Intramammary Infections In Heifers Research Articles

Sources of Intramammary Infections from Staphylococcus aureus in Dairy Heifers at First Parturition

The study objective was to identify probable sources and modes of transmission of 91 Staphylococcus aureus isolates obtained from the colostrum of 76 heifers at parturition. Sources cultured were milk (including colostrum), heifer body sites (teats, muzzle, rectum, vagina, and lacteal secretions), and environmental sites (bedding, insects, housing, water, feedstuffs, humans, nonbovine animals, air, and equipment). Staphylococcus aureus isolates were characterized by 63 phenotypic traits. A similarity coefficient was calculated by herd to identify the S. aureus that most closely resembled the S. aureus obtained from heifer colostrum. Staphylococcus aureus from a heifer's colostrum was compared with all preexisting S. aureus isolates from that heifer's herd. Isolates that were ≥90% similar were considered to be identical. Because 30 (of the 91) S. aureus isolates from heifer colostrum were collected prior to environmental sampling, only 61 S. aureus isolates from heifer colostrum were available for comparison among all three sources. Possible sources of S. aureus from heifer colostrum at parturition were milk (70%, 43 of 61 isolates), heifer body sites (39%, 24 of 61), environmental sites (28%, 17 of 61), or no identified source (16%, 10 of 61). Three heifers with intramammary infection (IMI) from S. aureus at parturition had the same S. aureus on their teats prior to parturition. Milk was the only source identified for 41% (25 of 61) of isolates from heifer colostrum. Isolates from heifer body sites were the only source identified for 5% (3 of 61) of heifer colostrum isolates. Staphylococcus aureus from the environment was never the sole possible source for S. aureus from heifer colostrum. Data suggest that the major sources of S. aureus IMI in heifers at parturition are milk and heifer body sites. Contact among heifers may be an important mode of transmission of S. aureus leading to IMI in heifers at parturition.

Minimum Inhibitory Concentrations for Selected Antimicrobial Agents Against Organisms Isolated from the Mammary Glands of Dairy Heifers in New Zealand and Denmark

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 ≤0.06, 0.5, 0.13, 0.13, 4.0, 1.0, 0.13, and ≤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, ≤0.06, 0.13, 1.0, and 0.5, respectively. The minimum inhibitory concentrations against the streptococci were ≤0.06, 0.13, 0.5, 0.5, 1.0, ≤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.

Coagulase-negative staphylococcal intramammary infections in cows and heifers during the nonlactating and periparturient periods.

Coagulase-negative staphylococci (CNS) are isolated frequently from unbred and primigravid heifers and from lactating and nonlactating dairy cows. The importance of CNS intramammary infections that occur during the nonlactating period has not been adequately delineated. Mammary secretions from udders infected with CNS during early lactation and the nonlactating period have increased somatic cell counts, CNS have been isolated in mammary secretions from cows with clinical mastitis, and a few studies have indicated that CNS infected mammary glands produced significantly less milk during lactation than uninfected mammary glands. In addition, mammary glands of postpubertal heifers infected with CNS were not as well developed as uninfected mammary glands. Consequently, CNS intramammary infections in heifers and cows during the nonlactating period could impair mammary gland growth and development and ultimately influence mammary function during lactation resulting in decreased lactational performance. Some CNS IMI detected in heifers and multiparous cows at calving do not persist into early lactation. Postmilking teat disinfection with an effective germicide and antibiotic therapy during the nonlactating period markedly reduces the prevalence of CNS in dairy herds. Methods of controlling CNS infections in primigravid heifers based on prepartum intramammary antibiotic therapy have been developed, and results have shown that prepartum antibiotic therapy is very effective against CNS and other mastitis pathogens as well. Additional research is required to determine the influence of CNS infections that occur during the nonlactating period on milk yield in the subsequent lactation.

Prepartum antibiotic therapy with a cephapirin dry-cow product against naturally occurring intramammary infections in heifers.

Intramammary infusion of a dry-cow antibiotic preparation containing 300 mg of cephapirin benzathine into 18 Jersey heifers, 10-12 weeks prepartum, resulted in cure rates of existing intramammary infection (IMI) of 96% (24/25), 100% (4/4), and 90% (28/31) for Staphylococcus aureus, Streptococcus species, and Staphylococcus species, respectively. Cure rates of IMI that had been treated with a lactating-cow therapy containing 200 mg cephapirin benzathine at parturition were 62.5% (15/24), 100% (22/22), and 100% (3/3) for Staphylococcus aureus, Streptococcus species, and Staphylococcus species, respectively. Initial somatic cell counts (SCC) of secretions from infected quarters were greater than from uninfected quarters. At 2 months postpartum, the SCC of milk from treated and cured quarters were reduced in comparison with quarters that remained infected. Cephapirin benzathine was present at detectable concentrations in 94, 80, 68, and 61% of treated quarters at 1, 2, 3, and 4 weeks after infusion of the cephapirin dry-cow product, respectively. At parturition, 24% of treated quarters were positive for antibiotic, however, no quarters remained positive for antibiotic at 5 days postpartum. An additional 40 heifers from a commercial herd were sampled and infused in all quarters with the cephapirin dry-cow product at 16-20 weeks prepartum. Cure rates for the commercial herd were 94% (29/31), 94% (16/17), 100% (44/44), and 100% (3/3), respectively, for quarters infected by S. aureus, Streptococcus species, Staphylococcus species, and coliforms.

Epidemiology of Heifer Mastitis

Until recently, it had been assumed that primigravid heifers were seldom affected by intramammary infections (IMI) at or near parturition. Recent research results now suggest that this assumption is false. A number of studies report a high rate of IMI in heifers at or near parturition.(1-3) Interestingly, the pathogens associated with these IMI's appear to have a regional distribution. A study in the southern United States found a high prevalence of IMI associated with Staphylococcus aureus.(2) Studies in the New England and Southeastern United States detected a high prevalence of IMI associated with coagulase negative staphylococci.(1,3) IMI's associated with Staphylococcus aureus are related to histopathologic lesions in the mammary gland which suggest that these infections may hamper the normal development of the lactating gland.(4) These findings have prompted research to investigate the use of antibiotic therapy to decrease the risk of IMI. This research has found that antibiotics administered prior to calving will decrease the prevalence of peripaturient IMI.(5,6) A question that has not been answered is: Do these infections in heifers, particularly IMI by the minor pathogens, warrant treatment? The objectives of this paper are to report preliminary data describing the incidence of IMI in heifers, the pathogens involved in the infections and the subsequent rates of clinical mastitis in first lactation heifers conditional on the IMI status at freshening.