Prefresh heifers: A might not equal B – Pat Hoffman, Vita Plus
By Peggy Coffeen, Progressive Dairyman
The ideal prefresh period is 21 days. Excess dietary salt causes udder edema. Too much corn silage makes heifers fat. Younger age at first calving is better.
These are just a few things we’ve been told about prefresh heifers, but are they facts or fallacies?
At Vita Plus Calf Summit, Pat Hoffman, Vita Plus dairy technical support specialist, challenged dairy farmers to dig deeper into four commonly held beliefs around prefresh heifers in order to better understand the unique needs of these animals and improve overall health, performance and longevity.
1. The ideal prefresh period is 21 days.
While a three-week time period before the predicted calving date is the standard for preparing a heifer for life as a lactating cow, it may not be enough. According to Hoffman, multiple factors are at play that can shorten the length of gestation, thus, heifers often calve in earlier than expected.
“Gestation length is variable,” he said, noting the influence of genetics, calf gender and seasonality. Genetically, predicted transmitting abilities (PTAs) for gestation length show many sires that throw females calve as much as three days early. Cows bred to sexed semen tend to calve 1.7 days sooner, and heat stress can take 3.5 days off gestation.
When a heifer calves in advance of her due date, she is short-changed precious prefresh time. “Days in the prefresh pen could be 11 days instead of 21, especially if using sexed semen,” Hoffman said.
Allowing adequate adjustment time for heifers is critical, particularly when multiple pen changes are involved. After a pen move, Hoffman said it takes three to five days for the animal to learn where to find feed, water, and rest, and up to a week to figure out the pecking order. These changes create stress on a cellular level, known as oxidative stress. Antioxidants, including certain vitamins, enzymes and other dietary components, can reduce this internal stress, which reduces inflammation and, ultimately, cell death, but heifers also need time.
“If 21 days doesn’t mean 21 days, maybe they need 28,” Hoffman noted.
2. Udder edema is caused by dietary salt.
A swollen mammary in a prefresh heifer is often said to be related to salt, but when Hoffman looked into the research behind this assumption, his findings raised a red flag. Limited studies with small treatment groups existed, and an experiment with less than a dozen heifers showed only 0.08 points of increased severity of edema among those fed sodium chloride.
If too much salt is not the offender behind udder edema, then what is?
“The truth: We really don’t know the mechanism behind it,” Hoffman admitted.
However, he has a hunch. The aforementioned term “oxidative stress” could be the culprit behind edema, and research out of the University of Tennessee suggests a similar cause.
“When plasma antioxidants are high, the risk of udder edema is five-fold lower,” Hoffman said. The inflammatory response triggered by stressors, such as disease exposure, vaccinations, crowding, pregnancy and diet, can lead to a build up of fluid.
“Perhaps udder edema is the result of oxidative stress,” he added, further noting how some evidence shows antioxidants, like Vitamin E and selenium, can increase udder shrinkage.
3. Excess corn silage creates over-conditioned heifers.
Hoffman pointed out that feeding too much corn silage may not be the single cause of heavy-weight heifers. Rather, the problem could be insufficient neutral detergent fiber (NDF) in the ration to regulate it.
“It’s not just corn silage, it’s the lack of having a high NDF forage available on the farm to cut consumption,” Hoffman explained. “Adding high NDF forage to the diet brings down average daily gain to regulate intake and calories in a heifer diet.”
Heifers will eat 1 percent of their body weight in NDF per day. For a 1,000-pound heifer, that means 10 pounds of NDF. According to Hoffman, breeding age and bred heifers require diets with 46 percent NDF or more.
“NDF regulates dry matter intake and feed costs of heifers more than anything else,” he said. “NDF is a really valuable commodity when it comes to how we set replacement heifers up.”
4. Early calving increases profitability.
Freshening heifers at a younger age does not guarantee a greater return on milk yield. “It doesn’t work that way,” Hoffman said, noting a loss of $100 to $300 of milk revenue for heifers calving at 21 months compared to 24 months. Instead, the value of that lost milk can be traded to give heifers more time in the rearing phase.
Heifers that calve earlier don’t go on to spend more days in the herd. “If you calve them four months earlier, they leave the herd four months earlier,” he said. All this achieves is changing the age of the herd.
“Do you get any benefit from that at all? No,” he added. “The faster you move the eighth-graders to high school, the faster the high schooler has to leave.”
“Calving heifers excessively young is not necessary,” Hoffman said. “Controlling age at first calving is necessary. This is what makes prefresh heifer programs tick.”
Hoffman suggested tightening the variance in the age by which heifers first freshen. This can be done with stricter heifer-breeding criteria. “It’s better to think about ‘four straws and your out,’” he said, adding that this will reduce the average calving age and “keep things in the middle” of the variance curve.
He proposed tightening up heifer criteria with a pre-breeding screening at 12 months old to cull animals with low genomics, lighter weights and a history of health events.
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