In most cases this procedure will keep lambs from getting an injurious load of parasites, but as an additional precaution the flock should be treated with a full therapeutic dose whenever it appears that the medicated salt is not holding the parasite in check. Also, the breeder flock should be treated again with the full dose early in the winter to condition ewes for the cold months. To show how extensively sheepmen have adopted the practice: In 1939—just after phenothiazine was shown to have value as an anthelmintic—only 900 pounds was used; in 1944, total consumption was nearly 3,000,000 pounds.

This type of covered trough will protect the phenothiazine and salt mixture from the weather.

The life cycle of the common liver fluke: A. An adult fluke about natural size. While in the liver of an animal it produces many eggs that are expelled in the droppings; B. An egg, enlarged about 100 times. It develops in wet places of pastures; C. A free-swimming larva (enlarged about 100 times) that comes from each egg; this larva is attracted to and penetrates certain aquatic snails, D. After development in the snail, a new type of larva with a tail, E, (enlarged about 30 times) emerges and settles on the grass, F, and becomes encysted there. Cattle eat the contaminated grass and the life cycle starts all over again.

Liver Flukes

Liver flukes are the most deadly of the trematodes that affect livestock. Cattle, sheep, goats, and wild ruminants are particularly susceptible, and acquire the parasites while grazing on low, wet pastures that harbor certain species of fresh-water snails that serve as intermediate hosts. The flukes, by their presence or the lesions they produce, make the livers unfit for food, bring about unthriftiness and loss of flesh in all domestic ruminants, and cause death, especially of sheep. European investigators say also the flukes impair reproductive capacity in cattle, reduce milk flow, and cause other damage.

Of these losses, only those resulting from the condemnation of livers for food and for medicinal use are well known. The figures obtained from meat packers operating under Government inspection show that the annual average infection of cattle with liver flukes in the Gulf Coast area is 37.5 percent in adult cattle and 6 percent in calves. The loss of beef and calf livers must be enormous, because flukes in cattle are prevalent in parts of the South, the Southwest, the Rocky Mountain States, and the Pacific Coast States. It is estimated that nearly 90,000 pounds of beef and calf livers are lost annually in the Gulf Coast area. The loss of beef livers in 1945 amounted to more than a million dollars.

During the war we prepared a medication based on hexachlorethane, a solid that is related chemically to carbon tetrachloride and tetrachlorethylene, drugs developed in the Department about 25 years ago for removing internal parasites from various classes of farm animals. Because hexachlorethane is insoluble in water and can be dissolved only in solvents that are more or less injurious to cattle, sheep, and goats, we combined it with bentonite, a finely powdered clay, to form an aqueous anthelmintic drench. It was determined that, in proper combination, hexachlorethane and bentonite form a stable suspension in water, suitable for administration with a dose syringe.

The ingredients are mixed thus: 1 pound of finely ground hexachlorethane, 1.5 ounces of bentonite, and 25 ounces of water. The addition of a quarter-teaspoon of white flour facilitates the mixing, which is done either with a power-driven apparatus of sufficient speed to insure even distribution or by passing the freshly prepared mixture twice through a 20-mesh screen. A dose of 6.5 ounces for cattle and half that amount for calves more than 3 months old is administered. Younger calves need not be treated. The treatment is especially effective in removing about 70 percent of the adult flukes and about half of the immature flukes.

The treatment was tested successfully in sheep and goats, but in a few instances cattle and sheep tolerated the drug rather poorly, and some died. Much work remains to be done, therefore, to perfect the treatment.