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CROP QUALITY & UTILIZATION

Protein Degradability and Forage Quality in Maturing Alfalfa, Red Clover, and Birdsfoot Trefoil

^a Southwest Res. and Extension Center, University of Arkansas, 362 Hwy 174N, Hope, AR 71801 USA
^b W.K. Kellogg Foundation, Battle Creek, MI USA
^c Dep. of Animal Sci., Michigan State University, East Lansing, MI 48824 USA
^d Cooperative Extension, Univ. of Maine, Orono, ME 04469 USA

kcassida{at}uaex.edu

Choice of forage species and harvest management may influence protein degradability in cattle diets. We measured forage yield, undegradable intake protein (UIP), and forage quality at three maturities in two cuttings (spring, regrowth) of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.) in the seeding and two subsequent years. At equivalent harvest stage, trefoil and clover were usually lower in neutral detergent fiber (NDF) and acid detergent fiber (ADF) than alfalfa. Crude protein (CP) was lower in red clover than trefoil or alfalfa for three of six cuttings, but red clover was equal to or higher in UIP than alfalfa or trefoil in all cuttings. Trefoil never had higher UIP concentrations than alfalfa. Trefoil tannin concentrations increased with maturity and were positively correlated with UIP concentration. For all species, UIP was positively correlated with NDF and ADF and negatively correlated with in situ dry matter disappearance (ISDMD). In alfalfa and trefoil, UIP was negatively correlated with CP. In all legumes, dry matter yield (DMY), NDF, and ADF increased with maturity, while CP and ISDMD decreased. Changes in NDF, ADF, CP, and ISDMD with maturity were usually most rapid in trefoil. The proportion of UIP increased with maturity for all species in all cuttings, but it never comprised more than 240 g kg^-1 CP. Small increases in UIP as legumes matured were gained at the expense of other forage quality measures.

Abbreviations: ADF, acid detergent fiber • CP, crude protein • DM, dry matter • DMY, dry matter yield • ISDMD, in situ dry matter disappearance • NDF, neutral detergent fiber • UIP, undegradable intake protein on dry matter basis • UIPIP, undegradable intake protein as fraction of intake (crude) protein

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