| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
METABOLISM AND NUTRITION |
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada N1G 2W1
1 Corresponding author: sleeson{at}uoguelph.ca
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Key Words: broiler • methionine • arginine • heat stress • dietary protein
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The objectives of the present experiments were to test the effect of Arg:Lys, Met source, and time exposure to HS on BWG and body protein accretion in broilers exposed to acute or chronic HS.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Day-old Ross 308 male chicks were housed in wire-floor cages in 1 of 4 separate rooms. Cages (51 x 60 cm and 16-cm height) were equipped with individual nipple drinkers and 51-cm-long feed troughs and were arranged in 2 tiers. Birds in 2 replicate rooms were maintained at high temperatures at all times and served as the CHS treatment. Birds in the other 2 replicate rooms were kept at a standard brooding temperature of 32°C at 1 d of age, and then the temperature was reduced to 19°C at 25 d of age. At d 26, the rooms were given a sudden temperature increase; this group served as the acutely heat-stressed (AHS) treatment. Both groups were maintained at 32.8 ± 1.0°C from 26 to 33 d of age (experimental period). Hourly measurements of temperature and RH were recorded using 2 HOBO H8 loggers (Onset Computer Corp., Bourne, MA) installed in each room. Environmental conditions are detailed in Figure 1
.
|
). Amino acid analyses (Experiment Station Chemical Laboratories, University of Missouri, Columbia) were performed by Method 982.30E (a,b,c) of Association of Official Analytical Chemists (1995), and dietary concentrations of HMB (Novus International Inc., St. Charles, MO) were analyzed using the method of Ontiveros et al. (1987). All nutrients, except for TSAA and Arg, were balanced in agreement with Leeson and Summers (2000). Synthetic DLM was added at 0 or 1.5 g/kg of diet and fed ad libitum to 4 replicates of 3 birds kept in AHS or CHS conditions.
|
Experiment 2
Three synthetic sources of Met (HMB, DLM, and L-Met) were supplemented in equimolar levels to the basal protein concentrate to attain levels of TSAA 5% lower than the requirement for this age of bird, whereas L-Arg monohydrochloride was added to give Arg:Lys of 0.95 and 1.40, for a total of 6 diet treatments. All amino acid supplements were at the expense of cellulose. The added Met equivalents accounted for 20% of the TSAA and for 45% of the total Met equivalents in these diets.
An isoenergetic N-free diet (Table 1
) was prepared in such a way that its mineral content was similar to that of the 6 protein concentrates detailed above. This N-free diet was fed alone or with varying proportions of each experimental diet, to give graded levels of protein (0.0, 3.5, 7, 10.5, 14, and 17.5%) for each treatment. These graded levels of protein equivalent were expected to elicit graded responses to growth and protein accretion. Each protein level was fed to 18 replicates of 3 birds within AHS and CHS environments, as detailed in Figure 1. Body weight gain and body N content of 1 bird per replicate cage were measured as described in Experiment 1. The experiment was carried out according to procedures approved by the University of Guelph Animal Care Committee.
Statistical Analysis
In both experiments, BWG and CP deposition (CPD) were measured from 26 to 33 d of age. Cage means of these parameters were plotted against protein intake (g/ bird per d). A linear regression for each Met source, related to the graded levels of protein supplementation, was obtained for birds under CHS and AHS conditions and fed at Arg:Lys of 0.95 and 1.40. The slope coefficients from birds fed protein concentrates with added L-Met were given a value of 100% for protein use. The protein use of those fed HMB and DLM were obtained by using the following equation
 |
where Y = dependent variable (g/bird per d of BWG or CPD); X1, X2, and X3 = intake of supplemental Met equivalents (g/bird per d) for birds under HMB, DLM, and Met added at 6 protein levels, respectively; ß0 = intercept; ß1 = slope coefficient for L-Met; ß2 = slope coefficient for DLM/ slope coefficient for Met; ß3 = slope coefficient for HMB/ slope coefficient for Met; and
= error term. Confidence intervals (95%) were generated for parameters ß1, ß2, and ß3.
To derive protein-use coefficients from birds with positive BWG or CPD, any observations of negative BWG or CPD were eliminated from the analysis (positive growth). Coefficients were also obtained using all observations (all data), both positive and negative, for comparative purposes.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). Heat-stressed birds were panting most of the time. In Experiment 1, regardless of the time of exposure to HS, birds fed the protein concentrate devoid of Met had significantly lower BWG and CPD (data not tabulated, P < 0.01 and P < 0.001, respectively) than those fed supplemental DLM (26 ± 3 vs. 38 ± 3 g; and 1.86 ± 0.92 vs. 6.57 ± 0.92 g, respectively), with no differences in average daily feed intake (P > 0.05; 77.7 ± 2.1 vs. 82.4 ± 2.5 g, respectively). These data confirmed that the diet was deficient in Met. No interactions between time of exposure to HS and Met-supplementation diet were detected (P > 0.05).
In Experiment 2, the effects of Met source, Arg:Lys, and time of exposure to HS on growth and body protein accretion were similar when using data from all birds (all data) or just those exhibiting growth (positive growth). Protein use of AHS birds fed HMB with low Arg was similar to those fed DLM and L-Met (P > 0.05), whereas those fed DLM had higher protein use than birds on L-Met (P < 0.05; Figures 2 and 3). Weight gain and protein deposition were unaffected by Met sources used at high Arg:Lys ratios for AHS birds (P > 0.05; Figures 4 and 5).
|
|
|
|
and 7). No differences were found among Met sources when fed to CHS birds at Arg:Lys of 1.40 (Figures 8 and 9).
|
|
|
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). During the brooding period, the source of heat was coming through the top part of the cages, although the thermometers were located at feeder level. Birds gathered close to the source of heat during those days without apparently suffering from hypothermia. In spite of this observation, the average BW of AHS birds was still higher (P < 0.001) than that of the CHS group at 26 d of age (932 ± 8 vs. 884 ± 8 g, respectively). During the experimental period, birds under AHS and CHS conditions were panting most of the time. Balnave and Oliva (1990) assessed the Met requirements of birds grown at various temperatures. They found that birds kept at a constant 30°C achieved optimum growth when fed Met:Lys of 0.31. Birds under cycling temperatures of 25 to 35°C required ratios of 0.37, whereas maximum growth was obtained with Met:Lys of 0.39 for birds at 21°C. The authors concluded that Met requirements decrease under conditions of HS. The protein concentrate used here contained Met:Lys at 0.38 after supplementation, which, according to Leeson and Summers (2000), is marginally lower than the requirements for birds at thermoneutral conditions but higher than the levels recommended by Balnave and Oliva (1990) for heat-stressed birds.
Brake et al. (1998) observed improved performance in birds fed Arg:Lys at 1.37 vs. those fed ratios of 1.10, as suggested by NRC (1994), only when housed at high temperatures. In 2 consecutive in vitro studies, these authors found that, under conditions of HS, the total uptake of Lys increased in mucosal cells due to an increase in the energy and Na-dependent mechanisms of absorption. The total intestinal uptake of Arg was found to be negatively affected only in the presence of Lys. This effect was mainly due to impaired mechanisms of the energy- and Na-independent pathways for the uptake of Arg. Brake et al. (1998) concluded that the Arg requirement of hyperthermic birds possibly increased due to an interaction with Lys. The basal protein concentrate tested in the present study had levels of Arg marginally deficient for birds at thermoneutrality (NRC, 1994). This deficiency may have been accentuated due to HS; however, the positive response to added Met obtained in Experiment 1 for AHS and CHS birds suggests that, under these conditions, the basal protein concentrate was first limiting in Met rather than Arg.
In Experiment 2, feeding graded levels of protein resulted in birds with variable growth and protein accretion. Concerns may rise if protein use is assessed by using birds with negative growth, and so protein use was measured using the data from experimental groups fed the protein-free diet (i.e., common intercept for the 3 sources of Met) and those having positive tissue accretion only (positive growth). For comparative purposes, protein use was also measured using data from all experimental groups, regardless of having positive or negative growth (all data). In all instances, similar results were obtained by using positive growth vs. all data. This situation relates to the fact that when fitting a linear-regression analysis with a common intercept, data observations on the far right have the greatest effect on the estimates of relative protein use (i.e., slopes for L-Met, HMB, and DLM), and observations located close to the common intercept (i.e., weight loss) have minimal effect on estimates.
Similar relative results were obtained by using BWG vs. CPD as dependent variables, with the exception of AHS birds fed at Arg:Lys of 0.95. These birds had lower protein use when fed L-Met vs. DLM (P < 0.05). Although the trend was similar when using BWG and CPD, this effect was significant only when using BWG. However, less variation was observed by using BWG rather than CPD in all instances, suggesting a better fit for estimates derived from BWG.
Protein use for growth and CPD was negatively affected in AHS and CHS birds fed L-Met compared with those fed HMB, DLM, or both at low Arg:Lys (P < 0.05). However, when supplemented with high Arg:Lys, protein use always remained unaffected by Met source. Arginine interacts with Met through the creatine biosynthesis pathway such that the growth-depressing effect of excess Met is partially alleviated when Arg, alone or in combination with glycine, is given to birds at thermoneutrality (Boorman and Fisher, 1966; Smith, 1968). In the current experiment, increasing the level of Arg may have helped eliminate a possible excess of methyl-group donors formed from HMB, DLM, and L-Met, thus equalizing the effect of Met sources on protein use. On the other hand, when supplemented at low Arg:Lys differences in absorption, metabolism, tissue distribution, or both among L-Met, HMB, and DLM may have occurred, affecting protein use.
Dibner et al. (1992) and Knight et al. (1994) reported reduced performance in birds fed DLM compared with those fed HMB. Subsequent in vitro studies revealed that the total intestinal uptake of Met remained unaffected after a short (<72 h) exposure to high temperatures. However, the uptake for DLM was impaired, whereas that of HMB increased. Dibner et al. (1992) and Knight (1994) also observed lower performance in birds fed D-Met when subjected to intermittent HS, whereas no differences were found with birds at thermoneutral conditions. These authors concluded that lower availability of D-Met may explain the lower performance observed in hyperthermic birds fed DLM. However, those findings also imply that hyperthermic birds fed DLM may limit the uptake of D-Met, which may be advantageous if TSAA are fed to excess.
Rostagno and Barbosa (1995) studied the digestibility of DLM and HMB in cecectomized roosters during a Brazilian summer season. These authors reported a lower net absorption for HMB vs. that for DLM after chronic stress. Given the fact that HMB is mainly absorbed by diffusion and that the total uptake of HMB increases during HS (Dibner et al., 1992), the study of Rostagno and Barbosa (1995) suggests greater kidney clearance for HMB, rather than lower intestinal uptake, may occur during prolonged hyperthermia. This may be beneficial, because Met requirements decrease as the severity of HS increases (Balnave and Oliva, 1990), facilitating the clearance of excess Met equivalents.
Feeding L-Met resulted in lower protein use compared with DLM supplemented at low Arg:Lys. Birds fed HMB at low Arg:Lys utilized dietary protein better than those fed L-Met only under CHS conditions. Given the fact that Met requirements decrease under HS (Balnave and Oliva, 1990), it is possible that birds fed L-Met at deficient Arg:Lys (0.95) had an excess of methyl donors that may have affected protein use. Birds fed DLM or HMB may have a lower load of methyl donors due to lower D-Met absorption or due to higher kidney clearance, respectively, or by a possible negative feedback mechanism to limit their conversion to Met. The mechanisms by which an overload of methyl donors could affect protein use in hyperthermic birds are unknown. In previous studies (our unpublished observations), we have shown lower apparent ileal digestibility coefficients in birds fed Met in high-Arg diets, but only under CHS conditions.
Under thermoneutral conditions, the detrimental effects of feeding high levels of Met are partially ameliorated by the addition of Arg through the formation of creatine and creatinine (Boorman and Fisher, 1966; Smith, 1968), which may be stored or eliminated in the excreta. However, under conditions of HS, the formation of these substances may decrease, as suggested by Chamruspollert (2001), who reported that creatine and creatinine concentrations in the manure of heat-stressed birds decreased without increases in muscle concentrations. This situation implies that birds under HS have lower creatine biosynthesis. Further studies on the metabolism of Arg, Met, or both under conditions of HS would help to clarify the causes of the interaction between Arg:Lys ratios and Met source in birds under HS. It is concluded that Arg:Lys, Met source, and time of exposure to HS affected the relative use of dietary protein in hyperthermic birds.
In summary, relative protein use was affected by Arg:Lys, Met source, and time of exposure to HS. Protein use was unaffected by Met source in AHS and CHS birds only when fed at high Arg:Lys. The AHS and CHS birds had lower protein use when fed L-Met rather than DLM at low Arg:Lys. Birds fed HMB at low Arg:Lys utilized protein better than birds fed L-Met only under CHS conditions. Protein use was always similar when feeding HMB vs. DLM. Changes in the requirements for Met and Arg under HS may predispose birds to a nutritional interaction between these amino acids when fed at marginally deficient levels for Arg. Adaptation mechanisms occurring during HS may result in a reduced load of methyl donors when HMB, DLM, or both, rather than L-Met, are fed. Changes in the metabolisms of Arg, Met, or both may explain the detrimental effect of L-Met on protein use when fed with low Arg:Lys to AHS and CHS birds.
|
ACKNOWLEDGMENTS |
|---|
Received for publication December 7, 2005. Accepted for publication April 6, 2006.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Balnave, D., J. Hayat, and J. Brake. 1999. Dietary arginine:lysine ratio and methionine activity at elevated environmental temperatures. J. Appl. Poult. Res. 8:1–9.
Balnave, D., and A. G. Oliva. 1990. Responses of finishing broilers at high temperatures on dietary methionine source and supplementation levels. Aust. J. Agric. Res. 41:557–564.
Boorman, K. N., and H. Fisher. 1966. The arginine-lysine interaction in the chick. Br. Poult. Sci. 7:39–44.[Medline]
Brake, J., D. Balnave, and J. J. Dibner. 1998. Optimum dietary arginine:lysine ratio for broiler chickens is altered during heat stress in association with changes in intestinal uptake and dietary sodium chloride. Br. Poult. Sci. 39:639–647.[Web of Science][Medline]
Chamruspollert, M. 2001. Interrelationships between dietary arginine, methionine and environmental temperature affect growth and creatine biosynthesis in young broiler chick. Ph.D. thesis. University of Georgia, Athens.
Chen, J., J. Hayat, B. Huang, D. Balnave, and J. Brake. 2003. Responses of broilers at moderate or high temperatures to dietary arginine:lysine ratio and source of supplemental methionine activity. Aust. J. Agric. Res. 54:177–181.
Dibner, J. J., C. A. Atwell, and F. J. Ivey. 1992. Effect of heat stress on 2-hydroxy-4-(methylthio)butanoic acid and DL-methionine absorption measured in vitro. Poult. Sci. 71:1900–1910.[Web of Science][Medline]
Knight, C. D., C. W. Wuelling, C. A. Atwell, and J. J. Dibner. 1994. Effect of intermittent periods of high environmental temperature on broiler performance responses to sources of methionine activity. Poult. Sci. 73:627–639.[Web of Science][Medline]
Leeson, S., and J. D. Summers. 2000. Scott’s Nutrition of the Chicken. 4th ed. Univ. Books. Guelph, Ontario, Canada.
National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC.
Ontiveros, R. R., W. D. Shermer, and R. A. Berner. 1987. A HPLC method for 2-hydroxy-4-(methylthio)butanoic acid analysis. J. Agric. Food Chem. 35:692–694.
Rostagno, H. S., and W. A. Barbosa. 1995. Biological efficacy and absorption of DL-methionine hydroxyl analogue free acid compared to DL-methionine in chickens as affected by heat stress. Br. Poult. Sci. 36:303–312.[Web of Science][Medline]
Sibbald, I. R., and A. Fortin. 1982. Preparation of dry homogenates from whole eviscerated chickens. Poult. Sci. 61:589–590.
Smith, R. E. 1968. Effect of arginine upon the toxicity of excesses of single amino acids in chicks. J. Nutr. 95:547–553.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
) = DL-Met; and HMB (
) = 2-hydroxy-4-(methylthio) butanoic acid. Relative utilization (%) was obtained from the equation BWG = ß0 + ß1 x [X1 + (ß2 x X2 + ß3 x X3)]; values with different superscript letters differ statistically (P < 0.05). Data from birds losing or gaining BWG were analyzed separately (all data; broken lines: ß0= –20.95; ß1 = 3.71; ß2 = 1.33 ± 0.22; and ß3 = 1.12 ± 0.19). Data from birds losing BWG were excluded from the analysis (positive growth; solid lines: ß0 = –13.73; ß1 = 3.15; ß2 = 1.29 ± 0.21; and ß3 = 1.09 ± 0.19).
