Regulation of Voluntary Intake of Ryegrass and Sorghum Forages in Cattle by Indigestible Neutral Detergent Fiber

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Abstract
In four experiments, intake and digestibility of forage diets selected by yearling heifers (204 ± 27 kg) and steers (275 ± 45 kg) and by cows (476 ± 67 kg) and nursing calves (196 ± 16 kg) were related to dietary fiber characteristics. Fresh or ensiled vegetative ryegrass and sorghum silage were offered separately in varying proportions. Yearlings that were allowed ad libitum amounts of ryegrass and sorghum selected diets with 67 to 69% digestible organic matter and 10 to 12% indigestible neutral detergent fiber and achieved higher digestible organic matter intakes than yearlings offered restricted amounts of either ryegrass or sorghum forage. Steers restricted to a diet of only ryegrass consumed less digestible organic matter than steers fed ad libitum amounts of ryegrass and sorghum silage. Mature lactating and non-lactating cows consumed more digestible organic matter per unit body weight (BW) and selected diets higher in digestible organic matter (73%) than did yearling cattle. The data are interpreted to suggest that indigestible neutral detergent fiber is the component limiting intake of less digestible forages. Yearling cattle were able to consume an average of 13 g/kg BW·75 of indigestible neutral detergent fiber, whereas the capacity of mature cows was about 50% greater. In these experiments, cattle, when given a choice, selected forage diets that maximized digestible organic matter intake. Copyright © 1986. American Society of Animal Science . Copyright 1986 by American Society of Animal Science.

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