In an earlier newsletter article, I wrote about the concern of human infection with the protozoal parasite, Cryptosporidium parvum (C. parvum).There is a growing concern among water districts and state and federal regulators regarding the potential for non-point source C. parvum contamination of surface water from rangeland cattle.

I wrote this article following a study in 1995 of 38 cow herds from across California, including 4 herds in Santa Barbara County. Forty to sixty percent appeared to be infected with C. parvum. Almost all infected cattle were limited to calves under 5 months of age. How did these calves become infected? At that time it was thought the herd itself was the reservoir of infection since replacement heifers and cows are typically negative on fecal examination.

This suggested that there could be one or more environmental reservoirs for this pathogen of calves on California rangeland. Another study was conducted to determine if one or more species of wildlife could serve as a C. parvum source of infection for rangeland beef calves.

Working with dr. Rob Atwill, Extension Environmental Animal Health Specialist, three cow-calf herds and co-habitating wildlife were monitored for C. parvum infection. These herds were located in 1) Santa Barbara County, 2) at the Sierra Foothill Research & Extension Center in Yuba County, and 3) at the San Joaquin Experiment Range in Madera County.

Calves at all three study sites became infected and shed C. parvum oocysts during the winter and spring of 1996-97. In general, shedding stopped by late spring, except for a prolonged period seen at the site in Yuba County. The pattern of C. parvum shedding by calves was consistent with the 1995 study.

Also found at these sites were one or more species of rangeland wildlife shedding Cryptosporidium oocysts either prior to calving or simultaneous with calving. Of the various wildlife species that we tested, all isolations were from ground squirrels except for one sample from a carnivore, most likely a coyote. In contrast to wildlife, none of the cows which were in intimate contact with the calves, either prior to or after calving, were found to be positive for C. parvum.

While this study does not prove that co-habitating wildlife are the primary source of infection for beef calves, it does suggest the possibility that wildlife plays a role in maintaining Cryptosporidium on a watershed year after year and in infecting the annual calf crop.

This would also suggest that there is one or more environmental reservoirs for this pathogen on California rangeland. It may be that beef calves born on rangelands each year serve as amplification hosts for this parasite, but that the initiating reservoir of infection is one or more species of co-habitating wildlife. If the primary reservoir host of C. parvum for beef calves can be identified, the primary mechanism for how this pathogen is maintained on a watershed year-to-year and how it is amplified to become a threat to water quality and human health will also be identified.

Dr. Atwill is working on developing DNA fingerprinting tools for the differentiation of species of Cryptosporidium and to compare C. parvum fingerprints isolated from different sources. Once these molecular tools are developed, he will attempt to confirm the relationship of the species of Cryptosporidium isolated from wildlife with those isolated from calves.

Dr. John Maas, Extension Veterinarian at UC Davis, provides farm advisors information on specific topics related to beef cattle health, and I try to pass it on to you. The following article deals with a subject that affects many producers in this area of the state - trace mineral nutrition. This article takes a statewide perspective, and while I have not found Iodine or Selenium deficiency to be a problem here, Copper deficiency certainly can be. You may have cattle in other areas of the state also, so the information about the other two minerals may be of interest.

One of the areas commonly found to limit health and production in California is trace mineral nutrition. Trace minerals are those mineral nutrients that cattle need in very small or trace amounts - usually less than one one-hundredth of an ounce per day. Small amounts of these minerals are very necessary (or essential) to cattle health and production. We usually talk in terms of parts per million (ppm) of the diet or in milligrams (mg) per day.

If not supplied in the diet or in supplements, significant losses can occur. While only trace amounts are needed, deficiencies can be devastating to cattle.

COPPER
Symptoms: Common symptoms of copper deficiency in cattle include chronic diarrhea, weight loss, poor weight gains in calves, sudden death in adult cattle, swollen joints, broken bones (ribs and legs), light hair coat (gray in Angus, yellow in Herefords), and increased susceptibility to disease.

Diagnosis: The best tissue for diagnosis of copper deficiency in cattle is the liver. In the last two years, many veterinarians in California have attended advanced training sessions on liver biopsy techniques in cattle. University of California Extension veterinarians have designed a new liver biopsy instrument that is very practical for chuteside use.

The use of serum (separated blood) samples can also be of value in screening herds for severe copper deficiency. If symptoms compatible with copper deficiency are observed, consult your veterinarian and have he/she take the appropriate samples to determine the copper status of the herd. DO NOT start increased copper supplementation without an accurate diagnosis and a plan for follow-up testing. Copper has the smallest margin of error of any of the trace minerals. Currently, there are several dairy herds in California that have been oversupplemented with copper, and losses have been severe.

Treatment and Prevention: Many veterinarians in California prescribe copper injections (copper glycinate) for their clients. These products are given subcutaneously and provide adequate supplementation for 6 to 12 months. Caution must be used when these products are given, as serious side effects can occur. Follow your veterinarian's advice carefully when using copper injections to avoid problems. Also available are slow release boluses that supply copper to cattle for a full 12 months. These products are now available through your veterinarian and come in two dosage sizes, 12.5 gram and 25 gram boluses. Copper can also be added to molasses mixtures, loose salt mixes and a variety of other supplements. Avoid relying on salt blocks to provide adequate copper supplementation.

IODINE
Symptoms: Goiter, weak calves, and an increased number of cases of foot rot, lumpy jaw, and woody tongue in cattle.

Diagnosis: Serum samples can be useful for diagnosis of iodine deficiency; however, most of the time the diagnosis is made on the basis of symptoms.

Treatment and Prevention: Iodine is usually added to supplements that contain other materials (trace minerals, energy sources {molasses}, protein supplements). Stable iodine compounds can be added to loose salt mineral mixes. Salt blocks are not a reliable source of iodine supplementation. The iodine compounds in the blocks are much more soluble (dissolve in water more readily) than the salt (sodium chloride) and move through to the bottom of the block before the cattle can "catch up to them" and ingest the iodine. The same problem occurs to a lesser degree with copper compounds and selenium compounds in salt blocks. Dr. Mass recommends: "do not rely on salt blocks" to supply any meaningful amounts of trace minerals.

SELENIUM
Symptoms: Common symptoms of selenium deficiency include white muscle disease in calves, abortions, infertility, retained placenta (afterbirth), chronic diarrhea, weight loss, poor weight gains (ill thrift), and decreased immune function (increased susceptibility to disease, decreased response to vaccines).

Diagnosis: Diagnosis is very simple in California with the current diagnostic laboratory system. A blood sample submitted by your veterinarian to the diagnostic laboratory will quickly and cheaply determine the selenium status of the herd or animal in question.

Treatment and Prevention: Selenium injections (Mu-Se®, Bo-Se®) have been used for some time to treat white muscle disease or other selenium deficiency syndromes. The injections provide selenium supplementation very rapidly and are very effective for therapy. However, they provide only partial supplementation for 28 to 45 days. Thus, if injectable selenium is the sole means of supplementation, injections would have to be repeated 8 to 12 times per year. Selenium added to salt mineral mixes at concentrations up to 120 ppm can be very effective at maintaining adequate selenium in cattle. Consumption of the salt mixes at about one ounce per head per day will provide 3 mg selenium per day, which is the legal limit. Selenium can also be added to molasses products and other supplements. Again, the maximum legal amount is 3 mg selenium per animal per day. As with iodine and copper, Dr. Mass does not recommend salt blocks as a reliable means of supplementing selenium or other trace minerals to cattle. Selenium boluses, that release no more than 3 mg per day, are currently legal; however no products are currently available. Selenium boluses or other forms of selenium supplementation may become available over the next few years.

Your veterinarian can be a great source of information regarding trace mineral nutrition for your beef herd. The new diagnostic methods, new products, and new information from research trials are very helpful for making decisions regarding these trace minerals that are often lacking in California.