Make use of milk records and SCC for SDCT

Use of selective dry cow therapy (SDCT) is an obvious way to help reduce antibiotic usage in the dairy herd but care must be taken with the procedure so that the risk of mastitis during the dry period and early lactation does not increase.

Keeping on top of mastitis is a constant challenge on a dairy farm and with most farmers having their antibiotic use monitored, the need to keep mastitis rates low to limit antibiotic use is a must.

At SRUC’s three dairy herds in the South west of Scotland, there has been a big focus on reducing antibiotic use through SDCT over the last few years. The farms started SDCT in early 2016 and over time confidence has increased with the procedure so that very few cows now receive antibiotics at drying off.

The criteria for drying off treatment of individual cows was set in conjunction with the farms’ vet, using somatic cell count (SCC) data from the last three CIS milk recordings before drying off and is as follows:

• SCC ≤10,000, cow gets antibiotic + teat sealant

• SCC ≥100,000, cow gets antibiotic + teat sealant

• SCC ≥11,000 and ≤99,000, cow gets teat sealant only

• If a cow has had a case of clinical mastitis in the last three months, regardless of SCC, she will get antibiotics at drying off.

Some concerns with SDCT are that cows may be more at risk of infection during the dry period, calve down with mastitis or have a high SCC at first recording post-calving.

However, the use of teat sealant is to prevent new dry period infections which helps deal with many of these concerns.

The main objective of administering antibiotics at drying off is to treat existing infections identified through cell counting and mastitis records, and monitoring failure to cure rates through the dry period is an important part of the health planning review process.

The industry target for mastitis cases is <30 cases per 100 cows per year and for cases of dry period origin (occurring within the first 30 days post-calving and including cases during the dry period), <1 in 12 or <8.3%.

While the case rate on two of the farms is above the industry target, the occurrence of cases in the first 30 days after calving is extremely low, which would suggest that SDCT is not detrimental to udder health.

Also, around three quarters of all cows meet the criteria for SDCT and can be dried off with teat sealant only. This is a saving of around £4200 per year for the three herds based on an antibiotic cost of nearly £9/cow.

The three herds are currently averaging between 32-34kg milk per cow per day and there are many cows being successfully dried off with relatively high milk yields of around 25 litres.

Very strict hygiene procedures are adhered to when drying off cows without antibiotics. This practice takes place after milking has finished and the parlour has been cleaned as normal. SRUC farms’ standard operating procedure for drying off cows is as follows:

• Ideally two people are present (lead and assistant) and have changed into clean overalls after milking.

• Lead has full length examination gloves on and then a separate pair of milking gloves per cow. Assistant also wears milking gloves.

• Cows are restrained in the parlour by rope and bar to prevent any kicking etc.

• Assistant will hand sterile cloths and tubes to lead and keep a count of equipment to enable lead person to carry out a surgical procedure (as hygienically as possible).

• Cows are initially sprayed with pre-spray milking teat spray then wiped with an individual cloth.

• Each teat end is disinfected with cotton wool soaked in surgical spirit, with a separate swab for each teat. The furthest away teats are disinfected first.

• Sealant will be inserted into nearest teats first and the furthest away teats last. If cows are also receiving antibiotics at drying off, antibiotic is massaged into the udder first before inserting sealant.

• The sealant is not massaged into the udder. The base of the teat near the udder is pinched off as the sealant is inserted as it must remain within the teat canal.

• Teats are then sprayed with a long-acting iodine-based teat spray.

• Once released from the parlour, cows are kept in a pen to ensure they stand for 30 minutes before being moved to dry cow cubicle housing away from the milking premises.

The basis for success of SDCT is making good use of milk records on SCC data and mastitis rates and carrying out the procedure as cleanly and hygienically as possible. SDCT is proven to work well at no detriment to udder health in either the dry period or early lactation, but good dry cow management and cleanliness of the housing environment is crucial to its success.

This article has been produced as part of work funded by the Universities Innovation Fund from the Scottish Funding Council.