Many factors can affect the body temperature of a dairy cow or heifer: illness, stress, breed, age, reproduction status, water intake, environmental conditions and diurnal cycles.

Holly Drankhan

These must all be taken into account if hoping to make meaningful predictions from temperature data, learned researchers from Colorado State and the Universidade Federal do Rio Grande do Sul in Brazil.

Their study, published this June in the Journal of Dairy Science, found that reticulorumen temperatures can successfully be used to make calving prediction algorithms, minimizing costs from labor and calf loss.

From November 2012 to March 2013, the team collected temperature data from 111 first-calf heifers and 150 multiparous Holsteins on a commercial dairy in Colorado.

Females were given a temperature-sensing reticulorumen bolus between five and 15 days before calving. TempTrack software manufactured by DVM Systems in Greeley, Colorado, was used to store data.

Each antenna could reach 90 meters (about 295 feet), and because the bolus could only store 12 readings internally, the cows had to be within this range two to three times a day. DVM Systems’ newest bolus, releasing this fall, is capable of sending readings automatically across distances of up to 800 feet, according to CEO Kevin Wild.

Reticulorumen temperatures may be preferred to vaginal or rectal because they take continuous, remote and automatic readings for the lifetime of the cow, says Wade Webster, chief science officer for DVM Systems.

“It’s like having another employee that works all day, every day of the year,” states the company on its website.

There is also a greater probability of lesions in vaginal and rectal areas, according to study authors. Many producers prefer equipment that can be placed inside the cow to those that are worn externally and, consequently, are more prone to damage or loss, Wild says.

After the females in the study gave birth, temperature data was analyzed retrospectively to generate baselines for each cow with which to compare temperature changes. One baseline averaged temperatures from four days prior to calving within one hour of an observed reading time, while the second used data within a five-hour window.

“The beauty of this whole experiment is: The cow is her own control,” says Jason Ahola, corresponding author and associate professor of beef production systems at Colorado State.

The researchers found that ruminal temperature drops from water intake must be accounted for, especially given that the study was conducted during winter months when water reached freezing.

Unlike temperature drops associated with calving, these declines are rapid and recover within two or three hours, says João B.G. Costa, Jr., lead author and coordinator of research and extension at Faculdades Associadas de Uberaba, Brazil.

Only temperature readings above 37.7ºC (99.86ºF) were used to rule out the effects of water intake. This significantly reduced variability and improved the predictive power of the temperature data.

“Not every reading that comes in is one you should keep,” Ahola says.

In future research, Costra plans to investigate how long body temperature can stay reduced if a cow consumes a large quantity of water in one day. On hot days in Brazil, Costra’s native country, it is not uncommon for cows to drink five to seven times per day, he says.

In the Journal of Dairy Science study, a drop in reticulorumen temperature was noted 24 to 48 hours prior to calving, as predicted from previous research.

This temperature change is a result of hormone levels, explains Costra. Progesterone is elevated throughout gestation to maintain pregnancy. Research has demonstrated that it acts on certain regions of the brain to activate neurons sensitive to cold and inhibits those sensitive to heat; as a result, the body produces more heat, according to the study.

However, this effect is counteracted by estrogen, which peaks in the final third of gestation. Thus, there is a detectable pre-calving temperature drop.

Primiparous Holsteins in this study experienced a larger temperature drop 48 hours prior to calving than noted in previous studies on Angus cows. Study authors hypothesized that this could be due in part to dairy cows’ greater metabolic heat production from larger food intake.

The predictive power calculated in this study was less than that of previous studies using vaginal and rectal Holstein temperatures. Authors speculated this could be due to the fermentation that occurs in the rumen, which causes greater temperature variation than in the other anatomic regions.

It was easier to predict calving within 24 hours rather than 12 hours, according to the study. However, the authors wrote that regardless of the baseline and prediction time used, as well as categorization as primiparous or multiparous, reticulorumen temperature could be used to “inform the likelihood of calving.”

A reticulorumen temperature drop of 0.2ºC (32.36ºF) or greater relative to an animal’s baseline was associated with the onset of calving.

While using a threshold of -0.4°C (31.28ºF) would result in very few false alarms, many animals could be missed that don’t experience this large of a temperature drop, study authors concluded. Using a threshold of -0.2ºC (31.64ºF) increases the number of animals monitored but with many false alarms.

“Even if false alarms occur, it may be better to have animals with a false calving alarm being monitored than animals not being monitored and calving without supervision,” study authors wrote.

Dystocia accounts for up to 65 percent of calf deaths, Wild says. If someone is present at the time of calving, newborn death can often be reduced by 50 percent.

“It won’t necessarily make your management easier; it will just allow you to be, I think, more efficient with your labor force,” Ahola said of reticulorumen temperature monitoring.

Ahola is interested in exploring whether an increase in false alarms could result in employees not respecting them, like a fire alarm that continues to go off without cause.

Future research into the bolus can explore its use in beef cattle, which have an even greater incidence of dystocia due to breeding for larger calves, Ahola says.

DVM Systems’ newest TempTrack algorithm is capable of providing producers with 12- to 36-hour notice via their smart devices for 80 percent of calving events, Wild says.

Calving detection through reticulorumen temperature can do more than just aid with dystocia. It also helps prevent hypocalcemia in fresh cows and ensures that calves consume antibody-rich colostrum before closure of the gut wall, Webster says.

In addition, the temperature-based predictions help managers avoid overcrowding of maternity pens, Wild says. Aside from monitoring pregnancy, the readings can be used for early illness detection.

Costra is planning to investigate if the bolus can be used to predict estrus events also associated with hormonally induced temperature changes. In Brazil, this is of particular concern because many dairy cows are ancient breeds that exhibit silent estrus.

The Girolando breed, for example, is a cross between Holsteins and Girs, a Zebu breed originating in India. Girolandos account for 80 percent of Brazil’s milk production, Costra says.

To help with these breeding predictions, DVM Systems has incorporated an accelerometer into their latest bolus design, Wild says.