Production responses following strategic parasite control in a beef cow/calf herd.

Strategic parasite control has been reported to improve performance in a beef cow/calf herd that does not demonstrate clinical parasitism. This study was conducted to determine if strategic anthelmintic treatment at turnout and at midsummer would improve growth and reproduction. Two cow/calf groups of similar composition were grazed on separate, but equivalent pastures in the spring, and at midsummer, they were moved to new pastures. The treated group was given fenbendazole at tumout (cows) and at midsummer (cows and calves). The control group was not treated. The study was repeated in the following year. Across both years of the study, parasite egg counts were substantially reduced in both the treated cows (P < 0.005) and treated calves (P < 0.0001). The calves in the treated group significantly (P < 0.0001) outgained the control calves in both years of the study by 19.3 kg and 13.2 kg, respectively. Average daily gain (ADG) after adjusting for birth weight and birth date for treated calves was 0.13 kg greater than for control calves (0.83 vs 0.70) for the 2-year study (P < 0.0001) There was also a significant (P = 0.0357) increase in the reproductive performance of the cows. The pregnancy rate averaged across years was 94% for the treated cows compared to 82% for the control animals.

Epizootiology of helminth parasitism in a beef cow/calf herd in Minnesota.

To test the effect of a parasite control program for cattle, 2 groups of similar composition were grazed on separate, but equivalent, improved pastures. Cattle in 1 group were treated with fenbendazole at 5.0 mg/kg of body weight at the time they were turned out on pasture in the spring and again at midsummer, when the cattle were moved to a new pasture. The control group was not treated. Parasite egg counts were significantly (P less than 0.04) lower in the treated group. Trichostrongyle-type eggs were the most prevalent throughout the year, except in the month of May, when Strongyloides papillosus eggs were predominant. The number of worms recovered from tracer calves was lower for those on pastures where the treated group grazed than for those on the control group's pasture. The most consistently recovered parasite was Ostertagia ostertagi, and hypobiosis was observed.

Detection of bovine leukemia virus in cattle by the polymerase chain reaction.

Bovine leukemia virus (BLV) is widely distributed in U.S. cattle herds. It infects B lymphocytes and causes neoplastic disease in 5-10% of infected animals. Direct economic losses are incurred as a result of death, reduced milk production and condemnation at slaughter. Thus the identification of cattle infected with BLV is of significant concern to the U.S. cattle industry. For this reason, polymerase chain reaction (PCR) amplification was used to examine seropositive and seronegative cattle for the presence of BLV DNA in peripheral blood mononuclear cells. Using an amplification protocol able to detect 1 viral genome in 100,000 cells, BLV was not detected in 7 seronegative cattle in an infected herd. BLV sequences were detected in 13 of 18 seropositive animals with various levels of infection as determined by in vitro lymphocyte culture and electron microscopy. An active infection was demonstrated in one animal, based on the presence of viral RNA. These findings indicate that PCR is a sensitive method for the detection of BLV in cattle and provides new information regarding the dynamics of the infection.

Failure to demonstrate transmission of enzootic bovine leukemia virus infection from cows to sheep by use of common injection needles.

Four bovine leukemia virus (BLV)-seropositive and 2 BLV-seronegative cows were used as donors in a study to provide evidence whether IM injection with common needles is a means of spreading bovine leukemia. Sheep were used as recipients. Of the 4 BLV-seropositive cows, 2 had high virus expression (VE; 43% and 28% of their lymphocyte thin sections had associated BLV-particles), whereas the other 2 cows did not have observed VE. After each of the 4 cows was given an injection of a 5-antigen Leptospira bacterin, a BLV-seronegative sheep was immediately given an injection of the same bacterin with the same needle. None of these sheep seroconverted, nor did either of 2 sheep given only the bacterin (with a previously unused needle). Sheep inoculated IM with 0.2 ml of whole blood from both of the cows with high VE and from 1 of the 2 BLV-seropositive cows that did not have observed VE did seroconvert. In contrast, the sheep inoculated with 0.2 ml of blood from the remaining BLV-seropositive (0% VE) cow and from the 2 BLV-seronegative cows remained seronegative. These results were interpreted to indicate that the quantity of infective lymphocytes passed during injection with common needles is too small to induce infection.

In vitro viral expression as a criterion for development of control procedures for enzootic bovine leukosis.

In a university beef herd of 304 cattle in which six died of lymphosarcoma between 1980 and 1984, 77% of the Angus and 26% of the Charolais cattle were determined to be infected with bovine leukemia virus (BLV). Changes in iatrogenic procedures were initiated as early control measures. In vitro viral expression (VE) was used as a criterion to identify cattle for subsequent segregation or culling. This involved determinations of percentages of BLV-associated lymphocyte profiles among thin-sectioned Ficoll-Paque-isolated blood lymphocytes that were processed into plastic after culture for 48 h. Cattle retained until completion of nutritional studies or as breeding stock were separated into two groups. The BLV-seronegative cattle, BLV-seropositive cattle with 0% VE, and BLV-seropositive cattle with 1% to 4% VE were placed in group 1. Seropositive cattle with greater than or equal to 5% VE were placed in group 2. In 1985, evaluation of in vitro VE in 108 mature BLV-seropositive cattle retained for breeding revealed 36 (33%) had no observable VE. In 1986, 58 of 108 cattle were available to be reexamined, and 21 (36%) had 0% VE in both years. The VE expression values for individual cattle were generally comparable over the 2-year period. Of 48 initial seronegative breeding stock housed in group 1 with BLV-seropositive cattle with low or no VE, 21 (44%) seroconverted during 1985 to 1986. A positive correlation of 0.585 was found between VE and age-related absolute lymphocyte number.

Deposition and early disposition of inhaled 233UO2(NO3)2 and 232UO2(NO3)2 in the rat.

Little information exists on the metabolism and potential health effects of 233U and 232U, high-specific-activity U isotopes associated with Th breeder systems. This paper describes the distribution and retention of the two isotopes following inhalation of uranyl nitrate, a simulated process solution. The lungs of rats exposed to 233UO2(NO3)2 and 232UO2(NO3)2 aerosols contained from 7 to 23% of the total amount of U retained in the rat after a 30-min inhalation exposure. Uranium was translocated rapidly from the lung and was retained mainly in skeleton, kidney and liver. Amounts equivalent to from one-quarter to one-half the initial lung burden (ILB) of U were excreted in urine the first day after inhalation. Radiation dose estimates based on 233U and 232U retention kinetics indicate that lung and skeleton would be the target organs for delayed radiation effects.

Bovine enteric colibacillosis.

In this article, the authors discusses procedures used to determine enteropathogenic strains of Escherichia coli, the history of the development of prophylactic procedures, including cow vaccination and specific monoclonal antibody, and other preventative measures with as proper management, nutrition, and sanitation.

Subclinical mastitis of beef cows.

Two beef cow herds were investigated to determine the prevalence of subclinical mastitis and to determine whether it contributed to decreased weaning weight of calves nursed by affected cows. Quarter samples obtained about 30 days after calving were evaluated by the California mastitis test and by direct microscopic cell count. In 1 herd, a 92-cow confinement operation, 17 quarters of 12 cows were infected with Staphylococcus aureus, Streptococcus sp other than agalactiae, or Klebsiella sp. Mean 205-day adjusted weights were 203.9 kg and 218.2 kg for calves nursed by infected vs noninfected cows. In the other herd, a 75-cow range-pasture operation, 8 quarters of 8 cows were infected, all with S aureus. Mean 205-day adjusted weights were 162.5 kg and 174.6 kg for calves nursed by infected vs noninfected cows.

Immunologic effects of experimental iodine toxicosis in young cattle.

A study was designed to evaluate effects of 4 dosage levels (0, 50, 250, or 1,250 mg) of daily iodine supplementation on cell-mediated and humoral immune mechanisms in 40 calves, 10 per group, for a 6-month period. Immune and inflammatory responses were measured by titers to brucella, leptospira, and infectious bovine rhinotracheitis virus vaccinations, by stimulation of lymphocyte mitoses with poke-weed, phytohemagglutinin (PHA), and conconavalin A mitogens, by intradermal PHA responses, by in vitro phagocytosis of Candida albicans by WBC, and by total WBC counts. Calves given 1,250 mg of iodine daily had significant (P = less than 0.05) decreases in persistence of antibody titers to brucella and leptospira organisms, in lymphocyte mitotic activity, in PHA injection induration, in phagocytosis by WBC, and in WBC counts. Calves fed iodine at 50 or 250 mg daily tended to have decreased leptospiral titers, lymphocyte mitoses, PHA injection induration, and in vitro phagocytosis by WBC compared with responses of controls. Seemingly, large amounts of dietary iodine interfere with titer maintenance to some antigens, with lymphocyte DNA synthesis, and with phagocytic activity of WBC.

Tetany associated with magnesium deficiency in suckling beef calves.

Sudden death losses occurred in 4-month-old beef calves with clinical signs of muscular dysfunction, including tetanic spasms. Gross lesions were not diagnostic. Microscopic lesions consisted of deposition of calcium salts in the elastic fibers of the arteries in the heart, lungs, and spleen and in the trabeculae of the spleen. Focal areas of interstitial nephritis were characterized by infiltration of lymphocytes and plasma cells. Samples of hay and silage that the cattle were consuming were low in magnesium. Calves with spasms responded to magnesium salts given intravenously, and losses ceased after a magnesium-containing supplement was fed free choice to the calves and cows.