Dry period infections are a very important part of the epidemiology of environmental pathogens such as E. coli and S. uberis. These infections often remain subclinical throughout the dry period, but are then an important cause of clinical mastitis in the first few months of the subsequent lactation period. This article will give more insight and information about the different stages of the dry period and their relation to mastitis.
The dry period
The dry period is an important resting period for the dairy cow, as it is when fresh udder tissue is formed in readiness for lactation, and it provides an important opportunity to rid the udder of many pathogens that can potentially cause mastitis.
There are three phases in the dry period:
1) The first 2 weeks. The teat canal slowly closes, and a plug of keratin is excreted into the teat canal to form a teat seal.
2) The rest phase during the mid dry period. The alveolar cells do not die, but simply collapse, so that the space within the alveolus disappears and the udder consists of a greater proportion of connective tissue.
3) The last two weeks before calving. New secretory tissue is laid down when the cow starts to ‘freshen’ ready for the next calving, and hence, the total amount of secretory tissue (and therefore yield) increases from one lactation to the next. The keratin plug slowly dissolves ready for the start of the new lactation period.
Tackling old infections
The dry period is essential for the recovery of the mammary gland, and also offers an opportunity to tackle udder infections. The recovery process alone will eliminate some infections, but it is much more effective when combined with antibiotic treatment. In fact, particularly for subclinical udder infections, the most effective time to treat is at drying off because higher doses (higher concentrations) can be used than with milking cows and antibiotics remain in the udder for a longer time (antibiotics on a slow-release base). This means that the cure rate for dry cow therapy is much higher than for milking cow therapy, especially for bacteria such as Staphylococcus aureus.
Preventing new infections
It is during the first and the last 2 weeks of the dry period (when the teat canal keratin plug forms and dissolves) that the cow is especially susceptible to new infections. The maximum level of new infections occurs just before and just after calving, which is when the teat canal keratin plug dissolves and milk is starting to accumulate in the udder. Therefore, this is the time of major risk for new dry period infections, and this is when management of the cow should be at its highest. Think about cleaning floors to reduce sites of potential infection, providing clean and comfortable cubicles, reducing stress during this period and keeping an eye on the health of the cow and udder (very important). During the dry period, there are no KPIs for the cow, so a manual check of the cow is required.
The greatest number of new cases of mastitis occur in the first 4 weeks of lactation, and, of the clinical cases, some 60% originate from infections that have become established during the dry period. It should also be noted that dry period infections continue to cause clinical mastitis up until the fifth month after calving. (Green et al., 2002)
New infections contracted during the dry period lead to clinical mastitis during the first 4 months after calving. The light blue bars are clinical mastitis cases arising from lactation infections and the dark blue bars are from dry period infections. (Green et al., 2002)
The keratin plug formed in the first two weeks of the dry period is very important; unfortunately, many cows do not form an effective teat seal, and in these cows the risk of new infections is even higher. The study by Woolford et al. from 1998 showed that 97% of dry period mastitis infections were in ‘open’ quarters. There are a lot of factors which have an influence on the forming of a teat seal:
- Overall production: cows with higher total yields form a less effective seal
- Milk flow rates: fast milkers form a less effective seal and are more likely to leak milk
- Milk yield at drying off: the higher the yield at drying off, the higher the risk of an ineffective teat seal
- Teat end damage
- Dry cow therapy: leads to a more effective seal
Dwingell et al., 2002. This graph shows cows with higher yield are more susceptible for open quarters during the dry period.
In conclusion, using teat-sealers dramatically reduces the incidence of mastitis in early lactation, and also provides a clean and comfortable environment for the dry cow, smooth and healthy teat ends and a lowering of the milk yield at the drying off. Dry cow tubes should be administered gently, hygienically, and according a good practice. Strict hygiene is essential, especially if teat sealant is being administered alone, as this has no antibacterial properties. Ensure that teats are dipped immediately after tubing, thereby removing any bacteria that might be able to colonise on the teat end and produce a new infection. As incorrect administration can cause severe consequences – both to the level of infections of the udder and the rate of infected cows – it is wise to check this standard operating procedure with a veterinarian. In addition, be aware of the negative effects of letting the teat seal enter into the robotic milk system, so make sure the seal is removed before the cow enters the robot.