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Relationships between Canopy Botanical Composition and Diet Selection in Aeschynomene-Limpograss Pastures¹

The proportion of aeschynomene (Aeschynomene americana L.) in diets of cattle (Bos spp.) grazing aeschynomene-limpograss [Hemarthria altissima (Poir.) Stapf et C.E. Hubb.] pastures is critical because protein concentration of the grass is often below levels thought needed to prevent intake depression (70 g kg^–1 dry matter). A study was conducted on a Pomona sand (sandy, siliceous, hyperthermic Ultic Haplaquod) to determine the effect of botanical composition of aeschynomene-limpograss canopies on the composition of diets selected by cattle. Esophageally fistulated steers were used to determine selection at first exposure to a pasture, and a sward difference technique was used to quantify the botanical composition of the herbage consumed during 48-h mob grazing periods. Fistulated steers selected a diet higher in percentage aeschynomene than that in the upper layer of the canopy, but over a 48-h grazing period, percentage legume in herbage consumed was not different than percentage legume in the grazed horizon. As the canopy was grazed down, total herbage bulk density of the surface layer increased and the legume leaf/stem ratio decreased. These factors ended selection for aeschynomene, and late in a grazing period animals were likely to choose the most accessible grass and weed forage and to avoid legume stems. These data are evidence of a dynamic plant-animal interface in that (i) canopy characteristics influenced diet botanical composition, (ii) the act of consumption changed the canopy, and (iii) animals responded by altering their degree of selection. The results show that aeschynomene leaf and fine stem are highly palatable to cattle. This finding, along with previous reports of excellent forage quality, suggests that aeschynomene is capable of providing satisfactory levels of protein in steer diets if legume stands are adequate and if grazing ends before all aeschynomene leaf and fine stem are removed from the grazed horizon.

Key Words: Aeschynomene americana L. • Hemarthria altissima (Poir.) Stapf et C.E. Hubb. • Legume-grass association • Plant-animal interface • Tropical forages • Esophageally fistulated steers

² Assistant professor of Agronomy, professor of Animal Science, professor of Agronomy, and biological scientist, Inst. of Food and Agric. Sciences, Animal Nutrition Lab., Univ. of Florida, Gainesville, FL 32611.

Received for publication September 5, 1986.