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In situ forage protein degradability characteristics in ruminants

University of British Columbia

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.

Thesis/Dissertation

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2009-06-05

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http://hdl.handle.net/2429/8819

Animal Science

University of British Columbia

UBCV

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