GOOD MANAGEMENT PRACTICES FOR DRY COW THERAPY (DCT)
Post no-1341 Dt 29/07/2019
(Compiled & shared by-DR RAJESH KUMAR SINGH, JAMSHEDPUR, JHARKHAND, INDIA, 9431309542, rajeshsinghvet@gmail.com)
All lactating dairy cows will undergo a ‘dry period’ every year, around 2 months before their calving date. During this period the cows are not milked; this allows the cow’s udder to regenerate its tissues and be restored back to its healthiest state, as well as getting rid of any mastitis that may have been acquired while lactating. As dry cows are not producing milk 24/7, they do not use as much energy and nutrients for milk production, which means they have more of these assets to divert towards the impending pregnancy and calving, which takes up huge amounts of both energy and nutrients. A deficiency in either of these can be catastrophic for both the calf and dam.
The dry period of cattle is sometimes referred to as ‘DCT’ – Dry Cow Therapy. It is one of the most crucial points in a cow’s cycle as it can reduce mastitis infections, provide a regeneration time and also lead to successful calving and a healthy calf.
Dry periods in cattle are an essential part of the cow’s lactation cycle; it allows the lining of the udder to be repaired and restored, so that when lactation starts again, milk production is optimal. A dry period of at least 40 days is needed to get optimal milk production after calving and throughout the following lactation cycle. If it is less than 40 days, milk production will be reduced.
NB:
• Every year lactating cows are not milked for 2 months before calving.
• This period is crucial for reducing mastitis infections.
• But also can be a crucial period for acquiring infections.
• It allows the cow to regenerate tissues and conserve energy.
• 2 months before calving a pregnant cow is dried off.
• This can help to cure existing mastitis infections of the udder.
• It also helps to prevent new infections, because long lasting antibiotics are used.
• These antibiotics provide protection against new bacteria and destroy bacteria that has already colonised in the udder.
• The antibiotics are most effective in the first few weeks so towards the end of the dry period, cows are most susceptible to new mastitis infections.
When are they dried off?
Lactating cows are dried off around 2 months / 60 days before their calving date. This means that they lactate for around 305 days per year, depending on how quickly they become pregnant.
If a cow becomes pregnant in January, she will be dried off (i.e. not milked anymore) in July and will calve in September. From the period between Jan and July she is lactating and so will be milked, between July and Sept she is not being milked. After she has calved in September she will start her lactation again, which will last for another 305 days; during this time she will become pregnant again, usually around 2-3 months after her previous calf.
What is dry cow therapy and why is it important?———
Dry cow therapy has traditionally been the use of intramammary antibiotic therapy immediately after the last milking of lactation.
The use of intramammary antibiotics at drying off can decrease the number of existing intramammary infections (i.e. mastitis) and prevent new infections during the early weeks of the dry period.
The use of dry cow treatment is one component of an effective mastitis control program; however should not be the only component of the prevention against mastitis.
Essentially what happens is, at a point of 60 days before calving, the cow is milked for the last time in that lactation and antibiotics are infused with the udder. Each teat is given a tube of antibiotic which is known as an intramammary long acting antibiotic. This means that at the end of this process, all 4 quarters of the udder will be protected for the forthcoming 60 days. This process must be kept as hygienic and sterile as possible in order to minimise the chance of bacterial invasion of the teat. There are several additional management options which are used optionally depending on the stockman’s choice. These are outlined further on in this document.
Curing existing infections…———-
The dry period is a much more effective time to treat existing mastitis infections, rather than during lactation. This is mainly due to the following reasons:
• The cure rate is higher than during lactation, particularly for S. aureus.
• A much higher dose of antibiotic can be used safely, meaning that the pathogens are more likely to be killed.
• The retention time of the antibiotic is longer, so giving protection for longer and ensuring that all pathogens are killed.
• Tissues damaged by mastitis can be regenerated before freshening.
• There is a reduced risk of contaminating milk with drug residues.
Preventing new infections…———
The risk of new intramammary infection is greatest during
the early and latter portions of the dry period. Most dry cow treatments provide sufficient protection after drying off so that:
A) The frequency of new infections during the dry period is reduced.
B) The incidence of clinical mastitis at freshening may be reduced.
There are very few products which provide activity for the whole dry period. Most have maximum activity in the first few weeks and activity declines as the dry period length increases. If they do have extended activity, the milk residues need to be kept in mind if a cow is due to calve early, as this may mean that milk is being given within the withdrawal period of that drug.
What products are used in dry cow therapy?
•
Antimicrobial infusions/Intramammary antibiotics:
Only approved commercial antibiotic products specifically for dry cow therapy in single dose containers for intramammary infusion should be used. These products contain high levels of one or more antibiotics in a slow release base which will maintain therapeutic levels in the dry udder for asignificant length of time. The aim of these products is to kill bacteria in the udder, whether the bacteria are already colonised on administration, or are invading due to new infection.
These antibiotics, and their administrative utensils, have been preparedaseptically (so they are sterile), it is important that the stockman takes all measures to provide the highest grade of aseptic technique possible. This will minimise the chance of bacteria invading the teat.
Most dry cow therapy products are designed to eliminate existing infections by Gram-positive bacteria, particularly S. aureus and the streptococcal infections at drying off and to prevent new infections in the early dry period.
Many producers have already eliminated Streptococcus agalactiae and dramatically reduced levels of S. aureus in their herds. In herds where confinement and stocking is high, a higher percentage of new infections during the dry period are caused by environmental bacteria.
Most dry cow therapy products are reasonably effective against environmental streptococci, especially S. uberis, but lack efficacy against Gram-negative environmental bacteria, especially coliforms (e.g. E. coli).
• Internal teat sealant infusion:
Sealing off the teat canal by the natural keratin plug that forms during the dry period is the primary natural component protecting against new intramammary infection in the late dry period. Potential damage to that protection is one of the reasons why repeated infusions are not recommended.
It has been documented that a significant proportion of quarters experience long delays or outright failure to form a complete keratin plug during the dry period, putting these quarters at increased risk for experiencing new mastitis infections. One study has reported that this risk is increased in cows producing high levels of milk at drying off.
One method of supplementing the teat’s defences throughout the entire dry period is by use of an internal teat sealant. An artificial internal sealant is available for use alone or in combination with an antibiotic infusion. This product has no antimicrobial activity, it simply acts as a physical barrier to bacteria, and is therefore if used alone it is recommended for use only in the uninfected udder.
As with other products, it is important that great care is taken over hygiene when administering the sealant.
• External teat sealants:
Another method to supplement the cow’s natural defences is to apply an externalsealant to teats by dipping. These products are adjuncts to antimicrobial infusion and should be used alongside, not instead of. As long as the teat end remains covered, protection from bacteria entering the gland is provided. Thus, for continuous protection, they require visual inspection and reapplicationevery 5-7 days throughout the dry period.
What is the infusion procedure?
Generally, on all farms and husbandry systems, there is a set of guidelines that should be routinely followed by dairy man when drying off cows…
1. Milk the cow as normal until she is finished.
2. Clean and dry the teats.
3. Dip the teats in an effective germicide product (i.e. iodine solution) and allow 30 seconds contact time before wiping off with an individual disposable towel.
4. Clean each teat end using a cotton swab soaked in surgical spirit/70% alcohol solution. Using a separate cotton swab for each teat.
5. Insert the tip of the cannula (nozzle) of the antibiotic tube into the teat and express all of the tube contents. Repeat this with the other 3 teats with separate tubes.
6. Dip teats in germicide again after infusion.
7. Isolate the cow from the main herd and do not milk for the next 60 days (until the cow calves).
8. It is ideal to have a group of dry cows acting as a herd in one field, this makes inspection easier.
What aspects are to be taken into consideration?
Feeding:
Concentrate feeding of high producing cows should be stopped 2 weeks before the anticipated drying off in order to reduce daily yield.
Nutritional management should also be considered. Negative energy balancesand trace element deficiencies during this period can result in impaired immune function.
Repeat infusions:
Research to date indicates there is little, if any, value in treating cows at drying off with multiple infusions, where multiple infusions refers to treating twice at drying off, or at dry off and at some later time.
Subsequent infusions may pose the additional risk of forcing bacteria into the gland as well as the increase risk of antibiotics in milk after freshening (the first milkings after the calf has been delivered).
Preventing drug residues:
Attention must be given to make sure that the drugs for the dry therapy do not remain in the milk or meat (which will be consumed by humans) when that cow is prepared for human consumption.
The period after administration at which the levels of the drug in the body or milk are unacceptably high is known as the withdrawal period. After this period, the animal is then safe to consume or consume from. If a cow calves early, this may be within the withdrawal period of the intramammary antibiotics used, especially if this cow has been given a repeated dose and so this cow’s milk should not be used for human consumption until it exceeds the dry period.
Sanitation / Dry cow management:
Because udders are not milked during the dry period, pathogens are not flushed out of the lower portion of the teat canal. This may lead to new intramammary infections especially by skin colonizing staphylococci. The number of new infections is related to the bacterial population on teat ends. Therefore, exercise lots, loafing areas, stalls and maternity pens should be clean, dry and free from unhygienic conditions. Animals on pasture should not be allowed in ponds or excessively muddy areas.
Dry cow treatment may be helpful in preventing new infections during the early dry period. However, the udder is vulnerable to new infections during the last 2 or 3 weeks of the dry period when the intramammary antibiotics are least effective.
Summer mastitis:
The dry period, as well as being a chance to rid of infections, is also an opportunity for summer mastitis to set in. This type of mastitis is caused by sheep headfly and is most commonly seen in the summer months, affecting dry dairy cows. It can be extremely damaging to udder health and a significant cause of economic loss.
The dry period has 3 stages:
1) Involution – after daily milking stops, milk secretions change and finally dry up. The lining of the udder regresses (reduces in activity and gets smaller) and the teat canal becomes plugged with keratin. This period lasts around 2 weeks.
2) Steady State – after involution the udder stops changing and there is no active secretion of any product. The length of this period depends on the length of the total dry period as the length of stages 1 and 2 are fixed – it is during this steady state that the recovery occurs which allows maximal future production of milk. Shortening this period to <2 weeks will reduce milk production.
3) Colostrum Production – and start of lactation. The machinery of lactation is switched on and the udder starts to enlarge and the lining becomes active. This period lasts around 2 weeks.
In light of these stages it is easy to see why the recommended time frame for drying off is 6-8 weeks before calving… Stage 1 takes 2 weeks to complete and stage 3 also takes 2 weeks, this means that 4 weeks are taken up by stages 1 and 3; the most crucial period, the steady state, has to be at least 2 weeks long as it is necessary for regeneration – this gives an overall total of at least 6 weeksof time that the dry period should last for.
Tackling Infection
As well as being essential for the recovery of the mammary gland, the dry period offers opportunity to tackle udder infection. The recovery process, alone, will eliminate some infections, but it is much more effective when combined withantibiotic treatment. In fact, the dry period can actually be the best time to treat udder infections due to two main reasons:
1) Higher doses of antibiotics can be used than in lactating cows.
2) Antibiotics remain in the udder for longer compared to milking cows, which lose a lot of antibiotic at each milking.
Antibiotics given to dry cows are different than those used to treat mastitis in milking cows – they have a high concentration of antibiotics in a slow-release base. This means that the cure rate for DCT is much higher than for milking cow therapy, especially for cases caused by S. aureus.
An advantage of dry cow antibiotics which is often appreciated is that clearing infections, even mild ones – can aid recovery of damaged mammary tissue and aid the speedy formation of the keratin plug in the teat canal.
Preventing New Infection:
DCT is not just about tackling existing infection. A second aim is in preventingnew infections during the dry period. Even though the cow is not being milked, the udder can still get infected during the dry period. However, each of the 3 stages has different risks associated with it for mastitis.
During the steady state the risk is low, but after drying off and immediately before calving the risks can increase dramatically.
In addition to treat existing infections, DCT has to prevent new ones. This is simple in the early dry period as the high-concentrations of antibiotic which treat infections will also prevent new ones. However, in the period just before calving, antibiotic concentrations will be lower and the risk of infection will be higher.
To make matters more complicated, the infections that dry cow therapy has toprevent tend to be different from those is has to treat (i.e. an existing infection may be caused by E.coli but a new infection may be caused by a different pathogen, e.g. S.aureus.). S. aureus is the most important bacteria to kill as this is the organism which causes most persistent infections. In contrast, dry cow infection, especially in the late dry period, tends to be caused by environmental organisms such as E. coli and S. uberis. Dry cow antibiotics tend not to be equally effective against all 3 bacteria, so choice of antibiotic should always be made based on the bacteria causing the problem.
Which Antibiotic to Use?
There are a range of products available from the vet. The best antibiotic to use will vary from farm-to-farm and often cow-to-cow and year-to-year. There is no simple answer. The key factors to look at are:
1) Length of action – if the average dry period of the cow is fairly long thenlong acting action may be beneficial, but if the dry period is short, withdrawal periods the duration of effect allowed in these cows.
2) Environmental vs Contagious mastitis – if the problem is the former, then preventing infections is key so use an antibiotic with activity against S. uberis and E. coli (as these are the main environmental pathogens causing mastitis); however in the case of the latter, then the cow will benefit more from sacrificingactivity against environmental pathogens by choosing an antibiotic specifically designed to kill S. aureus.
Antibiotic Alternatives
It should be noted that the following treatments are most successfully used in addition to antibiotic treatments and only used instead-of when the cow has extremely good SCC, immune system response and general health well-being.
The formation of the natural keratin plug during the dry period is key component of the cow’s natural protection against udder infection. However, not all cows will form a plug that is effective throughout the dry period…
Artificial internal teat sealants have been developed which can overcome the absence of the keratin plug. If used alone in uninfected cows, these sealants will reduce the risk of new infections during the dry period – they are at least as good as antibiotics in doing this. In infected cows than can be combined with antibiotics and will significantly reduce the risk of new infections in the later dry period, particularly in cows which are dry for longer than the active period of the antibiotic.
An alternative to internal sealants are persistent external teat dips, which protect against new infection by covering the teat end with disinfectant. However, as yet, we do not have products which persist long enough, most require new application every 5-7 days (which in most systems is either unachievable or not worth the labour)
Preparation of the Cow
Cows should be producing less than 15L of milk per day when dried off. This figure should be achieved by gradual reduction in feed intake, not by reducing water availability. Once the figure has been reached the cow can be abruptlydried off – do not skip milkings, the cow should be milked out to full potential and then not milked again.
Dry Cow Treatment Procedure
If done badly, dry cow treatment can result in udder infections and mastitis. These infections often cause extensive udder damage and can be extremely difficult to treat. Attention to detail and strict hygiene precautions are essential to prevent such infections. This is especially important if an internal teat sealant is going to be used without antibiotics.
All staff carrying out dry cow treatment should be familiar with the procedure and know how essential it is to follow it:
1) After milking for the last time, separate the cow off and dry her off after that milking has finished
2) Starting with the teats on the far side of the udder – clean the teat ends with separate teat wipes. Focus on the teat end not the udder
3) Move onto the teats on the near side of the udder and clean those
4) Then starting with the teats on the near side of the udder, infuse each quarter with antibiotic.
a. Insert the antibiotic tube just into the teat canal (<6 mm)
b. Insert the whole of each tube into teat
c. Massage the treatment up into each quarter
5) Immediately following treatment, dip all teats in an
effective teat dip
