Feed conversion ratio
In animal husbandry, feed conversion ratio (FCR), feed conversion rate, or feed conversion efficiency (FCE), is a measure of an animal's efficiency in converting feed mass into increases of the desired output. For dairy cows, for example, the output is milk, whereas animals raised for meat – such as beef cows, pigs, chickens, and fish – the output is the mass gained by the animal. Specifically FCR is the mass of the food eaten divided by the output, all over a specified period.
"Efficiency" is customarily expressed as the ratio of useful output to input. Thus, although FCR is commonly expressed as the ratio of feed mass input to body mass output, one sometimes sees "feed conversion efficiency" (FCE) figures, i.e. kg body mass gain per kg feed intake (or, in the case of dairy animals, kg milk solids per kg feed intake).
Factors affecting FCR
FCR a function of the animal's genetics and age, the quality of the feed, and the conditions in which the animal is kept.
Although FCR is commonly calculated using feed dry mass, it is sometimes calculated on an as-fed wet mass basis, (or in the case of grains and oilseeds, sometimes on a wet mass basis at standard moisture content), with feed moisture resulting in higher ratios. In cold weather, metabolizable energy requirements for warmth may result in less net energy of gain obtained from feed. Thus, when communicating FCR data for a species, it can be desirable to specify feed moisture content and provide information regarding breed, age, feed composition, and environmental conditions under which the ratio applies, to facilitate data interpretation.
Conversion ratios for livestock
Animals that have a low FCR are considered efficient users of feed. However, comparisons of FCR among different species may be of little significance unless the feeds involved are of similar quality and suitability.
For cattle, a FCR range from less than 5 to more than 20 kg feed dry matter per kg gain may be encountered.
Some data for sheep illustrate variations in FCR. A FCR (kg feed dry matter intake per kg live mass gain) for lambs is often in the range of about 4 to 5 on high-concentrate rations, 5 to 6 on some forages of good quality, and more than 6 on feeds of lesser quality. On a diet of straw, which has a low metabolizable energy concentration, FCR of lambs may be as high as 40. Other things being equal, FCR tends to be higher for older lambs (e.g. 8 months) than younger lambs (e.g. 4 months).
Crickets are the most efficient with a ratio of only 1.7. 
Farm raised Atlantic salmon have a very good FCR, about 1.2, according to farmed salmon industry representatives. When taking into account the true mass of material needed to make fish feed, however, the conversion ratio increases dramatically to 3:1 according to some sources.[dead link]
FCR 2.5 to 3.0 on high grain diet and 3.5 to 4.0 on natural forage diet, without animal-feed grain.
- Dairy Australia Feed Conversion Efficiency
- Dan Shike, University of Illinois Beef Cattle Feed Efficiency
- Pork production
- Feed conversion rate for chickens
- USAID Technical Bulletin #07: Feed Conversion Ratio (FCR): How to calculate it and how it is used
- See, for example, definition 2a of "efficiency" at http://education.yahoo.com/reference/dictionary/entry/efficiency
- Snowder, G. D. and L. D. Van Vleck. 2003. Estimates of genetic parameters and selection strategies to improve the economic efficiency of postweaning growth in lambs. J. Anim. Sci. 81: 2704-2713
- National Research Council (Subcommittee on Environmental Stress). 1981. Effect of environment on nutrient requirements of domestic animals. National Academy Press, Washington. 168 pp.
- National Research Council. 2000. Nutrient Requirements of Beef Cattle. National Academy Press. 232 pp.
- Quick Facts - The Pork Industry at a Glance
- Brown, L., Hindmarsh, R., Mcgregor, R., 2001. Dynamic Agriculture Book Three (2nd ed.). McGraw-Hill Book Company, Sydney.
- Knott, S. A., B. J. Leury, L. J. Cummins, F. D. Brien and F. R. Dunshea. 2003. Relationship between body composition, net feed intake and gross feed conversion efficiency in composite sire line sheep. In: Souffrant, W. B. and C. C. Metges (eds.). Progress in research on energy and protein metabolism. EAAP publ. no. 109. Wageningen
- Brand, T. S., S. W. P. Cloete and F. Franck. 1991. Wheat-straw as roughage component in finishing diets of growing lambs. S. Afr. J. Anim. Sci 21: 184-188.
- National Research Council. 2007. Nutrient requirements of small ruminants. National Academies Press. 362 pp.
- Fahmy, M. H., J. M. Boucher, L. M. Pose, R. Grégoire, G. Butler and J. E. Comeau. 1992. Feed efficiency, carcass characteristics, and sensory quality of lambs, with or without prolific ancestry, fed diets with different protein supplements. J. Anim. Sci. 70: 1365-1374
- Malik, R. C., M. A. Razzaque, S. Abbas, N. Al-Khozam and S. Sahni. 1996. Feedlot growth and efficiency of three-way cross lambs as affected by genotype, age and diet. Proc. Aust. Soc. Anim. Prod. 21: 251-254.
- Cronjé. P. B. and E. Weites. 1990. Live mass, carcass and wool growth responses to supplementation of a roughage diet with sources of protein and energy in South African Mutton Merino lambs. S. Afr. J. Anim. Sci. 20: 141-168
- Collavo, A., Glew, R.H., Huang, Y.S., Chuang, L.T., Bosse, R. & Paoletti, M.G. 2005. House cricket small-scale farming. In M.G. Paoletti, ed., Ecological implications of minilivestock: potential of insects, rodents, frogs and snails. pp. 519–544. New Hampshire, Science Publishers.
- TNAU Animal Husbandry ::Rabbit