Taking the study of milk fever in dairy cattle from a research environment into commercial Ontario farms produced largely predictable findings for the University of Guelph’s Department of Population Medicine, but also one unexpected result.
It found that reproductive performance of first-lactation heifers, in contrast to their older herd counterparts, was slightly impaired when eating a diet designed to prevent hypocalcemia.
Hypocalcemia is often called milk fever in its clinical form.
Why it matters: Blanket use of the targeted transition diet can add costs, so if farms can instead use it only on selected cows there may be financial benefits.
The finding was among various questions identified for possible future research during a recent Dairy at Guelph webinar highlighting transition cow health.
The webinar, organized by University of Guelph graduate students, featured faculty members Dr. Trevor DeVries, Dr. Stephen LeBlanc and Dr. Eduardo Ribeiro outlining various recent transition-cow research. For the hypocalcemia study, PhD student Rita Couto Serrenho compared a negative DCAD (dietary cation anion difference) diet with a slightly positive DCAD version for close-up cows on four commercial Ontario operations over one year, under LeBlanc’s direction.
Adding acidic minerals like chloride or sulphur (more anions, fewer cations) contribute to a negative DCAD diet, and can counteract the higher rumen pH that’s strongly associated with milk fever.
“It has been known for some time that a negative DCAD diet for close-up dry cows can help prevent hypocalcemia and milk fever but what hadn’t been done was to do this at scale on multiple commercial herds with enough experimental power to look at the health and production outcomes,” LeBlanc said.
Results for blood calcium levels were “what we had hoped for,” he reported. In older cows, the levels were improved between one and four days after freshening “up into a level that is thought to be a desirable zone.” Milk fever occurred less often, especially in older cows and in those that had been overconditioned compared to the recommended norm as they completed their dry period.
Other health effects
Results also indicated other health effects of feeding a negative DCAD close-up diet. There were fewer twisted stomachs. And for cows older than first lactation, the time to first breeding and time to confirmed pregnancy was, on average, less.
But the surprise came when those same reproduction parameters were tracked for first-lactation heifers. In that sub-group, reproduction was actually impaired for those on the negative DCAD diet.
“We don’t know,” LeBlanc said when asked why this was the case. One hypothesis is that feeding negative DCAD may have reduced the heifers’ close-up feed intake. But LeBlanc noted that’s one of the challenges of transferring studies from the research barn environment to commercial facilities: individual feed intake is nearly impossible to track in most barns.
He has his doubts on that explanation, given that reduced feed intake should have shown up in the form of decreased milk production, which wasn’t the case.
All three featured speakers highlighted areas of focus their students are pursuing in relation to transition cow health. These include:
- Dry cow diets: Maintaining good intake without having any gain or loss of body condition as they approach freshening.
- Precision nutrition management: More farms are installing automated milking and/or feeding systems, which can be individually tailored to each herd member.
- Wearable sensors and other electronically tracked metrics of cow behaviour: Can these parameters be used to identify animals more at risk of developing disease?
- Low blood glucose and ketosis: A study by Jessica Gordon showed the benefits of drenching with glycol as an early ketosis intervention and also revealed 35-40 per cent of affected early-lactation cows also had low blood glucose, which is undesirable and should be treated.
- Once-per-day milking and ketosis: Earlier work through LeBlanc showed this can be an effective strategy, but questions remain about the long-term production (and therefore financial) repercussions throughout the lactation.
- Economics of transition health: A study under Ribeiro estimated the cost of diseases happening in the first two weeks post-partum as well as the cost and effectiveness of measures aimed at preventing those diseases. The researchers found that if the average farm spends 77 cents per cow per day, this can be justified on the balance sheet.
- Uterine inflammation and oocyte quality: Poor-quality eggs due to inflammation have been shown to negatively affect pregnancy-per-insemination. Embryo transfer is one way to avoid reduced oocyte quality but Ribeiro noted that recent research reveals that “embryo transfer helps, but cannot fully re-establish the fertility of the cow.”