for pigs fed the SBM and SBM+L diets but only 68% for pigs fed the SBM+CGM diet. Consequently, diminishing returns were apparent for at least the upper 55 to 65% of the response curve. Whole-body lysine content increased (P < .03) from 5.5 to 6.0 g/16 g of N and glycine (9.6 to 7.9) and proline (6.4 to 5.4) content decreased (P < .001) as lysine intake increased. No changes were detected in body threonine content (pooled average = 2.8).
authors.affiliation: Dept. of Meat and Animal Sci., University of Wisconsin, Madison 53706.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gahl
authors.forename: T D
authors.initials: TD
authors.lastname: Crenshaw
authors.forename: N J
authors.initials: NJ
authors.lastname: Benevenga
mesh_terms: D000821:Animal Feed; D000818:Animals; D003433:Crosses, Genetic; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005260:Female; D005526:Food, Formulated; D005998:Glycine / Q000032:analysis; D008239:Lysine / Q000008:administration & dosage / Q000032:analysis / Q000494:pharmacology*; D008297:Male; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D011392:Proline / Q000032:analysis; D013025:Glycine max / Q000592:standards; D013552:Swine / Q000254:growth & development*; D015430:Weight Gain / Q000187:drug effects* / Q000502:physiology; D003313:Zea mays / Q000592:standards
chemical_list: D011392:Proline; D008239:Lysine; D009584:Nitrogen; D005998:Glycine