Dry Cow Therapy

Agdex#:	410/662
Publication Date:	06/03
Order#:	03-009
Last Reviewed:	06/03
History:	(Replaces OMAF Factsheet Dry Cow Therapy, Order No. 90-003)
Written by:	N.G. Anderson - Senior Veterinary Scientist/OMAFRA; J.F. Côté - Veterinary Scientist/OMAFRA

Table of Contents

1. Introduction
2. Rationale for Dry Cow Therapy
3. Types of Antibiotic Treatments
4. Drying Cows Off
5. Dry Cow Treatment Procedure
6. Treatment Precautions
7. Which Cows to Dry Treat
8. Blanket Dry Cow Treatment
9. Selective Dry Cow Treatment
10. Other
11. Summary
12. Related Links

Introduction

Mastitis is the single most influential disease affecting both the quantity and quality of milk produced on Ontario dairy farms. Therefore, the economic significance of adopting a mastitis prevention program should be a major concern to all producers. An effective mastitis management program includes:

1. Elimination of existing infections

• dry cow therapy
• lactating cow therapy
• culling chronically infected cows

2. Prevention of new infections

• environmental control
• equipment maintenance and function
  
• recommended milking procedures
• teat dipping
• dry cow therapy

3. Monitoring udder health

• individual cow somatic cell count (SCC) program
• California Mastitis Test (CMT)
• laboratory culture

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Rationale for Dry Cow Therapy

Treating the dry cow with specially formulated, long-acting antibiotics at drying-off, immediately following the last milking, is an effective practice in the battle against subclinical mastitis. Dry cow therapy eliminates existing infections and reduces the risk of new infections, thus improving udder health.

The advantages of dry cow therapy include:

• a reduced incidence of new infections during the first 3-4 weeks of the dry period;
• a much higher cure rate than lactational treatment of some organisms;
• an aid in the regeneration of damaged milk secretory tissues;
• a reduced incidence of mastitis in the next lactation;
• an avoidance of milk loss due to treatment of mastitis in lactation;
• a reduced level of mastitis, translating into increased milk production, better quality milk and greater dollar returns.

Types of Antibiotic Treatments

Intramammary infusion products fall into two general categories (see Table 1, Dry Cow Intramammary Products, for approved products):

1. the quick-release, short-acting types designed specifically to treat mastitis in lactating cows; and

2. the slow-release, long-acting types formulated specifically to treat subclinical mastitis in dry cows and to prevent new infections in dry cows.

When the slow-release preparation is infused into a dry cow, effective levels of antibiotics remain in the udder for 21 days or more. This antibiotic persistence achieves much higher cure rates during the dry period than that attained during lactation, especially for more resistant mastitis infections, such as those caused by staphylococci bacteria.

Selection of an effective infusion product should be based on laboratory culture and sensitivity tests that identify the organisms and the antibiotics to which they are sensitive. Consult your veterinarian for advice on the use of antibiotic products.

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Drying Cows Off

Aim to dry cows off 50-55 days and never less than 40 days - before the expected calving date. This dry period is necessary for repairing and replacing damaged milk secretory cells in the udder.

Two common methods of drying cows off are intermittent milking and abrupt cessation of milking. The abrupt method is preferred, in conjunction with dry cow therapy, because the technique reduces the number of new infections. To be successful with abrupt drying off, it is usually necessary to first lower the cow's milk production by reducing feed and water intake for 3-4 days prior to drying off.

Treat cows with clinical mastitis to eliminate the mastitis first before drying-off.

After drying-off, examine the udder periodically until it is completely collapsed. If a quarter becomes clinically infected immediately following drying-off, milk it, treat for clinical mastitis until eliminated, then re-treat with dry cow antibiotic.

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Dry Cow Treatment Procedure

Intramammary infusion is a highly recommended but potentially dangerous procedure. The danger lies in unsanitary infusion practices that can introduce antibiotic-resistant environmental organisms into the udder. These environmental organisms may cause more extensive udder damage and a more severe infection than the original organism for which treatment was intended.

To avoid this risk, adhere to the following dry cow treatment procedures:

• milk the udder out completely;

• immediately following teat cup removal, dip all teats in an effective teat dip;

• allow the teat dip to dry, then dab excess dip from teat ends with a clean single-service paper towel;

• starting with the teats on the far side of the udder, disinfect the teat ends by scrubbing each for a few seconds with a separate alcohol-soaked cotton swab;

• starting with the teats on the close side of the udder, infuse each quarter with a single-dose syringe of the recommended treatment. Insert the cannula only 6 mm (1/4 in.) into the teat end prior to infusing. Massage the treatment up into each quarter;

• single-dose syringes are recommended rather than bulk containers, which may become contaminated with antibiotic-resistant organisms and become a source of infection;

• immediately following treatment, dip all teats in an effective teat dip; and

• when practical, teat dip all treated cows at least once a day for 2 weeks after drying-off and for 2 weeks before calving.

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Treatment Precautions

Prior to infusing any antibiotic, always read the label instructions to determine the intended use, the recommended dosage level, the required withdrawal period, storage guidelines and expiry dates.

Never deviate from the recommended dosage level. Exceeding the dosage level will certainly increase the antibiotic withdrawal period.

In addition to meeting withdrawal period requirements, never administer dry cow treatment within one month of the expected calving date. Always seek the advice of your veterinarian in special cases where a valuable, high-producing cow might benefit from a second treatment during the dry period. Primary concerns should include treatment procedure and the recommended withdrawal period of the product to be infused.

Storage of dry cow products, at temperatures recommended by the manufacturer, will assure that the antibiotic retains potency until the expiry date. Never assume the risk of treatment failure by using products that have passed the expiry date on the package. Always discard products damaged by freezing or exposure to high temperatures.

Single-dose syringes of dry cow antibiotic treatment are recommended because the risk of contamination by environmental organisms and yeasts is much higher for bulk multiple-dose bottles than for single dose syringes.

When bulk containers are used, disinfect the rubber stopper with alcohol before each use; store the opened bottle in a clean, dry, dust-free place, use a new cannula for infusing each teat; use a sterile syringe for each administration. Do not return any unused product to the bottle; and never combine products from different containers.

Never use homemade antibiotic combinations for dry or lactating cow therapy. Efficacy, potency, quality assurance, freedom from adverse tissue reactions and withdrawal time guidelines are seldom available for such preparations.

If a slow-release dry cow antibiotic is accidentally infused into a lactating cow, do not market the milk from the treated cow until the milk has passed a drug residue test indicating that it is free of antibiotic residues. Contact your Dairy Farmers of Ontario field service representative or your veterinarian to arrange for residue testing.

Maintain complete and accurate records of all clinical mastitis cases, cows treated, culture results from the laboratory and the type of antibiotic treatments used. From these records, the effectiveness of treatments can be determined and decisions made regarding the selection of first-line therapies.

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Which Cows to Dry Treat

There are two methods of dry cow therapy and both have their merits. However, producers are advised to consult their veterinarian and select the most appropriate treatment strategy based on the udder health status of their herd. The two methods are blanket dry cow treatment and selective dry cow treatment.

Blanket Dry Cow Treatment

The most commonly recommended method is blanket dry cow treatment, the treatment of all quarters of all cows immediately following the last milking.

This method is simple to adopt, reaches all infected quarters, is more effective than selective treatment in preventing new dry period infections and does not require laboratory and screening procedures.

Although total treatment costs for this method are higher than for selective therapy, economics still favour blanket dry cow therapy.

In general, use blanket dry cow therapy when either:

• the bulk tank SCC > 500,000;
• 4 or more clinical cases/100 cows/3 days;
• the quarter infection rate > 15% or,
• the individual cow SCC average for all cows >250,000.

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Selective Dry Cow Treatment

The alternative strategy to the whole-herd blanket dry cow treatment approach is selective dry cow treatment immediately following the last milking.

Consider using selective dry cow therapy when the monthly bulk tank SCC stays consistently below 200,000 and the quarter infection rate is less than 15%. Treat only the following cows:

• individual cows with peak SCC > 250,000;
• cows that had clinical mastitis during lactation; and
• cows from which a major mastitis organism has been cultured from the milk.

Cow selection for treatment is based on updated monthly records of individual cow SCCs or CMT scores. In addition, laboratory culture of milk samples will determine which quarters are infected and require treatment. Antibiotic sensitivity testing will assist in choosing the appropriate antibiotic for treatment.

Regardless of the treatment method employed, cows with an elevated SCC and low production in late lactation should be dried-off early and treated. This action will benefit the cow that is treated, as well as the herd, by removing a potential source of infection to other milking cows.

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Other Management Practices

Controlled studies have shown that 35% of all new intramammary infections occur during the dry period, particularly during the critical high-risk period of 2-3 weeks after drying-off and two weeks before calving (Figure 1). Although dry cow therapy is an integral part of all mastitis control programs, effectiveness of therapy can be enhanced by other management practices, including:

• clipping the hair on the udders, the flanks and inside the hind legs;

• providing adequate space, ventilation, bedding, and lighting to ensure cleanliness and comfort at all times;

• ensuring that the dry cow feeding program is nutritionally balanced, thus reducing the risk of milk fever at calving, which predisposes the fresh cow to mastitis;

• adopting an effective fly-control program;

• examining the udder at weekly intervals throughout the dry period;

• taking precautions to prevent frozen teats; and

• milking the cow out completely following calving. Flare-ups of clinical mastitis at calving are frequently related to incomplete milking at this critical time, and not to the fact that the cow was dry-treated as many dairy producers believe. Researchers report that a reduction of milk production by as much as 10% is probable when fresh cows are milked intermittently the first few days of lactation.

Figure 1. Frequency Distribution of New Intramammary Infections During the Dry Period (Courtesy of Dr. J.K. Reneau, University of Minnesota)

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Summary

Mastitis remains the single most economically important disease affecting both milk production and quality. Mastitis can be prevented when an effective control program is adopted. Dry cow therapy is an essential part of this control program. To be fully effective, dry cow treatment should be used in conjunction with recommended practices for environmental control, equipment management, and milking management.

Related Links

• Mastitis Prevention: Environmental Control

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