Amino acid and Protein in Broiler Ration:
Essential amino acids must be supplied by the diet, and a sufficient amount of non-essential amino acids must also be supplied to prevent the conversion of essential amino acids into non-essential amino acid. Additionally, if the amino acids supplied are not in the proper, or ideal, ratio in relation to the needs of the animal, then amino acids in excess of the least limiting amino acid will be de-aminated and likely used as a source of energy rather than towards body protein synthesis. This breakdown of amino acids will also result in higher nitrogenous excretions.
The best way to reduce N in poultry excreta is to lower the amount of CP that is fed by supplementing diets with amino acids. Reductions in the non-essential amino acid pool, coupled with supplying a more “ideal” amino acid profile in the diet can substantially increase the efficacy of overall N retention by the bird. On a practical basis, however, bird performance can be hindered by these lower CP diets due to a number of factors that tend to be associated with dietary CP and amino acid reductions.
Formulation based on bird amino acid requirements rather than CP can minimize N excretion by simply reducing total dietary N intake. For example, Ferguson et al. (1998) demonstrated with broilers that litter N could be reduced more than 16% when dietary CP was reduced by 2%, while maintaining similar levels of dietary amino acids.
Reduced Dietary Protein Reducing the amount of CP and excess amino acids being fed is the most obvious method to curb N excretion and the amount of ammonia (NH3) that can be formed and volatilized. However, the extent to which N reduction can be accomplished is largely limited due to meeting the most limiting amino acid after threonine and through economic decisions on ingredient selection.
Amino acids which are said to be essential cannot be synthesized by the bird. These essential amino acids must therefore be fed in order to supply the building blocks needed in the synthesis of body proteins thereby supporting growth. When supply of a single amino acid does not meet the bird’s requirement, it is considered to be “limiting”. At any given physiological stage of growth –or- age, a specific amino acid profile is needed to support optimal growth, with no limiting amino
acids or surpluses. This profile has been termed an “ideal” ratio, or “ideal protein”
Possible Impact of Crude Protein Reduction
Angel et al. (2006) also studied the possibility of reducing dietary N intake in broilers to 42 days of age. In their studies, an industry control 4-phase feeding program (corn-SBM based) with synthetic Met and Lys was compared with a 6-phase feeding program with supplemental Lys, Met, isoleucine (Ile), Thr, valine (Val), Trp, and arginine (Arg) (even though only Lys, Met, Thr, and Trp are commercially available). Birds were reared on the same litter for 5 consecutive flocks. Feed conversion was similar between groups after 5 flocks, but live body weight was 77 g lighter in birds fed on the 6-phase program. In a sampling of 40 birds per diet, however, dressing or breast yield (%) were not affected by diet in the third or fourth flocks (i.e. the only flocks where processing data was determined). Consumption of N with the 6-phase feeding program was 8.3% lower than those on the
4-phase feeding program (7.04 versus 7.68 g/bird) resulting in a 20% reduction in N excretion (2.3 versus 2.9 g/bird). The 6- phase feeding program resulted in a 15.4% reduction in daily NH3 emission (1407 versus 1663 mg/d per 50 birds) over the first three flocks (Powers et al., 2006). Pope et al. (2004) also has looked at the advantages to increasing the number of phases during the broiler growth cycle. By changing diets every other day to more closely meet the bird’s amino acids from 21 to 63 days of age, performance and meat yield did not change, but N excretion was reduced by 7 to 13%.