Short dry periods have been the talk of the dairy sector for the past year or so. To help you understand what they are and how they could help your herd profits Farmers Weekly and Intervet have assembled a team of experts to look at the issues they present.
So, what are the main considerations when assessing whether short dry periods are right for your herd? Consultant vet James Husband says nutrition is a key issue which must be addressed.
“When we consider the dry cow’s nutritional requirements, we need to think about keeping condition constant and preparing the cow for the next lactation,” says Mr Husband.
“This traditionally involves using two dry cow groups and two – or more in some cases – rations being fed. The far-off ration is usually fed from drying off to about three weeks before calving.
“Getting the cow back in gear for the next lactation means altering the ration prior to calving from the high-fibre far-off diet to the transition ration,” he adds.
The core issue of the dry period is change. Negative energy balance can start to occur before cows calve, mainly through decreased appetite pre-calving.
This is almost certainly due to underlying hormonal changes associated with late pregnancy, but will be exacerbated by diet and group changes. The effect is seen as a drop in dry matter intake. This causes a negative energy balance immediately before calving which is made worse by the energetic demands of colostrum/milk production.
But it looks as if shortening the dry period for more modest periods can allow a single dry cow ration to be fed for the whole period.
The aim for dry cow mastitis control is preventing new infection and removing existing infection. As antibiotic control is the main tool for this, it means when the dry period is shortened there are some key issues, says Somerset vet Andy Biggs.
“The first of these is the length of action of any antibiotic dry cow therapy (DCT). The second is whether there is enough time to establish a cure for any infection present from the last lactation or picked up during the dry period. And, lastly, that it will not increase infection risk at either end of the dry period.”
The level of new infection during the dry period is much more likely to determine the overall balance of infection over the dry period than is the cure rate from previous infections, he says. Shortening the dry period and using an appropriate treatment should reduce the window for infection and, hence, mastitis cases.
“Preventing new infection should also be no problem with a short dry period. The early risk phase is well covered with good levels of DCT present soon after drying off. There should be more chance of the DCT being active in the important risk period just before calving.”
In recent studies designed to examine different dry periods in cows and assess the subsequent lactation yield, it looks as if there is a consistent picture emerging, says Stroud vet Chris Watson.
“For dry periods down to 30 days there is little or no change in the subsequent milk production. Studies show between 0% and 3% decrease in yield. For cows that have no dry period there is a subsequent reduction in milk yield of about 18-25%. This is a consistent and large effect.
Research work has also shown that milk composition improves with short dry periods, which clearly has an economic benefit.
The table sets out the cost factors involved for milk production by shortening the dry period where 60 days is the standard dry period.
There are a number of factors which can negatively affect cow welfare. These are overcrowding, social problems, disease, and changing diets that lead to changes within the body’s digestive system, reckons vet Rob Drysdale.
“Changing diets often involves group changes, too, which cause considerable social stress. Cows are hierarchical animals.”
The addition of cows to a group causes a period of destabilisation and increased social interaction while re-establishment of the hierarchy occurs, he adds.
These changes in social ranking have detrimental effects on the cow’s nutrition, milk yield and the amount of time it spends lying down. “A typical cow transferred from one dry group to another is involved in about 10 social interactions an hour immediately after the move.”
This is twice as many as occur with other normal social interactions within the group. “On top of this the cow is under a changing hormonal regime as calving approaches, which in itself reduces appetite and food intake,” he adds.
Simplification of dry cow management not only has beneficial effects on the cows. Labour is often limited on farms. A strategy of shortening dry periods to 40 days or so can allow the feeding of one ration. This takes a degree of complexity out of the system and leaves less room for human error.
Short dry periods allow a single dry cow ration to be fed, greatly reducing the risk of negative energy balance post-calving.
|HAVE YOUR SAY|
|COST FACTORS FOR SHORTER DRY PERIOD|
|30 days||40 days||50 days||60 days||70 days|
|Yield @ drying off (litres a day)||16||16.4||17||17.6||18.3|
|Milk difference – extra litres in current lactation||500||340||173||0||-179|
|Dry cows/100 cows||8.2||11||13.7||16.4||19.2|
|Margin over concentrate feed £(1)||66||45||23||0||-24|
|Total savings per cow £(2)||96||65||33||0||-34|