Some environmental effects on relationships between in sacco degradability of protein and dry matter and chemical composition of Italian ryegrass.

The environmental effects on chemical composition and the rate and extent of crude protein (CP) and dry matter (DM) degradation of Italian ryegrass (Lolium multiflorum Lam.) in the rumen were studied. More intensive nitrogen (N) fertilizing (40, 80 and 140 kg N/ha) increased the content of the water, CP, true proteins and the effective degradability of CP (P < 0.05). Especially in the spring harvest such fertilizing increased the content of acid detergent fibre (ADF), neutral detergent fibre (NDF), cellulose and crude fibre (CF) as well as the rate of DM degradation (P < 0.05) and caused lower DM solubility while the content of hemicellulose was not affected. The most rapid changes due to grass ageing occurred in springtime. The content of DM, ADF, NDF, cellulose, hemicellulose and CF increased with maturity while the degradation rate and effective DM degradability decreased. The season and the trial location influenced the chemical composition of grass and the degradability of both DM and CP (P < 0.05). The closest multiple regression (the lowest RSD) was between the effective protein degradability and CP, NDF, ADF and and acid detergent lignin (ADL) (R2 = 0.97). Relatively good estimation of effective protein degradability was obtained using an exponential regression equation on the basis of CP content (R2 = 0.72), NDF content (R2 = 0.67) or effective DM degradability (R2 = 0.71) while the effective DM degradability may be estimated on the basis of DM solubility (R2 = 0.94), CF content (R2 = 0.93), ADF content (R2 = 0.94), ADL content (R2 = 0.85) or NDF content (R2 = 0.96). When estimating the effective CP and DM degradability from chemical composition, the error that occurs is most evidently influenced by N fertilizing and by time of harvest.