由食物變成肉的比率, 在養殖業行話稱之為飼料換肉率(Feed Conversion Ratio, FCR), 其定義如下:
FCR = (consumed food weight)/(body weight gained).
FCR = 消耗食物的重量/動物增加的體重

http://en.wikipedia.org/wiki/Feed_conversion_ratio

Specifically FCR is the mass of the food eaten divided by the body mass gain, all over a specified period of time. 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. Poultry usually can convert 2-3 kg of feed into 1 kg of live weight, while sheep and cattle need more than 8 kg of feed to put on 1 kg of live weight. The U.S. pork industry claims to have an FCR of 3.4-3.6 [1].

具有低飼料換肉率值的動物能夠有效的轉換飼料為體重(蛋白質,脂肪,核苷酸 ...) . 通常禽類增加1公斤體重需要消耗 2~3 公斤的食物, 與此相較, 綿羊與牛增加1公斤體重需要消耗多於 8 公斤的食物. 美國養豬業宣稱的飼料換肉率為 3.4-3.6.

Farm raised Atlantic salmon apparently have a very good FCR, about 1.2.
乍看之下, 人工蓄養之大西洋鮭魚的飼料換肉率僅為 1.2; 或是大西洋鮭魚每消耗 1.2 公斤的飼料就能增加 1.0 公斤的體重.

Nonetheless this value is an underestimation of the FCR, for it does not take in account that more than often the feed is in kg of “dry” weight and the live weight is in kg of “wet” weight.
儘管飼料換肉率的計算方式是如此的簡單而直接, 實際上此種直接計算方式反而嚴重的低估實際的飼料換肉率. 因為在最原始的飼料換肉率計算式子裡所用的飼料重量通常是 "乾重" 計算, 而飼養動物所增加的體重通常是用 "濕重" 計算. (e.g. 體重 70% 為水分重量)

When both factors are transformed to either dry or wet weight the FCR increases to between 4 and 5, depending on the feeding practice.
所以當此二數值皆轉換為等效的乾重或是濕重時, (譯註: 應該是指前文所提 - 大西洋鮭魚的) , 此 "真實"FCR 會根據飼養方式之不同而暴增到4-5.

Presently, technological advances in feed research are enabling salmon farmers to lower the “true” FCR to 4 and under (i.e. by substituting fish meal and fish oil with plant products such as soy and derivatives) which in consequence lowers the Salmon's average trophic level.
目前, 飼料科技的進步可以使養殖的大西洋鮭魚之 "真實飼料換肉率" 可以降到4或是更低. 例如用植物製品 - 大豆及相關衍生產品來取代原先飼料配方所使用的魚粉和魚油.但是此舉也會降低養殖大西洋鮭魚的Omega-3 脂肪酸之含量, 所以一昧提高飼料換肉率的後果之一就是降低了養殖鮭魚的平均營養價值.

It is important to understand that the above discussion of dry weight vs. wet weight for FCRs in Salmon also applies to other animals, such as poultry, cattle, and beef. Those FCR's are also a conversion of dry feed to wet animal weight, so really the FCRs are still to the same proportions.
同理可知, 以上所提及大西洋鮭魚之 "真實飼料換肉率-true FCR" (乾重/乾重) 與 "飼料換肉率-FCR" (乾重/濕重)之間的轉換關係也同樣適用於其他動物例如家禽, 牛, 豬, 羊.