Improving performance of broilers fed lower digestible protein diets

<strong>Background and Problem Statement</strong> There is a great interest in recent years to replace soybean meal by cost effective protein sources such as rapeseed meal and maize gluten in animal feed. In poultry, this replacement, however, may result in a poorer performance due to among others its low ileal digestibility, which may lead to hindgut protein fermentation. This hindgut protein fermentation can result in the production of harmful compounds such as ammonia, branched chain fatty acids, biogenic amines and different sulfur containing compounds such as skatole, indole and phenolic compounds. This can negatively affect the cost of broiler meat production. When digestibility is low gut health may be compromised. Also feed to gain ratios will be high and overall performance will be low. Apart from the economic losses, good digestible protein sources may be preferably used for human consumption. Thus, the challenge is to provide the basis for the development of a new feeding strategy that meets the nutrient requirements of modern-day broilers, especially when they are fed a low ileal digestible protein source, i.e. rapeseed meal and maize gluten, thereby minimizing the interruption of their production performance. <strong>Objectives of the Study</strong> The aim of the study was to find ways to improve protein digestibility of poor ileal digestible resources, to reduce potential hindgut protein fermentation by developing appropriate dietary strategies such as an adequate diet structure, the supplementation of organic acids and/or fermentable energy that improve nutrient availability at ileal level and gut health in broilers. The specific objectives of the present study were to: Review various factors that influence hindgut protein fermentation in broilers and nutritional strategies that may reduce hindgut protein fermentation (Chapter 2). Determine the effects of protein source, differing in fermentation characteristics, and of digestible dietary protein content on performance, gut morphology and cecal fermentation characteristics in broiler (Chapter 3). Investigate the effects of diet structure combined with different levels of indigestible dietary protein source on performance and gut morphology in broilers (Chapter 4). Study the main and interactive effects of protein source, diet structure, butyric acid and fermentable energy supplementations on performance, gut morphology and cecal fermentation characteristics (Chapter 5). Analyze the effects of protein source, diet structure, butyric acid and fermentable energy supplementation on cecal microbiota population and composition (Chapter 6). <strong>Major Findings of the Thesis</strong> This thesis provides a literature review and describes the results of three experiments in which different nutritional strategies were tested. All experiments were carried out with Ross-308 broilers. Chapter 2 reviews the literature on hindgut fermentation in broilers with special attention to protein fermentation, its detrimental effects on performance, gut health and on gut microbiota population. A wide range of harmful products such as ammonia, branched chain fatty acids, biogenic amines and different sulfur containing compounds such as skatole, indole and phenols are produced as a result of protein fermentation. Greater concentrations of biogenic amines, branched chain fatty acids, hydrogen sulfide, ammonia, indole, phenols, cresol and skatole in the cecal indicate more proteolytic fermentation. Low concentrations of some of the protein fermentation products including biogenic amines are necessary for a normal gut development. This may result in distinct differences in protein digestibility when measured at the ileum and the total digestive tract. It was concluded that nutritional strategies, such as a reduction in dietary CP, supplementation of pre- and probiotics and organic acids, or feeding diets with coarse particles may increase ileal CP digestibility, thereby reducing the amount of substrate available for fermentation. These nutritional interventions can potentially enhance protein digestion in the upper gastrointestinal tract and, therefore, reduce the chances of protein fermentation in the hindgut. In Chapter 3, effects of three major protein sources, soybean meal, rapeseed meal and maize gluten at two different digestible CP levels (15.8 and 17.2%) were studied to test the hypothesis that broilers fed a diet with high levels of indigestible protein, will result in a reduced growth performance, lower villus heights, deeper crypts, and more protein fermentation products in cecal digesta. In total, 288 one-day-old male broilers were used for this study. Broilers fed soybean meal diet showed a better performance compared with those fed rapeseed meal and maize gluten diets due its greater ileal digestibility compared with the other two protein sources. High digestible CP (17.2%) diet fed broilers showed better performance compared with those on low digestible CP (15.8%) diet. No significant effects of protein source as well as digestible CP level were found on gastrointestinal tract development, cecal ammonia and volatile fatty acid concentrations. Broilers fed soybean meal had improved duodenal morphology compared with those fed the rapeseed meal and maize gluten diets. A lower cecal pH and greater branched chain fatty acids concentrations in the cecal digesta were observed in broilers fed the rapeseed meal diet compared with those fed the soybean meal and maize gluten diets, indicating more proteolytic fermentation. In conclusion, protein source as well as digestible CP level affected growth performance, gut morphology and protein fermentation characteristics in broilers. In Chapter 4, a hypothesis that a coarse diet improves performance of broilers fed a poorly digestible protein source was tested by using 210 one-day-old broilers. A highly digestible protein diet based on soybean meal was gradually replaced by a low digestible protein diet based on rapeseed meal (RSM) in five steps (RSM-0%, RSM-25%, RSM-50%, RSM-75% and RSM-100%) with two diet structures (fine vs. coarse). An increase in indigestible dietary protein decreased the performance of broilers. Total cecal volatile fatty acid concentrations decreased from 209 to 126 mmol/kg DM digesta in broilers with increasing rapeseed meal in diets. Increase in the indigestible protein level, from RSM-0% to RSM-100%, decreased villus heights (1782 vs. 1574 µm), whereas crypt depths increased (237 vs. 274 µm). A coarse diet improved the performance with a 15% heavier empty gizzard weight and changed gut morphology. Coarseness of the diet reduced the empty weights of the crop, proventriculus and jejunum, and reduced gizzard pH by 16%. Protein fermentation indices such as branched chain fatty acids and biogenic amines were reduced by 24 and 12%, respectively, in the cecal digesta of broilers fed coarse diets compared with those fed fine diets. In conclusion, feeding coarse particles improved the performance of broilers even with a poorly digestible protein source. Hindgut protein fermentation was reduced in broilers fed diets with a low CP digestibility by coarse grinding of the diet. In Chapter 5, the effects of protein source, diet structure and supplementation of butyric acid and fermentable energy on growth performance and cecal digesta characteristics were investigated to test the hypothesis that a coarse diet supplemented with butyric acid and fermentable energy improves growth performance of broilers fed a poorly digestible protein source. The interaction effects of diet structure (fine vs. coarse), fermentable energy (with vs. without) and butyric acid supplementation (with vs. without) in a poorly digestible diet based on rapeseed meal were evaluated. Coarseness of the diet positively affected performance and improved relative empty gizzard weights by on average 14%. The relative empty weights of the crop, duodenum, jejunum and ileum, were reduced in coarse diets fed broilers compared with those fed fine diets. Broilers fed coarse diet showed a 6% greater ileal protein digestibility, 20% lower gizzard pH, improved gut morphology, and 23% reduced cecal branched chain fatty acids compared with those fed the fine diets. Broilers fed butyric acid supplemented diets had improved performance and gut morphology compared with those fed the diets without butyric acid. Fermentable energy supplementation did not influence growth performance nor gut development and contents of total branched chain fatty acids and total biogenic amines in the cecal digesta. Supplementation with fermentable energy, however, decreased the concentration of spermine by approximately 31%. In conclusion, feeding a coarse diet supplemented with butyric acid improves growth performance of broilers even if they are fed a diet containing a poorly digestible protein source. The negative effects of a low digestible protein source can thus be partly counterbalanced by coarse grinding and butyric acid supplementation in the diet. In Chapter 6, the effects of protein source, diet structure, butyric acid and fermentable energy supplementations on cecal microbiota population and composition in broilers were evaluated. Cecal digesta samples collected in experiments 1, 2 and 3 were therefore, analysed for some microbiota. The results indicated that cecal microbial diversity was suppressed by dietary coarseness. Similarly, butyric acid and fermentable energy supplementation also resulted in a lower microbial diversity. Soybean meal promoted the average relative contribution of health beneficial <em>L. paracasei</em> and <em>C. lactifermentans</em> spp. compared with those fed rapeseed meal. Dietary coarseness reduced the average relative contribution of <em>E. coli</em>. Butyric acid supplementation promoted the average relative contribution of <em>C. lactifermentans</em> and <em>R. bromii</em>, and suppressed the pathogenic <em>C. perfringens</em> in the cecal digesta. Fermentable energy, in contrast, promoted <em>C. perfringens</em>. In conclusion, feeding a poorly digestible protein source, with coarse grinding and supplemented with butyric acid may be an effective strategy to promote health beneficial and suppress pathogenic microbiota in the cecal digesta. <strong>Conclusions </strong> The main conclusion of the study is that rapeseed meal diets reduce performance and gut health, but these negative effects can be partially counterbalanced by coarse grinding and butyric acid supplementation. Some specific conclusions based on the results of the studies described in this thesis are: Rapeseed meal is a poorly digestible protein source for broilers and results in reduced growth performance and gut morphology (Chapter 3). Coarse diet feeding enhances the development of the foregut, specially the gizzard, and it increases villus heights and reduces crypts depths in the duodenum (Chapters 4 and 5). The negative effects of moderate inclusion of indigestible protein can be counterbalanced to some extent by feeding a coarse diet (Chapters 4 and 5). The improved foregut development and villus height in the duodenum is associated with an enhanced ileal digestibility of protein, thereby allowing less protein available for fermentation in the hindgut (Chapter 5). Butyric acid supplementation improves growth performance and gut morphology (Chapter 5). Both soybean meal and dietary coarseness suppress cecal microbial diversity and promotes health beneficial microbiota (Chapter 6). Dietary coarseness suppresses pathogenic bacteria and promotes health beneficial microbiota in the ceca (Chapter 6). Coarsely ground diet with a moderate inclusion of poorly digestible protein source, supplements with butyric acid, is a good strategy to improve the ileal digestibility of protein and thus growth performance of broilers (Chapters 4 and 5). <strong>Practical Implementations</strong> This study might have some practical conclusions. Rapeseed meal can be used as a protein source in a broiler ration. Coarsely ground rapeseed meal, supplemented with butyric acid (approximately €2.1/100 broilers), can potentially replace soybean meal. It will not only provide a cheaper protein source but will also reduce the cost of feed production by reducing the steps in grinding the feed ingredients or using a roller mill instead of a hammer mill. These coarse particles will improve gut morphology and growth performance of broilers as well as increase the profitability of broiler feed producers and also broiler farmers (approximately €6/100 broilers). The most perspective feeding strategy to enhance the growth performance of broilers fed a poorly digestible protein source is the use of coarsely ground supplemented with butyric acid.