In recent years, the poultry and pig industry has been successfully developing reduced crude protein (CP) diets to reduce Nitrogen pollution and improve the litter quality. It is reported that 2.5%-unit crude protein reduction in poultry or pig diets will reduce ammonia by 25%. Considering 1 MT ammonia is equivalent to 2.11 MT carbon dioxide, this trend will have a tremendous impact on climate change. However, nutritionists need to do more to deal with reduced protein diets.
1. Reduced protein diets and limiting amino acids (AA)
Traditionally, in wheat-soybean meal-based poultry diets, unbound crystalline L-methionine, L-Lysine and L-Threonine have been routinely added to meet chicken growth requirements. It is clear now that by further adding L-Valine, L-Isoleucine and L-Arginine, the crude protein level could be reduced by 1.5 to 2% unit but not compromise chicken performance. It is noticed that in reduced protein diets, dietary valine or arginine deficiency will result in plasma Lysine, Methionine and Threonine accumulation; Dietary isoleucine deficiency will result in plasma methionine and threonine surplus, indicating that in reduced protein diets, if L-Valine, L-isoleucine and L-Arginine were not added, dietary lysine, methionine and threonine cannot be fully utilized by chickens to contribute to muscle growth. In particular, dietary Arginine deficiency resulted in a considerable surplus of threonine, affecting mucus secretion. (Figure 1).
Figure 1. Plasma AA concentrations in response to dietary AA deficiency
2. Optimal SID Lysine (g/kg) to AME (MJ/kg) ratio in reduced protein diets
While formulating a reduced protein diet, nutritionists will usually use more grains and reduce oil or fat contents. Considering the higher energy efficiency of oil or fat, it is not clear yet if we need to increase apparent metabolizable energy (AME) requirement in reduced protein diets. However, in 2018, the University of New England (UNE) published a broiler chicken trial paper to show that AME requirement might mainly depend on dietary lysine concentration. In grower period, the optimal SID lysine (g/kg) to AME (MJ/kg) was determined to be 0.88 (Figure 2).
Figure 2 Body weight gain in response to SID Lys/AME ratio on 14-35 days
3. Endogenous loss of taurine in reduced protein diets
It is noticed that in reduced protein diets, more starch will replace fat as the dietary non-protein energy source, leading to more faecal bile acids loss. Recently, the research in Massey University demonstrated that the major endogenous amino acid loss in broiler chicken bile would be taurine. Considering taurine is an important anti-oxidant to regulate immune system health, in stress situation, the reduced protein diet might result in disease infection. It is widely known that taurine is produced by cysteine in chicken body and dietary methionine can convert to cysteine. In a recent broiler chicken trial conducted in the University of Sydney, adding exogenous bile acids to the reduced protein diets significantly reduced mortality rate due probably to increased plasma methionine concentration (Figure 3).
Figure 3. Plasma methionine concentration in response to bile acids addition
4. Reduced protein diets by exogenous protease supplements
To some degree, in reduced protein diets, dietary protein levels are determined by dietary standard ileal digestible (SID) lysine concentrations because other SID essential amino acids to SID lysine ratios are used in ideal amino acids profile. It is estimated that 5% SID lysine reduction will reduce dietary crude protein by 1% unit. In practice, the efficacy of protease is mainly determined by undigested protein concentration in feed ingredients. Usually when SID lysine (%) to undigested protein (%) ratio is lower than 0.3, dietary SID lysine and other essential amino acids could be reduced by 5% (Figure 4).
Figure 4. Bodyweight gain in male Ross 308 broilers from 22-35 days post-hatch (P = 0.061).
5. Phosphorus and phytase in reduced protein diets
In reduced protein diets, soybean meal and other protein ingredients will be partially replaced by grains and crystalline amino acids. Phytate phosphorus and available phosphorus variation in feed ingredients (Table 1) may increase inorganic phosphorus usage. We also need to reconsider phosphorus matrix value in phytase and absorption rate in inorganic phosphorus (Table 2). In table 1, it is clearly show that in sorghum-based diets, the matrix value of phosphorus in phytase may be higher than that in wheat-based diets, but it will be lower in reduced protein diets because of lower inclusion levels of soybean meal. In table 2, it is shown that when formulating reduced protein diets, both inorganic phosphorus contents and their bioavailability should be considered. In general, inorganic phosphorus bioavailability is strongly related to citric acid solubility and current DCP and MDCP practical bioavailability could be predicted by citric acid solubility.
Table 1. Total P and available P in feed ingredients (%)
Table 2. Phosphorus bioavailability from different sources
6. Nucleotide supplements in reduced protein diets
In reduced protein diets, almost all essential amino acids requirements could be met by adding crystalline amino acids. The reduced protein contents mainly come from non-essential amino acids concentration including glutamine and aspartic acids, which are precursors to produce nucleotides in the chicken body. In cocci vaccination and high-stock density stress situation, this exogenous production of nucleotides might not be sufficient to support a healthy immune system. Table 3 clearly shows that in Eimeria challenging situation, adding Nucleotides (IMP) significantly alleviate the challenging impact on chicken body weight gain (BWG) and feed conversion ratio (FCR)
Table 3. Effect of Nucleotides on chicken performance at d 11-15 after challenging
7. Gut health concern in reduced protein diets
In Australia and USA, coccidiostats are considered as antibiotics and are banned in antibiotics free production. Currently in breeder and claimed antibiotics free chicken production, Eimeria vaccination has been widely practiced controlling cocci infection. However, broiler chicken feed intake is sufficiently reduced by the vaccination challenging dose and each double dose will worsen FCR by 9 points (Figure 5). Some new gut health related feed additives are necessary in reduced protein diets for young animals to fight against disease challenging.
Figure 5. Feed intake in response to graded dose Eimeria vaccination challenging
- Mannanase: Β-Mannan in soybean meal is one of the main antinational factors to decrease the efficiency of nutrient use. Supplementation of the exogenous mannanase has been demonstrated to increase chicken feed intake, significantly reduce coccidial lesion sores and increase breast production. Dietary AME can be saved by 50 kcal/kg due to reduced immune response sensitivity. The efficacy of Mannanase addition is strongly related to soybean meal inclusion levels and optimal crude fiber (%) to SID Lysine ratio is about 1.45 for Mannase response.
- Glucose oxidase: Cell-mediated immunity is thought to be important in the resistance of chickens to infection by coccidia. It has been demonstrated that sporozoites of Eimeria tenella are very sensitive to superoxide ions. Adding exogenous glucose oxidase to reduced protein diets could consume surplus oxygen and increase the shelf life of diets. More importantly, it can endogenously produce hydrogen peroxide to directly kill Eimeria and improve gut health. The heat tolerable glucose oxidase is commercially available now.
- Antimicrobial peptide: Previously it targets Gram negative bacteria such as E coli and Salmonella. Right now, new product is available to protect from Gram positive and negative bacteria infection including colostrum perfringens. Usually, Gram positive bacteria are acids resistance and organic acids are useless in Gram positive bacterial infection.
- Postbiotics: different from traditional probiotics, this postbiotics also includes metabolites from probiotics such as peptides, lipoprotein and bacteriocins, more widely building up the first defense line
- Tri-butyrin: it will promote the overall gut health by facilitating tight junction assembly.
8. Other concerns regarding to reduced protein diets
In reduced protein diets, feed grains such as wheat inclusions will usually increase at the expense of soybean meal. The current supplemental dosage of xylanase needs to be increased to completely degrade soluble Xylan in wheat and reduced viscosity.
In addition, compared with wheat, soybean meal contains more potassium and choline (Table 4). Therefore, extra potassium bicarbonate or potassium chloride and choline chloride may be increased in reduced protein diets.
Table 4. Potassium and choline concentration in feed ingredients (%)
A study compiled by Redox Animal Nutritionists.