Effects of Heat Stress and Dietary Tryptophan on Performance and Plasma Amino Acid Concentrations of Broiler Chickens

Hayford Y Tabiri,Masaaki Toyomizu,Yukio Akiba,Kan Sato,Kazuaki Takahashi

doi:10.5713/ajas.2002.247

Abstract

Two experiments were conducted to investigate the impact of high temperature and dietary tryptophan (Trp) on performance, selected organ weights and plasma free amino acid (AA) concentrations in broiler chickens. In Experiment 1, exposure to 27-33°C of chickens for 2 weeks from 2 weeks of age did not affect growth and plasma free AA concentration except for a decrease in the concentration of plasma tyrosine (Tyr). In Experiment 2, 2-week-old birds were allocated to one of three temperature treatments; 24°C (control), 36°C (heat stress, HS) and 24°C pair-fed (24PF) for 2 weeks and fed on diets containing 50, 100 and 300% of NRC requirement for Trp. Heat stress caused a reduction of weight gain and feed intake irrespective of dietary Trp levels compared with control counterparts, while feeding of 300% Trp diet did not attenuate the reduced performance by HS exposure. In groups fed the 100% Trp diets, plasma aromatic AA (AAA) and Tyr concentrations were decreased in the HS birds compared with the 24PF group. Plasma concentrations in most of AA groups were increased by HS in chickens fed the 50% Trp diet, while those were not changed by HS in chickens fed the 300% Trp diet, compared with 24PF counterparts. The plasma Trp/LNAA (LNAA=large neutral AAs, which are comprised of BCAA, AAA and Trp) ratio was increased by HS in chickens fed the 100% Trp diet, while it was decreased in chickens fed on 50% Trp diet as compared with 24PF group. From these results, it is suggested that performance and plasma amino acid profile deranged by heat stress are modulated, at least, to be relieved from the heat stress by feeding 50% Trp diet but not at all by feeding 300% Trp diet. The involvement of altered plasma AA profiles, in particular plasma Tyr concentrations and Trp/LNAA ratio, is discussed in association with the performance characteristics of HS chickens. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 2 : 247-253)

Highlights

High ambient temperature constitutes a significant hindrance to poultry production in the tropical world.Thermal stress exerts its deleterious effects on feed intake and body weight gain (Howlider and Rose, 1987; MacLeod and Hocking 1993; Geraert et al, 1996a), as well as on carcass yield and mortality rates (Smith, 1993)
The plasma Trp/LNAA (LNAA=large neutral amino acid (AA), which are comprised of branched chain AA (BCAA), aromatic AA (AAA) and Trp) ratio was increased by HS in chickens fed the 100% Trp diet, while it was decreased in chickens fed on 50% Trp diet as compared with 24PF group
Even though heat stress alters amino acid (AA) nutrition and metabolism, relatively few AAs, namely methionine (Met), lysine (Lys) and arginine (Arg), have been studied far in birds reared at high environmental temperature

Summary

Introduction

Thermal stress exerts its deleterious effects on feed intake and body weight gain (Howlider and Rose, 1987; MacLeod and Hocking 1993; Geraert et al, 1996a), as well as on carcass yield and mortality rates (Smith, 1993). Several research efforts have been made to overcome the negative effects of heat stress on chickens by manipulating the breeding programs, as well as the housing and nutrition of birds raised under high temperature environments (Howlider and Rose, 1987). With regards to nutritional manipulations in heat stressed birds, research has been conducted on energy, protein, fat, mineral and vitamin concentrations in chicken diets (Smith and Teeter, 1987; Sonaiya, 1989; Balnave and Oliva, 1990). Even though heat stress alters amino acid (AA) nutrition and metabolism, relatively few AAs, namely methionine (Met), lysine (Lys) and arginine (Arg), have been studied far in birds reared at high environmental temperature

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Conclusion