1. A preliminary study has been made of some aspects of rumen development and fermentation patterns in groups of ewes and lambs fed perennial rye-grass (P), perennial rye-grass plus white clover (P + C), short-rotation rye-grass (S) and short-rotation rye-grass plus white clover (S + C).(2) For ewes there was a significant effect on the weight of the rumen contents from the grass species. The treatment (P) which caused the lowest live weight gave the highest rumen contents weight. There were also significant pasture effects on empty live weight both from grass species differences and from the addition of clover.3. No difference in rumen dry-matter percentages was found between the four groups.4. There was no significant difference in the concentration of volatile fatty acids in the rumens of the P and S fed ewes but the addition of white clover had a significant effect.5. The S + C sheep had a lower proportion of acetic acid, a greater proportion of propionic and butyric acids and greater development of the rumen papillae than the P animals.6. With the lambs there were no significant differences in rumen characteristics caused by grasses but the addition of white clover caused a greater live weight and a reduction in the weight of the rumen contents.7. These results are discussed in relation to present knowledge of ruminant metabolism.
1. Two trials are described in which the live weights of sheep grazing four different pastures were compared. The four pastures comprised perennial rye-grass (P), perennial rye-grass plus white clover (P + C), short-rotation rye-grass (S), short-rotation rye-grass plus white clover (S + C).2. Large and highly significant differences existed between the mean live weight of the sheep on the various pastures in each trial. Thus the P sheep had a mean live weight of 107 and 102 lb. in trials I and II, respectively, at the end of each investigation, the P + C sheep 123 and 122 lb., the S sheep 125 and 126 lb., and the S + C sheep 140 and 137 lb.3. The differences in live-weight growth on the four pastures contain two major effects; an effect due to the difference between P and S and an effect which can be attributed to the presence of white clover in the pasture treatment.
The only serious limitations of field growth studies are due to the erratic nature of the curves caused by short-term weather variations and the less apparent deviations caused by secular changes. The method of constant-fitting is applied, via a suitable mathematical model and experimental design, to separate growth and weather effects. A detailed account of the analysis is given, using a trial conducted as a test of the technique as an example, and the future possibilities of the technique in field growth studies are discussed.
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