Featured in the Aug. 10 issue of Progressive Dairyman
The ideal pre-fresh period is 21 days. Too much maize silage makes heifers fat. Excess dietary salt causes udder oedema. The younger the age at first calving, the better.
These are just a few things we've been told about pre-fresh heifers, but are they facts or fallacies?
At the 2018 Vita Plus Calf Summit, Pat Hoffman challenged dairy farmers to dig deeper into four commonly held beliefs around pre-fresh heifers in order to better understand the unique needs of these animals and improve overall health, performance and longevity.
- The ideal pre-fresh 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 are often calving earlier than expected.
"Gestation length is variable," he said, noting the influence of genetics, calf gender and seasonality. Genetically, PTAs for gestation length show many sires that throw females into calving as many 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 shortchanged precious pre-fresh time. "Days in the pre-fresh pen could be 11 days instead of 21, especially if using sexed semen," Hoffman said.
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 that leads to inflammation and ultimately cell death, but heifers also need time.
"If 21 days doesn't mean 21 days, maybe they need 28," Hoffman noted.
- Udder oedema is caused by dietary salt
A swollen mammary in a pre-fresh 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 of less than a dozen heifers showed only .08 points of increased severity of oedema among those fed sodium chloride.
If too much salt is not the offender behind udder oedema, 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 oedema, and research out of the University of Tennessee suggests that. "When plasma antioxidants are high, the risk of udder oedema 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 buildup of fluid.
"Perhaps udder oedema is the result of oxidative stress," he added, further noting there is some evidence that antioxidants like vitamin E and selenium can increase udder shrinkage.
- Excess maize silage creates over-conditioned heifers
Hoffman pointed out that feeding too much maize silage may not be the single cause of heavyweight heifers. Rather, the problem could be inadequate neutral detergent fibre (NDF) in the ration to regulate it.
"It's not just maize 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 bodyweight in NDF per day. For a 450 kg heifer, that means 4.5 kg of NDF. According to Hoffman, breeding-age and bred heifers require diets with greater than 46 percent NDF.
"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."
- 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 £80 to £230 of milk revenue for heifers calving at 21 months compared to 24 months. Instead, the value of that lost milk can be traded for giving heifers more time in the raising 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. "
"Calving heifers excessively young is not necessary," Hoffman said. "Controlling age at first calving is necessary. This is what makes pre-fresh 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 you're 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 the 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.
The 2018 Vita Plus Calf Summit was held June 20-21 in Green Bay, Wisconsin.