Factors characterizing degradation of feedstuffs in the rumen and intestine are critical components
of modem ration formulation equations. This study was undertaken to determine the in situ
degradability characteristics of forages commonly fed to lactating dairy cattle. In Experiment 1,
dry matter (DM) and crude protein (CP) degradation characteristics of 12 corn silages and 22 grass
silages were evaluated using both the rumen and mobile nylon bag in situ techniques. In
Experiment 2, 16 alfalfa hays and 14 grass hays were evaluated using the same procedures.
Significant (P<O.05) differences in degradation characteristics occurred within each forage type in
both the soluble and potentially degradable DM and CP fractions. These differences (P<O.05) were
also observed in the effective degradability of DM and CP at varying fractional rates of passage
through the rumen. In Experiment 3, the total amino acid content in all four forage types was
determined. There was a considerable range between the minimum and maximum values in all
amino acids analyzed within each forage type. In Experiment 4, the amino acid composition of
rumen undegradable protein in 19 grass silages was determined using the in situ rumen and mobile
nylon bag techniques. Predicting the concentrations of individual amino acids in rumen incubated
residues presented to the duodenum from the dietary amino acid profiles was also examined.
Except for arginine(r²=O.76) and serine (r²=O.82), there was a poor relationship between the amino
acid concentrations of grass silages and the 12 h rumen incubation residues. The amino acid
composition of the rumen undegradable portion of grass silage differs from that of the unincubated
silage. In the concluding Chapter an assessment of the cost is made of using incorrect rumen
degradability characteristics. It was determined that the use of such values may result in large
changes in income over feed cost. The work presented in this thesis demonstrates that the range in degradability characteristics of CP and the range in amino acid supply from forages is much
larger than currently accounted for in ration formulation systems, thus resulting in errors in
formulated ruminant rations.Land and Food Systems, Faculty ofGraduat
