60-day dry period for

older cows may be too long

Scientist talks to dairy producers about research on 30-day dry periods - none at all

Dairy producers may want to re-think their handling of dry cow periods - a shorter "vacation" for the pregnant cow may be better for her than farmers have thought.

That's what a large crowd of dairy farmers and students heard from Robert Collier, an animal scientist with the University of Arizona, at the 15th annual Arlington Dairy Day on Dec. 8.

The traditional 60-day dry period for dairy cows, just before they give birth, was adopted during World War II as a way to maximize milk production, Collier said.

But research since that time has shown that the theory of "the cow needs a rest" just isn't true.

Collier says that if cows could continue lactating all year around they would be healthier because they wouldn't have the series of changes in their diet and housing that can wreak havoc on the transitioning cow.

Older cows may be able to do just fine with a dry period as short as 30 days, he told his audience, which can increase income on the farm and actually be better for the cow.

But he cautioned that first lactation animals have a greater dry period requirement than older cows and such shortened dry periods shouldn't be tried on them.



Mammary cells

regenerating

Dairy scientists are learning that there is an effect at the cellular level in the udder of the dry cow, with mammary cells regenerating at a more rapid rate when a cow is dry than when she is milking.

"This growth in cells continues in milking cows, but it is slower. The lactating mammary gland has a slower rate of mammary cell development," he said.

The development and changeover of these mammary cells is completed by 25 days of the dry period, he said, suggesting that 30 days may be enough of a dry period.

If the producer uses recombinant bovine somatotropin (bST) on the cows, research has shown there is no loss of production using a 30-day dry period.

The added benefit, he said, is that the 30-day dry period eliminates one ration change for the cow and reduces one opportunity for her to have problems.

Collier cited a study that showed a 21 percent improvement in dry matter intake in cows that were dry 28 days compared to those that were dry 56 days.

Cows that are lactating are easier to put body condition on than dry cows he said, because they have an improved energy balance.

Most cows have reached their maximum milk production by their third lactation and once they reach that point they require less of a dry period. But the mammary cells in a first-calf heifer must be given time to develop and these younger animals need a longer dry period, he said.



Older cows best

candidates

Older cows are good candidates for 30-day dry periods and continuous milking if bST is used. But even in some studies where the supplemental hormone was not used, cows showed no loss in subsequent production from dry periods as short as 28 days.

A lot of things go on between dry off and peak lactation. Feed intake doesn't keep up with the loss of body energy stores and cows get into metabolic problems and transition disorders.

"The cow will be healthier if she can avoid three different ration changes," he said. When cows are dried off their feed intake drops precipitously.

Only about half of dairy cows complete the transition without one of a group of 10 disorders, Collier said, including milk fever, retained placenta, metritis, ketosis, fatty liver and others.

When low-dose somatotropin is used it appears to improve the cow's ability to ward off these disorders.

That's because researchers are finding that the hormone can up-regulate receptors in the liver and also enhances immune response.

Collier added that too much bST will down-regulate these receptors. (Such low-dose supplementation is only experimental and is not allowed by federal drug regulations, he added.)

"If high-producing dairy cows are not managed properly they will be stressed. This comes from poor facilities, over- or under feeding protein or energy, insufficient environmental control and dry-off strategy," he said.

Collier said the components in the milk are not altered by the length of the dry period but colostrum quality may be affected and should be monitored.

Milk yield in these cows with short dry periods is equal to that of cows that had the traditional 60-day dry period. Research is ongoing into continuously milking cows - that is not giving them a dry period at all.

This eliminates the rations changes and increases the dry matter intake of the cow resulting in improved body weight and improved energy balance.

"Most producers are leery of no dry period, but some are trying the 30-day," he said. Some producers in the audience told him they were utilizing 45-day dry periods.