Evaluating net energy and protein feed conversion efficiency for dairy ruminant systems in France

Modern systems of animal production are facing increasing challenges on issues such as animal welfare, product quality, and environmental impact. Ruminants in particular are often regarded as being inefficient with respect to feed conversion for both protein and energy. Efficiency is defined as the ratio between resources and production; when applied to dairy production systems, it corresponds to the total amount of feed (kg of dry matter of roughages and concentrates) consumed per kg of milk and meat produced. This ratio underlines the biological ability of dairy cows, ewes, and goats to convert feed into products that are edible by humans while maintaining other physiological functions. Feeds consumed by animals can be "human-edible", i.e. directly usable for human nutrition (cereals, legumes, maize silage), or not (grasslands, wild grass areas). Calculations of livestock efficiency are strongly influenced by whether or not they consider, and distinguish between, the consumption of human-edible or -inedible plant resources (roughages and concentrates) as well as the production of edible and/ or inedible animal products (e.g., milk, meat, wool, leather). An improved understanding of the inedible fraction of both energy and protein in animal feed will be invaluable in analyses of feed-food competition, especially in ruminants. In this study, we investigated the feed conversion efficiency (FCE) of dairy ruminant systems in France (cow, goat, ewe) with respect to both energy and protein. We hypothesized that FCE would be influenced by the composition of the diet and its grass content, as well as, by animal type. Data from a French database (Diapason) provided information on land, labor, herds, and production from 2012 to 2016 for 274 dairy goat farms, 108 dairy ewe farms, and 498 dairy cow farms. These herds consumed feeds that were human-edible (cereals, legumes, maize silage) as well as -inedible (grasslands, wild grass areas). We estimated that French dairy systems are, on average, net consumers of energy and net producers of protein, with higher efficiencies for grass-based systems compared to maize-based systems. At the national scale, average net protein efficiencies were 1.16, 1.12, and 1.88 for ewes, goats, and cows, respectively. These results on the net FCE in dairy systems will promote a more objective quantification of their contribution to food security, which should be taken into account in assessments of feed-food competition and its impact on human nutrition. When combined with other factors such as greenhouse gas emissions and land and resource use, such considerations will help to inform discussions of the future of livestock production.