University of Guelph
Introduction
The proper management of dry
cows is an extremely important component of a mastitis control program. The dry period offers a valuable opportunity
to improve udder health, while cows are not lactating. On the other hand, both the beginning and
the end of the dry period represent times of increased risk of intramammary
infection (Eberhart, 1986). The
objective of udder health management during the dry period is to have as few
infected quarters as possible at calving.
In order to achieve this objective, two of the three major principles of
udder health management must be met.
Infections present at the time of drying off should be eliminated. In addition, the rate of new intramammary
infections during the dry period must be minimized. If these two principles are achieved, udders will be free of
infection at calving, and can be expected to produce a maximum amount of low
cell count milk in the subsequent lactation.
Epidemiology of Intramammary
Infection During the Dry Period
In order to develop effective udder
health management strategies for the dry period, it is important to understand
the epidemiology of intramammary infections in dry cows. This requires having knowledge of the
incidence of new infections during the dry period and the types of bacteria
involved. Risk factors that affect the
susceptibility of dry cows should also be understood.
1. Incidence of New Infections
The rate of new
intramammary infections is significantly higher in the dry period than during
lactation (Eberhart, 1986). The greatest
increase in susceptibility is during the first three weeks of the dry period,
when the new infection rate is many times higher than during the preceding
lactation as a whole. A second period
of heightened susceptibility occurs just prior to calving, and in the immediate
postpartum period. The reported rates
of new intramammary infection in the dry period vary widely. Some reasons for
these differences include the diagnostic criteria used, and the types of organisms
considered to be major pathogens. There
are also important herd-level effects, such as the prevalence of existing
infections at drying-off and the method of dry-off (Busche and Oliver,
1987). The average rate of new
infections in untreated dry cows is expected to be between 8 and 12% of
quarters (Eberhart, 1986).
2. Types of Bacteria Causing new Infections
During the Dry Period
Both contagious and
environmental bacteria need to be considered in designing mastitis control
schemes for the dry period. Contagious
organisms are transmitted among cows and quarters in association with the
milking process, and are the predominant prevalent infections at the time of
dry-off. Effective long-acting
antibiotic therapy offers the best opportunity to eliminate these existing
infections.
Environmental pathogens are
primarily contracted from contamination with organisms in manure and bedding
(Smith, 1983).
Exposure to
environmental pathogens is likely to continue throughout the dry period. These organisms are primarily contracted
from contamination of udders by manure and bedding. Thus, prevention of new dry
period infection with environmental agents represents a considerable challenge
(Eberhart, 1986). Herds that have
implemented a basic mastitis control program, still need to be aware of the importance
of preventing environmental infections in the dry period. There are different rates of infection
caused by the various environmental agents as the dry period progresses (Smith et. al., 1985a and b).. For example, infections with environmental Streptococci, Klebsiella, and Enterobacter
occur more frequently early in the dry period.
On the other hand, E. coli
infections tend to occur immediately before and after calving. Dry cow management strategies need to
account for the risk of infection during the entire period from last milking
until the next calving.
3. Risk Factors that Affect Susceptibility in
Dry Cows
Several risk factors
contribute to the variation in susceptibility to new intramammary infection
during the dry period. These factors
include:
a)
Bacterial populations on the teat end
The
cessation of milking management hygiene practices, such as teat dipping, allows
bacterial sub-populations on teat skin to increase. It has been shown that S.
aureus and environmental Streptococci
bacterial numbers on teat skin are high immediately after drying-off. Coliform organisms are more prevalent on
teat skin late in the dry period and at calving time (Eberhart, 1986). Further study is needed to correlate the
numbers of bacteria with the rate of new infections.
b)
Variations in the Teat Streak Canal
The
results of challenge studies suggest that the teat canal is more easily
penetrated by bacteria during the early dry period (Cousins et. al., 1980). Similarly, swelling of the mammary gland,
the increasing volume of secretion, and the leaking of colostrum, contribute to
the high risk of new infection during the prepartum period.
c)
Resistance Mechanisms Within the Mammary
Gland
Throughout
the dry period, there are marked changes in the composition of mammary gland
secretions. There is an increase in the concentration of protective factors
such as leucocytes, immunoglobulins, and lactoferrin. These changes influence the variation in susceptibility to both
environmental and contagious pathogens.
When the gland is completely involuted, resistance to new intramammary
infections is high (Oliver and Sordillo, 1989).
1.
Antibiotic Therapy
Antibiotic
therapy at the end of lactation has been one of the key steps in the National
Mastitis Council control program. It has become the most effective and widely
used mastitis control methods for dry cows.
Its efficacy and advantages are well documented (Yancey, 1998). The use of effective dry cow products results
in 70 to 90% elimination of most existing infections (Natzke, 1981). However, elimination of S. aureus is less successful (Osteras, 1999). Dry cow therapy also reduces the incidence
of new intramammary infections caused by Streptococcus
uberis by 50 to 75% (Williamson, 1995).
A variety of
long-acting antibiotic preparations have been formulated specifically to treat
subclinical mastitis, and to prevent new infections, in dry cows. These preparations include banzathine
cephapirin, benzathine cloxacillin, and sustained-release formulations of
erythromycin, novobiocin, and penicillin.
The withholding period for milk, from animals treated with these dry cow
formulations, ranges from 30 to 42 days after treatment. It is important that the label directions be
followed carefully as to the recommended dosage level, required withdrawal
period, storage guidelines, and expiry dates.
A general recommendation is that dry cow treatment should never be
administered within one month of the expected calving date. Single-dose syringe preparations of dry cow
antibiotic treatment are recommended.
The risk of contamination by environmental bacteria and yeast is much
higher for multiple-dose bottles than for single-dose syringes. If bulk containers are used, great attention
should be paid to maintaining sterility.
Although
intramammary infusion is highly recommended, there is a potential for the
introduction of organisms during the infusion process. Unsanitary infusion
practices can introduce antibiotic-resistant environmental organisms into the
udder. Infection with opportunistic
microorganisms, such as yeast or Nocardia,
may cause more extensive udder damage than the original organism for which
treatment was being administered.
Adequate teat-end preparation and careful dry cow treatment procedures
can reduce this risk.
The importance
of these procedures has been vividly demonstrated during an outbreak of udder
health problems across Canada. From
1987 to 1989, a dramatic increase in the rate of isolation of Nocardia from milk samples submitted to
diagnostic laboratories has been documented (Dohoo, 1991). Three separate case control studies have
been conducted to determine risk factors associated with this increase in Nocardia mastitis (Stark and Anderson,
1990; Ollis et. al., 1991; Ferns et. al., 1991). Each of these studies reported that blanket
dry cow therapy, especially neomycin-containing products, was an important risk
factor for the occurrence of Nocardia mastitis. However, Nocardia
organisms were not found as a contaminant of the suspected products. In one study, teat-end preparation by
scrubbing with an alcohol-soaked cotton swab was found to be protective against
the occurrence of Nocardia infection,
when teats were experimentally contaminated with Nocardia organisms immediately before drying off (Leslie et. al.,
1992). Most commercial dry cow
treatment products provide individually wrapped alcohol-soaked cotton swabs for
use with each syringe. The use of good
teat-end preparation prior to intramammary infusion, needs to be continually
emphasized.
The problem of
new dry period infections associated with the method of treatment has been the
subject of some investigation. Partial
insertion of the infusion cannula (up to 4mm) has resulted in fewer new intramammary
infections, and improved cure rates (Boddie and Nickerson, 1986). The improvement with a short cannula is
attributed to fewer organisms being delivered beyond the streak canal. In addition, antibiotic that is deposited
and left within the streak canal should control local infections. Major pharmaceutical companies have
developed modified infusion canulae for the convenient use of a partial
insertion method of administration.
These devices are now commonplace on commercially available dry cow
syringes.
The necessity of
using dry cow treatment procedures cannot be over-emphasized. Dry cow treatment
procedures should be carried out in the following manner:
Ø Milk the udder out completely.
Ø Immediately following teat-cup removal,
dip all teats in an effective teat
dip.
Ø Allow the teat dip to dry. If necessary, remove excess dip from the
teat-ends with a clean single-service paper towel.
Ø Disinfect each teat-end by scrubbing for
a few seconds with a separate alcohol-soaked cotton swab. Start with the teats on the far side of the
udder, and work towards the near side.
Ø Infuse each quarter with a single-dose
syringe of a recommended dry cow treatment.
Use the partial insertion method of administration into the teat streak
canal. A modified infusion canula is provided with most dry cow treatment
products to facilitate use of the partial insertion method.
Ø Dip all teats in an effective teat dip
immediately following treatment.
Another approach
to preventing the problems associated with intramammary infusion, would be the
development of an effective, systemically-administered dry cow treatment. This would also be an attractive approach
for therapy in pregnant nulliparous heifers.
Preliminary results have indicated improved efficacy against S. aureus infections using a
systemically administered quinoline antibiotic (Norfloxacin nicotinate) (Soback
et. al., 1990). However, no further information has been
published on this therapy regimen.
Furthermore, no systemically administered antibiotic has gained
regulatory approval for treatment of intramammary infections in dry dairy
cows. A systemically administered
long-acting tetracycline product was not effective as a dry cow treatment
(Erskine et. al., 1994). Furthermore, tilmicosin administered
systemically, according to label indications for pneumonia in cattle, was not
efficacious for elimination of S. aureus
intramammary infections (Owens et. al.,
1999). However, tilmicosin administered
by intramammary infusion at dry-off was highly effective for treatment of
infections by major pathogens (Nickerson et.
al., 1999).
Despite blanket
dry cow therapy, some cows calve with persistently infected quarters, and some
with clinical mastitis. Several risk
factors affecting the success of dry cow treatment for S. aureus mastitis have
recently been identified (Sol et. al.,
1994). These factors are:
1.
Numbers of quarters infected.
With S. aureus infections,
there is a significant
decrease
in cure rate as the number of quarters infected per cow increases. Quarters from cows with either three or four
of their quarters infected have a very poor cure rate.
2.
Age of the cow. As the age of the cow increases, the
probability of S. aureus infections
being
cured by dry cow therapy decreases.
3.
Somatic cell count prior to drying off. The cure rate of S. aureus infected quarters
diminishes,
as the SCC prior to treatment increases.
There is a significantly lower cure rate in quarters with an SCC of
greater than one million cells per mL (Sol et.
al., 1994).
4.
Herd of origin.
There is a distinct herd effect on the success of dry cow therapy. The cure
rate
of S. aureus has been shown to be
higher in herds with good hygiene, and with a low prevalence of S. aureus infections at drying-off (Sol et. al., 1994).
There is
considerable potential in using individual cow and herd-level information to
predict the likelihood of a cure with dry cow therapy. For example, an older cow with
three-quarters infected with S. aureus
, and a persistently high SCC, has a low probability of a cure. Continued development of information
management systems to assist with therapy and culling decisions will clarify
the expectations of dry cow treatment.
Several
different strategies to improve the efficacy of dry cow antibiotic treatment
have been studied; in particular to
improve the cure rates for persistent S.
aureus infections. In general,
these methods have met with limited success.
Hogan et. al. (1994) studied
the efficacy of an immuno-stimulant product (Proprionibacterium acnes extract) as an adjunct to dry cow
treatment. It did not provide
significantly improved therapy or prevention over dry cow treatment alone. Erskine et.
al. (1998) studied the usefulness of a cytokine(recombinant bovine
interleukin 2, IL-2) in addition to dry cow antibiotic treatment. There was no significant improvement in cure
rate or prevention of new infections.
Furthermore, there was a significant increase in rate of abortions
following IL-2 treatment. Using a
double dry cow treatment regimen (at dry-off and one month later) did not
improve the cure rate of persistent S.aureus
infections (Leslie, 1994). In lactating
cows, it has been shown that simultaneous intramammary and intramuscular
treatment improved the cure rate of S.
aureus infections (Owens et. al.,
1988). However, this approach for
treatment of cow at dry-off has not been reported in the literature. Of particular interest, a recent study has
reported dramatic improvements in the efficacy of extended antibiotic therapy
of chronic S. aureus infections in
lactating cows by specific immunization with a S. aureus bacterin prior to, and during, the course of therapy
(Sears and Belschner, 1999). This
approach has not yet been reported as an enhancement to dry cow antibiotic
therapy. In general, there are no real
breakthroughs with respect to enhancing the efficacy of dry cow therapy. Treatment of all quarters of all cows with
an approved dry cow antibiotic product remains the recommended approach.
Persistent S. aureus infections represent only one
of the shortcomings of antibiotic treatment for dry cows. Most dry cow products are formulated for
efficacy against gram-positive cocci.
These antibiotics are of limited usefulness against gram-negative
bacteria. In other words, new coliform
infections would not be prevented by this therapy. Even though dry cow products are formulated for sustained
activity, the provision of adequate protection during the critical prepartum
period is questionable (Smith et. al.,
1985). The persistence of effective levels of antibiotic has been evaluated for
various dry cow treatments (Oliver et.
al., 1990c). Dry cow products are
not formulated to have persistent activity until the time of calving. One potential solution for protection
through the critical periparturient period is infusion of a lactating cow
product one to three days prepartum (Pankey et.
al., 1982b). This approach merits
investigation. However, there are
concerns about the predictability of calving, accuracy of predicted calving
dates, and the risk of antibiotic residues in milk of cows that calve
early. A more promising approach
involves protection of the teat streak canal during the prepartum period, which
will be discussed later in this paper (Timms et. al., 1997)
Although dry cow therapy is a
cornerstone of mastitis control programs, there is a continuing controversy
concerning blanket versus selective dry cow therapy. This debate has gained momentum as the implementation of basic
udder health management practices has resulted in reduced prevalence of
infection (Schultze, 1983). Large observational studies have shown an
association between selective dry cow therapy programs and improved
profitability (Gill et. al., 1991).
The major reasons that producers consider using selective therapy are to reduce the expense of treatment, to
avoid the possible emergence of antibiotic resistant organisms and to prevent
the elimination of minor pathogens which may provide some resistance to
infection with environmental agents (Eberhart, 1986). Each of these reasons should be carefully considered in deciding
between selective and blanket dry cow therapy.
Selective therapy programs have been assessed in Scandinavian countries,
where antibiotic use in food animals is highly regulated and supervised
(Osteras et. al., 1991).
Selective
therapy requires a decision as to which cows are to be treated. The predictive value of any currently
available screening test is unacceptable as the basis for a decision concerning
selective therapy. The history of
clinical mastitis, CMT results, individual cow SCC, and even bacteriological
culture are valid decision-making tests, but they all result in leaving some
infected cows untreated. In addition,
many uninfected cows are treated unnecessarily. An important pre-requisite for large scale implementation of
selective dry cow therapy would be the development of a cheap, practical,
sensitive and specific test to identify infected cows.
Blanket dry cow
therapy will reduce the prevalence of infection with minor udder pathogens,
such as coagulase negative Staphylococcal species. There is mounting evidence that reduction of these minor
infections will be associated with an increase in new intramammary infections
and clinical mastitis (Schukken et. al.,
1999). However. one large
epidemiological study did not find an association between dry cow treatment and
the rate of clinical mastitis (Schukken et.
al., 1989). The study followed 125
farms with low bulk milk SCC. Dry cow
treatment had neither a beneficial nor a detrimental effect on the rate of
clinical mastitis during lactation.
Environmental conditions and individual cow factors were the more
important risk factors. More recently,
cessation of aggressive port-milking teat disinfection resulted in a
significant decrease in clinical coliform mastitis (Lam et. al., 1997). However,
conclusive evidence that selective dry cow therapy will reduce clinical
mastitis the next lactation has not been reported.
The final
compelling argument against complete dry cow therapy is the potential emergence
of antibiotic-resistance strains of bacteria.
It has been shown that some organisms were not successfully eliminated
by dry cow treatment with penicillin and dehdrostreptomycin and became resistant
to those antibiotics (Schultze, 1983; Osteras et. al., 1999). The
surviving pathogen population was not a threat to the udder health status of
the study herd in the next lactation (Schultze, 1983). However, the demonstration that such
resistance could develop is cause for some concern. Further study is needed to determine the long-term impact of this
development.
It is noteworthy
that the prevention of new intramammary infections is effectively lost with the
selective approach. Methods to protect the
cow from new intramammary infections need to be in place. Natzke (1981) has estimated that blanket dry
cow therapy reduces new infection rates from approximately 14% to 7% of
quarters. The increase in milk
production from preventing these infections is alone enough economic return to
offset the cost of antibiotic treatment for all cows. Currently, it is clear that replacement of complete dry cow
therapy with a selective program cannot be economically justified in North
America. Information presently
available indicates that the general recommendation should be for routine treatment of all quarters of all
cows at the time of drying off. Yet, it
is important to consider evidence in support of selective dry cow therapy. There is a need to identify important
management practices to limit new infections in untreated dry cows, and to
develop new screening tests to determine which cows should be treated. Perhaps the combined use of CMT information
and the results of bacteriological analysis, such as the HyMast test, combined
with modern information processing, will lead to the development of better
selective dry cow treatment programs (Jansen et. al., 1997).
2. Management of the Environment for Dry Cows
Dry cows should
be provided an environment that is
as clean and dry as possible. Variations in the load of coliforms and
environmental Streptococci, in the
environment are important predictors of new infection rates (Smith et. al., 1985). Minimizing the exposure to environmental
bacteria will reduce the new infection rate. However, some pasture conditions
promote the crowding of cows under shade trees. In hot, humid and muddy conditions, heavy contamination of such a
small area can result in a significant risk of new environmental infections in
the dry period. In good weather, it is
ideal to hold parturient cows in a clean, grassy area; where they can be
observed and assisted if necessary.
In confinement
housing systems for dry cows, it is important to provide adequate space,
ventilation, bedding, and lighting to ensure cleanliness and comfort. When maternity stalls are used, they should
be bedded with clean straw, or shavings.
Studies have reported lower coliform populations, but higher numbers of
environmental Streptococci, in straw
(Rendos et. al., 1975). Other important procedures for managing the
environment for dry cows include adopting an effective fly control
program. Clipping or flame singeing the
hair on the udders, flanks, and inside the hind legs will help reduce
contamination. The words clean and dry
summarize the concept of management of the environment for dry cows.
3. Nutritional Management of Dry Cows
A
nutritionally balanced dry cow feeding program is important to ensure udder
health. Furthermore, specific
nutritional factors have important roles in resistance to mastitis, especially
over the dry period (Eberhart, 1986).
For example, adequate levels of vitamin E and selenium in dry cow
rations appear to be important for udder health at calving and in early lactation (Weiss et. al., 1997). This effect
may be mediated through enhanced resistance mechanisms. Other vitamins and minerals, such as copper
and chromium, may be important in udder health although their role is less
substantiated.
Nutritional
management of dry cows is also important for reducing the risk of
periparturient diseases, which is an important predisposing factor to mastitis
in fresh cows. Appropriate body
conditioned can be achieved by good nutritional management in late
lactation. There is more and more evidence
of an important association between body condition, energy balance and udder
health. Ketosis can be an important
predisposing factor for the occurrence and severity of clinical mastitis
(Kremer et. al., 1993). In some countries, ionophores have been
approved for use in lactating dairy cattle to prevent subclinical ketosis,
which may have considerable benefit for general health of periparturient dairy
cattle.
4. Methods of
Drying Cows off
The method used
to dry-off late lactation cows may affect
new intramammary infection rates, in the early dry period. Udder involution can
be hastened by a regimen of intermittent milking, and of limiting feed intake
to hay only, during the last week of lactation (Eberhart, 1986). However, the effects of various drying-off
methods on udder health is the subject of considerable controversy. Drying-off by intermittent milking, and a
change in ration, has been shown to result in fewer infections at subsequent
calving (Bushe and Oliver, 1987; Natzket et.
al., 1975). Yet, these differences
in prevalence of infection are most evident in cows that are not treated with
dry-cow antibiotic therapy. The method
of drying-off is probably less important with blanket dry-treatment
programs. As the use of selective dry cow
therapy becomes more economically sound, the method of drying-off will gain
importance. Furthermore, after
drying-off enhancement of mammary gland involution may play an important role
in preventing new infections (Oliver and Sordillo, 1989).
5. Teat-End Protection for Dry Cows
Post-milking
teat disinfection is a very effective means of reducing new infections in
lactating cows. However, the efficacy
of teat disinfection in the dry period has been discouraging (Eberhart, 1986). Daily teat dipping for the first week of the
dry period was not effective in reducing Strep.
uberis infections. The objective of
teat dip application in the dry period is to provide a physical barrier over
the teat canal for the first two weeks of high risk in the dry period. This does not appear to be achieved by the
barrier products currently available for lactating cows. There is a continuing search for effective
barrier products. Teat sealers may be
of some use for the prevention of environmental infection in the immediate
prepartum period. Recently, a polyether-polymethane product has been developed
and marketed as a dry cow teat sealant (Timms, et. al., 1997). Pending
successful adherence until the keratin plug has formed in the teat streak canal
(Leslie et. al., 1999), this type of
product has promise for protection against new environmental Streptococcus infections in the dry
period. It is recommended that the teat
sealant be used as an adjunct to dry cow treatment and vaccination against
Coliform mastitis. In addition, the dry
cow teat sealant may be useful to protect teat-ends from environmental
contamination in the critical prepartum stages of the transition and maternity
groups. A dry cow teat sealer that is
infused into each quarter has been developed by researchers in Ireland (Meaney,
1977). This product has been approved
for commercial use in dry cows in New Zealand (Wootford, 1998). Further developments for the protection of dry
cows are expected.
6. Vaccination
Vaccination with
a gram negative core antigen vaccine has become an extremely important method
of minimizing the severity of coliform mastitis. The vaccine produces immunity against the E. coli endotoxin. When
given strategically in the early and late dry period, and shortly after
calving, protection is available during the high risk period for coliform
infection. It must be stressed that
immunity is short-lived. Thus,
strategic use is crucial. The cost
benefit of this program is clear, even when the herd-level incidence of
coliform mastitis is low (Yancey, 1999).
In summary, appropriate dry cow management is
extremely important for the maintenance of optimal udder health. Antibiotic therapy at the end of lactation
is the most effective method of eliminating existing infections. Dry cow therapy also significantly reduces
the rate of new infections during the dry period. Until better diagnostic tests and data management methods are
available, the preferred approach is a blanket dry cow therapy program. This involves the treatment of all quarters
of all cows immediately following the last milking. In addition, providing a clean, dry environment, and a properly
balanced ration, will assist in the prevention of new dry period infections. Better methods of enhancing mammary involution
and protecting the teat-end need to be developed. In addition, special attention is required in the pre-calving
period.
References
Boddie, R.L.,
and S.C. Nickerson. 1986. Dry cow therapy: effects of method of drug
administration on occurrence of intramammary infection. J. Dairy Sci. 69:253.
Bushe, T., and
S.P.Oliver. 1987. Natural protective factors in bovine mammary
secretions following different methods of milk cessation. J. Dairy Sci. 70:696.
Cousins, C.L.,
T.M. Higgs, E.R. Jackson, F.K. Neave and F.H. Dodd. 1980. Susceptibility of
the bovine udder to bacterial infection in the dry period. J. Dairy Res. 47:11.
Dohoo, I.R. 1991.
Canada. Update on Nocardia sp. mastitis. Can. Vet. J. 32:116.
Eberhart, R.J. 1986.
Management of Dry Cows to Reduce Mastitis. J. Dairy Sci. 69:1721.
Erskine, R.J., P.C. Bartlett,
P.C. Crawshaw and D.M. Gombas.
1994. Efficacy of intramuscular
oxytetracycline as a dry cow treatment for Staphylococcus
aureus mastitis. J. Dairy Sci. 77:3347.
Erskine, R.J., P.C. Bartlett,
S.R. Tavernier, L.H. Fowler, R.D. Walker, J.H. Seguin, and D. Shuster.
1998. Recombinant bovine interleukin-2
and dry cow therapy: efficacy to cure
and prevent intramammary infections, safety, and effect on gestation. J. Dairy Sci. 81:107.
Ferns, L., I.
Dohoo and A. Donald. 1991. A case-control study of Nocardia mastitis in Nova Scotia dairy herds. Can. Vet. J. 32:673.
Gill, R., W.H. Howard, K.E. Leslie and K.D. Lissemore. 1990.
Economics of mastitis control.
J. Dairy Sci. 73:3340.
Hogan, J.S.,
K.L. Smith, D.A. Todhunter and P.S. Schoenberger. 1994. Efficacy of dry cow
therapy and a Propionibacterium acnes
product in herds with low somatic cell count.
J. Dairy Sci. 77:3331.
Hogan, J.S., K.L.
Smith, D.A. Todhunter, and P.S. Schoenberger.
1995. Efficacy of recombinant bovine interleukin-2 as an adjunct to dry
cow therapy. J. Dairy Sci. 78:1062.
Jansen, J., K. Leslie, and D. Kelton. 1997.
Utilizing and Evaluating the HyMast Test on Dairy Farms. National Mastitis Council Regional Meeting
Proceedings: 1.
Lam, T.J.G.M.,
J.H van Vliet, Y.H. Schukken, F.J. Grommers, A. van Velden-Russcher, H.W.
Barkema, and A. Brand. 1997. The Effect of Discontinuation of Postmilking
Teat Disinfection in Low Somatic Cell Count Herds. II. Dynamics of
Intramammary Infections. Vet Quart
19:47.
Leslie, K.E.,
D.A. Barnum and K.D. Lissemore. 1992.
The role of pre-treatment teat-end preparation in the safety and efficacy of
dry cow therapy. Proc. 31st Nat.
Mastitis Council: 234.
Leslie,
K.E., K.J. Day, J. TenHag, D.F. Kelton, T.F. Duffield, and
T. L. Kerbler. 1999. Factors Affecting the Adherence of a Dry Cow
Teat Sealant. National Mastitis Council
Annual Meeting Proceedings:136.
Meaney,
W.J. 1977. Effect of a dry period teat
seal on bovine udder infection. Ir. J.
Agric. Res. 16:293.
Natzke,
R.P. 1981. Elements of mastitis control.
J. Dairy Sci. 64:1431.
Natzke, R.P., R.W. Everett and
D.R. Bray. 1975. Effect of drying off practices on mastitis
infection. J. Dairy Sci. 58:1828.
Nickerson, S.C.,
W.E. Owens, L.K. Fox, C.C. Scheifinger, T.R. Shryock and T.E. Spike. 1999.
Comparison of Tilmicosin and Cephapirin as therapeutics for Staphylococcus aureus mastitis at
dry-off. J. Dairy Sci. 82:696.
Oliver,
S.P. 1988. Frequency of isolation of
environmental mastitis-causing pathogens and incidence of new intramammary
infection during the nonlactating period.
Am. J. Vet. Res. 49:1789.
Oliver, S.P.,
J.L. Maki and H.H. Dowlen. 1990(b).
Antibiotic residues in milk following antimicrobial therapy during lactation. J.Food Protect. 53:693.
Oliver, S.P.,
E.P. Shull and H.H. Dowlen. 1990(c).
Influence of different methods of milk cessation on intramammary
infections during the peripartum period.
Proc. Intl. Mast. Symp., Indianapolis, Ind.:92.
Oliver, S.P. and L.M.
Sordillo. 1989. Approaches to the
manipulation of mammary involution. J.
Dairy Sci. 72:1647.
Ollis, G.W., M.
Schoonderwoerd and C. Schipper. 1991.
An investigation of risk factors for nocardial mastitis in central Alberta
dairy herds. Can. Vet. J. 32:227.
Osteras, O., L.
Sandvik, J. Aursjo, G.G. Gjul and A. Jorstad.
1991. Assessment of strategy in
Selective dry cow therapy for mastitis control. J. Vet. Med. 38:513.
Osteras, O., V.L. Edge and
S.W. Martin. 1999. Determinants of
success or failure in the elimination of major mastitis pathogens in selective
dry cow therapy. J. Dairy Sci. 82:1221.
Owens, W. E.,
J.L. Watts, and R.L. Boddie, et. al.. 1988. Antibiotic
treatment of mastitis: Comparison of
intramammary and intramammary plus intramuscular therapies. J Dairy Sci 71:3143.
Owens, W.E.,
S.C. Nickerson and C.H. Ray. 1999. Efficacy of parenterally or intramammary
administered Tilmicosin or Ceftiofur against Staphylococcus aureus mastitis during lactation. J. Dairy Sci. 82:645.
Pankey, J.W.,
R.M. Barker, A. Twomey and G. Duirs. 1982. Comparative efficacy of dry-cow
treatment regimens against Staphylococcus
aureus. N.Z. Vet. J. 30:13.
Rendos, J.J.,
R.J. Eberhart and E.M. Kesler.
1975. Microbial populations of
teat ends of dairy cows and bedding materials.
J. Dairy Sci. 58:1392.
Schukken, Y.H., F.J. Grommers,
D. van de Geer and A. Brand. 1989. Intramammary infections and risk factors for
clinical mastitis in herds with low somatic cell counts in bulk milk. Vet. Rec.
125: 393.
Schukken, Y.H.,
J. van Vliet, D. Vandegeer and F.J.
Grommers. 1993. A randomized blind trial on dry cow
antibiotic infusion in a low somatic cell count herd. J. Dairy Sci. 76:2925.
Schultze,
W.D. 1983. Effect of a selective
regimen of dry cow therapy on intramammary infection and on antibiotic
sensitivity of surviving pathogens. J.
Dairy Sci. 66:892.
Sears, P.M. and
A.P. Belschner. 1999. Alternative Management and Alternate
consideration in Staphylococcus aureus
elimination programs. National Mastitis
Council 38th Annual Meeting Proceedings: 86.
Smith, K.L. 1983.
Mastitis control: a
discussion. J. Dairy Sci. 66:1790.
Smith, K.L, D.A. Todhunter and
P.S. Schoenberger. 1985a. Environmental
Mastitis: Cause, Prevalence,
Prevention. J. Dairy Sci. 68:1531.
Smith, K.L.,
D.A. Todhunter and P.S. Schoenberger. 1985b. Environmental pathogens and
intramammary infection during the dry period.
J. Dairy Sci. 68:402.
Soback, S., G. Ziv, M.Winkler
and A. Saran. 1990. Systemic dry cow
therapy - a preliminary report. J.
Dairy Sci. 73:661.
Sol, J., O.C. Sampimon and
J.J. Snoep. 1994. Factors associated with bacteriological cure
after dry cow treatment of subclinical Staphylococcal mastitis with
antibiotics. J. Dairy Sci. 77:75.
Stark, D.A. and
N.G. Anderson. 1990. A case-control
study of Nocardia mastitis in Ontario
dairy herds. Can. Vet. J. 31:197.
Timms, L.L. 1997.
Field trial evaluation of a persistent barrier teat dip for preventing
mastitis during the dry period. J Dairy
Sci 80: Suppl.1, 225.
Weiss, W.P., J.S. Hogan, D.A.
Todhunter and K.L. Smith. 1997. Effect of Vitamin E Supplementation in Diets
with a Low Concentration of Selenium on Mammary Gland Health of Dairy
Cows. J Dairy Sci 80:1728.
Williamson,
J.H., M.W. Woolford, M.W. and A.M. Day.
1995. The prophylactic effect of
a dry-cow antibiotic against Streptococcus
uberis. N.Z. Vet. J. 43:228.
Woolford, M.W., J.H.
Williamson, A.M. Day and P.J.A. Copeman.
1998. The prophylactic effect of a teat sealer on bovine mastitis during
the dry period and the following lactation.
N.Z. Vet J. 46:12.
Yancey R.J. Jr., 1999. Mastitis therapy – efficacy of antibiotics and
alternative treatment of different pathogens.
Adv Vet Med 41:257.
Ziv, G., M.
Storper and A. Saran. 1981. Comparative efficacy of three antibiotic
products for the treatment and prevention of subclinical mastitis during the
dry period. Vet. Quart. 3:74.
Source:
Presented at the National Mastitis Council 1999 Regional Meeting; Published in
the 1999 National Mastitis Council Regional Meeting Proceedings, pg. 35.