Cows after completing lactation period of 305 days or more, if advanced pregnant need to be dried off to give rest to the udder to prepare for the next lactation. Both onset of lactation and drying off are complex biochemical processes associated with switching a number of genes to start the process of milk synthesis and in case of drying off switching of lactation genes and activating the apoptosis genes. Any error during the drying off dairy cows would lead to loss of udder tissues and affect the cows’ health and the next lactation.
When the cow should be dried-off?
This a dilemma many farmers face, especially if the cows are high yielders. If a cow is pregnant and in advanced stage, the udder should be given a rest period of 45-60 days. Many studies have shown this to be important. Although there are researchers who believe that there is no need to dry-off a cow, but this is not an accepted approach. In case a cow is not advanced pregnant and giving enough milk, the farmers can continue milking such cows until the production cost is less than the feeding cost. For how long a cow should be milked also depends on several factors. Elongated lactation period indicates breeding problems in the herd and should be given attention first. A cow on extended lactation period is not considered as economic converter of feed to milk. In India, however, there are farmers who continue to milk animals beyond even one year, for simple reason that any amount of milk they get pays for cows’ sustenance. Ideally, an advanced pregnant cow should be dried off 45-60 days prior to expected date of calving. In case of early-pregnant or non-pregnant the cow can be milked till the cost of feeding (additional concentrate) is less than the revenue from the milk produced.
Why drying-off methodically is essential?
Approximately 60% of all early lactation mastitis and pulmonary infections has origin in the dry period. In case of sub-clinical mastitis, it is difficult to get rid of infections due to lactation process and fear of milk contamination. Such cases can also be handled at the time of drying-off. During drying off there are two critical phases: (a) the first week after drying-off and (b) one week prior to calving. In the first phase, a keratin plug is formed as a seal that takes care of ascending infections during the dry period, whereas one week prior to calving the plug slowly disappears in preparation of the lactation. The udder is highly susceptible to infections in both phases. The farmers must be careful when the cows are producing large volume of milk at the time of drying off as such cows, if not properly handled have 100% chance of contracting udder infections. The reason is when lot of residual milk is present in udder, the white blood cells are diverted to clear-off milk fat and other molecules present in mammary alveoli and hence these can’t fight invading pathogens.
Management of drying-off
There are two different approaches. In the first the advice is to stop milking the cows abruptly and the second approach is to stop milking in phases, that is first milk the cows once a day, then alternate day and so on. Many researchers are of a view that slow-stopping of milking may pose problems because removing milk leads to stimulating milk synthesis and if lot of residual milk is left in the udder, it might lead to infections. The general sound advice is to adapt complete stoppage of milk. The process of drying off should start at least 15 days before actual drying off date. The cows should receive restricted feed, preferably only high- quality forages enough to supply maintenance energy. This would lead to severe reduction in milk synthesis.
Should acriflavine or lugol’s iodine be administered to induce udder involution?
In early 1950s with a view to sanitize the pathogen in udder acriflavine or weak lugol’s iodine was used. But, these cause severe inflammatory response, swelling and pain and in many cases it may be severe enough to cause irreparable damage to the udder secretary tissues. There few reports published on the use of prolactin antagonist Cabergoline. It is an ergoline derivative which inhibits prolactin hormone responsible for milk synthesis. A single injection of 5.6 mg cabergoline in trials was found to mammary apoptosis and onset of drying-off. The drug has been found to reduce mammary infection contracted during the dry-off period.
Dry-cow therapy- with or without antibiotics
This is also debatable issue. The choice depends on general management in the farm, incidence of clinical mastitis cases during the year and the somatic cell count profile of the cow. The thumb rule is that if you suspect the cow must be having residual udder infection then antibiotic should be added at the time of drying off therapy. Should this be a short-acting or slow-release antibiotic will also depend on the vet choice. In farms where the cows are tied on concrete floors (like in India), I always prefer using antibiotic with a sealant. If the sealant is efficient then antibiotic later than one week would not be needed as by that time the physiological seal would form assisted by the sealant. But since in high yielding cows due to sub-clinical hypocalcaemia and the stress of milking during the lactation the seal formation might be delayed. If a sealant is used there is no justification for use of slow-release long acting antibiotics beyond a week. Once sealant is administered, the teat canal should not be disturbed.
In India long-acting antibiotic containing non-sealant dry cow therapy is available. A novel dry cow therapy formulation with a natural polymer sealant and slow release antibiotic is undergoing clinical trials. The in vitro and in situ studies have shown good sealant property and release of antibiotic for around 45 days. In high risk-cows, dry cow therapy could be followed by Novadip treatment daily for 15 days to high yielding cows to provide total protection during the dry period.
High risk period one week prior to calving:
In crossbred cows such reports are increasing and two questions are commonly posed: (a) the cow udder is leaky with milk, should colostrum be removed? (b) Should any intramammary administration is necessary to take care of the infection. In case the cow is leaky and colostrum is synthesized and udder pressure is high, it is always advisable to remove milk else it will cause infections and negative feedback to milk synthesis. Should the cow be milked even if the calf is not born? The answer is yes. In case the cow is otherwise ready to face the calving process, termination can be induced by administering dexamethasone 40-80 mg intramuscular. This will induce normal birth within 72 hours of administration.
Should cows teats be dipped daily one week prior to calving?
Yes, I advise teat dipping with a barrier type teat dip two-to three weeks prior to calving daily to take care of leaky teat even if dry cow sealant has been administered at the time of drying off. One such barrier teat dip is now available in India (Novadip-Saife Vetmed). On dipping, it forms a barrier film which does not permit bacteria to enter teat canal and act as external short-duration sealant.