gestibility of nutrients in clipped plants also 
remains high (Mellin et al. 1962). 
In some pasture plants the increase in pro- 
tein percentage in clipped plants is great 
enough and prolonged enough to result in a 
greater total yield of protein in clipped than in 
unclipped plants even though clipping reduces 
total herbage yield. Jameson (1963) concluded 
that “. .. cutting treatments are less detri- 
mental to protein yields than to dry matter 
yields. If the cutting treatment does not have a 
severe effect on dry matter, protein yield is 
often increased.” 
On arid ranges clipping may not increase 
total protein content of many plants if soil 
moisture is limited. Aldcus (1930) found that 
native prairiegrasses clipped at 2-week inter- 
vals had lower dry-matter production but 
higher protein content than unclipped plants. 
This decrease in yield of herbage produced a 
decrease in actual quantity of protein despite 
the higher percentage of protein. Blaisdell et 
al. (1952) found that despite decreases in per- 
centages of protein and phosphorus in un- 
clipped bluebunch wheatgrass and arrowleaf 
balsamroot plants as the season advanced, total 
quantities of these constituents increased in 
the plants because of the relatively large in- 
crease in the total amount of herbage. 
In evaluating how changes caused by graz- 
ing affect the diet of animals, digestibility as 
well as amount of protein must also be consid- 
ered because digestibility of protein generally 
decreases as plants mature (Blaser 1964; Cook 
et al. 1961; Staples et al. 1951; and many oth- 
ers). The class of grazing animal must also be 
considered. Some studies have shown that 
sheep digest protein more efficiently than cattle 
(Cook and Harris 1968; and Forbes 1950). 
Response of shrubs to browsing or clipping 
is similar to that of herbaceous plants. Remov- 
al of leaves and twigs during the growing 
season generally stimulates new twig growth 
that is higher in moisture content, phosphorus, 
protein, calcium, and ash and lower in crude 
fiber than undisturbed twigs (Reynolds and 
Sampson 1943). However, if plants are browsed 
too closely, they may eventually die (Leopold 
1950; Reynolds and Sampson 1948). 
However, the higher protein content in 
young twigs does not necessarily mean that 
young twigs furnish more protein to the ani- 
mal. According to Bissel and Strong (1955) the 
high moisture content of young twigs results in 
less protein and other energy-containing mater- 
ials per unit of material eaten than when plants 
are eaten later in the season or during the dor- 
mant period. However, the digestibility and the 
percentage and total amount of protein during 
the two periods would have to be known to de- 
42 
termine the effect of the differences in protein 
content on the nutrition of the animal. 
Effect of Range Condition and 
Nutrition of Livestock 
Range managers often assume that a decline 
in range condition results in a decline in nutri- 
tive value of the available forage plants. In 
some cases this decline does occur. Esplin et al. 
(1937) found that annuals and other species 
that invaded overgrazed desert ranges in Utah 
were less palatable, less nutritious, and less de- 
pendable as a source of forage than the native 
climax plants. However, in another study in 
Utah, Goebel and Cook (1960) found that good 
forage species on desert ranges were higher in 
cellulose and other carbohydrates but lower in 
ether extract, protein, calcium, and phosphorus 
than poor species. They concluded that im- 
provement of range condition will not always 
result in a higher nutrient content of the for- 
age. 
In other studies on desert ranges in Utah, 
Cook et al. (1962, 1965) have shown that the 
overall nutrient content of herbage on ranges 
depends on the species present. If poor ranges 
have a predominance of shrubs, the diet of 
sheep will be high in protein, ash, lignin, and 
ether extract. If palatable grasses predominate 
on any range, diets will be high in cellulose, 
other carbohydrates, and metabolizable energy. 
Even if chemical composition of plants on 
good and poor ranges does not greatly differ, 
herbage production, and thus total nutrient 
production, usually are lower on poor ranges. 
In this situation, livestock are often forced to 
consume more of the less nutritious and often 
less digestible portions of plants (stems, leaf 
bases, etc.) than they do on good ranges (Cook 
et al. 1954, 1962; Piper et al. 1959). Cook et al. 
(1953) found that as degree of utilization in- 
creased, lignin increased and the amount and 
digestibility of desirable nutrients (protein, 
phosphorus, and cellulose) and the gross en- 
ergy decreased. 
Effect of Selectivity on Diet 
Animals are highly selective in regard to the 
species and parts of plants they eat; therefore, 
the botanical composition of a range or pasture 
alone is not a good indication of diet. For ex- 
ample, on California annual range, sheep fitted 
with esophageal fistulas consistently consumed 
forage that was higher in protein and lower in 
crude fiber than samples clipped from the same 
pasture (Weir and Torell 1959). The same re- 
lationship was found for the diet of steers by 
Smith et al. (1959) and by Hardison et al. 
(1954). 
Even chemical analysis of whole plants 
