Researchers at Johns Hopkins University have called into question the validity of the means by which FCR is measured, suggesting aquaculture does not stack up as well against terrestrial livestock as we like to think. FCR is a limited measure of efficiency, they argue, because it only accounts for the weight of feed inputs and not the nutritional content of the feed, the portion of the animal that is inedible, or the nutritional quality of the final product. Using FCRs relies on an implicit assumption that various species are similar across these areas, making FCR a potentially flawed tool for cross-species comparisons.
Focusing on commercial production, the researchers collected data on feed composition, feed conversion ratios, edible portions (i.e. yield), and nutritional content of edible flesh for nine aquatic and three terrestrial farmed animal species.
“Based on our review, a more precise measure than FCR is the efficiency with which an animal converts nutrients in feed into nutrients for the human food supply,” stated the authors. They estimate that 19% of protein and 10% of calories in feed for aquatic species are ultimately made available in the human food supply, with significant variation between species.
The study included nine major aquaculture species: common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella), channel catfish (Ictalurus punctatus), pangas catfish (Pangasius pangasius), Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), giant tiger prawn (Penaeus monodon), whiteleg shrimp (Litopenaeus vannamei), tilapia (Oreochromis niloticus and other cichlids); and three livestock groups (cattle raised for beef, pigs, and chickens raised for meat).
Comparing all terrestrial and aquatic animals in the study, chickens are most efficient using these measures, followed by Atlantic salmon. Despite lower FCRs in aquaculture, protein and calorie retention for aquaculture production is comparable to livestock production. This is, in part, due to farmed fish and shrimp requiring higher levels of protein and calories in feed compared to chickens, pigs, and cattle.
“The relatively high mean protein retention for Atlantic salmon (28%) is due to a low FCR (1.2–1.5) and high edible portion (0.58–0.88); these factors offset the high levels of protein in Atlantic salmon feed (35.5%–44%).”
Current efforts to reduce FCRs in aquaculture and livestock production focus on genetic improvements through breeding and genetic engineering, development of nutritionally superior feeds and supplements, identification and implementation of improved husbandry practices including ideal environmental conditions for faster animal growth, and overcoming cost and other barriers to increase producer access to all of these developments. Researchers suggested that in addition to FCR, the impact of these changes on protein and calorie retention should be explored. For example, it is possible that providing feed higher in protein could result in a more efficient FCR but less efficient protein retention.
Researchers concluded that moving forward, discussions of sustainable food systems should be informed by a combination of factors including FCRs and nutrient retention, and also environmental footprint measures including resource use (e.g. land, water, fertilizer), greenhouse gas emissions, and negative externalities including biodiversity loss and water pollution.
Read the complete study results in the paper “Feed conversion efficiency in aquaculture: do we measure it correctly?” by Jillian P Fry, Nicholas A Mailloux, David C Love, Michael C Milli and Ling Cao / Published February 6, 2018 on IOP Science
