Udder health during the dry period
Approximately 60% of all early lactation mastitis cases has an origin in the dry period (please refer to Figure 1). Therefore, to prevent new infections from occurring prior to calving and to cure any existing infections, dairy cows should be dried off methodically and carefully.
Figure 1: Origin of clinical mastitis cases during lactation (Green et al. Journal of Dairy Science 2002)
Two critical stages of the dry period when udder health is at risk are: the first week after drying off and the week prior to calving (please refer to Figure 2). During the first critical stage, the udder’s natural defence mechanism − a keratin plug in the teat canal − is formed, while in the second stage, prior to calving, this plug slowly disappears in preparation of lactation. The keratin plug prevents bacteria from entering the teat canal during the dry period.
Figure 2: Frequency of new coliform intramammary infections during the lactation cycle (Green et al. In Practice 2002)
The udder is very susceptible to new infections at the beginning and end of the dry period. Furthermore, some cows do not form a keratin plug in the teat canal during the entire dry period (please refer to Figure 3).
Figure 3: Evolution of teats without a keratin plug during the dry period (Green et al. Journal of Dairy Science 2002)
Good milk yield management at the point of drying off is very important because a high milk yield will increase the risk of developing a new intramammary infection by 100% after drying off. A high volume of residual milk in the udder will stimulate the white blood cells to concentrate on absorbing milk fat cellular debris and become less active in preventing bacteria from entering the udder. In addition, cows with a high milk volume at drying off have a weaker keratin plug compared to other cows due to delayed keratin plug formation in the teat canal.
Dry off treatment
An intramammary antibiotic treatment at drying off will eliminate existing infections and prevent new infections during the first few weeks of the dry period. However, this treatment alone will not prevent new infections later on in the dry period due to the limited coverage of antibiotics. Research conducted at international level and by Lely indicates that using an internal teat sealant in combination with antibiotics further reduces the risk of new infections. This product mimics the natural keratin plug and prevents bacteria from entering the teat canal. The use of an internal teat sealant alone is possible in low Somatic Cell Count (SCC) cows, however extra hygienic care has to be taken when administering the teat sealant. Make sure the internal teat sealant is removed after calving, so that the plug does not end up in the milking system.
The proper dry off treatment should be discussed with the herd veterinarian and noted in a Standard Operating Procedure manual. The therapy depends on the duration of the dry period, the occurrence of specific mastitis pathogens, treatment success, farm specific situation, etc. By monitoring the SCC level of cows prior to the start of the dry period and again after calving, dry-off therapy and management can be objectively evaluated and adjusted, if necessary.
Reducing the risk of infection early in the dry period
- One of the main factors involved in determining dry off success is the amount of milk the cows are still producing during the dry period. The aim is to decrease milk yield to less than 15 kg. This can be achieved through a timely reduction of concentrates and by reducing energy and protein content in the feed (i.e. feeding more fibrous roughage such as hay or haylage). For more information about the settings in the T4C management programme, please refer to Figure 4.
- Milking should be stopped abruptly. It is not advisable to continue milking cows less than twice a day before dry-off, since this increases the risk of new infections and delays the formation of the keratin plug after cessation of milking.
- The dry-off therapy should be applied in a safe and clean environment, after the last milking. The teat ends should be disinfected prior to administering the treatment and after administration the teats should be dipped.
Figure 4: Advised T4C settings; this will ensure a timely decrease in concentrates to 2 kg at the expected moment of dry off. In larger herds, drying off groups of cows can be done routinely after being fed a specific drying off ration.
Reducing the risk of infection during the entire dry period
- A clean environment: good hygiene and a good barn climate prevent growth/persistence of bacteria in bedding material and possible contamination of the udder when lying down.
- A well-balanced ration of energy, protein, minerals and vitamins: important in keeping the immune system of the cow at an optimal level and in maintaining an optimum Body Condition Score (3 - 3.5).
- Minimise stress: stress reduces the cow’s immune system.
- Maximise cow comfort (comfortable bedding, exercise area): this will result in better overall health and may help to reduce udder oedema.
Reducing the risk of infections during calving
- Prevent udder oedema: oedema compromises the blood flow and immune function in the udder thus increasing the risk of mastitis. Udder oedema is mainly related to the intake of too much Na+ and K+ during the dry period, which causes the retention of fluid. An increased intake of these ions will increase the risk of hypocalcaemia. Grassland products are especially rich in Na+ and K+. Exercise will help to reduce the risk of udder oedema.
- Cows that leak milk before calving should be milked and their colostrum should be stored in the freezer: milking will flush out any pathogens in the teat canal. In addition, free fatty acids are removed from the blood through the milk, decreasing the risk of fatty liver syndrome and ketosis.
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