Net food supply from livestock: a matter of quantity and quality
The animal article of the month for November is ‘An approach to including protein quality when assessing the net contribution of livestock to human food supply‘
Worldwide, livestock provide more than a quarter of the protein in human diets. Nevertheless, livestock production is often criticized from a food security perspective because of the low efficiency of converting plant protein from feeds into animal protein. This criticism often fails to consider the fact that much of the plant-based protein fed to animals may be inedible for humans (e.g. feed protein in grass). A further aspect is that the nutritional value of animal proteins is usually superior to plant proteins. Although these quality differences have often been discussed, an approach to effectively quantify them has not yet been developed.
Our study aimed to assess the changes in protein quality that occur when potentially human-edible plant proteins (e.g. from grains or pulses) are converted into animal products via livestock production. To do so, we conducted a case study with data from 30 Austrian dairy farms. A further goal was to develop an approach for combining these quality changes with quantitative aspects (i.e. the amount of human-edible protein in feeds as compared to the amount of protein in the animal products). The protein quality of potentially human-edible inputs and outputs was assessed using two different methods proposed by the FAO to describe the nutritional value of proteins for humans.
The ratio between animal protein quality and potentially human-edible feed protein quality is termed PQR (protein quality ratio) and was between 1.40 and 1.87. These PQR indicate substantial increases in the protein quality through the transformation of plant proteins into animal proteins by dairy cows. Changes in protein quality can be combined with existing concepts that quantitatively relate animal protein output to potentially human-edible protein inputs in animal production systems by multiplying the two ratios (output / input) for quantity and quality. The resulting value allows us to interpret how efficiently an animal production system converts potentially human-edible protein inputs of usually lower nutritional quality into high-quality animal proteins. It also helps to identify strengths (i.e. the conversion of large amounts of human-inedible feedstuffs such as forages into high-quality animal protein and the improvement of the quality of human-edible protein) and weaknesses (i.e. input of large proportions of high-quality plant proteins into livestock diets) of livestock production systems in terms of their contribution to food security and, more specifically, to the overall protein supply. The results of our study also emphasize the necessity of including the differences in protein quality when assessing the role of animal production systems with regard to overall protein supply or when comparing the environmental impacts of the production of animal- vs. plant-source proteins.
This article is freely available for one month:
An approach to including protein quality when assessing the net contribution of livestock to human food supply
Authors: P. Ertl, W. Knaus and W. Zollitsch.
The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month. View the recent selections