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Symposium on Factors Influencing the Voluntary Intake of Herbage by Ruminants: Selection and Intake by Grazing Animals¹

Virginia Polythechnic Institute², Blacksburg

Abstract

Grazing behavior in sheep does not appear to be influenced by color vision. Probably sense of smell is of no importance in selection of herbage species by sheep, although it appears to be important in initial stimulation of appetite. Rate of digestion of the cellulose and hemicellulose in forages and rumen fill appear to be important in determining voluntary consumption of forage by cattle.

Cattle and sheep graze selectively when there is an opportunity for selection. Usually, herbage selected by ruminants is higher in crude protein and ether extract and lower in crude fiber content than the whole plant. Digestibility of the proximate components is usually higher for the selected herbage. Grazing intensity affects the composition, digestibility and intake of grazed herbage. Also, plant species selection by cattle was shown to be related to grazing intensity.

Cattle allowed to graze the top half of the giazeable herbage under rotational grazing produce at a higher level than those which graze the remainder. Rate of production for whole-plant grazers was intermediate. The top grazers select a herbage that is more nutritious and higher in digestibility, and the animals consume more of it.

There appear to be differences in forage selection by cattle and sheep, although both species graze selectively. Total forage intake of ruminants appears to be related to live-weight, at least within limits.

¹ Presented by the senior author at the meeting of the North Atlantic Section, ASAS. and the Eastern Division, ADSA, July 22, 1964. at Cornell University, Ithaca, New York. ² Departments of Animal Science, Biochemistry and Nutrition, and Agronomy.

² Departments of Animal Science, Biochemistry and Nutrition, and Agronomy.

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