Amino acids are the foundation of numerous metabolic and physiological pathways for skeletal muscle accretion, internal organ development, skeletal development, and immune function. One widely studied subject in monogastric nutrition is dietary crude protein. However, birds do not have a crude protein requirement but have a clear requirement for essential amino acids. As individual amino acid requirements of swine and poultry are investigated and modern feed formulation tools and feed-grade amino acids are available cost-effectively, the dynamics of how we look at crude protein in the feed have evolved. With the modern tools available, nutritionists are able to formulate the feed to meet the amino acids required for optimal performance of animals. This approach reduces the excess nitrogen in the feed, making the diets friendlier for the gut, reducing substrates for harmful proliferating bacteria, reducing nitrogen excretion in manure, and improving the ecology and sustainability. Apart from growth, amino acids have a functional role in the metabolic and physiological pathways. Amino acids like threonine and arginine have additional functional roles in intestinal turnover, immune function, wound healing, vasodilation and oxidative, and heat stress alleviation. Such specific amino acids can be increased in the diet to support the physiological needs during the growth of animals without increasing the unwanted dietary nitrogen content. As the industry moves toward reducing crude protein while meeting the essential amino acid needs, more research is needed to understand the requirement of specific lower limiting and non-limiting amino acids as well as the dynamics of those amino acids in health, welfare, cost of production and ecological impact in poultry and swine production.

Bone health and body weight gain have significant economic and welfare importance in the poultry industry. Mesenchymal stem cells (MSCs) are common progenitors of different cell lineages such as osteoblasts, adipocytes, and myocytes. Specific oxysterols have shown to be pro-osteogenic and anti-adipogenic in mouse and human MSCs. To determine the effect of 20(S)-hydroxycholesterol (20S) on osteogenic, adipogenic, and myogenic differentiation in chicken, mesenchymal stem cells isolated from compact bones of broiler chickens (cBMSCs) were subjected to various doses of 20S, and markers of lineage-specific mRNA were analyzed using real-time PCR and cell cytochemistry. Further studies were conducted to evaluate the molecular mechanisms involved in lineage-specific differentiation pathways. Like human and mouse MSCs, 20S oxysterol expressed pro-osteogenic, pro-myogenic, and anti-adipogenic differentiation potential in cBMSCs. Moreover, 20(S)-Hydroxycholesterol induced markers of osteogenic genes and myogenic regulatory factors when exposed to cBMSCs treated with their specific medium. In contrast, 20S oxysterol suppressed expression of adipogenic marker genes when exposed to cBMSCs treated with OA, an adipogenic precursor of cBMSCs. To elucidate the molecular mechanism by which 20S exerts its differentiation potential in all three lineages, we focused on the hedgehog signaling pathway. The hedgehog inhibitor, cyclopamine, completely reversed the effect of 20S induced expression of osteogenic and anti-adipogenic mRNA. However, there was no change in the mRNA expression of myogenic genes. The results showed that 20S oxysterol promotes osteogenic and myogenic differentiation and decreases adipocyte differentiation of cBMSCs. This study also showed that the induction of osteogenesis and adipogenesis inhibition in cBMSCs by 20S is mediated through the hedgehog signaling mechanism. The results indicated that 20(S) could play an important role in the differentiation of chicken-derived MSCs and provided the theory basis on developing an intervention strategy to regulate skeletal, myogenic, and adipogenic differentiation in chicken, which will contribute to improving chicken bone health and meat quality. The current results provide the rationale for the further study of regulatory mechanisms of bioactive molecules on the differentiation of MSCs in chicken, which can help to address skeletal health problems in poultry.

Arg is an essential AA for chickens that has secondary functions beyond protein synthesis and accretion, including roles in innate immunity. Therefore, the objective of this study was to evaluate the effects of dietary Arg ratio on the local and systemic innate inflammatory responses of the broiler chicken. A total of 280 male chicks from a Cobb 500 line were fed a common diet for 2 wk before being fed 1 of 5 target dietary dArg:dLys ratios (0.77, 0.91, 1.05, 1.19, or 1.33) across grower (14 to 28 d) and finisher (28 to 42 d) phases. Birds were reared in battery cages and immune parameters evaluated over 39 to 42 d using a growing feather (GF) model. Specifically, the GF-pulps of broilers were intradermally (i.d.) injected with 10 μL phosphate buffered saline (PBS; 2 birds/diet, 12 GF/bird) as a vehicle control or 10 μL of lipopolysaccharide (LPS; 6 birds/diet, 12 GF/bird; 1 μg LPS/GF) to stimulate an inflammatory response. Blood and GF were collected at 0 (before), 6, 24, and 48 h after GF injection. GF-pulp and blood cell suspensions were analyzed for indicators of the local and systemic inflammatory response, including GF-pulp and blood leukocyte profiles, relative GF-pulp cytokine mRNA expression, and plasma alpha-1-acid glycoprotein (AGP) and nitric oxide (NO) concentrations. Data were analyzed by 2-way repeated measures ANOVA for blood or 2-way ANOVA for GF, with time and diet as main effects. Linear and quadratic contrasts of dArg:dLys ratio were also performed. Statistical significance was determined at P ≤ 0.05. The local (pulp) and systemic (blood) inflammatory response to i.d. injected LPS was marked by a linear increase in heterophils with increasing dArg with a drop or no effect on lymphocytes, leading to changes in heterophil to lymphocyte ratios (P < 0.05). On average, plasma AGP responded quadratically (P < 0.0001) to dArg:dLys ratio within a 2-fold range, while NO increased linearly (P < 0.0001) by 7-fold at 6 h post-injection. Relative mRNA expression of IL-1β, IL-6, and IL-8 in GF-pulps also responded in a dose-dependent manner (P < 0.05). These data indicate that the GF model may be sensitive for detecting differences in immune responses of broilers fed different dietary treatments, and that Arg can influence the selected indicators of the LPS-induced inflammatory response in broilers.