Knowing what defines a dry period

Short dry periods were set to be the hot talking point at two Farmers Weekly supported Intervet discussion forums, particularly following the discussion the topic has provoked on the FWi forums.

Like many new ideas, there are some areas of uncertainty for farmers, particularly just what length of dry period is considered short and which cows are suitable for managing in a short dry period system.

Leading the way with the questions on the forum was contributor Milkman who quizzed the experts on whether a short dry period would give a first lactation heifer sufficient time to recover before her next calving.

Responding, vet Chris Watson of the Wood Vet Group, Gloucester, said there were two main issues to consider, first how short the dry period was and second whether the dry period is critical for younger cattle.

“There is definite evidence to show first lactation heifers prefer a longer dry period to allow them to complete udder development. This is less critical in older cows, unless the dry period drops below 30 days when the cellular structure of the udder has insufficient time to completely undergo repair and replacement.

“This progressively reduces yield in the next lactation as the cow is relying on older udder secretory cells for the next lactation.”

But, in first lactation heifers a dry period of 40-45 days will have little or no effect on subsequent milk production, so an overall dry period policy of about six weeeks for all cattle will do no harm and could have many advantages, he explained.

Independent vet consultant James Husband agreed and said reducing heifer dry periods below 45-50 days would be unsuitable for a heifer.

A question vexing forum user Johno was the potential loss of yield from short dry periods. “As I understand it heifers could have a dry period of say 45 days. Cows on the other hand could go down to 30 days, but the loss of milk in the next lactation would be 0-3%. Well 0% would be fine, but 3% would cost me £22,500 in lost income, enough to pay the assistant herdsman.

“My real question is, at what cell count could you use a 30-day dry period, assuming a higher cell count means a greater infection so longer time needed for a dry cow cure. Or would you treat high cell count cows at the end of lactation and then use a standard 30 days for all cows?”

Andrew Biggs of the Vale Vet Group, Tiverton responded to this one and said there was too little experience of short dry periods in the UK to be clear on the effects on cell counts.

“Much of the USA still has an upper limit of 750 for bulk tank cell count, so it is perhaps not quite the same issue as in UK and EU. As I am sure you know the two main risk periods in the dry period are the first two or three weeks after drying off and the two or three weeks up to and around calving.

“The bit in the middle, the true dry period, is less susceptible to letting new infections in and probably when most natural cures take place,” he explained.

“It is thought that the length of these two risk periods are not really changed by changing the dry period length, so by shortening the dry period it is the bit in the middle that is affected most.

“So antibiotic dry cow – with a suitable minimum dry period to allow for short dry periods – in combination with teat seal seems to me to be the best route to get the more certain potential benefits of shorter dry periods.”