Cyst(e)ine imbalance and its effect on methionine precursor utilization in chicks

¹ Department of Animal Sciences and Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801

^* To whom correspondence should be addressed. E-mail: rdilger2{at}uiuc.edu.

	Abstract

Five 9- or 12-d chick growth bioassays were done in batteries using 2 different Met-deficient diets: a purified AA-based diet containing (by analysis) 20.3% CP, 0.12% Met, and 0.05% cyst(e)ine, and an AA fortified corn-peanut meal diet containing (by analysis) 19.0% CP, 0.22% Met, and 0.23% cyst(e)ine. Feed-grade DL-Met (99%) was compared to feed-grade DL-OH-Met, Ca (84%). When the purified diet was modified to contain 0.12% Met and 0.20% or greater cyst(e)ine, slope-ratio assays involving graded dosing of DL-Met (DL-M) (0, 404, 808, and 1,212 mg DL-M/kg) or isosulfurous levels of DL-OH-Met, Ca (OH-M) resulted in linear (P < 0.01) BW gain and G:F responses. Multiple linear regression analysis (BW gain vs. supplemental sulfur intake, R² = 0.98) resulted in an average bioefficacy estimate of 78.1% for OH-M vs. DL-M (equivalent to 65.6% on a supplemental compound basis). In assay 3, the purified diet was modified to be equally deficient in Met and cyst(e)ine (i.e., 0.12% Met, 0.12% cyst(e)ine). When this diet was supplemented with either 404 mg DL-M/kg or 476 mg OH-M/kg, BW gain and G:F responded (P < 0.01) markedly to either compound, and differences between DL-M and OH-M were not significant (P > 0.10). Assays 4 and 5 employed the corn-peanut meal basal diet containing 0.22% total Met and 0.23% total cyst(e)ine. In both assays, addition of either 465 mg DL-M/kg or 554 mg OH-M/kg resulted in increased (P < 0.01) BW gain and G:F, regardless of dietary cyst(e)ine concentration. In the absence of excess cyst(e)ine, BW gain responses to DL-M and OH-M were similar, but when 0.10% excess cyst(e)ine was provided as L-cystine or feather meal, DL-M responses tended to exceed those of OH-M. Moreover, this small excess of dietary cyst(e)ine, regardless of source, depressed (P < 0.01) feed intake and BW gain when added to the basal diet. Overall, these results suggest that excess dietary cyst(e)ine, when included in Met-deficient diets, has the potential to be both anorexigenic and pernicious to OH-M utilization.

Key Words: bioefficacy, chicks, cysteine, hydroxy methionine, methionine