Mineral Requirements

We know quite definitely now the phosphorus requirements of swine, beef cattle, and sheep. Of the more recent studies, those of W. M. Beeson and others at the Idaho Agricultural Experiment Station emphasize that phosphorus deficiency decreases the utilization of feed of fattening lambs to a greater extent than it does the appetite. The minimum phosphorus requirement is placed at 2.4 grams of phosphorus per 100 pounds of body weight. This is somewhat higher than the figure for fattening steers, namely 2.0 grams, as given by the Idaho scientists. The phosphorus requirements, as stated in tables of the National Research Council, are adjusted to different classes and weights of animals. They also provide about a 25-percent margin of safety for beef cattle and sheep. The actual values, expressed on the basis of percentage of phosphorus of ration of 90-percent dry-matter content, are higher than the 0.13 figure given by W. H. Black, and others, in the 1939 Yearbook. Adding a 25-percent margin of safety to this 0.13 value gives a figure that is generally within the range of the recommendations of the National Research Council.

In areas where the range grasses are low in phosphorus, as in southern Texas, the low calf crops and retarded growth of the young stock can be remedied by supplying about 6.5 grams of phosphorus a day to dry cows and heifers and 14 grams to lactating cows, according to Black and his Colleagues. Bonemeal and disodium phosphate were equally effective in preventing aphosphorosis and just as beneficial as a complex mineral mixture containing salts of iron, manganese, copper, cobalt, zinc, and boron in increasing the calf crop and the weaning weights of calves.

During the war the problem of meeting the national requirements for additional sources of phosphorus suited for feeding was met largely by working out methods for manufacturing defluorinated phosphates. In one procedure, fertilizer grade of superphosphate is utilized as the starting material. In another, rock phosphate is used. In both cases fluorine, the harmful element that is usually present at toxic levels in the starting materials, is largely driven off by heating the phosphates to high temperatures. Feeding tests on the defluorinated superphosphates and rock phosphates have been made by a number of investigators. We discovered some variation in utilization by animals of the phosphorus in the products produced in different manufacturing plants, much of it traceable to the temperatures of defluorination and the kind of phosphate compound formed, whether of the ortho, meta, or pyro type. A temperature of approximately 1,000° C., for example, was found to produce a defluorinated superphosphate superior to those made at lower temperatures and about as good as bonemeal.

The search for phosphates has served to reemphasize the dangers of fluorine in livestock nutrition and prompted H. H. Mitchell, working under the auspices of the National Research Council, to review the existing information in order to express the safe limits at which the element may be consumed. These permissible levels may be stated as 0.003 percent of fluorine in the total dry ration of cattle, sheep, and swine and .015 percent for poultry.

A further contribution by H. R. Seddon on the effects of fluorine in the water supply of sheep indicates that a content of 12 parts per million gradually leads to the characteristic mottling and irregular wear of the teeth. Under such conditions of borderline fluorine intake, the symptoms do not appear until the third and fourth years of life. Other effects of fluorine in the nutrition of -sheep have been studied at the Indiana Agricultural Experiment Station by C. L. Shrewsbury and others. They fed breeding ewes and growing lambs on rations containing rock phosphate that supplied different levels of fluorine. Approximately 3 milligrams a pound of body weight was enough to retard the growth of lambs and to affect the metabolism of the thyroid gland, especially the iodine content.

The place of copper, cobalt, manganese, and other trace elements in the nutrition of livestock was reviewed in the 1942 Yearbook. Since then, we have obtained more evidence on their importance, and some new findings on their exact method of functioning. Both copper and cobalt are associated with iron in the building of hemoglobin and of red blood cells. Thus far, reports on the occurrence of sway-back disease, a form of anemia in sheep due to copper deficiency, have been largely confined to Great Britain and Australia. Mineral deficiency in animals can usually be traced to inadequate levels in the soil and the crops produced on the particular soil. That such is not necessarily always the case with sway-back disease is discussed by G. D. Shearer and E. I. McDougall, who point out that sheep in certain districts in England respond to copper therapy even though the grass the animals ate was of normal copper content. The possibility that some other element interferes with copper metabolism has been recognized; both lead and molybdenum have been mentioned. Considerable progress, however, has been made in controlling the disease by adding copper to the soil or feeding it directly.

Instances of cobalt deficiency, on the other hand, have been shown in several widely separated areas in this country and elsewhere. The occurrence of cobalt deficiency in cattle was observed some years ago in the Southeastern States, especially Florida. Later it was diagnosed in the Grand Traverse Region in Michigan, where the condition had been known for many years as "lake shore disease." More recently, unthrifty and emaciated cattle in Door County and nearby localities in northeastern Wisconsin have responded to treatment with 3 to 6 milligrams of cobalt a day. This amount has been supplied by adding to the grain mixture 1 percent of salt containing in each 100 pounds 1 ounce of cobalt sulfate, or by feeding 1 teaspoonful of a water solution containing 1 ounce of cobalt sulfate or cobalt chloride per gallon. The hemoglobin values on the blood and the appetite and gains of the cattle have improved markedly. Poor condition in sheep flocks also has been traced to cobalt deficiency. The deficiency exists in an extensive area in New Hampshire. There have been suggestions of its presence in sheep in Illinois, New York, and western Canada. Usually, the soil and the forage grown on it are suspected, or known to be deficient in cobalt. In New York, unthriftiness in fattening lambs was corrected by giving 4 milligrams of cobalt in a water solution of cobaltous chloride twice a week.

Technicians have established the needs of poultry and the laboratory rat for manganese, but the evidence on other farm animals is not so clear. What seemed like good proof of the needs of swine for this element has since been questioned by S. R. Johnson, of the Arkansas station, who has shown that pigs grow at a normal rate on a ration with less than 0.5 part per million and sows reproduce normally on 6 parts per million and even less. On the basis of this work, it appears that if manganese is essential for swine the requirement must be very low.

A troublesome disorder in sheep and cattle that seems to be associated in some way with mineral metabolism is that of urinary calculi formation. Investigations of feeding steers in west Texas have shown calculi involvement when the ration was made up of grain sorghum and sorgo products, along with cottonseed meal. The disorder is accentuated by increasing the magnesium content of the diet and relieved somewhat by using bonemeal, a calcium and phosphorus supplement, instead of limestone, which supplies only calcium.

Vitamin A therapy has been of no avail, but replacement of mild grain with corn in the concentrate feed has largely eliminated calculi. I. E. Newsom, J. W. Tobiska, and H. B. Osland, at Fort Collins, Colorado, studied the effects of different rations on calculi formation in lambs. It appeared that alfalfa and beet tops were protective feeds, but cane fodder, bran, and white corn seemed to favor calculi formation. In Australia, W. I. B. Beveridge has suggested that consideration be given to improper ratios of calcium, magnesium, and phosphorus, to vitamin A deficiency, to low water intake, and to highly alkaline urines as possible factors favoring calculi formation. Some of these are not in agreement with work done in this country, so the exact cause and the remedy, as far as feeding methods are concerned, still remain in doubt.