EFFECT OF FEED HYDRATION ON THE DYNAMICS OF IN-SITU RUMINAL DIGESTION

Lucerne haylage (Medicago sativa), maize silage (Zea mays), ground mai ze, soyabean meal, and a totally mixed diet received hydration for 7 d ays or no hydration ro test treatment effects on the dynamics of in si tu dry matter (DM) and nitrogen digestion in the rumen. Duplicate samp les of all feed and treatment combinations were placed in the rumen of two cannulated lactating Holstein cows for 0, 1, 2, 4, 8, 16, 32 or 6 4 h. Soluble, degradable, aid indigestible fractions, fractional diges tion rates and lag times estimated for DM differed among feeds but wer e unaffected by hydration. On average, 13% more DM and 19% more nitrog en were solubilized or rinsed from hydrated bags at time 0. Nitrogen d isappearance was also unaffected by hydration except that the soluble and degradable fractions were higher and lower, respectively, for hydr ated feeds. Although feed dry matter and nitrogen disappearance were : increased by hydration at time 0, the effects of hydration on the kine tics of in situ digestion in the rumen were minor. Other factors (e.g. , feed composition, particle size, microbial attachment, and rumen env ironment);Ire likely more important determinants of the kinetics of di gestion in the rumen than hydration. (C) 1998 Elsevier Science B.V. Al l rights reserved.