Efficacy evaluations on five chlorhexidine teat dip formulations.

Three developmental postmilking teat dip formulations containing chlorhexidine digluconate were evaluated against Staphylococcus aureus and Streptococcus agalactiae in sequential experimental exposure trials. Two additional commercial chlorhexidine digluconate teat dip products were evaluated in natural exposure trials. Under conditions of experimental challenge, the developmental formulations were efficacious against Staph. aureus but did not significantly reduce incidence of new IMI by Strep. agalactiae. None of the three formulations of a conventional germicide used as teat sanitizers effectively reduced incidence of new Strep. agalactiae IMI under experimental challenge conditions. In the natural exposure trials with negative controls, a .35% chlorhexidine teat sanitizer had efficacy of 88.7% against Staph. aureus and 51.4% against Strep. agalactiae. The .5% chlorhexidine product reduced Staph. aureus and Strep. agalactiae IMI by 86 and 56%, respectively.

The influence of intensively managed rotational grazing, traditional continuous grazing, and confinement housing on bulk tank milk quality and udder health.

Monthly bulk tank milk samples and veterinary records were analyzed for 1 yr on 15 Vermont dairy farms. Data were evaluated using ANOVA to compare effects of grazing management systems on milk quality and udder health. Systems evaluated were intensively managed rotational grazing, traditional continuous grazing, and confinement housing. Bulk tank samples were evaluated for standard plate count, bacterial type counts on tryptose-blood-esculin agar, and SCC. Veterinary records were evaluated for incidence of clinical mastitis, udder edema, and teat injuries. Within- and between-treatment group analyses were conducted by season, herd size, and udder sanitation systems. Mean standard plate counts were lower in rotationally grazed herds than counts of confined herds during the grazing season. Similarly, rotationally grazed herds with fewer than 60 cows had lower standard plate counts than confined herds of similar size. Mean bulk tank counts of streptococci other than Streptococcus agalactiae during the grazing season differed among treatments. The lowest counts occurred in rotationally grazed herds. Among herd using predip products recognized as efficacious, fewer streptococci other than S. agalactiae were isolated from bulk tank milk of rotationally grazed herds than confined herds. Rotationally grazed herds using postdips recognized as efficacious had lower SCC than those using unrecognized postdips. No udder health differences were observed among grazing treatments.

Mastitis prevalence in primigravid heifers at parturition.

Prevalence of intramammary infection was determined for 382 primigravid heifers within 3 d postpartum on 11 Vermont dairy farms. Data collected during a 5-yr period are summarized. Duplicate quarter milk samples were cultured on tryptose-blood agar plates containing .1% esculin. Intramammary infections were diagnosed in 45.5% of the heifers and 18.7% of quarters. Staphylococcus species were the most prevalent bacteria isolated: they appeared in 25.4% of the heifers and 12.1% of quarters. Only 2.6% of the heifers were diagnosed with Staphylococcus aureus; 22.8% had udder infection caused by other staphylococcal species. Environmental mastitis pathogens, coliforms, and streptococci other than Streptococcus agalactiae were isolated from 14.9% of the heifers and 4.8% of quarters. The prevalence of mastitis among these primigravid heifers at parturition indicates a need to improve methods of diagnosis and control programs.

Efficacy of a Low Concentration Iodine Postmilking Teat Disinfectant Against Contagious and Environmental Mastitis Pathogens in Two Dairy Herds.

Two natural exposure herd studies were conducted at separate geographic locations to evaluate efficacy of a postmilking teat disinfectant that contained 0.25% available iodine. One study was conducted for 11 months in a commercial dairy with a high prevalence of contagious mastitis pathogens. Postdipping was compared with a negative control using a split-herd experimental design. The other study was conducted for 12 months in a research herd with a high prevalence of environmental mastitis pathogens. Postdipping was compared with a negative control using a split-udder experimental design. New intramammary infections by Staphylococcus aureus and Streptococcus agalactiae were reduced significantly in quarters with teats dipped in iodine compared to undipped teats in the herd with a high prevalence of contagious mastitis pathogens. However, the experimental teat dip was not effective against environmental pathogens in either herd. New infections by minor mastitis pathogens (coagulase-negative Staphylococcus species and Corynebacterium bovis ) were significantly lower in quarters of dipped teats compared to undipped teats in both herds. No irritation or chapping of teats was detected and no adverse effects were observed. These data suggest that the low concentration iodine teat dip is effective against contagious pathogens and minor mastitis pathogens, but ineffective against environmental mastitis pathogens.

Evaluation of a chlorous acid-chlorine dioxide teat dip under experimental and natural exposure conditions.

A postmilking teat dip containing chlorous acid-chlorine dioxide was evaluated by experimental challenge and in two herds under natural exposure. The test product had an efficacy of 78.9% against Staphylococcus aureus and 52.5% against Streptococcus agalactiae in the experimental challenge trial. The product was compared with a 1% iodine product in a 15-mo natural exposure study. Post-dipping with chlorous acid-chlorine dioxide reduced incidence of udder infection by major mastitis pathogens 36.1% when data were combined from the two herds. The 1% iodine and the chlorous acid-chlorine dioxide products were not equivalent for major mastitis pathogens; the test product was more effective. Incidence of udder infection by environmental mastitis pathogens was reduced 36.8% in both herds combined. Efficacy of the two teat dips was equivalent for environmental pathogens.

Field trial evaluation of premilking teat disinfection.

Efficacy of premiliking teat disinfection (predipping) with good udder preparation was compared with good udder preparation alone on four well-managed, commercial dairy farms. Three teat dip formulations containing iodophor were used for predipping. Predipping reduced the rate of intramammary infection with major mastitis pathogens approximately 54%. Infection rate with esculin-positive streptococci and coliforms was reduced more than 51%. Udder infections with coagulase-negative staphylococci were not controlled by predipping.

Detection of penicillin, cephapirin, and cloxacillin in commingled raw milk by the Spot test.

The objective of this study was to compare Spot Test results with the results of the Bacillus stearothermophilus disc assay. Commingled raw milk samples were subdivided and spiked with penicillin, cephapirin, or cloxacillin. All subsamples, including unspiked subsamples, were analyzed by the Spot Test (3 or 9 replicates) and disc assay (9 replicates). Mean zone diameter for every subsample was calculated; subsamples having a mean zone diameter greater than or equal to 16 mm were considered positive. At penicillin concentrations less than or equal to 3.7 ng/ml, agreement between the Spot Test and disc assay was 83.4%, and false positive and negative percentages were 14.4 and 2.2%, respectively. Above 3.7 ng/ml, agreement was 100%. At cephapirin concentrations less than or equal to 12 ng/ml, agreement between the two tests was 67.9%, and false positive and negative percentages were 28.8 and 3.3%, respectively. Above 15 ng/ml, agreement was 99.3% with .7% false negatives. At cloxacillin concentrations less than or equal to 50 mg/ml agreement between the two tests was 54.5 with 45.5% false positives. At cloxacillin concentrations greater than or equal to 62.5 ng/ml, agreement between the two tests was 87.2% and false positive and negative percentages were 12.6 and .2%, respectively. In a field trial consisting of 823 bulk samples, Spot Test and disc assay agreement was 100%. The Spot Test is a rapid and reliable method for detecting penicillin, cephapirin, and cloxacillin residues in raw milk at concentrations that will produce a 16-mm zone.

Metabolic profiles in Virginia dairy herds of different milk yields.

This study examined metabolic profiles of commercial dairy herds differing in milk production. Thirty herds were selected with 10 herds averaging more than 7258 kg milk, 10 herds between 6350 and 7258 kg, and 10 herds averaged below 6350 kg. In each herd, 28 cows were selected for blood sampling, which was collected every 3 mo during 12 mo. Cows varied in estimated relative producing ability. Metabolic profiles were established for 19 blood components. Differences among treatment means were significant between high and low producing herds and little between profiles for milking and pregnant nonlactating cows. Metabolic profiles of problem herds remained within normal ranges for all herds except one. Profiles of herds with breeding or mastitis problems remained in the normal range. Metabolic profile testing was of limited value in screening a dairy herd for potential problems or deficiencies.

Nutritive value of potato-based silages for dairy bulls.

Diet acceptability, nutrient digestibility, and nitrogen and energy partition were measured in growing Holstein bulls to compare corn silage with three potato-based silages which consisted of (fresh basis): 1) 50% potatoes, 20% hay; 2) 60% potatoes, 20% hay, 20% whole oats; 3) 50% potatoes, 25% hay, 25% whole oats. The 50% potato 50% hay silage dry matter was consumed at 3.0% of body weight per day which was greater than for any of the other three silages. Consequently, daily consumption of each nutrient was generally higher for this silage even though it was lower in content of many nutritional components. Except for ether extract, the digestion coefficients for the 50% potato 50% hay silage were higher than for the other three silages. The addition of whole oats to the potato-based silage tended to depress apparent digestibility of the nutritional components below those for corn silage. Both nitrogen and energy utilization were higher for the 50% potato 50% hay silage than for any of the other three experimental silages. Efficiency of use of absorbed nitrogen was higher for the oat-containing potato-based silages than for corn silage while the oat-containing silages were comparable to corn silage in energy efficiency. The 50% potato 50% hay silage was equal or superior to corn silage in dry matter intake, overall overall digestibility, nitrogen and energy balance for growing Holstein bulls.