It’s got to the time of year when the talk down at the pub/Facebook/discussion group has turned to scanning results, 6 week in calf rates and empty rates, but are we actually making fair comparisons with the neighbours results? Are we comparing apples with apples, or are we comparing them to oranges and orangutans?
You may have noticed over the past few years a shift from using the term “empty rate” to “not in calf rate”. The empty rate that most people discuss is the number of animals that are pregnancy tested but are not pregnant on the day of scanning, as a proportion of the total number scanned (ie. If I scan a herd of 850 animals and 68 and not pregnant, then the “empty rate” often discussed is 8%.
But what about if you were a bit short of feed over summer and decided to cull 20 animals and used visual observation of heats to identify animals you didn’t believe to be pregnant and removed them from the herd before the pregnancy check. Suddenly the number of animals that were actually “empty” at the end of mating would be 88, and the “empty rate” would actually be 10.1% (88 not pregnant out of 870 animals). Or do they not get counted, because they weren’t there?
What about if you culled some other animals after the start of mating, but before pregnancy checking without knowing what their reproductive status is? In the above example they wouldn’t even be included in the total number of animals pregnancy checked.
This is why the industry has standardized the “Not in calf rate” or “NICR”. This is the percentage of cows that have not been recorded as pregnant and works on the number of cows that calved that season that were in the herd at the start of mating, not just on the day of scanning.
However, we often hear from farmers that they didn’t have as many “empty” cows, or that the NICR isn’t a reflection of what they believe to have happened on their farm. Below are a couple of reasons that could explain that:
- Cows that are culled without a pregnancy test result will be included in the NICR
- Cows that are still in the herd, but haven’t had a pregnancy test result recorded against them will be included in the NICR
- Cows that are still recorded as “doubtful” will be included in the NICR.
- If you purposely choose to not mate cows (such as definite culls) then they will be reflected in both the empty and NICR.
- If you had culls or deaths early in the season, but didn’t record them, then those cows are also in the “eligible to mate” group, despite not being on the farm.
As we are aware, there are a lot of factors that come into account when getting cows in calf, but there are three key measures that dictate the number of animals we expect to not get pregnant in a herd. These are the submission rate, the conception rate and the length of mating. The longer you mate for, the lower we expect the NICR to be, and the gap between a herd with a good 6 week incalf rate and a average one will decrease the longer mating goes for – this comes down purely to the mathematics of submission, conception and opportunities to be mated. On a farm that has a nine week mating, a cow typically has three chances to cycle during the mating period, whereas a 12 week mating she has an additional chance.
Some numbers from LIC (based on 2016 spring matings) show that the average NICR for an average herd increases from 15% to 20% when going from a 13 week mating to a 10 week mating, and for the top quartile of herds this increase is from 12% to 15%.
We all know there are a lot of parts to the reproduction pie, so if you would like a hand to help understand your performance to date, and assist with coming up with plans to improve for next season, please get in touch with one of our consultants.