Nutritive Value of Sorghum Grains in Diets for Broiler Chickens

Abstract

<p>Detailed findings of the potential use of sorghum grain in diets for broiler chickens are presented in this thesis. A comprehensive literature on the above subject was reviewed, followed by feeding trails.</p><p> An initial experiment (Chapter 3) in this thesis evaluated the chemical composition and nutritive value of South African sorghum varieties as feed for broiler chickens. Physical and proximate composition, total phenolic and antioxidant activity, mineral content, amino acid profile and digestibility and true metabolisable energy of four sorghum varieties were studied. The thousand-kernel-weight ranged from 33 to 28 g and kernel texture was somewhat corneous to floury. The condensed tannin sorghum varieties, PAN8625 and NS5511, had higher total phenolic content and antioxidant activity than the non-tannin varieties, PAN8816 and PAN8906. Starch and gross energy contents differed significantly across the sorghum varieties. The sorghum varieties had somewhat similar total and individual mineral contents. Threonine, leucine, phenylalanine, valine, proline and alanine contents of varieties PAN8625 and PAN8906 were higher than those of NS5511 and PAN8816, which had similar contents. The amino acid digestibility and metabolisable energy of the tannin sorghum varieties were generally lower than those of the non-tannin varieties.</p><p> In addition to determining the physio-chemical properties of sorghum grains the influence of xylanase inclusion in sorghum-based diets on performance of broiler chickens was determined in another experiment (Chapter 4). Gross performances were assessed and carcass yield and visceral organ weights were measured at day 21. On day 25, birds were euthanized by intravenous injections of sodium pentobarbitone, and digesta contents from the distal ileum were collected and processed to determine the nutrient digestibility. Broiler chickens offered sorghum variety Pan8816 supplemented with xylanase had higher feed intake, weight gain, and better feed conversion ratio (FCR) than those given diets composed of sorghum variety Pan8625 without xylanase addition at 1-7 days of age. Crude protein digestibility of Pan8625, a tannin variety not supplemented with xylanase, was lower than that with xylanase. Enzyme inclusion significantly increased the crude protein digestibility. </p><p> In Chapter 5 of this thesis the response of broiler chickens to whole sorghum inclusion and feed form were evaluated. Body weight and feed intake were measured on a pen basis at 10, 25, and 35 days of age and feed conversion ratio (FCR) calculated. Pellet diets affected feed intake, body weight and carcass parts of broiler chickens aged 1-35 days. Heavier relative gizzard weights with lower pH were recorded for broiler chickens offered mash diets at ages 1-35 days. FCR at 1-35 days increased with an increase in WS and levelled off with higher inclusion rates. Relative gizzard weights at 35 days marginally increased with the increase in whole sorghum inclusion levels. Similarly, relative bursa and liver weight at 35 days increased with the increase in WS inclusion. Overall, the results showed that pelleted diets were superior to mash diets. Although higher levels of WS inclusions enhanced the gizzard development, performance parameters of birds offered these levels were not affected.</p><p> The influence of age of introducing whole sorghum grain and xylanase supplementation to broiler chicken diets was evaluated in this thesis (Chapter 6). A whole sorghum inclusion level of 50 % with or without xylanase was offered to birds at different ages. Gross performance parameters on a pen basis at 10, 24, and 35 days of age were measured. Age of introduction had improved feed intake and body weight of broiler chickens at ages 1-10 and 1-35 days. Chickens offered whole grain from hatch had higher feed intake and body weight at 1-10 days. The relative visceral organ weights, meat parts yield, meat colour and pH were not influenced by age of WSG introduction or xylanase supplementation. Apparent metabolizable energy (AME) of diets and of the sorghum was improved by age of introduction. Birds to which whole grain was introduced from hatch or day 11 had significantly higher AME than birds not receiving whole grain inclusion. Age of introduction had an effect on gross performance of broiler chickens. Feeding whole grain as early as hatch marginally improved body weight and feed intake of broiler chickens.</p><p> The main finding in this thesis is that non-tannin sorghums fed to broiler chickens are superior to the tannin-containing varieties although the relatively high anti-oxidants activities of the latter may have health-promoting benefits. Feed form affected the performance of broiler chickens offered pelleted diets, resulting in better performance than mash diets. Whole sorghum grain inclusion level did not affect feed intake and body weight gain of broiler chickens; however, feed efficiency increased with an increase in whole sorghum. This indicates that WSG can be added to broiler diets at any inclusion rate without negatively affecting performance.</p>