Dietary selectivity by steers grazing two types of pasture

Although there is currently much interest in increased concentrate feeding in the production of beef, pastures still remain a major source of nutrients for the growing beef cattle industry. Numerous grazing trials at the Tennessee Experiment Station indicate that there are definite differences in the amount and seasonal distribution of animal gains on different pastures common in this State. There is a need for more information regarding the identification of factors which contribute to the differences in quality among various pastures. Grazing trials must be employed to accurately evaluate the beef-producing potential of pastures. These require a large outlay of land and animals to obtain accurate information, and also require considerable time. It would be desirable to have some more easily obtained measurements which would have a high degree of relationship to animal performance. Tennessee workers have for many years routinely conducted visual appraisals of pastures in connection with steer grazing trials. These appraisals included estimated percentage ground cover and average height of each species, with general considerations of maturity, succulence and other factors. Chemical analyses of hand-clipped samples have often seemingly held little relationship to animal performance. This could have been due to the failure of the clipped samples to duplicate the diet of the grazing animal, since many studies have indicated that cattle exert a considerable degree of selectivity of species and plant parts in a pasture mixture. Recently, ruminal and esophageal fistulated cattle and sheep have been used to obtain estimates of the diets selected by grazing animals. The use of ruminal fistulated animals for this purpose is a laborious and distasteful task that requires emptying and flushing the rumen, allowing the animal to graze, and replacing the original contents after the sample is collected. Much time and labor is required. More recently, the development of improved esophageal fistula surgical techniques and fistula closure devices has led to the adoption of this type of fistula by many researchers working in this area. The objectives of the research reported herein were: 1. To gain information and experience regarding esophageal fistulated animal methodology. 2. To estimate the degree of selective grazing by esophageal fistulated steers grazing fescue-lespedeza and orchardgrass-Ladino clover pasture. 3. To compare certain characteristics of the diets of esophageal fistulated steers grazing these two types of pasture. 4. To determine relationships between characteristics of dietary samples, of clipped samples and of botanical composition of the pasture, and to derive equations for predicting the composition of the grazing animal's diet. 5. To obtain estimates of variation between different observers in making estimations of species composition of pastures.