Variability in nutrient measurement of feed ingredients

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Accurate measurement of the nutritional value of feed ingredients is largely dependent on the sampling method (Photo courtesy of Foss)

AMY MOSS, PETER CHRYSTAL, TAMSYN CROWELY and GENE PESTI* demonstrate that high variability in nutrient measurement of feed ingredients can drastically reduce the profitability of poultry production.

Feed accounts for more than 65% of poultry production costs; thus, accurate feed formulation is vital to ensure poultry are receiving an optimal diet and nutrients are not in under- or over-supply. However, this is difficult when the nutrient specifications of feed ingredients are extremely variable. Importance of sampling

In order to help reduce this variability, appropriate sampling methodology is critical. Nevertheless, recommended methodology and depth of detail within technical articles varies greatly and doesn’t always reflect the recommendations of the Association of Official Analytical Chemists (AOAC), a non-profit scientific association that publishes standardised analytical methods. 

This has been an ongoing issue for some time; 45 years ago it was concluded that improper sampling technique is a major component of ingredient variability. Nevertheless, few animal nutrition studies report the sampling technique used, nor is the potential economic cost of variability often discussed. Protein is an expensive and crucial macronutrient component of poultry diets; thus, the extent that variation in protein in feed ingredients affects expected performance and profits for the Australian poultry industry was modelled.

Despite being commonly used, grab samples were the worst of 17 methods tested in Petersen et al. (2004). Sampling methods in the literature are inconsistent and lacking in detail. Despite this, the Grain Trade Australia fact sheet states “as there has not been any data provided on the financial loss to industry of inappropriate sampling systems, this research to date has not been considered a high priority”.

Figure 1: Frequency plot of dietary crude protein level for withdrawal feed. 

Economic impact of crude protein variability

Standard Australian wheat-soybean meal-canola meal-based starter, grower, finisher and withdrawal diets were formulated and profitability modelled using EFG Broiler Model software (EFG Software, 2020). The variability (coefficient of variation; CV) in crude protein of the components of Australian poultry diets were estimated, and simulations were performed to estimate the likelihood a diet would fall below nutrient recommendations using Excel 2016, NORMINV function (10,000 simulations/diet). All prices are in Australian dollars. 

Coefficients of variation grew larger in finisher and withdrawal diets compared to starter and grower diets, and wheat was the single greatest source of variability in crude protein content of diets. Within withdrawal diets formulated to 19.2 g/kg crude protein from book values, there is approximately a 10% probability (or one in 10 diets) that it will fall below 182 g/kg CP, and diets may fall as low as 162 g/kg CP (Figure 1). This variation was modelled to lower the gross margin from AUD 21.26/m2 (AUD 1.417/bird/cycle) to 7.88/m2 (AUD 0.525/bird/cycle) − a reduction in profits of 63%. Therefore, it is possible to incur a difference of up to AUD 26,753 in gross margin from one cycle of 30,000 broilers by simply overestimating the nutrient content of feedstuffs.

Conclusion

Poor sampling methodology is costly to the poultry industry. Identifying the most accurate, and simple and practical sampling methods, and improving awareness of its importance deserves investment in research and development.

Amy Moss ([email protected]) and Gene Pesti are with the School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia. Peter Chrystal is with Complete Feed Solutions, Australia. Tamsyn Crowley is with the Poultry Hub Australia, University of New England, Armidale, NSW, Australia, and the School of Medicine (IMPACT), Deakin University, Geelong, VIC, Australia. This paper was presented at the 2021 Australian Poultry Science Symposium. The authors would like to acknowledge and thank Poultry Hub Australia for funding this project and for their guidance, encouragement and support. References are available from the lead author.

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