Animal Nutrition

Activity Monitors May Provide Insight on Cows’ Calcium Status

Diary Calf nuzzles mother standing in green pasture

A good cow person just seems to know when a cow feels off or acts different and needs to be checked. Whether it is a keen eye for detail, the ability to quickly pick up on subtle changes or just an innate ability, a good cow person is an asset to any dairy, especially when caring for transition cows. 

The introduction of new technologies allows those who use them to become better cow persons, too. These tools can detect small differences in rumination, cow activity and lying time, just to name a few. Activity monitors have provided producers with new tools to help manage cows. And researchers continue to look for behavioral differences that can be quantified and used as early-warning indicators to improve cow health. 

Two articles in the November Journal of Dairy Science used activity monitors to study transition cow behavior as it relates to blood calcium status during the transition period. The new data is encouraging. It indicates that behavioral differences can be quantified and correlated to blood calcium concentration, which may provide a new avenue for the early identification of cows at-risk for hypocalcemia. 

New Zealand Research 

In the first study, Hendriks et al. (2020), multiparous transition cows from grazing dairies were used. The New Zealand researchers conducted a retrospective analysis using data from two previous studies Roche et al. (2015, 2017) from which they selected 72 multiparous cows for further analysis. All animals had blood samples collected weekly from 4 weeks prior to 5 weeks post calving and daily for 5 days starting on the day of calving. Total plasma calcium was used to separate the cows into three groups of 24 cows each: Clinical ≤1.4 mmol/L from 1 or more tests within 48 hours of calving; Subclinical > 1.4 mmol/L and < 2.0 mmol/L from 2 consecutive tests within 48 hours of calving; and Normal ≥ 2.0 mmol/L from 3 consecutive tests within 72 hours of calving. The cows classified as clinical and subclinical by blood test did not display any signs of paresis (muscle weakness). 

The researchers examined cows’ lying behavior and daily step counts to determine if there was a correlation with blood calcium levels that could be used as a possible indicator of cows at risk for subclinical or clinical hypocalcemia. Results showed that cows classified as clinical (≤ 1.4 mmol/L) without evidence of paresis were less active on the day of calving. Daily step counts were 3,118 for clinical cows, 3,853 for subclinical cows and 4,448 for cows classified as normal. That’s a difference of 1,330 steps/day between clinical and normal cows. 

In addition, on the day of calving clinical cows spent 9.4 hours lying down compared to 6.8 hours for subclinical and normal cows—a difference of 2.6 hours/day. There also was a difference in the number of lying bouts; clinical cows had 19.2 vs. 18.2 for subclinical cows and 16.3 for normal cows. 

Prior to calving a difference in step count that could be positively correlated to blood calcium concentration was detected. An increase of 1,000 steps/day from 2 weeks prepartum to the day of calving was associated with an increase of 0.07 mmol/L in blood calcium concentration within 24 hours of calving. 

“We found a consistent theme that cows experiencing hypocalcemia are more restless and less active,” explains Stacey Hendriks, postdoctoral fellow at Massey University in New Zealand. “The extent of the decline in activity depends on the extent of hypocalcemia” as measured by total blood calcium. The changes in step count and lying time were short-lived and non-detectable by 2 days post-calving. 

University of Edinburgh Research 

In a second study by Barraclough et al. (2020), researchers also used activity monitors to track animal behaviors and tested blood calcium concentration of transition cows. Multiparous and primiparous cows entered the close-up pen approximately 3 weeks prior to predicted calving date. Blood samples were taken within 24 hours of calving. Cows were classified by their blood calcium concentration as either normal ≥ 2.0 mmol/L or subclinical < 2.0 mmol/L without any clinical signs. Cows classified as clinical had signs of milk fever, required treatment and recovered. Blood samples were not always collected from clinical cows. The final data set for analysis included 51 multiparous cows and 21 primiparous cows. 

Researchers found that blood calcium status had an effect on some of the behavior variables tracked and that results differed by parity. With primiparous cows, steps/day decreased by nearly half from 842 steps/day at 2 weeks prior to calving to 427 steps/day on day of calving for normal cows. Subclinical cows’ daily step count remained steady. 

After calving, daily step counts for normal cows and subclinical cows both declined from 1 day in milk to 21 DIM. However, the decrease for subclinical cows was three times greater than for normal cows. This decline in step count could be from primiparous cows getting used to a new environment, social hierarchy and new rations and then settling into their new routine. 

With multiparous cows during the prepartum period researchers found no statistically significant interaction between blood calcium status and step count or lying time. But there was a difference in postural transitions (cows getting up or lying down) with normocalcemic cows having fewer transitions (18.5/day) compared to subclinical and clinical cows with 23.5/day.

During the 21-day post-calving period blood calcium status affected lying time, step counts and the number of postural transitions per day. The lying time of clinical cows averaged 10.7 hours/day compared to 9.2 hours/day for subclinical and 8.6 hours/day for normocalcemic cows. During the first 21 DIM step counts for clinical cows averaged 503 steps/day compared to 774 steps/day for subclinical cows and 948 for normocalcemic cows. 

While this study needs to be replicated with a greater number of animals, it did show that blood calcium status affects cows’ activity levels and that even when clinical cows are treated with successful resolution, differences in the behavioral variables studied still remained at 21 DIM. 

Barraclough et al., 2020. J. Dairy Sci. 103:10604.

Hendriks et al., 2020. J. Dairy Sci. 103:10546.