Papers have been presented at the past two APSS meetings on the subject of low protein diets (Kidd and Choct, 2017; Hilliar and Swick, 2018; Lambert and Corrent, 2018). Few, if any, have taken note of the economics of such diets. This paper is an examination of the costs of low protein diets. A brief history of amino acids is worth reviewing. Each time a limiting amino acid became available commercially, and was used, the protein level of broiler diets was reduced. Methionine and its hydroxy analogue were the first amino acid sources to be made commercially available in the late 1950’s (Gordon and Sizer, 1955). If broiler diets are formulated with the methionine and methionine + cysteine requirements used today, but without D,L-methionine, it would result in protein levels of about 28%! Lysine became commercially available in the 1960s (Waldroup and Harms, 1963) and threonine in the 1980s (Edmonds et al., 1985). In the 2000s valine, arginine and isoleucine became commercially available. However due to cost, only small amounts are used. Benefits for lower protein diets are suggested as reduced water consumption, drier litter, better foot pad health, environmental benefits and improved FCR (Garland, 2018) and lower odour production (Sharma et al., 2016). Excess protein may be associated with necrotic enteritis (Drew et al., 2004).
Each time a new amino acid became available and was used, the level of soybean meal has been reduced. Essentially, what is happening is that soybean meal is replaced with amino acids. This will continue to be the case when we find ways to use valine, arginine and isoleucine. This exercise has been done with wheat-based diets for Australia. If this exercise was done in the USA or other locations using corn-soy diets, the numbers would be quite different, but the conclusions would probably be similar. Which amino acids are available? The amino acids LMT (lysine, methionine and threonine) are widely used in Australian broiler diets. They are priced in the range of $2-4/kg. Small amounts of valine and glycine are also being used. Demand for valine in the market has increased since June 2018. Other amino acids that are available but not widely used in broiler diets due to price are valine, arginine and isoleucine (VAI). Prices used for these amino acids in this exercise are $8.5, 13.3 and 18.9/kg respectively.
These are prices in the Australian marketplace over the past 12 months. Tryptophan does not appear to be limiting in wheat-based diets, and as such is not considered in this exercise. However, in corn-based diets seeking a 30 g/kg reduction in protein, crystalline tryptophan would be required. There is a reasonable knowledge of the absolute requirements for lysine, methionine, methionine + cysteine, tryptophan, threonine, arginine, isoleucine and valine. Requirements for amino acids other than lysine are normally calculated based on the ideal protein ratio (Baker and Han, 1994). For this exercise, the 2018 recommendations for Cobb 500 have been used. The requirement for the “non-essential” amino acid glycine is not clear. Requirements for glycine and glycine + serine are not well understood. Several researchers have shown improvements in broiler performance with added glycine in lower protein diets not containing meat and bone meal (MBM) (Hilliar et al., 2017; Dean et al., 2006). MBM is high in glycine, and it is unlikely that diets containing MBM would need added glycine. Should MBM not be used, the inclusion of 500 grams- 1 kg glycine/t might be advisable. At less than $3/kg, this would not be expensive.
II. FORMULATION EXERCISE
A least cost formulation exercise was conducted, using wheat-based diets, with MBM, canola meal and soybean meal as the protein sources, and tallow as the supplemental oil. Ingredient prices (AUD) for June 2018, for Eastern Australia were used. Xylanase and phytase enzymes were used with recommended nutrient matrices. Formulations are based on Cobb 500 recommendations for SID amino acids (Cobb-Vantress 2018). Diets are shown in Table 1. The starter diet was not included in this exercise since this diet makes up only about 10% of total feed used. The starter diet may be a special case where increased levels of high quality protein may be advantageous to growth and have little potential issues on litter quality, health, odour production and/or economics.
The formulations were established without any protein restrictions. Note the protein levels are 207, 196 and 190 g/kg respectively as shown in Table 2. Then protein was restricted by 20 g/kg, to 187, 176 and 170 g/kg in grower, finisher 1 and finisher 2 respectively. Protein restriction was achieved by placing a number in the “protein maximum” column in the formulation program, for example 187 g/kg for the grower diet. Formulations were done by 3 methods: 1) No protein restrictions, 2) Protein restricted to 20 g/kg lower than 1. 3) Protein restricted as in method 2, but with prices of arginine, valine and isoleucine reduced by 50%.
Results of the formulation exercise are shown in Table 2 and summarised in Table 3. Grower diets are $468.63/t without protein restriction, $480.99/t with protein restriction and current VAI prices, and $467.10/t with VAI at 50% of current prices. Finisher 1 diets are $450.17/t without protein restriction, $462.03/t with protein restriction and current VAI prices, and $448.43/t with protein restriction and VAI at 50% of current prices. Finisher 2 diets are $441.63/t without protein restriction, $451.80/t with protein restriction and current VAI prices, and $439.21/t with protein restriction and VAI at 50% of current prices. This suggests the protein reduced diets will cost $10-12/t more with current VAI prices. Costs of VAI would need to come down by 50% of current prices, for the lower protein diets to be of equal price to the higher protein ones.
There are significant ingredient effects of these low protein diets. These are: 1) wheat levels are increased, 2) soybean meal levels are decreased, 3) levels of canola meal are unchanged, 4) added oil (tallow) levels are reduced by almost 50%, 4) MBM remains about the same, 5) amounts of lysine, methionine and threonine are greatly increased. On average of grower, finisher 1 and finisher 2, lysine addition is increased by 60%, methionine by 25% and threonine by almost 300%, 5) valine, arginine and isoleucine are used in these lower protein diets, at levels of 0.2-0.7 kg/t for valine, 1.2-1.6 kg/t for arginine, and 0.1-0.6 kg/t for isoleucine. Arginine is used at the highest level.
It is clear that, if lower protein diets are to be produced, the amino acids valine, arginine and isoleucine will be needed. As shown in this exercise, current prices of these 3 amino acids prevent the formulation of lower protein diets at equal cost to higher protein ones. Therefore, the key to lower protein diets is dependent on future prices for these 3 amino acids.
Abstract presented at the 30th Annual Australian Poultry Science Symposium 2019. For information on the latest edition and future events, check out https://www.apss2021.com.au/.