In poultry nutrition, most attention is given to protein products, due to the importance of protein as a major constituent of the biologically active compounds in the body. It also assists in the synthesis of body tissue, for that renovation and growth of the body. Furthermore, protein exists in form of enzymes and hormones which play important roles in the physiology of any living organism. Broilers have high dietary protein requirements, so identification of the optimum protein concentration in broiler diets, for either maximizing broiler performance or profit, requires more knowledge about birds' requirements for protein and amino acids and their effects on the birds' growth performance and development. It also requires knowledge about the protein sources available that can be used in poultry diets. The broad aim of this review is to highlight the importance of some of the available high-quality specialized protein products of both animal and plant origins which can be explored for feeding broiler chickens. Minimization of the concentration of anti-nutritional factors (ANFs) and supplementation with immunologically active compounds are the main focus of gut health-promoting broiler diets. These diet characteristics are influenced by feed ingredient composition and feed processing. The general hypothesis is that these protein products are highly digestible and devoid of or contain less ANFs. Feeding these products to broiler chicks, especially at an earlier age, can assist early gut development and digestive physiology, and improve broiler growth performance and immunity.

Global interest has emerged for the implementation of reduced-protein diets for meat chickens. The necessity of their development stems from environmental impacts and health and welfare concerns surrounding current meat-chicken production. Reduced crude-protein diets are possible with the increasing affordability of supplemental crystalline amino acids. Supplementing broiler feed with methionine, lysine and threonine is common practice in industry and has enabled a reduction of dietary crude protein to the levels currently used. However, further reduction of dietary protein often results in poor performance. Several nutritional options have been investigated with a focus on crystalline essential and non-essential amino acids such as glycine. However, reducing the crude protein of meat-chicken diets does change the ingredient and nutrient profile aside from the amino acid composition. Alterations in non-protein nitrogen concentrations, dietary electrolyte balance, minerals, fibre and carbohydrates, methyl-donors and polyphenols must be considered in formulations to ensure successful implementation of reduced-protein diets. The ability to maintain performance with reduced-protein diets may benefit sustainability and longevity of the meat-chicken industry.

The effectiveness of the addition of oat hulls (OH) as an insoluble fiber for improving nutrient digestibility and performance of birds fed diets containing full-fat canola seed (CS) was studied. A 2 × 2 × 2 factorial arrangement of treatments was used to assess the main effects of canola source (CS vs canola meal plus oil as control), OH (0 or 3%), pellet temperature (75 and 90°C) and their interactions. A total of 576 male day-old Ross 308 chickens were assigned to 8 experimental treatments, each replicated 6 times (12 birds per replicate). All birds were fed a same commercial starter diet for the first 10 d of age. Canola meal and canola oil in the control diets were replaced with CS at 11.6% and 13.5% in the grower (d 10 to 24) and finisher (d 24 to 35) diets, respectively. An interaction was observed between canola source and OH led to improved body weight gain (P < 0.01) and FCR (P < 0.05) in birds fed the combination of CS and OH in grower phase. Pelleting temperature at 75 vs 90°C did not affect performance of broilers. Birds fed diets containing OH had heavier gizzards at 24 and 35 d of age. Inclusion of CS in the diets depressed fat digestibility at d 24 (P< 0.001) and AME of the grower diets. At d 35, there was a significant interaction (P< 0.05) between CS and pellet temperature where birds fed CS diets pelleted at 75°C had higher fat digestibility than birds fed CS pelleted at 90°C. Regardless of canola source or pellet temperature, OH increased fat utilization at d 35 (P< 0.001) but had no effect on AME of the grower diets. In conclusion, CS can replace supplemental oil in broiler diets when an adequate source of insoluble fiber is included in the diet, which may help to maintain feed intake of broilers fed CS in steam-pelleted diets.

A 3-factor, 3-level Box-Behnken design was used to investigate the interaction effect of dietary digestible lysine (dLys, 9.5, 10.5, 11.5 g/kg), apparent metabolizable energy (AMEn, 12.77, 13.19, 13.61 MJ/kg) and available P (avP, 3.0, 4.0, 5.0 g/kg) levels on performance and amino acid (AA) digestibility of Ross 308 male broilers (n = 1,050) from d 14 to 34. The design consisted of 15 treatments each replicated 5 times with 12 birds per replicate. On d 34, 3 birds were sampled from each pen to collect ileal digesta (pooled per pen) to analyze AA. Response surface was fitted by first-, second-, or third-degree polynomial regressions in JMP statistical software v. 12.0.1. Feed intake (FI), weight gain (WG) and feed conversion ratio (FCR) were affected by dLys (linear and quadratic, P < 0.01), AMEn (linear, P < 0.01) and AMEn × avP (P< 0.01). Increased dLys increased FI but increased AMEn decreased FI in the birds fed the low-avP diet. However, when the avP level in the diet was increased, FI decreased to 13 MJ/kg AMEn and remained constant thereafter. Increased dLys increased WG whereas an increase in AMEn decreased WG in the birds fed the low-avP diet but had no effect on WG in those fed the high-avP diet. Increased dLys decreased FCR whereas increased AMEn decreased FCR in the birds fed the low-avP diet but had no effect on FCR in those fed the high-avP diet. Increased dLys increased breast yield percentage (linear, P < 0.01 and quadratic, P< 0.05) whereas increased AMEn decreased breast yield percentage (linear, P< 0.01). Dietary levels of dLys or avP had positive, linear effects on apparent ileal digestibility (AID) of methionine (P< 0.01) and threonine (P< 0.01) but had no effect on other AA (P> 0.05). These results indicate that increasing dLys levels above current industry standard would improve broiler performance irrespective of AMEn or avP levels of the diet.