Date of Award:

1978

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Advisor/Chair:

John C. Malechek

Abstract

This study examined the nutritional responses of mule deer during winter on range subjected to a system of spring livestock grazing. The specific purposes were 1) to determine the quality (crude protein, digestible energy, and digestibility) of diets consumed by mule deer in winter on ranges grazed and ungrazed by sheep in spring, 2) to determine the level of forage intake, as determined by the external indicator chromic oxide, for deer under the same grazing regimes, 3) to compare forage intake estimates determined by the external indicator (chromic oxide) with results obtained by ocular estimation, and 4) to determine the forage intake level and quality consumed by fawns, adult does, and yearling male castrates used as experimental subjects during one season of the study.

The study was conducted within the framework of a completely random experimental design with two treatments. Variables noted for each unit observed included treatment (previously grazed and not grazed by sheep), season (early-winter versus late-winter), weeks within season (four weeks per season), and sex-age class of animal (fawns, does, castrates). The study site , located at Hardware Ranch, Cache County, Utah, was a shrub:grass:forb community with sagebrush and bitterbrush as co-dominants.

Two adjacent 2.4 hectare pastures were fenced. A sheep grazing treatment of 150 sheep days per hectare was applied in late May, 1974 and again in late May, 1975 to one pasture. Hand-reared mule deer were placed in each pasture at a stocking rate of about 100 deer days per hectare for three six-week seasons, two beginning in early November 1974 and 1975, and the other beginning near the middle of March, 1975. Artificial diets were carefully formulated for analyses of the forage quality indices. These formulations were based on the determined botanical composition of diets consumed by the mule deer. Forage intake was determined for two seasons by use of the external indicator method utilizing chromic oxide and these values derived were compared to intake levels determined by an ocular estimation method.

No treatment differences existed for forage quality across the three seasons of this study. Mean values for the three qualitative parameters evaluated were: crude protein content, 9.9 percent; digestible energy content, 2.2 kcals/g forage consumed; and dry matter digestibility, 45.5 percent. There were no treatment differences in the level of forage intake, as determined by the external indicator, across two seasons of this study. Mean intake level was 38.1 g/kg body weight per day. No treatment differences existed for the ocular estimation method of determining forage intake and this method was judged to be inferior to the external indicator method of determining forage intake.

Few temporal changes between treatments occurred in forage quality and quantity during the early-winter seasons. Some t emporal differences between treatments did exist for forage quality and quantity during the late weeks of the late-winter 1975 season. Deer displayed a marked shift from browse to herbaceous plant material during spring green-up. Deer on the pasture previously grazed by sheep began this shift about one week earlier than those deer on the pasture not grazed by sheep.

Interpretation of the results of the forage quality and forage quantity evaluations suggest that deer on the sheep- grazed treatment deferred use of available browse plants and consumed more herbaceous plant material. Therefore, by shortening the length of time that over-wintering deer are dependent upon a browse-dominated diet of lower palatability, lowered quality, and lowered intake, the animals should survive the winter in better physical condition.

Thus, this study has shown that sheep grazing of mule deer winter range caused no detriment to the nutritional well-being and may indeed benefit deer to a small degree, particularly at the time of spring green-up. This suggests that a greater animal production per unit area of rangeland can be realized through common use grazing.

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