Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2006
Publication Date: 7/10/2006
Citation: Grabber, J.H. 2006. Polyphenols and mechanical maceration shift protein fractions in legume hays from rapidly to slowly degraded forms [abstract]. In: Proceedings of the ADSA and ASAS Annual Meeting, July 9-13, 2006, Minneapolis, MN. 2006 CDROM.
Technical Abstract: Rapid proteolysis of forage protein during rumen fermentation can impair protein use by dairy cattle. The severity of conditioning at harvest may influence protein degradability in forages, particularly if protein-binding polyphenols are present. In 2002 and 2003, first and second cuttings of alfalfa, red clover with o-diphenols and polyphenol oxidase, and three birdsfoot trefoil populations with low to high tannin levels were conventionally conditioned with rolls or macerated and then dried as hay. Forage protein was partitioned with buffer and detergent solutions into rapidly (AB1), moderately (B2), and slowly (B3) degraded and undegradable (C) fractions. Treatment differences noted below were significant at the 0.05 level. Averaged over years and harvests, crude protein averaged 222 g/kg for alfalfa and 207 g/kg for trefoils and clover. Protein in roll conditioned alfalfa was comprised of 440 g/kg of AB1, 451 g/kg of B2, 75 g/kg of B3, and 34 g/kg of C. The high tannin trefoil had 64 g/kg less AB1, 59 g/kg more B2, similar B3, and 7 g/kg more C than alfalfa. Red clover had 107 g/kg less AB1, 40 g/kg more B2, 68 g/kg more B3, and similar C compared to alfalfa. Shifting from roll conditioning to maceration decreased AB1 by an average of 115 g/kg in all forages. Maceration increased B2 by 53 g/kg in alfalfa, decreased B2 by 41 g/kg in red clover, and had no effect on B2 in high tannin trefoil. Maceration increased B3 by 63 g/kg in alfalfa, 94 g/kg in high tannin trefoil, and 163 g/kg in red clover, and increased C by 15 g/kg in high tannin trefoil and 7 g/kg in red clover without altering C in alfalfa. The results indicate that polyphenols and maceration shifted protein fractions from rapid to slowly degraded forms. Maceration enhanced the action of polyphenols, shifting protein to the slowly degraded B3 and undegradable C fractions. The impact of these shifts on milk production and nitrogen utilization by dairy cattle will be evaluated using nutrition models.