Are empty rates up this year?
Using the spring 2017 mating results1, we looked into the national average not-in-calf rate2 (NICR). The national average NICR for this year was 17%. This is the same as it was for the 2015 and 2016 seasons.
So for the 2017 season, the NICR/empty rates have not increased, but remained the same.
Are empty rates higher than they used to be?
We collated the last 6 season’s data3 to see if the national average NICR had gone up over time (Table 1).
Table 1: Average 6-week in-calf rate, not-in-calf rate and mating length for the 2012 to 2017 spring matings
|
6-week in-calf rate |
Not-in-calf rate |
Mating length |
|
|---|---|---|---|
|
Spring 2012 |
6-week in-calf rate 67% |
Not-in-calf rate 14% |
Mating length 85 days |
|
Spring 2013 |
6-week in-calf rate 67% |
Not-in-calf rate 15% |
Mating length 84 days |
|
Spring 2014 |
6-week in-calf rate 67% |
Not-in-calf rate 16% |
Mating length 78 days |
|
Spring 2015 |
6-week in-calf rate 67% |
Not-in-calf rate 17% |
Mating length 76 days |
|
Spring 2016 |
6-week in-calf rate 66% |
Not-in-calf rate 17% |
Mating length 76 days |
|
Spring 2017 |
6-week in-calf rate 66% |
Not-in-calf rate 17% |
Mating length 75 days |
The national average NICR increased by 3% over the last 6 years. Given the two main drivers of NICR are 6-week in-calf rate and mating length, we looked more closely into these two measures.
6-week in-calf rate
In general, the higher your 6-week in-calf rate, the lower your NICR rate will be. This is illustrated by the 2017 spring mating results1 in Table 2 (quartiles based on 6-week in-calf rate). In general, a 2% drop in 6-week in-calf rate results in a 1% increase in NICR (and vice versa).
Table 2: The relationship between 6-week in-calf rate and not-in-calf rate
|
Average 6-week in-calf rate |
Average not-in-calf rate |
|
|---|---|---|
|
Top Quartile |
Average 6-week in-calf rate 76% |
Average not-in-calf rate 13% |
|
2nd Quartile |
Average 6-week in-calf rate 70% |
Average not-in-calf rate 15% |
|
3rd Quartile |
Average 6-week in-calf rate 65% |
Average not-in-calf rate 18% |
|
Bottom Quartile |
Average 6-week in-calf rate 55% |
Average not-in-calf rate 23% |
Mating length
Mating length has a large influence over NICR - the longer you mate for, the more cows that will be in calf by the end of mating.
For a herd with an average 6-week in-calf rate (66%), Table 3 shows the expected NICR for 6 different mating lengths4. These figures show that when 6-week in-calf rate stays the same, NICR increases as mating length is shortened.
Table 3: The relationship between mating length and expected not-in-calf rate
|
Mating length |
Expected not-in-calf rate |
Not-in-calf rate increase |
|---|---|---|
|
Mating length 13 weeks |
Expected not-in-calf rate 15% |
|
|
Mating length 12 weeks |
Expected not-in-calf rate 16% |
Not-in-calf rate increase +1% |
|
Mating length 11 weeks |
Expected not-in-calf rate 18% |
Not-in-calf rate increase +2% |
|
Mating length 10 weeks |
Expected not-in-calf rate 20% |
Not-in-calf rate increase +2% |
|
Mating length 9 weeks |
Expected not-in-calf rate 22% |
Not-in-calf rate increase +2% |
|
Mating length 8 weeks |
Expected not-in-calf rate 25% |
Not-in-calf rate increase +3% |
Is a drop in mating length to blame for the rise in NICR?
Inductions were fully phased out in 2015. To try and maintain a good calving pattern, many made the choice a season or two before 2015 to reduce how long they mated for. This resulted in the national average mating length dropping from a little over 12 weeks (85 days) in 2012 to just under 11 weeks (75 days) in 2017 (Table 1). Since 6-week in-calf rate stayed pretty much the same over that time, we’d have expected a 2% increase in NICR due to the shorter mating (based on Table 3).
It looks like two thirds of the reason for the 3% increase in NICR over the last 6 seasons is due to us shortening mating length by 10 days (without lifting our 6-week in-calf rate).
Using the rule of thumb that a 2% change in 6-week in-calf rate generally results in a 1% change in NICR, to compensate for the expected 2% increase in NICR, we’d have needed to lift our average 6-week in-calf rate by around 4%.
Thinking ahead
If you’re thinking about shortening your herds mating length in the future, make sure you have a plan to get more cows in calf in the first 6 weeks to help minimise the impact of reducing mating length.
To find out more about lifting your herd’s 6-week in-calf rate, check out the reproduction resources on our website.
1 Herds included in this analysis were 4,032 spring calving seasonal herds that had a 2017 Spring Detailed InCalf Fertility Focus Report.
2 Not-in-calf rate is the percent of the herd that have not been recorded as ‘pregnant’. As well as cows recorded as empty, the not-in-calf rate includes cows without a pregnancy test result recorded and those still recorded as ‘doubtful’. The ‘herd’ is the number of cows that calved that season and were still there at mating start.
3 Herds were included in the analysis of a seasons results (e.g. the spring 2012 season) if they were a spring calving seasonal herd that had a Detailed InCalf Fertility Focus Report. The number of herds included ranged from 2543 herds for the 2012 season to 4032 herds for the 2017 season.
4 These figures are from the analysis of the 2016 spring mating results for 3,852 herds. Herds were included in the analysis if they were spring calving seasonal herds that had a Detailed InCalf Fertility Focus Report.
Disclaimer: The reproduction measures analysed were calculated from data and information entered by herd owners and collected by LIC & DairyNZ. Accuracy of the results reported here is subject to the accuracy of the data entered.
