14 CIRCULAR 870, U. S. DEPARTMENT OF AGRICULTURE 



With the midspring surge in plant growth, cattle become more selective. 

 Many of the forbs (broadleaved herbaceous plants) are discriminated 

 against after they flower and are no longer good forage plants. Of the 

 species selected by cattle, soft chess and the late-growing species of 

 broadleaf filaree are the most abundant and in most years provide the 

 bulk of the forage. Seed heads of soft chess, which mature in late spring, 

 are especially sought out in years when heavy heads are produced. The 

 annual grasses and perennial rushes on bottom lands are heavily grazed. 

 The clovers, which make most growth in April or early May, are greedily 

 taken wherever they occur, and in "good clover years" furnish a large 

 part of the spring forage eaten by cattle. During this time of rapid 

 growth, there is an abundance of green vegetation in several stages of 

 development, from full leaf to mature fruit. The forage selected by cattle 

 is well balanced nutritionally, and the most rapid gains of cattle are made 

 at this time of year. Gains of yearling heifers that had not been supple- 

 mented during the winter usually ranged from 2 to 2J^ pounds per day. 



After the herbaceous vegetation starts to dry, cattle can still find an 

 adequate amount of green forage for several weeks. Early maturing 

 species start drying on south slopes by the middle of April in most years. 

 In years of low rainfall drying will start in March, or even as early as 

 February, and the south slopes will have a mottled yellowish-green 

 appearance by the first of April. But the bulk of the herbage does not 

 dry until temperatures rise sharply and the upper soil dries. Then most 

 of the herbage may dry within a few days. This rapid drying usually 

 occurs early in May, but may occur during the last half of April in years 

 of limited late spring precipitation, as in 1939, 1946, and 1947. 



Cattle become quite selective in their search for green vegetation at 

 this stage of the spring period. Grazing is concentrated on soft chess, 

 filaree, and littlehead clover on the lower slopes and on whitetip clover, 

 toad rush, grasses, and perennial rushes in the drainage bottoms. Cattle 

 also make considerable use of the green plants under trees; and of the 

 scattered green plants such as late-flowering godetias, summer-growing 

 Spanish-clover, and yellow-tarweed. By such selection cattle can obtain 

 an adequate amount of nutritious green forage for 2 to 6 weeks after the 

 bulk of the range herbage has dried. 



In June the cattle are usually forced to graze largely on dry herbage. 

 The crude protein content in their diet drops below the level considered 

 necessary for maintenance of mature cattle. This may occur in May — 

 as in 1939, 1944, 1946, and 1947 — when the supply of late growing species 

 is limited by light total annual or late-spring rainfall. In years of heavy 

 annual and late-spring rainfall (1935 and 1938), adequate green forage 

 is available until late in June. The yearling heifers continued to gain in 

 weight after they were eating considerable dry herbage, but the rate of 

 gain dropped rapidly during June. 



DEFICIENT DRY FORAGE IN SUMMER AND FALL 



Cattle are forced to graze almost entirely on dry forage for about 5 

 months during the summer-fall period (fig. 7). Most of the forage is 

 from dry annual grasses. These provide a roughage high in carbohydrates, 

 but they usually contain less than 5 percent crude protein (1, 3). A 

 supplemental feed is needed to supply protein. Heifer calves weaned in 



