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Protein Distribution in Four Cool-Season Grass Varieties Alone or in Combination with Trefoil

Cornell University², Ithaca, NY 14853

Abstract

An experiment was conducted over 2 yr to determine the protein distribution in four grasses (bromegrass, orchardgrass, timothy and fescue) grown alone or in combination with trefoil (birdsfoot trefoil) at two hay harvest dates. Evaluated were forage content of protein soluble in the rumen and protein that is slowly degraded or undegraded in the rumen (protein resistant to protease degradation and that remaining after refluxing in neutral detergent solution, respectively). The fixed effects of year, harvest, forage type and grass variety were evaluated along with the two-way interactions. All protein fractions were different (P < .05) in yr 2 vs yr 1. Crude protein was 18.4% higher, and the percentage of protein in protease-resistant and NDF-protein fractions was 11.7 and 19.2% lower, respectively, whereas that in the soluble protein fraction was 68.4% higher during yr 2 vs yr 1. The difference between years may reflect differences in sample preservation methods (air-dried in yr 1 vs collection in liquid N followed by freeze-drying in yr 2). Forage from harvest 2 averaged 45.1% more CP than that from harvest 1; 37.2 and 120.2% more of the protein was in the protease-resistant and NDF fractions. Forage type (trefoil plus grass vs grass alone) did not influence (P > .05) protein distribution. Among grass types, fescue had the lowest proportion of protein in the NDF fraction. Forages varied from year to year and among harvest dates within a year in distribution of protein. Because extent of ruminal protein degradation influences metabolizable protein values, protein solubility and degradation should be determined on forage samples for use in diet formulation.

¹ Present address: Anim. Prod. Dept., Univ. of Gezira, Sudan.

² Dept. of Anim. Sci.

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