Mingan Choct

There is momentum for the poultry industry to transition from an apparent metabolisable energy (AME) system to a net energy (NE) system for diet formulation. This review is not a rehash of the in-depth details of the feed energy system. Rather, it focuses on the practical issues related to the broiler chicken industry's transition to NE, such as the various terminologies associated with metabolisable energy (ME) and their implications, heat increment (HI) and factors that affect it, the use of NE and the impact of feed additives, and the correct use of the key NE equations commonly recommended for poultry.

This study aimed to investigate the limitations and interactive effects of dietary crude protein (CP; 15%, 17% and 19%), excess branched-chain amino acid (BCAA) inclusions (0%, 20% and 40%), and net energy (NE; 9.0, 9.7 and 10.4 MJ/kg) on performance and nutrient utilization for Cobb 500 mix-sex broilers, using a Box-Behnken design. The study consisted of 2 experiments: Exp. 1 involved 1092 chickens, and their performance was measured from d 19 to 35, and Exp. 2 employed 156 birds for NE measurements from d 25 to 28. Both experiments used the same diets (n = 13), each replicated 7 times for Exp. 1 and 6 times for Exp. 2. On d 35, 4 birds per pen (2 males and 2 females) were sampled to collect ileal digesta and weigh carcass parts. Feed intake (FI), NE intake (NEi), weight gain (WG), feed conversion ratio (FCR) and breast yield were affected by CP × NE (P < 0.001) and CP × BCAA (P = 0.041). Diluting NE in the reduced CP (RP)-diets led to a higher FI (P < 0.001) and breast yield (P < 0.001) than high NE, but the NE levels had no effect (P > 0.05) on FI and breast yield in high CP (HCP)-diets. Breast yield increased (P = 0.041) with BCAA in HCP-diets, whereas in the RP-diets, the yield lowered (P = 0.041) with increased BCAA. A similar trend was observed with fat content: in HCP-diets, fat content increased (P = 0.007) with BCAA, while in RP-diets, fat content decreased (P = 0.007) with higher BCAA levels. In addition, increasing BCAA in the RP-diets decreased (P < 0.001) FI, NEi, WG and increased FCR (P = 0.001) than low BCAA. However, BCAA levels had no effect (P > 0.05) on these measurements in HCP-diets. High NE increased (P < 0.001) NEi and decreased (P < 0.001) FCR compared to low NE in the HCP-diets. However, the NE effect on both measurements did not differ (P > 0.05) in RP-diets. These results indicate that increasing BCAA levels beyond the recommended amounts in RP-diets impairs energy utilization, leading to poor performance.

Different energy systems have been proposed for energy evaluation of feeds for domestic animals. The oldest and most commonly used systems take into account the fecal energy loss to obtain digestible energy (DE), and fecal, urinary and fermentation gases energy losses to calculate metabolizable energy (ME). In the case of ruminants and pigs, the net energy (NE) system, which takes into account the heat increment associated with the metabolic utilization of ME, has progressively replaced the DE and ME systems over the last 50 years. For poultry, apparent ME (AME) is used exclusively and NE is not yet used widely. The present paper considers some important methodological points for measuring NE in poultry feeds and summarizes the available knowledge on NE systems for poultry. NE prediction equations based on a common analysis of three recent studies representing a total of 50 complete and balanced diets fed to broilers are proposed; these equations including the AME content and easily available chemical indicators have been validated on another set of 30 diets. The equations are applicable to both ingredients and complete diets. They rely primarily on an accurate and reliable AME value which then represents the first limiting predictor of NE value. Our analysis indicates that NE would be a better predictor of broiler performance than AME and that the hierarchy between feeds is dependent on the energy system with a higher energy value for fat and a lower energy value for protein in an NE system. Practical considerations for implementing such an NE system from the commonly used AME or AME_n (AME adjusted for zero nitrogen balance) systems are presented. In conclusion, there is sufficient information to allow the implementation of the NE concept in order to improve the accuracy of feed formulation in poultry.

Current methods for feed formulation are based on minimizing costs, not maximizing profits. Complex models of bird growth and reproduction as functions of genetic, feed and other environmental variables are being developed, but their adaptation has been slow. The development of profit maximizing models will evolve to center on the production functions of broilers and layers. The production functions are the relationship between the value of products (mainly meat and eggs) and the cost of feed. The production function is the tool used to maximize profits subject to all the various inputs, not just feed or nutrition. The production function is subject to the law of diminishing returns. The most profitable output levels are those where the marginal value (price) of the meat or eggs is just equal to the marginal cost of the inputs including feed, housing, processing and all other costs. Anything that affects the production function, bird genetics, feed quality, housing and environment, will be considered to maximize profits for the poultry firm. The profit maximizing models of poultry firms will improve as various technical improvements are made: metabolizable energy to describe ingredients will evolve to net energy systems that consider that the heat production (and therefore energetic efficiency) of broilers is different depending on the ingredients used to formulate the feed and the environmental temperatures under which they are reared. Amino acid needs will include a method to find the birds' needs for the non-essential amino acids. “Digestible” amino acid assays will differentiate between digestion and absorption to best balance various sources. The carbohydrate fractions of feed ingredients will be determined to optimize the use of exogenous enzymes. The value of meat and egg co-products will reduce overall costs (e.g., organic fertilizer for crop enhancement). Future profit maximizing production models will be ever evolving processes where field conditions and results are continually being utilized to re-calibrate the technical models so that the management team can use them with cost and return projections to decide on the best choices of inputs and outputs.

[This corrects the article DOI: 10.1016/j.aninu.2021.06.015.].

The present study evaluated the impacts of fibre-degrading enzymes on the profiles of non-starch polysaccharides (NSP) and oligosaccharides (OS) in the ileum of broiler chickens offered wheat- or maize-based diets under subclinical necrotic enteritis (NE) challenge. A 2 × 2 × 4 factorial arrangement of treatments was used. Factors were the following: NE challenge, no or yes; diet type, wheat- or maize-based; and supplemental enzymes, control (no enzyme), family 10 xylanase (XYN10), family 11 xylanase (XYN11) or β-mannanase (MAN). Birds in the challenged group were inoculated with Eimeria on d 9 and Clostridium perfringens on d 14 and 15. A 3-way interaction (P = 0.047) occurred on overall (d 0 to 16) weight gain. When NE was present, all the supplemental enzymes increased weight gain in birds fed the wheat-based diet; whereas in those fed the maize-based diet supplemental XYN10 and XYN11 decreased weight gain. When NE was absent, birds fed the wheat-based diet supplemented with XYN10 or MAN presented increased weight gain compared to non-supplemented birds, but no improvements with enzyme addition were observed in birds fed the maize-based diet. A 3-way interaction (P = 0.002) was observed on insoluble NSP level in the ileum. When NE was absent, all the supplemental enzymes reduced the ileal level of insoluble NSP, regardless of diet type. In the challenged birds, supplementing XYN10 and MAN reduced insoluble NSP level in the ileum, but only in birds fed the wheat-based diet. Ileal soluble NSP level was reduced by supplemental XYN11 and MAN, but only in birds fed the wheat-based diet, resulting in a 2-way diet type × enzyme interaction (P < 0.001). Ileal OS arabinose (P = 0.030) level was highest in birds offered the wheat-based diet supplemented with XYN11. Collectively, supplementation of NSP-degrading enzymes to the wheat-based diet enhanced bird performance regardless of NE challenge, with XYN11 significantly increasing oligosaccharide release. However, enzyme addition did not improve growth performance in birds fed maize-based diet, with supplemental XYN10 and XYN11 impeding weight gain when NE was present.