Masters Theses

Date of Award

12-1969

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

Karl M. Barth

Committee Members

Robert R. Shrode, C. C. Chamberlain

Abstract

During the summer of 1969 (May 30 to September 19), five grazing trials were conducted at 4-weekly intervals, to study the effect of selective grazing on the chemical composition and in vitro dry matter digestibility of forage samples. In addition, the effects of saliva contamination, partial mastication, and sample preparation of fistula samples (squeezed and non squeezed) also were investigated at 4-weekly intervals by means of pen feeding studies. Five esophageal-fistulated Hereford steers and two types of pastures, tall fescue and orchardgrass, were used in this study. To estimate the effect of saliva contamination and partial mastication, hand-clipped forage samples from each pasture plot were each divided into two portions. One portion was fed to an esophageal-fistulated steer and then collected (clipped-fistula sample) through the fistula. The other part (clipped-control sample) was not subjected to further treatment. The differences between the chemical components and in vitro dry matter digestibility (DOM) of clipped-fistula and clipped control samples were used to show the effect of the esophageal fistula. The results from both types of pasture showed that clipped-fistula samples contained more ash, crude protein, acid detergent fiber (ADF). acid insoluble lignin (AIL) and less of the nitrogen free extract + ether extract fraction than clipped-control samples. The differences were statistically significant (P < .05) except with respect to crude protein. The in vitro DDM was higher in the clipped-fistula samples than in the clipped control; however, the difference between the two sample types was statistically significant (P < .05) only in tall fescue samples, not in orchardgrass samples. The results of this study indicate that non-squeezed samples represent the true situation of contamination and mastication better than squeezed samples. Therefore, the following results were obtained from the non-squeezed samples only. To estimate the degree of selective grazing, a comparison was made between grazed-fistula samples (selected forages) and clipped-fistula samples (available forages) in chemical components and in vitro DDM. Crude protein was significantly higher (P < .05), and ADF and NFE + EE were lower in the selected fescue forages. In orchardgrass samples, animals selected forages higher in crude protein and lower in NFE + EE than were available forages. From this study we assume, therefore, that beef cattle are capable to select forages which are higher in crude protein and lower in NFE + EE than are the average of the available forages in the pasture. This study shows also that hand-clipping is an inadequate method of measuring the nutritive value of pasture forages.

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