Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Animal Science

Major Professor

J.T. Miles

Committee Members

M.J. Montgomery, R.G. Cragle, H.J. Smith


An investigation was undertaken in which dry matter digestibility and voluntary dry matter intake data were used to compare the following chemical constituents of forages as predictors of digestibility and intake of dry matters acid detergent fiber (ADP), lignin, lignin in ADP, cell wall constituents (CWC) and crude protein.

Two experiments were conducted: (1) with alfalfa hays harvested at six stages of maturity and (2) with three forage species: alfalfa, red clover and Lindsey 77F, The relationships of stage of maturity and forage species with forage composition, digestibility and intake were investigated.

As forage advanced in growth the fibrous fractions - ADP and CWC, increased and crude protein decreased, also in Experiment II ADP and CWC were lowest in alfalfa, intermediate in red clover and highest in Lindsey 77F, A highly significant negative correlation between the fibrous fractions and crude protein was obtained. Dry matter digestibility, dry matter intake and nutritive value index (NVl) were significantly lower with advance in stage of maturity in Experiment I and in Experiment II were highest on alfalfa, intermediate on red clover and lowest on Lindsay 77F.

Lignin digestibility was quite variable and some negative digestibility of lignin was observed. Heat damage to feces and/or the presence of hemicellulose in lignin determination might be the factors contributory to artifact lignin values. There was a decreasing trend in CWC digestibility as influenced by stage of maturity; alfalfa was significantly higher than red clover in digestibility of CWC, while alfalfa and Lindsey 77F were similar. Digestibility of cell contents ranged from 85 to 44 cent. Low digestibility of cell contents might be due to the non-cell-wall matter in feces, which comprises bacterial and endogenous excretions.

Increase in butyrate (rumen VPA) was associated with higher protein content of forages. Acetate:propionate ratios were significantly lower at the bud stage than at the half bloom; this ratio with red clover and Lindsey 77P was significantly higher than that for alfalfa. Dry matter digestibility (DDM) showed highly significant positive correlations with voluntary dry matter intake, digestibilities of crude protein, ADF, CWC, cell contents and per cent of lignin in ADP, crude protein content and NVI. Highly significant negative correlations between DDM and ADP or CWC, dry matter intake and ADF or CWC were observed. These results indicated that with an increase in the forage fibrous fractions digestibility and intake of dry matter decreased significantly. In this study Availability Index and Summative Equation were poorly related to dry matter digestibility and intake and would be poor expressions of the value of feeds. NVI being dependent on energy digestibility and dry matter intake appears to be an excellent measure of feeding value. Highly significant negative correlations between ADF and CWC with either DDM or intake and NVI would indicate that the chemical components ADF and CWC, have real value for predicting the value of a feed.

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