Prepare In Advance For Drying Off

This post from

Eamon Guineavan MRCVS| Veterinary Surgeon at McLaughlin’s Veterinary Clinic

 

For a typical spring calving herd, we are in the final months of lactation 2020. The last weeks of any lactation is an important time for mastitis control. Somatic Cell Count (SCC) can creep up during this time; a small rise in an individual cow’s SCC may be normal at this stage, however large increases in SCC in individual cows may indicate a significant sub-clinical infection. Now is the time to put the final plan in place for this year’s dry period.

What is the ideal dry period length?

A dry period of at least 60 days has been shown to increase milk yield in subsequent lactations when compared with a 32 day dry period. This length of time is needed for the renewal of the producing cells in the udder.

The goals of dry period treatment

1. Cure infections
2. Prevent new infections at the time of drying off at the time of drying off and throughout the dry period.

Blanket treatment or selective dry cow treatment (DCT)

Blanket treatment involves treating all cows in the herd with antibiotic DCT with or without teat sealer. Selective DCT refers to treating a selection of cows with antibiotic DCT and all other cows in the herd receive teat sealer only. This treatment allows for more prudent use of antibiotics, however it is not without risk therefore veterinary consultation should be sought before moving to selective DCT.

Selective DCT may be considered for herds with the following:

• Good evidence of a low prevalence of infection eg bulk milk SCC consistently <200,000 cells/ml, clinical mastitis rate <2% during the three months to drying off etc.
• Regularly milk recording, with a recording in the last month prior to  drying off
• Records of all clinical mastitis cases, including culture and sensitivity results
• High standard of hygiene at drying off, throughout the dry period and at calving

Within these herds; cows with a SCC consistently <100,00 cells/ml throughout the lactation and with no history of clinical mastitis may be considered suitable candidates for receiving teat sealer only. All other cows should receive antibiotic DCT and teat sealer.

There is a proposal that by January 2022 selective DCT will be compulsory in Ireland.

Choice of dry cow treatment

There are two main types of dry cow treatment; antibiotic dry cow tubes and teat sealers.

The antibiotic in dry cow tubes is designed to remain in the udder for a prolonged period of time (differs with various products) at a concentration that is capable of killing specific mastitis causing bacteria. Antibiotic DCT and teat sealers also protect against the formation of new infections in the dry period. New Zealand research has shown that quarters receiving dry cow treatment had a higher rate of teat canal closure than untreated quarters.

Your choice of antibiotic DCT should be based on:

• Culture and sensitivity results from previous clinical mastitis cases
• Culture and sensitivity results from high SCC cows identified on the problem cow report
• Activity against certain bacteria eg. Staph. aureus, Strep. uberis & E. coli
• Period of protection for new infections
• Length of the dry period

It is not recommended to rotate your antibiotic DCT unless you have a reason eg. identified antibiotic resistance within the herd.

A word on antimicrobial resistance

AMR is the ability of a bug to develop resistance to the effects of a drug which it was previously susceptible too. Antibiotic resistance is a subset of this; when a type of bacteria develops resistance to a particular antibiotic. The use of antibiotics in both humans and animals increases the risk of AMR developing and therefore responsible use is encouraged. The World Health Organisation (WHO) classify antibiotics based on their importance in human medicine into a number of categories. One such category is “Highest Priority Critically Important Antibiotics for Human Health (HP-CIA)”. In 2018 8% of antibiotic dry cow tubes used contained a HP-CIA. This class of antibiotic should not be used as a first line treatment i.e. if there is an effective alternative available.

Consider early drying off for certain cows

Plan the drying off time based on expected calving dates. For seasonal calving herds this often means drying off cows in batches. It may be worth considering drying off high SCC cows earlier to a) lower bulk tank SCC and b) reduce the risk of spread of infection. Other possible candidates for early drying off may be thin cows or those with a concurrent issue eg. lameness.

Consider culling persistently infected cows

Cure rates from antibiotic DCT are best for younger cows and worse for older cows with chronic infections. Some types of bacteria, eg Staph. aureus are difficult  to successfully treat regardless of age. Chronically infected cows are a source of infection for the rest of the herd nd a small number of SCC cows may be responsible for a significant increase in bulk tank SCC. Culling persistently infected cows is a key part of mastitis control.

Consider culling cows;

• With high SCC in two consecutive lactations despite treatment with antibiotic DCT in the dry period in between
• Which have three clinical cases of mastitis during the lactation. If only one quarter was involved it may be an option to dry off that quarter and milk on.

Do not use antibiotic DCT on cows that will be culled immediately and ensure adherence to withdrawal periods for subsequent culling of treated cows.

Preparation of dry cow housing

Providing a clean, dry environment around the time of drying off and during the dry period plays a vital role in mastitis control. Now may be a good time to address housing issues from last year and provide general maintenance to water troughs etc. Studies have shown that 35% of all new intramammary infections occur during the dry period; particularly during the critical high-risk periods of two to three weeks after drying off and two weeks before calving.