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Variations in the Digestible Sulfur Amino Acid Requirement of Broiler Chickens Due to Sex, Growth Criteria, Rearing Environment, and Processing Yield Characteristics

B. S. Lumpkins^*, A. B. Batal^*,1 and D. H. Baker

^* Poultry Science, University of Georgia, 208 Poultry Science Building, Athens 30602; and Department of Animal Science, University of Illinois, Urbana 61801

¹ Corresponding author: batal{at}uga.edu

	ABSTRACT

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Four experiments (Exp.) were conducted with Cobb 500 chicks to evaluate variations in the estimated digestible sulfur amino acid (DSAA) requirement of broilers due to rearing environment, sex, or growth performance during the starter period (7 to 19 d), and live performance response and carcass yield characteristics during the grower period (21 to 42 d). In the first 3 experiments conducted during the starter period, chicks were allocated to battery or floor pens, and in the fourth experiment birds were reared in floor pens. For Exp. 1, 2, and 3 a sulfur amino acid deficient corn-soybean meal-corn gluten meal basal diet and for the grower experiment a corn-soybean meal-peanut meal basal diet was formulated to be isocaloric and isonitrogenous within experiment. Graded levels of DSAA ranged from 0.54 to 0.94% in Exp. 1, 0.53 to 1.03% in Exp. 2, 0.49 to 0.89% in Exp. 3, and 0.43 to 0.83% in Exp. 4. True digestibility of the diets was determined using the precision-fed rooster assay. The DSAA requirements were estimated using 1-slope broken-line methodology. During the starter period, the average DSAA requirement of males and females was similar when based on the gain to feed ratio (G:F; 0.71 and 0.71%, respectively) and BW gain (BWG; 0.67 and 0.67%, respectively). In Exp. 3 involving battery and floor pens, males and females had similar DSAA requirement estimates, but the DSAA requirement based on maximal G:F (0.68%) was higher than the maximal BWG requirement (0.61%). In the grower period, the estimated DSAA requirement for males based on G:F was higher than that based on BWG, but the BWG and G:F requirements were similar for females. The DSAA requirement estimates were similar for males and females based on BWG (0.55%), but the DSAA requirement based on G:F was higher for males than females. The DSAA requirement for maximum breast meat yield was similar for males (0.55%) and females (0.56%), and the requirement for maximal breast meat yield was similar to that for maximal BWG. The DSAA requirements were similar based on sex, rearing environment, or both; however, there was a difference in the estimated DSAA requirements between growth and carcass responses.

Key Words: digestible sulfur amino acid requirement • broiler • rearing environment • growth performance • carcass yield

	INTRODUCTION

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Sulfur amino acids (SAA) are essential for growth, methylation reactions, and feather synthesis and are important precursors for synthesis of glutathione, taurine, coenzyme A, selenoenyzmes, and polyamines. Because of the important role SAA play in the body, determining a proper requirement is of the utmost concern. The development of synthetic sources of Met has made it easier for nutritionists to adjust the levels of TSAA for experimental purposes in addition to making it easier for proper feed formulation through supplementation of DL-Met or DL-OH-Met. Researchers have generally accepted the NRC recommendation of 0.50% methionine and 0.90% TSAA as the minimal requirement for broilers from 0 to 3 wk of age, yet most researchers and commercial nutritionist tend to use slightly higher TSAA levels (NRC, 1994). However, some have questioned how the TSAA requirement might be affected by different CP levels, addition of drugs to the diet, and the conditions under which the requirements were estimated. Han and Baker (1993) conducted an experiment to determine if the lysine requirement of chicks varies because of sex, heat stress, BW, and genetic strain. They concluded that males had a higher requirement than females and also that requirements were higher based on maximal gain to feed (G:F) than maximal BW gain (BWG), regardless of sex. Subsequent research confirmed the finding that the lysine requirement was higher for maximal G:F than maximal BWG (Mack et al., 1999; Baker et al., 2002). Considering that all other essential amino acids (e.g., SAA) are often expressed as a percentage of lysine, based on the ideal protein concept (Baker and Han, 1994; Emmert and Baker, 1997), it would make sense that the SAA requirement would vary in a similar manner as the lysine requirement based on the reports of Han and Baker (1993). Baker et al. (1996), Mack et al. (1999), and Kalinowski et al. (2003) reported higher SAA requirements for G:F than for BWG, but Morris et al. (1992) reported that there was no difference in TSAA requirements based on G:F or BWG. Additionally, Huyghebaert and Pack (1996) reported that the TSAA requirements during the grower period (14 to 38 d) were similar for BWG and G:F. However, it was observed that breast meat yield (BMY) increased with the further addition of SAA, indicating higher requirements based on this criterion than on live performance responses. A higher estimated SAA requirement based on BMY was further supported by other researchers (Hickling et al., 1990; Jeroch and Pack, 1992; Schutte and Pack, 1995b), suggesting that a SAA requirement based on growth responses may not be sufficient for optimal carcass responses. Schutte and Pack (1995a) agreed with the idea of a higher SAA requirement based on carcass characteristics and reported that the SAA requirement was higher for BMY than for BWG during the finisher period.

Most of the research conducted in determining amino acid requirements during the first 3 wk posthatch has been carried out in battery cages, which is not the same as conditions in a commercial setting (Jensen et al., 1989). Because a number of experiments have been conducted in determining the SAA requirement under different conditions, it is difficult to draw definitive conclusions as to how SAA requirements may vary based on different performance parameters, sex, and rearing environment. Therefore, the objective of our experiments were to evaluate how the DSAA requirement might change because of sex, live performance response, rearing environment, and processing yield characteristics in broiler chickens during the starter and grower periods.

	MATERIALS AND METHODS

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Experiments 1, 2, and 3

All procedures were approved by the University of Georgia committee on Laboratory Animal Care. The objective of these experiments were to evaluate any differences in the DSAA requirement based on BWG and G:F due to sex or rearing environment during the period from 8 to 19 d of age. Two rearing environments were used, floor and battery pens with 24 h lighting. For each experiment, 1-d-old Cobb 500 broiler chicks were vent-sexed and allocated by sex. In Exp. 1 and 2, 500 birds were placed in battery brooders (Petersime Incubator Co., Gettysburg, OH) with trough type feeders and waterers. In Exp. 3, 240 birds were placed in battery brooders with raised wire floors, and 960 birds where placed in floor pens with Ziggity nipple drinkers (Ziggity Systems Inc., Middlebury, IN), Chore-Time feeders (CTB Inc., Milford, IN), and wood shavings in environmentally controlled rooms. All birds received a conventional broiler starter diet (23% CP and 3,200 kcal of ME/kg) and water ad libitum until d 7, at which time the chicks were weighed and randomly assigned to the dietary treatments so that each pen had a similar initial weight and weight distribution. Body weights ranged from 113 to 139 g for males and from 113 to 141 g for females. Following an overnight fast, the birds received their experimental diets from 8 to 16, 8 to 18, and 8 to 19 d of age for Exp. 1, 2, and 3, respectively. The experimental diets consisted of 5 graded levels of DSAA, except for Exp. 2, which had 6 graded levels. Every dietary treatment had 6 replicate pens of each sex (12 replicate pens for each dietary treatment), with the exception of Exp. 3, where because of space limitations of floor pens there were 5 replicate pens per treatment. There were 6 birds per pen in the battery studies with a 35.6 x 99.1 x 25.4 cm dimension (density of 588 cm² per bird), and there were 20 birds per pen in the floor studies, with a 96.5 x 228.6 cm dimension (density of 1,103 cm² per bird). Body weight and feed intake were recorded throughout the experiments, and BWG and G:F were calculated. At the occurrence of mortality feed intake was adjusted based on bird days on feed.

Experiment 4

The objective of this experiment was to evaluate the differences in the DSAA requirement for males and females during the grower period, based on growth performance and processing yield parameters. One thousand eight hundred 1-d-old Cobb 500 broiler chicks were vent-sexed and allocated by sex to floor pens in an environmentally controlled room under 24 h lighting conditions with Ziggity nipple drinkers and Chore-Time feeders. The birds were fed a conventional starter diet with 23% CP and 3,200 kcal of ME/kg from 0 to 21 d of age. At d 21, the birds were sorted by sex and weighed, so that every pen had a similar initial weight and weight distribution. Body weight ranged from 789 to 860 g in males and from 730 to 824 g in females. The birds were randomly assigned to 5 dietary treatments consisting of 5 graded levels of DSAA. In every treatment there were 5 replicate pens of each sex (totaling 10 replications per dietary treatment) containing 25 birds in each pen, with a dimension of 121.9 x 309.9 cm (density of 1,151 cm² per bird). Body weight and feed intake were recorded, and BWG and G:F were calculated per pen at d 42 when the experiment was terminated. At the occurrence of mortality, feed intake was adjusted based on bird days on feed. For processing yield evaluation, 10 birds per pen were randomly selected and wing-banded. After an overnight fast, the birds were weighed individually at the processing plant, slaughtered, and eviscerated, after which carcasses were chilled for 12 h. The yield was obtained for the entire carcass, BMY, wings, and front and back halves. The carcass was weighed, and the back half yield, consisting of the leg quarters attached to the lower back, was removed and weighed, leaving the white meat front half. The wings and the breast meat (pectoralis major and minor) were removed from the front half and weighed.

Diets

For the starter experiment, a corn-soybean meal-corn gluten meal basal diet was formulated to meet or exceed the NRC (1994) recommendations from 0 to 21 d of age (Exp. 1, 2, and 3) for all nutrients except Met and cystine (Table 1). The grower experiment (Exp. 4) used a SAA-deficient corn-soybean meal-peanut meal basal diet from 21 to 42 d of age (Table 1). Graded levels of L-Cys and L-Met were added to the basal diet in a 1:1 ratio at the expense of glutamic acid and dextrose to keep the diets isonitrogenous and isocaloric within experiment. Levels of DSAA for each experiment were as follows: 0.54, 0.64, 0.74, 0.84, and 0.94% for Exp. 1; 0.53, 0.63, 0.73, 0.83, 0.93, and 1.03% for Exp. 2; 0.49, 0.59, 0.69, 0.79, and 0.89% for Exp. 3; and 0.43, 0.53, 0.63, 0.73, and 0.83% for Exp. 4. The true amino acid digestibilities of the basal diets were determined using the total excreta collection precision-fed rooster assay, using adult, cecectomized, Single-Comb White Leghorn roosters (Han and Parsons, 1990). Five roosters were given a 30-g sample of each basal diet via crop intubation, and 5 additional roosters were feed-deprived to estimate endogenous losses. After 48 h, the excreta were collected, freeze-dried, and the samples were sent to a commercial laboratory (Experiment Station Chemical Laboratories, University of Missouri, Columbia) for amino acid quantification in the feed and excreta [method 982.30 E (a,b,c) in AOAC, 1995]. Performic acid preoxidation preceded acid hydrolysis in the determination of Met and Cys (Spackman et al., 1958). Tryptophan was quantified similarly, but a 24-h LiOH hydrolysis preceded chromatographic analysis.

Growth performance data at 16, 18, and 19 (Exp. 1, 2, and 3) and 42 d of age plus carcass yield results (Exp. 4) were fitted to linear and quadratic response curves (Draper and Smith, 1981) using the GLM procedure of SAS (SAS Institute, 1990). The DSAA requirements for BWG, G:F, carcass yield (CY), and BMY were estimated by 1-slope broken-line methodology (Robbins et al., 1979).

	RESULTS

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Experiment 1

A significant (P < 0.05) quadratic and broken-line response to increasing dietary levels of DSAA was observed for males and females reared in battery pens (Table 2). The estimated DSAA requirement for BWG and G:F (0.75 and 0.76%, respectively) was similar for males reared in batteries. However, females had higher DSAA requirement estimates based on G:F (0.79%) than BWG (0.75%). The males and females had a similar DSAA requirement of 0.75% based on BWG, but females had a higher DSAA requirement than males based on G:F.

Performance of males and females reared in battery pens followed a significant (P < 0.05) quadratic and broken-line response to increasing dietary levels of DSAA (Table 3). Males and females had a lower estimated DSAA requirement based on BWG (0.72 and 0.67%, respectively) than for G:F (0.78 and 0.73%, respectively). The estimated DSAA requirement was higher for males (0.72 and 0.78%) than for females (0.67 and 0.73%) based on BWG and G:F, respectively.

A significant (P < 0.05) quadratic and broken-line response to increasing dietary levels of DSAA based on BWG and G:F for males and females was observed for birds reared in battery or floor pens (Table 4). Males and females reared in battery pens had similar average DSAA requirement estimates based on G:F (0.63%) and BWG (0.63%). When chicks were reared in floor pens, males and females required higher DSAA levels to maximize G:F (0.68% average) than to maximize BWG (0.61% average). When comparing the 2 rearing environments, the estimated DSAA requirement for maximal G:F was higher in males and females raised on the floor (0.68% average) than in birds reared in battery cages (0.63% average). However, there was little to no difference in the estimated DSAA requirement for maximal BWG of males and females when reared in battery or floor pens.

Growth performance responses, CY, and BMY of males and females during the grower period (21 to 42 d of age) followed a significant (P < 0.05) quadratic and broken-line response with increasing levels of dietary DSAA (Tables 5 and 6). The estimated DSAA requirement for males was 0.55, 0.64, 0.51, and 0.55% and for females was 0.55, 0.57, 0.52, and 0.56%, based on BWG, G:F, CY, and BMY, respectively. Among these criteria, only the G:F DSAA requirement was higher for males (0.64%) than for females (0.57%). The estimated DSAA requirement for maximal BMY was similar for males and females, and the BMY requirement (0.55%) was similar to the BWG requirements (0.55%). The DSAA requirement estimates based on CY (0.51%) was the lowest among all the criteria evaluated.

	DISCUSSION

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Our results showing higher DSAA requirements for maximal G:F than maximal BWG are in contrast to the findings of Mendonca and Jensen (1989), Morris et al. (1992), and Huyghebaert and Pack (1996). These workers found no consistent difference in TSAA requirements for maximal BWG and maximal feed efficiency. Mack et al. (1999), however, found that the SAA requirement during the 20- to 40-d growth period was substantially higher for maximal G:F than for maximal BWG or BMY. Likewise, Baker et al. (1996) and Kalinowski et al. (2003) observed higher G:F than BWG requirements for SAA in chicks during the period 21 to 42 d of age. After reaching a peak in feed intake, additional increments of DSAA caused gradual decreases in feed intake, but weight gain remained relatively constant. Thus, feed efficiency plateaus occurred at higher concentrations of DSAA than was the case for weight gain.

Assuming a 0.71% DSAA requirement is an acceptable average estimate of the broken-line requirement during the first 3 wk posthatching, extrapolation of this (statistical) estimate to practical conditions is necessary. Requirements based on the plateau intercept of a quadratic fit superimposed on a broken line (Baker et al., 2002) or based on 90% of the upper asymptote of a quadratic fit generally result in a increase of about 10% in the DSAA requirement [i.e., relative to broken-line estimates (Baker et al., 2002)]. Adding 0.07% to 0.71% gives a DSAA requirement estimate of 0.78% for broiler chicks in the second and third week of life. This equates to 0.89% TSAA for chicks fed a typical corn-soybean meal diet, i.e., assuming SAA digestibility in this diet is 88% (NRC, 1994). Our requirement estimate of 0.78% DSAA and 0.89% TSAA is very similar to the Emmert and Baker (1997) estimate of 0.78% DSAA and the NRC (1994) estimate of 0.90% TSAA (0.79% on a digestible basis). Likewise, if one extrapolates the DSAA requirement of our 21- to 42-d-old chicks (Tables 5 and 6) to a TSAA basis, assuming a corn-soybean meal diet, a TSAA requirement of close to 0.72% is obtained, which is similar to the NRC (1994) estimate for birds of this age.

From the results presented herein, it is safe to assume that DSAA requirements for broiler chicks are higher based on G:F than BWG. The difference in sex has little impact on the variation of DSAA requirements and should not be a contributing factor in feed formulation. Furthermore, variation in the DSAA requirement estimates due to rearing conditions (i.e., battery brooders vs. floor pens) is minimal, if any. The estimated DSAA requirements based on BMY were similar to those based on performance responses. However, the requirement of DSAA for BWG, G:F, or BMY may depend on the production objectives of a given company.

	ACKNOWLEDGMENTS

 
This study was supported by a grant from the US Poultry and Egg Association.

Received for publication June 26, 2006. Accepted for publication November 9, 2006.

	REFERENCES

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Lumpkins, B. S. Articles by Baker, D. H. Search for Related Content PubMed PubMed Citation Articles by Lumpkins, B. S. Articles by Baker, D. H.