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To understand how different techniques might affect diet estimates for cattle, the esophageal-fistula and bite-count techniques were compared using trained cattle. For the Texas Coastal Bend, bite-count was not as reliable a technique as the esophageal fistula. These techniques differed in estimation of forage classes and plant species in cattle diets. The esophageal-fistula technique was more accurate however, the bite-count technique may be acceptable if analyses are limited to only those plant species making up >2% of the diet.

Two trials were conducted to compare diet samples collected in the evacuated rumen or through the esophageal fistula. Hypotheses tested were (1) rumen evacuation would not decrease selectivity, (2) being in the rumen during collection would not alter the sample, and (3) both techniques accurately estimated nutritional characteristics of the feed offered. Five steers bifistulated at the esophagus and rumen were used in a grazing and a stall trial. Three collection techniques were used in each trial: rumen collection after evacuation (RC), esophageal collection with the rumen evacuated (ECRE), and esophageal collection with the rumen full (ECRF). Comparison of RC and ECRE assessed the influence of being in the rumen, and ECRE vs ECRF tested selectivity. Hay was sampled before feeding in the stall trial to test hypothesis 3. All samples were analyzed for organic matter (OM), nitrogen (N), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose, and cellulose. In the grazing trial, collection technique affected only ADL (P = 0.05), with ECRE depressed compared to ECRF. Organic matter, N, ADL, and hemicellulose responded (P < 0.05) during the stall trial as follows. Salivary ash contamination depressed OM (P = 0.03) in all collected masticate compared to the feed offered. Rumen collection elevated N (P = 0.04), but esophageal samples and feed were equal. Hemicellulose was depressed slightly (P = 0.01) in all collected masticate. Both techniques elevated ADL (P = 0.001), with RC having a greater effect than ECRF. Both collection techniques should provide satisfactory results in grazing trials if precautions are taken. Comparison across techniques appears appropriate if caution is exercised, particularly concerning N and ADL.

A low cost plug constructed from polyethylene is described which reduces the maintenance problems associated with esophageally fistulated grazing animals. The esophageal fistula offers a practical means of obtaining samples of the diet selected by grazing ruminants. Split rubber plugs (McManus et al. 1962) are commonly used in Australia to close the fistula. Under range conditions this plug pulls out relatively easily when caught in fences, shrubs or as a result of the animal scratching its neck with its rear hooves. In addition, if the animal is grazing dry fibrous forage or browse, the ingesta can become impacted around the plug, completely blocking the esophagus. If not rectified qucikly, morbidity or death can occur from thirst, starvation or loss of saliva. Consequently esophageally fistulated animals need to be inspected at least three times per week which is unsatisfactory, especially if they are located at remote sites. In order to establish esophageal fistulated sheep and goats on trials sites, 180 miles from our research base, I needed an improved plug which would not require regular inspection. This paper describes the construction of such a plug from polyethylene.

An esophageal fistula dilator is described. The tool can he used to exert an even pressure around the tistuln perimeter to stretch a shrunken fistula and allow the successful insertion of a closure device larger in diameter than that of the original fistula. With this instrument the process of enlarging the esophageal fistula is accomplished immediately in a time-saving, efticient manner compared to increasing the diameter of the fistula gradually by periodically increasing the diameter of the closure device.

An esophageal fistula plug was constructed from polyvinyl chloride pipe at a material cost of approximately S3.50. The plug has a plastisol and metal washer and is held together with a hose clamp. The hose clamp is adjusted to exert light pressure on the neck by the washers to reduce scar tissue around the tistula. The size of the plug can be varied by changing the diameter of the pipe allowing it to be used as a fistula dialator. Successful diet sampling with esophageally fistulated animals requires maintenance of an adequate tistula opening. Closure of the fistula because of swelling or accumulation of scar tissue will restrict passage of extrusa from the fistula. Loss of fistula plugs or extended sampling from animals with removable plugs usually results in swelling and closure of the fistula opening (Anderson and Mertz 1982). This makes replacement of the plug difficult and stressful to the animal. The accumulation of scar tissue around the fistula is normal and may limit the usefulness of a fistulated animal. This paper describes an inexpensive removable fistula plug that reduces formation of scar tissue and assists in expanding fistula openings that have closed because of trauma or were not of the desired size following initial surgery.

Highlight: Cattle diets were determined by esophageal fistula and fecal material collection procedures from yearling cattle grazing shortgrass range in northeastern Colorado. Diets were quantified by microhistological procedures from samples collected in June, July, August, and December of 1969; and June, July, and August of 1970. Total grasses occurred significantly less in esophageal samples, while total forbs were significantly lower in fecal samples. Individual grass species did not appear to follow a set pattern of variation from esophageal to fecal sampling; some were greater in fecal samples while others were greater in fistula samples. Forbs occurred at greater percentages in fistula samples, with the exception of burning bush (Kochia scopuriu) in 1969. Correlation and regression analysis revealed little relationship in botanical composition determined on fecal and esophageal samples. However, an importance value ranking revealed esophageal and fecal samples were similar when individual species were ranked from the most common to the least common in the diet.

One of the foremost problems in range and pasture nutrition is making an accurate assessment of the chemical and botanical composition of the diet of grazing livestock. In recent years the esophageal fistula has been used to obtain samples of the forage grazed by ruminants. These studies have been conducted under a wide variety of conditions in at least six countries on four continents. The purpose of this article is to review the development and use of the esophageal fistula and to discuss present problems and practices. The medical literature is replete with references to human and animal esophageal fistulas due to congenital abnormalities, disease, and accidental injury. However, this article is restricted to experimental studies with domestic animals and reviews the literature through mid-1963.

Highlight The effect of saliva on esophageal fisfula samples was minimal. Regression equafions are presented which compare crude protein and crude fiber confenfs of esophageal fisfula samples with those of forage of known composifion. Squeezing esophageal fisfula samples, air drying the solid portion, and treating the liquid portion with phenol will preserve samples where laboratory facilities are not available.