A survey was conducted to determine and contrast prevalence of IMI in nulligravid and primigravid dairy heifers pre- and postpartum. Contrasts were made to evaluate the risk factors of location of dairy, trimester of gestation, and season of sampling on IMI. Twenty-eight dairies in California, Louisiana, Vermont, and Washington were studied. Lacteal secretions were collected aseptically from heifers at breeding age (8 to 19 mo) from one side of the gland and again at 4 d postpartum from all quarters. Of the quarters sampled, 65.6% prepartum and 64.0% postpartum were free of IMI. The percentages of quarters with IMI from coagulase-negative staphylococci or Staphylococcus aureus IMI were 27.1 and 9% prepartum and 21.8 and 2.9% postpartum. Staphylococcus aureus IMI were most prevalent in Louisiana during the months other than summer. Location, herd, and season significantly influenced prevalence of IMI. The prevalence of IMI was greatest during the last trimester of pregnancy, ranging from 49.2% in the winter to 36.8% in the summer. The significant effects of herd location and season suggest that management variables influence prevalence of heifer IMI. Because prevalence of IMI was greatest during the last trimester of pregnancy compared with prevalence during earlier stages of pregnancy, the heifer may be most susceptible to this disease during this period of first gestation.

Minimum inhibitory concentrations were determined for selected antimicrobial agents against 872 bacteria isolated from intramammary infections in heifers in New Zealand (n = 401) and Denmark (n = 471). These values were reported in micrograms per milliliters. Antimicrobial agents tested against isolates from New Zealand were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. The minimum inhibitory concentrations that inhibit 90% of the strains tested for these antimicrobial agents with Staphylococcus aureus were 4.0, 0.5, 0.5, 2.0, 1.0, 0.25, 0.5, and 1.0, respectively. The minimum inhibitory concentration values that inhibit 90% of the strains tested against the Staphylococcus spp. ranged from 0.5 to 1.0 for all antimicrobics. The minimum inhibitory concentrations against streptococci were < or = 0.06, 0.5, 0.13, 0.13, 4.0, 1.0, 0.13, and < or = 0.06, respectively. Antimicrobial agents tested against isolates from Denmark included penicillin, ampicillin, oxacillin, cephalothin, ceftiofur, penicillin plus novobiocin, erythromycin, and pirlimycin. Against S. aureus, the minimum inhibitory concentrations were 0.13, 0.5, 0.5, 0.5, 1.0, 0.25, 0.5, and 0.5, respectively. The minimum inhibitory concentrations against Staphylococcus spp. were 0.25, 0.25, 0.5, 0.5, 1.0, < or = 0.06, 0.13, 1.0, and 0.5, respectively. The minimum inhibitory concentrations against the streptococci were < or = 0.06, 0.13, 0.5, 0.5, 1.0, < or = 0.06, 0.13, 0.5, and 0.5, respectively. Minimum inhibitory concentration values for staphylococci from New Zealand and Denmark were similar to values reported for US isolates. Streptococci from New Zealand and Denmark had lower minimum inhibitory concentration values than did US isolates. Only ceftiofur and enrofloxacin were active against the Gram-negative bacilli.

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.

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.

Unsatisfactory milking conditions, including high milking vacuum, ineffective pulsation, heavy clusters, unsuitable liners, poor teat preparation and over-milking, are known to create poor, but undefined, teat conditions and pose a risk to an increased probability of intramammary infection (IDF, 1994). It has been shown that poor teat condition, seen as discolouration, abnormal firmness or thickened rings of tissue distally, after cluster removal may be common in a variety of commercial milking operations (Hillerton et al. 2000). That field study was observational and teat conditions were influenced by a number of variables. A small experimental study has been undertaken to develop an experimental model, under controlled milking conditions, to allow investigation of potential causes of teat trauma. Over-milking was suggested as highly important in the field observations and so has been examined in this study.

No abstract

Incidence of intramammary infection is highly correlated to the number of mastitis pathogens on the teat end at milking. The objective of premilking teat sanitation is to reduce the microbial population in order to minimize the probability of mastitis. Milking time hygiene is extremely important due to the potential interaction between milking machine functions and microflora of teat skin. Current recommended procedures for premilking udder preparation range from water hose wash, manual drying, wet paper towel wash plus paper towel dry, to predipping alone plus paper towel dry. Regardless of udder cleaning procedure, manual drying of teats is a significant factor in reduction of total bacteria counts. Predipping with iodine-based sanitizers, .1 to .25% iodine concentration, reduced intramammary infection with environmental pathogens 51% compared with good udder preparation in a field trial on four commercial dairy farms. Infections by coagulase-negative staphylococci were not reduced by predipping. Effective premilking udder hygiene is essential for the production of high quality milk. Bacteria, preincubation and pasteurized milk counts are reduced. Sediment is minimized. Incidence of mastitis is reduced. Proper udder hygiene procedures should be practiced at every milking.

Minimum inhibitory concentrations were determined with 1494 microorganisms isolated from the mammary glands of dairy heifers. The antimicrobial agents tested were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. All minimum inhibitory concentrations were expressed as micrograms per milliliter. The isolates tested included 135 Staphylococcus aureus, 1222 Staphylococcus sp., 42 Streptococcus sp., 15 Enterococcus sp., 60 enteric species, and 20 miscellaneous organisms. The minimum inhibitory concentrations for 90% of isolates for the various antimicrobial agents with Staph. aureus were as follows: penicillin, .13; cloxacillin, .5; cephapirin, .5; ceftiofur, 1; novobiocin, .5; enrofloxacin, .5; erythromycin, .5, and pirlimycin, .5. In comparison, the minimum inhibitory concentrations for 90% of isolates for the Staphylococcus sp. were 1, 1, .5, 1, .5, .5, 1, and .5 for penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin, respectively. The minimum inhibitory concentrations for 90% of isolates for the Streptococcus sp. were 2, 32, 2, 2, 8, 1, 64, and 32 for the respective antimicrobial agents; the minimum inhibitory concentrations for 90% of isolates were 4, 64, 32, 64, 4, 1, 4, and 4 for the enterococci. Against the Gram-negative enteric bacilli, only ceftiofur and enrofloxacin were active; minimum inhibitory concentrations for 90% of isolates were 1 microgram/ml for ceftiofur and .25 microgram/ml for enrofloxacin. Results indicated that the majority of staphylococcal strains were susceptible to the antimicrobial agents tested but that antimicrobial susceptibility varied for Streptococcus sp. Compounds currently available in intramammary infusion products demonstrated poor activity against the enteric organisms.