The effects of supplemental threonine on performance, carcass characteristics, immune response and gut health of broilers in subtropics during pre‐starter and starter period

Abstract

Three hundred thirty‐day‐old unsexed commercial broiler chicks (Vencobb‐400) with initial average body weight of 44.04 ± 0.42 g were allocated into five experimental groups, in a completely randomized design (CRD) with 21‐day experiment. Groups were formed according to dose of supplemental L‐threonine in various rations i.e., 100% NRC specification, 100% threonine of Vencobb‐400 strain specification, 110% threonine of Vencobb‐400 strain specification, 120% of threonine of Vencobb‐400 strain specification and 130% threonine of Vencobb‐400 strain specification. Average daily feed intake (ADFI), average daily body weight gain (ADG), cumulative feed conversion ratio (CFCR), carcass characteristics, immune response, intestinal morphometry and biochemical profile were studied. The ADFI and ADG increased linearly and quadratically as dietary threonine levels were increased. However, the CFCR did not differ (p ˃ 0.05) among the groups. Though the carcass weight and drumstick yield did not differ (p ˃ 0.05) among the groups, the relative breast yield increased linearly (p = 0.007). The relative dressing yield and relative thigh weight increased linearly (p = 0.05 and p = 0.03, respectively). The relative weight of immune organs like bursa and thymus increased linearly. The mean total serum immunoglobulin, ND‐ELISA titre and the mean lymphocyte proliferation response index increased linearly, whereas mean phagocytic activity index of neutrophil increased linearly (p < 0.001) and quadratically (p = 0.001). The mean villus height (VH), crypt depth (CD), villus surface area and mean goblet cell number/villus increased linearly and quadratically, whereas the villus width (VW) and goblet cell density increased quadratically. The serum glucose increased linearly (p = 0.001), whereas serum total protein concentration and serum globulin level increased both linearly and quadratically. The albumin: globulin ratio tended to decrease linearly. There was a significant decrease (p < 0.05) in serum cholesterol and VLDL cholesterol level. However, a linear increment (p = 0.04) in the blood serum HDL cholesterol level with a linear reduction (p = 0.01) in the blood serum LDL cholesterol was noticed.

Interactive effects of threonine levels and protein source on growth performance and carcass traits, gut morphology, ileal digestibility of protein and amino acids, and immunity in broilers

“…Extra Thr improved the gut morphology in broilers as supported by higher duodenal VH and greater ratio of VH to CD that resulted in a better digestibility of protein and AA. These findings are in accordance with expectations (Wang et al, 2010 ; Min et al, 2017 ; Debnath et al, 2019 ) since Thr is an essential amino acid involved in mucin production, which constitutes about 40% of gastrointestinal tract proteins (Carlstedt et al, 1993 ). This mucin makes a thin covering on the inner side of the gut, protects it from pathogens and anti-nutritional factors (Li et al, 2007 ).…”

“…The greater immune organs weight of broilers fed diets having high levels of d-Thr is in line with findings already reported in broilers (Chen et al, 2016 ; Debnath et al, 2019 ). The greater spleen weight may be indicative of more production of immune cells and antibodies that in turn positively influence immunity of the broilers.…”

“…The greater spleen weight may be indicative of more production of immune cells and antibodies that in turn positively influence immunity of the broilers. The greater relative weight of thymus in d-Thr supplemented diet fed broilers may be due to more T-lymphocyte production from thymus (Debnath et al, 2019 ) that positivly influenced immune status of broilers. Threonine levels influence the immune system response in broilers by manipulating the gut microbial population and moderating immune system by enhancing immunoglobulin A ( IgA ) secretion and regulating the expression of the inflammatory genes (Chen et al, 2016 ).…”

“…Threonine ( Thr ), the third limiting amino acid after methionine and lysine in corn-soy diets, is an indispensable amino acid for broilers (Berres et al, 2007 ) that is involved in the development and proper functioning of the gut. Synthesis of body protein, collagen, elastin, antibody as well as production of uric acid and pancreatic enzymes also requires Thr (Debnath et al, 2019 ). The influence of Thr on growth parameters, gut health, immunity, and carcass traits was reviewed in broilers (Qaisrani et al, 2018 ).…”

Nutritional significance of amino acids, vitamins and minerals as nutraceuticals in poultry production and health – a comprehensive review

“…Amino acids are functional and structural units of protein, nutritionally classified into two groups: non-essential (synthesized in the body) and essential amino acids (cannot be synthesized rapidly enough to meet the metabolic requirement). Amino acids play vital physiological roles in the body (Bortoluzzi et al 2018;Debnath et al 2019). After absorption, amino acids are assembled and metabolized to form proteins that are used to build different body tissues.…”