Zeroing in on Subclinical Hypocalcemia
New research from Cornell University has identified a cut-point for blood calcium concentrations in prepartum cows that can be used to predict which cows are more likely to develop subclinical hypocalcemia (SCH) at calving. In the study, cows with a blood calcium concentration of ≤2.4 mmol/L at one week prior to calving were 40% more likely to be SCH at calving. Subclinical hypocalcemia was defined as a blood calcium concentration of ≤2.1 mmol/L.
“Our goal with this research was to better define subclinical hypocalcemia in the periparturient period,” explains Jessica McArt, assistant professor in the Department of Population Medicine and Diagnostic Sciences at Cornell University. “We would like to be able to identify cows in the prepartum period that we can manage differently to improve their transition into lactation.” This research is another step in that direction.
The research, which was reported in the May 2017 Journal of Dairy Science, utilized 296 cows at two New York dairies to identify risk factors for SCH. Prepartum total blood calcium status, parity and herd were found to be significant predictors.
At one week prepartum, all multiparous animals with a blood calcium concentration of ≤2.4 mmol/L were 40% more likely to be classified as SCH at parturition. When just third or greater parity cows were considered, they were 70% more likely to be classified as SCH at parturition.
Blood samples also were collected within four hours of calving. Results from the 296 cows showed that at calving 2% of first lactation cows, 40% of second lactation cows and 66% of third or greater lactation cows had a blood calcium concentration of ≤2.1 mmol/L and were diagnosed as SCH.
Cows in Herd B were 50% more likely to be classified as SCH than cows in Herd A. While there were some management differences between the two herds, McArt believes the lack of a negative DCAD diet in Herd B was a large contributor to the increased prevalence of SCH in Herd B; 42% vs. 24.7% for Herd A. Dairy A fed a prepartum diet with a DCAD of -6.9 mEq/100g of dry matter. Dairy B changed its prepartum diet partway through the observation period, but cows were always fed a prepartum diet with a positive DCAD.
“I’m a big proponent of feeding a negative DCAD diet in the close-up ration as well as keeping the stocking density in the fresh pen under 85%,” says McArt. “These management strategies, along with optimizing cow comfort during the transition period, go a long way for disease prevention.”
LAMENESS A FACTOR TOO
In addition to testing for blood calcium, cows were locomotion scored within one week of calving. Subclinical hypocalcemia at calving and locomotion score were significant predictors of SCH at two days in milk.
Cows with normal blood calcium (>2.1 mmol/L) at calving and not lame served as a reference point.
- Cows with normal blood calcium at calving but were lame were 3.2 times more likely to be SCH at two days in milk.
- Cows that were SCH at calving (<2.1 mmol/L) but not lame had the same 3.2 times higher risk to be SCH at two days in milk.
- Cows that were SCH at calving and lame were 3.4 times more likely to be SCH at two days in milk.
These results show that lame cows with normal blood calcium at calving are more likely to develop SCH in early lactation. In addition, when cows are SCH at calving, being lame doesn’t really increase their risk for persistent SCH at two days in milk. McArt’s theory is that lame cows do not have the same intakes as non-lame cows and are thus not able to take in as much calcium as non-lame cows, thus the continued issues with hypocalcemia. Pen changes after calving also may increase social turmoil and further limit access to the bunk for the newly-fresh lame cow.
Research on transition cows is ongoing at Cornell and at several other research institutions. This new cut point for blood calcium can be used to identify a subset of cows a week prepartum that are more likely to develop SCH at calving. This in turn may allow researchers to better understand SCH and to develop strategies to improve cows’ transition.
Cornell researchers are currently trying to determine the best timing of blood sampling relative to calving to classify SCH and what blood calcium threshold should be used to define it. “There has been some debate on the threshold for SCH without consistent supporting data,” explains McArt. Several research groups are currently working on this. In all of the research, the goal remains the same: A healthy transition for every cow.