Implications of excreta uric acid concentrations in broilers offered reduced-crude protein diets and dietary glycine requirements for uric acid synthesis

The cost of amino acid catabolism for energy utilization in broiler chickens

This review highlights that utilization of dietary amino acids for energy metabolism in broiler chickens imposes a metabolic cost, as their primary role is to support body protein synthesis. This issue becomes more critical in reduced-crude protein (CP) diets. When amino acids are used as fuel for enterocytes or undergo catabolism in the liver, they are diverted from body protein accretion. Catabolism of amino acids for energy generates α-keto acids and ammonia. α-Keto acids can be fully oxidized to produce ATP or converted into pyruvate, ketone bodies, and intermediates of the tricarboxylic acid cycle. Meanwhile, ammonia must be detoxified through the uric acid cycle, a process that requires energy, glycine, and aspartic acid. Derivatives of α-keto acids can contribute to gluconeogenesis and de novo lipogenesis, leading to glucose and fatty acid synthesis, respectively. The α-keto acid derivatives are more likely to undergo de novo lipogenesis in broilers, as evidenced by consolidated data in this review. However, de novo lipogenesis is also an energy-intensive process. Therefore, enhancing the efficiency of dietary amino acid conversion to body protein requires reducing their utilization for energy metabolism. This may be achieved through dietary manipulations, as previous studies indicate that amino acid catabolism in enterocytes and the liver is influenced by starch and protein digestive dynamics, dietary amino acid compositions, and the primary feed grain used in diets. In reduced-CP broiler diets, supplementation of glutamic acid and potentially glutamine, aspartic acid, and proline could mitigate the catabolism of essential amino acids in enterocytes. Additionally, moderating starch digestion rates may reduce amino acid catabolism in enterocytes. Moreover, optimizing the balance of dietary protein-bound and non-bound amino acids could minimize amino acid catabolism in the liver. In summary, reducing the contribution of amino acids to energy metabolism in broiler chickens is particularly beneficial in reduced-CP diets, ultimately supporting more sustainable chicken meat production.

Black soldier fly larvae oil downregulated gene expression related to fat metabolism of broilers fed low protein diet

Feeding low crude protein (LCP) diets supplemented with crystalline amino acids improves environmental and welfare parameters of broilers. However, increased body fat contents in broilers fed LCP diets have become a concern. Black soldier fly larvae oil (BSFLO), rich in lauric acid, has been reported to inhibit lipogenesis and reduce body fat. A 3 × 2 factorial experiment was conducted to evaluate the effect of BSFLO on performance, blood biochemistry, carcass quality, fat metabolism gene expression, and litter quality in broilers fed protein-reduced diets. A total of 288 broilers were divided into 6 treatments: three CP levels (200, 185, or 170 g/kg; high [HCP], medium [MCP], or low [LCP]) and two oil sources (BSFLO and Crude Palm Oil [CPO]), with 6 replicate pens of 8 birds each. Results showed a 15 g/kg CP reduction had no effect on body weight and feed intake (P > 0.05) but increased FCR (P = 0.001). A 30 g/kg CP significantly reduced the body weight and feed intake with inferior FCR (P < 0.05). However, negative effect of low CP diets on FCR was mitigated by BSFLO (P = 0.008). Reducing CP by 30 g/kg increased fat pads (P = 0.033), whereas BSFLO reduced fat pads (P = 0.049) at all three CP levels. Protein-reduced diets increased blood cholesterol (P = 0.002), HDL (P < 0.001), and LDL (P = 0.002). BSFLO decreased blood triglyceride (P = 0.026) and cholesterol (P < 0.001). Reducing 30 g/kg CP increased meat cooking loss (P = 0.035), while BSFLO decreased cooking loss (P < 0.001). BSFLO increased meat protein (P < 0.001) and decreased cholesterol (P = 0.003). The inclusion of BSFLO in protein-reduced diet down-regulated the gene expression of FAS, ACC, SREBP-1, and HMGR in broilers (P < 0.001). Reducing CP levels decreased litter pH (P = 0.011), nitrogen (P < 0.001), ammonia (P < 0.001) and moisture (P = 0.018). The study concludes that BSFLO reduced body fat by down-regulating the lipogenesis gene expression. In addition, BSFLO enhanced feed efficiency in broilers fed protein-reduced diet.

Dynamic responses of blood metabolites to nutrient depletion and repletion in broiler chicken nutrition

A total of 720 male Cobb 500 broiler chicks were used in a 5 treatment and 8 replicate experiment to explore dynamic changes in blood metabolites in response to short-term nutrient depletion and repletion. Day old chicks were offered a corn and soybean meal-based common starter diet from d1 to 14 that was formulated to meet all nutrient requirements of the birds. From d15 to 17, the experimental diets were offered, before returning all groups to a common diet from d18 to 20, at which point the experiment was terminated. A total of 5 experimental diets were designed. A standard grower diet served as a control and was offered to 1 of the 5 groups of chicks. The additional 4 experimental groups comprised diets that were low in digestible phosphorus (P), total calcium (Ca), crude protein and digestible amino acids (AA) or apparent metabolizable energy (AME). The common grower diet that was offered from d18-20 was designed to be nutritionally complete and was intended to explore dynamic response to nutrient repletion. Blood was drawn from 8 chicks per treatment at time 0 (immediately prior to introduction of the experimental diets) and then again 3, 6, 12, 24, and 48h after introduction of the nutrient depleted diets. Additionally, blood was drawn 3, 6, 12, 24, and 48h after the introduction of the nutritionally complete common grower diet. Chicks were not sampled more than once. Feed intake, body weight and feed conversion ratio (FCR) were assessed on d14, 17, and 20. Blood metabolites were analyzed using the iSTAT Alinity V handheld blood analyzer, the Vetscan VS2 Chemistry Analyzer and the iCheck Carotene Photometer. Live performance metrics were not affected by the short-term nutrient depletion and all chicks grew normally throughout the experiment. The diet with low digestible P generated a rapid temporary decrease in plasma P and an increase in plasma Ca, that were returned to baseline following the re-introduction of the common grower feed. Introduction of the diet with low total Ca resulted in a significant increase in plasma P, effects which were also mitigated during the nutrient repletion phase. Total plasma protein, albumin and uric acid (UA) were decreased, and plasma glucose increased, in the chicks that received the diet with low crude protein and digestible AA. There was a delayed increase in aspartate amino transaminase (AST) associated with the diets with low digestible P and low AME. These results demonstrate the capacity of blood biochemistry to adapt to quantitative and qualitative changes in nutrient intake. Point-of-care analysis of blood biomarkers offers nutritionists a valuable opportunity to calibrate nutritional matrices for common dietary ingredients, zootechnical feed additives and to optimize diet phase changes. It can be concluded that many blood biomarkers are plastic to changes in diet nutrient density and offer an objective index for optimization of nutritional programs for commercial broiler production.

Effect of Dietary Crude Protein and Apparent Metabolizable Energy Levels on Growth Performance, Nitrogen Utilization, Serum Parameter, Protein Synthesis, and Amino Acid Metabolism of 1- to 10-Day-Old Male Broilers

This research compared how different levels of dietary crude protein (CP) and apparent metabolizable energy (AME) affect the growth performance, nitrogen utilization, serum parameters, protein synthesis, and amino acid (AA) metabolism in broilers aged 1 to 10 days. In a 4 × 3 factorial experimental design, the broilers were fed four levels of dietary CP (20%, 21%, 22%, and 23%) and three levels of dietary AME (2800 kcal/kg, 2900 kcal/kg, and 3000 kcal/kg). A total of 936 one-day-old male Arbor Acres broilers were randomly allocated to 12 treatments with 6 replications each. Growth performance, nitrogen utilization, serum parameter, gene expression of protein synthesis, and AA metabolism were evaluated at 10 d. The results revealed no interaction between dietary CP and AME levels on growth performance (p > 0.05). However, 22% and 23% CP enhanced body weight gain (BWG), the feed conversion ratio (FCR), total CP intake, and body protein deposition but had a detrimental effect on the protein efficiency ratio (PER) compared to 20% or 21% CP (p < 0.05). Broilers fed diets with 2800 kcal/kg AME showed increased feed intake (FI) and inferior PER (p < 0.05). Broilers fed diets with 3000 kcal/kg AME showed decreased muscle mRNA expression of mammalian target of the rapamycin (mTOR) and Atrogin-1 compared to those fed diets with 2800 kcal/kg and 2900 kcal/kg AME (p < 0.05). Increasing dietary CP level from 20% to 23% decreased muscle mTOR and increased S6K1 mRNA expression, respectively (p < 0.05). The muscle mRNA expression of Atrogin-1 was highest for broilers fed 23% CP diets (p < 0.05). The mRNA expression of betaine homocysteine methyltransferase (BHMT) and Liver alanine aminotransferase of the 22% and 23% CP groups were higher than those of 20% CP (p < 0.05). Significant interactions between dietary CP and AME levels were observed for muscle AMPK and liver lysine-ketoglutarate reductase (LKR) and branched-chain alpha-keto acid dehydrogenase (BCKDH) mRNA expression (p < 0.05). Dietary AME level had no effect on muscle AMPK mRNA expression for broilers fed 21% and 22% CP diets (p > 0.05), whereas increasing dietary AME levels decreased AMPK mRNA expression for broilers fed 23% CP diets (p < 0.05). The mRNA expression of LKR and BCKDH was highest for broilers fed the diet with 2800 kcal/kg AME and 22% CP, while it was lowest for broilers fed the diet with 3000 kcal/kg AME and 20% CP. The findings suggest that inadequate energy density hindered AA utilization for protein synthesis, leading to increased AA catabolism for broilers aged 1 to 10 days, and a dietary CP level of 22% and an AME level of 2900 to 3000 kcal/kg may be recommended based on performance and dietary protein utilization.

Influence of increasing glycine concentrations in reduced crude protein diets fed to broilers from 0 to 48 days

Two experiments investigated broiler growth performance and processing characteristics when fed increasing Gly concentrations in reduced CP diets fed from 0 to 48 d. In experiment 1, birds were allocated to 1 of 4 dietary treatments: a control (CTL) diet containing feed-grade L-Met, L-Lys, and L-Thr, a reduced CP (RCP) diet with additions of feed-grade L-Val and L-Ile, or the RCP diet with moderate (M Gly) or high Gly (H Gly) inclusion levels to achieve a total Gly + Ser of 100 or 112%, respectively, of the CTL diet. Birds in experiment 2 were assigned to 1 of 6 dietary treatments: a CTL diet, a RCP diet, or a low CP (LCP) diet without or with added Gly to achieve 88, 100, 112, or 124% total Gly + Ser concentrations of the RCP diet. For experiment 1, 0 to 14 d broiler performance was similar (P > 0.05) among dietary treatments. From 0 to 48 d, broilers fed the H Gly diet had the lowest (P = 0.006) body weight gain (BWG) and highest (P = 0.003) feed conversion ratio (FCR). Feeding either the RCP or M Gly diet resulted in similar (P > 0.05) growth and processing characteristics to the CTL. For experiment 2, increasing Gly levels in the LCP diet linearly reduced (P ≤ 0.027) 0 to 14 d FI and FCR. From 0 to 48 d, broilers had similar (P > 0.05) performance when fed the CTL or RCP diet, but had a higher (P < 0.001) FCR when fed the LCP88 diet. Increasing Gly levels linearly reduced (P = 0.033) FCR. Total breast meat yield was negatively affected (P ≤ 0.020) when feeding the LCP88 diet and did not respond to Gly levels. In conclusion, effects of increasing total Gly + Ser levels on 0 to 48 d broiler performance are likely dependent on the content of dietary CP and other potentially interacting nutrients.

Identifying the shortfalls of crude protein-reduced, wheat-based broiler diets

The objective of this review is to identify the shortfalls of wheat-based, crude protein (CP)-reduced diets for broiler chickens as wheat is inferior to maize in this context but to inconsistent extents. Inherent factors in wheat may be compromising gut integrity; these include soluble non-starch polysaccharides (NSP), amylase trypsin inhibitors (ATI) and gluten. Soluble NSP in wheat induce increased gut viscosities, which can lead to compromised gut integrity, which is not entirely ameliorated by NSP-degrading feed enzymes. Wheat ATI probably compromise gut integrity and may also have the capacity to increase endogenous amino acid flows and decrease apparent starch and protein digestibilities. Gluten inclusions of 20 g/kg in a maize-soy diet depressed weight gain and feed intake and higher gluten inclusions have been shown to activate inflammatory cytokine-related genes in broiler chickens. Further research is required, perhaps particularly in relation to wheat ATI. The protein content of wheat is typically higher than maize; importantly, this results in higher inclusions of non-bound amino acids in CP-reduced broiler diets. These higher inclusions could trigger post-enteral amino acid imbalances, leading to the deamination of surplus amino acids and the generation of ammonia (NH₃) which, if not adequately detoxified, results in compromised growth performance from NH₃ overload. Thus, alternatives to non-bound amino acids to meet amino acid requirements in birds offered CP-reduced, wheat-based diets merit evaluation. The digestion of wheat starch is more rapid than that of maize starch which may be a disadvantage as the provision of some slowly digestible starch in broiler diets may enhance performance. Alternatively, slowly digestible starch may result in more de novo lipogenesis. Therefore, it may prove instructive to evaluate CP-reduced diets based on maize-wheat and/or sorghum–wheat blends rather than entirely wheat. This would reduce non-bound amino acid inclusions by lowering dietary CP derived from feed grains and may enhance starch digestive dynamics by retarding starch digestion rates. Also, the use of biomarkers to monitor gut integrity in broiler chickens is examined where calprotectin, ovotransferrin and possibly citrulline appear to hold promise, but their validation requires further research.