Publisher Summary Forages are grown for ruminant feeding, and most ruminant animals eat forages. Thus, a review of the nutritive value of forages is essentially a review of ruminant nutrition, with the difference that the nutritionist can treat the animal and the forage it eats in isolation. However, the agronomist must also consider the problems that arise when the animal and its feed are brought together in practical systems of forage production and utilization. To continue as a significant sector of agriculture, the efficiency of soil-forage-ruminant systems must be greatly increased in terms of (a) the efficiency of the use of incident light energy by the growing plant; (b) the proportion of the energy in the plant that is actually eaten by the ruminant animal; and (c) the efficiency with which different animal populations convert the energy they eat into products that can be used by humans. Thus, the nutritive value of a forage should be considered not as a single parameter, but as composed of a complex of parameters that determine the nutrient intake of ruminant animals fed on that forage. This chapter considers the nutritive value of forages in terms of the factors that determine the level of nutrient intake by ruminant livestock.

The Nutritive Value Of Forage Crops

Relationship of Nitrogen Fertilization and Chemical Composition of Forage to Animal Health and Performance

The nutritive value of sown binary- and multi-species grassland mixtures may differ from the values expected based on single-species swards of their constituent species. Field plots were established in a split-plot design to assess the nutritive value of binary- and multi-species mixtures compared to single-species swards of three grass species and red clover (RC) ( Trifolium pratense L.) managed for intensive silage production. The nutritive value of grass–legume binary mixtures reflected the values of the constituent species grown on their own, and thus may be predicted from monoculture values. The relatively low digestibility (dry matter digestibility [DMD]) and crude protein (CP) content of the Italian ryegrass ( Lolium multiflorum L.) sward compared to perennial ryegrass ( Lolium perenne L.) and timothy ( Phleum pratense L.) suggests that it may have a limited role in binary- or multi-species swards. Herbage nutritive value in the multi-species swards (Mix 1: perennial ryegrass, timothy, RC and white clover [ Trifolium repens L.]; Mix 2: perennial ryegrass, timothy, RC, ribwort plantain [ Plantago lanceolata L.] and chicory [ Cichorium intybus L.]) appeared to be influenced more by the presence of legumes than herbs. Compared to perennial ryegrass, the multi-species swards had a slower rate of DMD decline prior to Cut 1, but subsequently had lower DMD values at the mid-season harvests. Both multi-species mixtures exhibited DMD, water-soluble carbohydrate (WSC) and CP values that would not have been predicted from their constituent species and thus need to be measured on herbage from field plots growing these mixtures.

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Herbage nutritive value of binary- and multi-species swards relative to single-species swards in intensive silage systems

Conventional digestion experiments were conducted with wethers to determine the effects of varying nitrogen fertilizer application rates to grass on the intake and digestibility of mature grass hays.Nitrogen fertilizer rates had little effect on dry matter intake.The apparent digestibility of crude protein increased and that of dry matter and nitrogen-free extract decreased linearly (P < 0.01) with increasing nitrogen fertilizer rates.The mean dry matter intake was greater (P < 0.01) per unit body weight and less (P < 0.01) per unit metabolic body size (wt. 0.75) than that previously reported for concurrent digestion experiments with steer calves fed these forages. The apparent digestibility of the dry matter, crude protein, crude fiber, and nitrogen-free extract was less (P < 0.01) in wethers than in steers. There were no significant interactions of species × nitrogen rates for intake and nutrient digestibility.

C. D. T. Cameron

Papers

Intake and digestibility of nitrogen-fertilized grass hays by wethers