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 increased body mass.
Specifically FCR is the mass of the food eaten divided by the body mass gain, all over a specified period. FCR is dimensionless, i.e. there are no measurement units associated with FCR.
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. The U.S. pork industry claims to have an FCR of 3.4-3.6 . Farm raised Atlantic salmon apparently have a very good FCR, about 1.2.
Tilapia, typically, 1.6 to 1.8. Poultry has a feed conversion ratio of 2 to 1.
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 variation of 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). 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.
"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).
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