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/14/2002 Dairy Today: Double Trouble

From the pages of the April 2002 edition of Dairy Today magazine.

By Paula Mohr More and more cows are giving birth to twins these days, with a 5% to 8% incidence reported in second-lactation cows and older.

Those cows end up with higher levels of metabolic disease and reduced productivity. And the twin calves--if they survive--have reduced birth weights.

Research shows that twinning decreases the number of replacement heifers by increasing neonatal calf mortality. It also skews gender ratios; there are more male twins than female or female-male twins, says Paul Fricke, University of Wisconsin. It is, however, a misconception that freemartins (sterile female born with male twin) decrease the number of replacement heifers.

Scientists are trying to figure out what might be causing more cows to drop twins. Researchers in California, Wisconsin and Pennsylvania also are, or will be, studying how to manage those cows identified as carrying two calves.

The increase in twins might be due to several factors, Fricke says. Genetics, breed, season, number of calves previously born (parity), ovulation rate and milk production may all play some role. Different research studies have shown:

• Genetic selection based on cows calving with twins and later combined with cows that had double ovulations increased twinning rates from 4% to 31% over an 11-year period.

• Twinning rates vary among dairy breeds and among individual herds. However, Holsteins have more twins.

• More twins are born during summer months, possibly due to better nutrition and more viable embryos in the cooler fall when cows were bred.

• Twinning increases with parity, ranging from 1% in virgin heifers to almost 10% later in life. Fricke says it's not clear why this happens. It may be because older cows can support twins throughout gestation, or they might have increased incidence of double ovulation or both.

• There's a 14% incidence of double ovulation in milk cows and it increases with parity. Cows with above-average milk production that have estrus synchronized by management are three times more likely to have double ovulations than cows that give less milk.

• There's a positive association between increased milk production and increased twinning over the years. However, cows calving with twins produce less milk during their lactations than cows giving birth to single calves. Yet cows carrying twins have higher peak milk.

Bovine somatotropin is not believed to cause twinning, Fricke says. The Food and Drug Administration removed the product's label warning on twinning after finding no detectable effect. "My data on double ovulation would suggest that any strategy that increases feed intake and milk production has the potential to increase twinning," he says.

Research has yet to define the nutritional and environmental effects on twinning. Veterinarian Bob Van Saun, Pennsylvania State University, conducted a small nutrition trial on cows carrying twins.

He fed two levels of protein--14% and 12%--to the two groups. Those with the higher protein level didn't have reproductive problems; cows fed the lower-protein diet had retained placentas, milk fever, ketosis and other metabolic disease.

Van Saun also monitored dry-matter intakes (DMI). Dry cows with twins dropped DMI five weeks before calving. The dry cows without twins dropped DMI two weeks before calving.

"If nutrition requirements are higher and intakes are lower earlier, then the problem with twinning is a nutritional imbalance issue," Van Saun says. "Cows carrying twins are put in a precarious metabolic condition, and when they begin lactation, they fall apart."

While producers wait for research answers, the following managementpractices may positively impact animal health and productivity:

• Identify cows carrying twins early in their pregnancy. Van Saun recommends that your veterinarian preg-check cows between 30 and 90 days postbreeding. Using ultrasound can increase the diagnostic capability of identifying twins, he says. The success rate of veterinarians in identifying twins during rectal palpation varies a lot. Manual palpation in a recent California study detected a low number of cows carrying twins and a high incidence of false positives.

• Feed a better or denser ration to cows carrying twins. There may be some benefit to improved nutrition, especially in the last trimester.

• Move these cows to the special-needs pen for daily observation. Provide assistance at calving to reduce the chance of complications.

• Dry off cows carrying twins a week or two earlier. Gestation length of cows carrying twins is shortened by six to 10 days so it might make sense to dry them off sooner.

A California study looked at the impact of the first 120 days in lactation on cows with twins dried off 12 days earlier than controls. Cows in all treatment groups averaged 105 lb. of milk for four months. So early dryoff had no impact on performance in the first 120 days of lactation.

"We don't know yet why drying off early is not working," Van Saun says. "There are other complicating effects. If you dry off earlier but don't do anything with the nutrient density, it's not going to help."
 

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