OESTRUS is one of the most important indicators of whether a cow or heifer will be successfully bred. However, not all oestrus cycles are the same for individual females within a herd.

According to University of British Columbia (Canada) animal reproduction professor Dr Ronaldo Cerri, some cows will display oestrus with less intensity for a shorter duration – they won’t walk around or be ridden as much.

“A cow in high oestrus intensity typically has longer oestrus and very intense physical activity that can be monitored,” Dr Cerri said.

His research aims to improve cattle fertility by identifying which cows and heifers are the best candidates to breed using artificial insemination and embryo transfer, with oestrus intensity as the deciding factor.

Cattle have typical baseline activity when they aren’t in oestrus, his research shows. When they start to enter oestrus, their activity rises as the intensity of the oestrus increases. Pinpointing when oestrus is about to peak is crucial to a successful pregnancy.

More obvious breeding decisions

After analysing extensive data from oestrus detection sensors, Dr Cerri and other researchers have pinpointed patterns based on what’s occurring during oestrus.

“The patterns are very consistent in many of the studies we’ve done,” he said. “Cows with lower oestrus intensity always display less physical activity, but they also have lower pregnancy rates. On the flip side, cows with high oestrus intensity display more activity and have higher pregnancy rates.”

Studies across the United States, Canada, Brazil and Germany have all shown this same trend.

Cows exhibiting low oestrus intensity tend to have lower concentrations of progesterone during the growth of the ovulatory follicle and fail to ovulate more often than those with high oestrus intensity. Similarly, ET recipients that show high oestrus intensity have more consistent pregnancy results.

“Oestrus intensity serves as a quality marker for a good cycle that leads to a better pregnancy via AI and ET,” Dr Cerri said.

Evaluating oestrus intensity with the help of heat detection tools can help cattle managers pick and choose which cows are the best candidates to breed at a particular time. If implementing a mass breeding protocol, there is also the option to use oestrus intensity to direct choices on what type of genetics to use.

“The more targeted you want to be in your breeding program, the more you can use oestrus intensity information to make a breeding decision,” Dr Cerri said.

“For example you can identify high oestrus intensity cows to receive sexed semen or embryo transfer because they are more likely to get pregnant. Then you can use conventional semen in AI for the low oestrus intensity females.”

Operators could monitor oestrus intensity by watching movement and mounting activity, but this was often not practical, he said.

“That’s why we need to utilise tools to helps us identify these events.”

A variety of tools are available to monitor oestrus, such as activity monitors, tail paint or chalk and breeding indicator patches. Some offer more information than others and come with tradeoffs.

“Activity monitors are quite effective at measuring oestrus intensity, but not everyone can utilise them,” Dr Cerri said.

“Breeding indicator patches are another option that can give a subjective measure and score oestrus intensity, which is probably better than other inexpensive options like tail chalk.”

With breeding indicator patches, users can monitor oestrus by looking for patches that have 50pc or more of the surface ink rubbed-off as being in high estrus intensity and are ready to breed. Females with less than 50pc of the surface ink rubbed off are in low oestrus intensity and could be bred with lower-cost genetics or bred later when they’ve reached high oestrus intensity.

“Oestrus and the intensity of oestrus within those cows are important pieces of information to add to your reproduction program,” Dr Cerri said.

“Once you have this information, you’ll have better predictions of what your cows will do, making you more efficient and profitable.”

Genetics Australia has information on Estrotect breeding indicator patches on its website.