when it comes to ‘empty rate’, this often isn’t the case because it’s not always
calculated the same way on-farm.
Levelling the playing field
rate is usually the percentage of the herd that was diagnosed as ‘empty’ on the
day of pregnancy testing. Depending on
which cows are scanned on the day, your empty rate could look better than it
actually is, leading to you to compare ‘apples with elephants’.
and Jane compare their empty rates:
- Farmer Joe
pregnancy tests his whole herd, and on the day of scanning his ‘empty rate’ is
- Farmer Jane has been watching her herd leading up to
scanning day. She knows that there are
30 cows that are not pregnant as she’s seen them bulling. Jane knows she’ll be culling all of her
empties, so decides to help her cash flow by not paying to get those 30 cows
pregnancy tested. On the day of
scanning, her ‘empty rate’ is 13%.
on these results, it looks like farmer Jane has the better empty rate. But if those 30 empty cows she didn’t scan were
added to her empty rate, her empty rate would actually be 16%. This is why it’s important to use an industry
standard measure when comparing your results with your neighbours, or across
Use not-in-calf rate
The industry standard measure used is not-in-calf rate
(NICR) - the percentage of the herd that have not been recorded as ‘pregnant’.
NICR calculations are based on the number of cows that
calved that season and were still there at mating start date (the eligible cows
group used in the Fertility Focus report), rather than just the cows scanned on
the day. This means everyone’s results
are based on the same group of cows, making it a level playing field for
However, when looking at NICR, we often hear “I didn’t have
that many empty cows”. And you’re right,
you may not have.
often higher than empty rate because it’s not just the percent of the herd
recorded as empty. As well as the cows
recorded as empty, NICR includes:
- Cows culled without a pregnancy test result
- Cows in the herd without a pregnancy test
- Cow still recorded as ‘doubtful’
From the scenario above, those empty cows that Jane didn’t
scan would be included in NICR as ‘cows in the herd without a pregnancy test
result’, giving Jane an accurate reflection of her herd’s performance.
Mating length matters
Another important factor to keep in mind when comparing NICR
is mating length.
Almost anyone can get a 6% NICR/empty rate if they mate for
long enough. This is because, as mating
length increases, in general, NICR decreases.
Plus, the difference in NICR between a herd with a good vs. an average
6-week in-calf rate gets smaller the longer you mate for*.