Forage management effects on protein and fiber fractions, protein degradability, and dry matter yield of red clover conserved as silage

Abstract

Due to the action of o-quinones formed via polyphenol oxidase, conserved red clover ( Trifolium pratense L.) contains abundant rumen undegradable protein (RUP), but inadequate rumen degradable protein (RDP) for dairy cattle. This study examined how forage management influences RDP, RUP, crude protein (CP) and fiber fractions in red clover silage and dry matter (DM) yields during the first full production year. In 2003 and 2006, red clover was cut early on 7 June or late on 14 June with two ∼40 d regrowth cuts. For comparison, alfalfa ( Medicago sativa L.) was cut early on 26 May with three ∼32 d regrowth cuts or late using the same schedule as early cut red clover. After ensiling at 370 g/kg DM, CP and fiber were fractionated according to the Cornell Net Carbohydrate and Protein System (CNCPS). RDP and RUP were calculated from CNCPS fractions or estimated by a more convenient Streptomyces griseus protease procedure, which gave highly related ( R 2 ≥ 0.95) estimates of CP degradability. Early cutting of red clover favorably decreased RUP, neutral detergent fiber (NDF), and acid detergent fiber (ADF) and increased RDP and CP in the first two harvests. Regression analyses indicated desirable levels of RDP (>150 g/kg DM) and NDF (∼400 g/kg DM) could be obtained by harvesting red clover at a mean stage weight maturity of 2.0 at first cut, 3.0 at second cut, and 3.5–4.0 at third cut. Averaged across harvest schedules, red clover had lower RDP, CP and ADF, higher RUP, and similar NDF compared to alfalfa. Total DM yields of red clover and alfalfa were not influenced by harvest schedule. Time of establishment had little effect on silage quality, but it did influence total DM yields; April vs. August seeding depressed red clover yields (12.3 t/ha vs. 13.1 t/ha) but enhanced alfalfa yields (12.5 t/ha vs. 11.9 t/ha) during the first full production year. Overall, these results suggest protein utilization and performance of dairy cattle could be moderately improved without sacrificing DM yield by taking a very early first cutting of red clover followed by regrowth cuttings made at progressively later maturities.