Growth Performance, Carcass Characteristics, Nutrient Digestibility and Serum Biochemical Parameters of Broilers Fed Low-protein Diets Supplemented with Various Ratios of Threonine to Lysine

L M Gong,Y L Liu,C H Lai,Y X Ma,Defa Li,S Y Qiao

doi:10.5713/ajas.2005.1164

Abstract

This study was conducted to evaluate performance, breast (thigh) muscle yield, nutrient digestibility and serum biochemical parameters of broilers fed low-protein diets supplemented with various threonine to lysine ratios (Thr/Lys). Three hundred and twenty four day-old male Arbor Acres broilers were randomly allotted to six dietary treatments with six replicates per treatment and nine broilers per replicate. Six treatments included one control diet (formulated according to NRC (1994)), and five experimental diets (treatments 1-5). In treatments 1-5, the crude protein level was 2% lower than that of the NRC control diet. The Thr/Lys in treatments 1- 5 was 0.65, 0.70, 0.75, 0.80 and 0.85 during the starter and grower phases and 0.70, 0.75, 0.80, 0.85 and 0.90 during the finisher phase with other nutrient levels kept consistent. The results showed that: (1) With increasing Thr/Lys, ADG of treatments 1, 3 and 4 were lower (p<0.05) than those of the NRC control diet during the starter phase; ADG of treatments 1-5 were lower (p<0.05) than those of the NRC control during the grower phase, and ADG of treatment 1 was lower (p<0.05) than that of the NRC control during the finisher phase. Average daily feed intake in treatments 1 and 4 were lower (p<0.05) than that of broilers on the NRC control diet during the grower phase. Feed/gain (F/G) of the NRC control diet was lowest (p<0.05) during the starter phase. F/G in treatments 2 and 5 were higher (p<0.05) than that of NRC during the grower phase. (2) Breast muscle proportion on d 21 increased linearly (p<0.05) in response to graded levels of Thr/Lys. (3) No differences were detected for dry matter, energy and crude protein digestibility among all seven treatments. (4) On d 21, serum triglyceride of broilers on dietary treatments 3 and 5 was higher (p<0.05) than that of broilers in control. The results indicate that the low-protein diets supplemented with an appropriate Thr/Lys could not support the same performance that was achieved by the broilers fed the NRC control diet. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 8 : 1164-1170)

Highlights

Threonine (Thr) is an essential amino acid that cannot be synthesized in the animal body and has to be supplemented in the diet
Broilers fed low-protein, threonine supplemented diets achieved the same high level of growth performance that was achieved by broilers fed high-protein diets (Kidd et al, 1997), while the amount of protein feedstuff and feed cost were both reduced
Regression analysis of treatments 1-5 showed that average daily gain (ADG) during the finisher phase tended to increase with increasing Thr/Lys

Summary

Introduction

Threonine (Thr) is an essential amino acid that cannot be synthesized in the animal body and has to be supplemented in the diet. In the past ten years, threonine has become one of the main factors limiting animal performance as inclusion of crystalline lysine and methionine in complete diets has increased. Several researchers have found that weight gain, feed conversion ratio (Li and Guo, 2000), carcass characteristics (Dozier et al, 2000) and immunity of broilers (Dozier et al, 2001) could be improved with an increase of threonine in the diet. Little research has been conducted to investigate this interaction, especially regarding the ratio of threonine to lysine (Thr/Lys) in broilers. Growth performance, carcass characteristics, nutrient digestibility and serum biochemical parameters of broilers fed low-protein diets supplemented with various Thr/Lys were determined

Methods

Results

Conclusion