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Mechanical Maceration Divergently Shifts Protein Degradability in Condensed-Tannin vs. o-Quinone Containing Conserved Forages

U.S. Dairy Forage Research Center, USDA-ARS, Madison, WI 53706. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may also be suitable

^* Corresponding author (John.Grabber{at}ars.usda.gov).

Conditioning and conservation methods may interact with polyphenols to alter forage crude protein (CP) solubility and degradability. In this study, forages with 200 g CP kg^–1 dry matter were roll conditioned or macerated, conserved as hay or silage, and then analyzed for CP fractions. Shifting from roll conditioning to maceration of polyphenol-free alfalfa (Medicago sativa L.) reduced buffer soluble protein (SP) with little effect on protease rumen-undegradable protein (RUP) and intestinal available protein (IAP, RUP minus acid-detergent insoluble CP). In birdsfoot trefoil (Lotus corniculatus L.), condensed tannin (CT) and maceration independently reduced SP and increased RUP to yield up to 62% more IAP in hay and 145% more IAP in silage than alfalfa. Based on results with trefoil, roll-conditioned forage with 70 to 120 g CT kg^–1 CP or macerated forage with more modest CT levels should meet a 350 g RUP kg^–1 CP target to support 35 kg d^–1 milk yield by cattle. In roll-conditioned red clover (Trifolium pratense L.), o-quinones formed by polyphenol oxidase reduced SP and increased RUP to yield 50% more IAP in hay and 88% more IAP in silage than alfalfa. Surprisingly, maceration reduced SP, RUP, and IAP in clover. Following maceration, RUP and IAP in conserved clover and trefoil responded similarly to CT, suggesting that maceration disabled o-quinone protection of protein substrates. Although red clover has high RUP, low reported milk yields indicate o-quinones might depress IAP.

Abbreviations: CP, crude protein • CT, condensed tannin • DM, dry matter • IAP, intestinal available protein • IRDP, insoluble rumen-degradable protein • NPN, nonprotein N • RDP, rumen-degradable protein • RUP, rumen-undegradable protein • SP, soluble protein

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Received for publication August 27, 2007.