Dr Andrew Jemmeson BVSc MVS (dairy) & Dr Verity Ambler BVSc (hons)
Tallangatta Veterinary Clinic
It comes as no surprise that our dairy cows are more difficult to get in calf today than they have been in the past. The InCalf project collected data from herds between 1996 and 2009, which shows typical results in Australian seasonal calving herds.
That data shows that in the past 13 years or so:
- Three week submission rate has dropped five per cent;
- First service conception rate has dropped eleven per cent;
- Six week pregnancy rate has dropped thirteen per cent;
- 21 week empty rate has risen twelve per cent.
The reason for this primarily is increased milk production.
Increased Production → Increased weight loss early lactation → Increased time to start cycling → Increased time to get back in calf
The reality is that today's cows are still fertile, it just takes them longer to get in calf than it did ten to twenty years ago.
Subsequently, in a seasonal dairy herd, with a set amount of time available we can't get as many cows pregnant in 83 days as we used to!
We perceive this as reduced genetic fertility.
Mark and Narelle McDonald's 2011 joining
The McDonalds run a split calving dairy herd in the Mitta Valley. As for many other dairy regions split calving is becoming more common as cows become more difficult to get in calf in our designated joining periods.
The autumn calving herd was joined from 14 June – 22 August 2011. The first five and a half weeks of mating used AI, followed up by four weeks natural mating with Friesian bulls. No synchronisation was used during this joining.
The spring calving herd was joined from 18 November 2011 – 26 January 2012. A double OvSynch program was used to synchronise the herd and three fixed time AI matings were carried out on 18 November, 9 December and 30 December 2012. Cows were pregnancy tested using Ultrasound at 39 days and if found not to be in calf, were recycled into the synchrony program. A further four weeks of bull matings up until 26 January 2012 completed the joining.
The double OvSych synchrony program is set out below.
A Voluntary Wait Period (VWP) of 60 days from calving to Mating Start Date (MSD) is applied to ensure that all cattle enrolled have sufficient time after calving to clean up and cycle. Unfortunately due to a miscommunication, the VWP of 60 days was applied to the first double OvSynch injection rather than MSD. Subsequently cows were not mated until at least 87 days after calving, which is 27 days longer than intended.
During analysis of these joinings the following industry standard parameters were used:
|Calving-MSD interval||The number of days between when a cow calves and the start of the mating period|
|Calving-Conception interval||The number of days between when a cow calves and when she conceives|
|Three week Submission Rate (SR)||The percentage of the herd submitted for mating in the first three weeks of joining|
|Six week Pregnancy Rate (PR)||The percentage of the herd pregnant after the first six weeks of joining|
|First Service Conception Rate (CR)||The percentage of cows that conceive to their first service|
|12 week Not In Calf Rate (NICR)||The percentage of cows empty after 12 weeks of joining|
|Parameter||Autumn 2011||Spring 2011||InCalf Typical 2009|
|Average calving-MSD days||111||129|
|Average calving-conception days||135||164|
|1st Service Conception Rate %||44.8||44.4||38|
|3 wk Submission Rate %||81.0||34.6||72|
|6 wk Pregnancy Rate %||51.7||45.9||50|
|12 wk Not in Calf Rate %||33.2||40.5||31|
|Bull Pregnancy Rate %||31.3||9.8|
The stand out parameters here are:
- very long calving-MSD and calving-conception intervals. To maintain a seasonal round calving pattern, cows need to conceive in 83 days;
- conception rates for both joinings are very similar and out-perform the typical InCalf data from 2009;
- three week Submission Rate is very low in the spring joining;
- pregnancy rate for the spring joining is a little lower than autumn and the typical InCalf data; and
- not In Calf Rate in spring is worse than typical InCalf data. There appears to be very low numbers of cattle conceiving to the bulls in the spring joining.
Ultimately, while it is important to investigate these fertility parameters further – the results as listed above include carry-over cows. That will skew results to varying extents and so not allow a true reflection of how each joining has performed. To more accurately analyse and compare the two joinings we have separated out the carryover cows in the table below.
|Parameter||Autumn 2011||Spring 2011||Carryovers||InCalf Typical||InCalf Best|
|3 wk Submission Rate||75.3||98.5||100||72||98|
|6 wk Pregnancy Rate||49.4||51.9||67.9||50||70|
|1st Service Conception Rate||45.4||45.8||55.4||38||65|
|12 wk Not In Calf Rate||32.2||45.1||21.4||31||10|
|Bull Pregnancy Rate||36.4||10.6|
Separating out the carry-overs has created another area of confusion. In the spring joining, the first mating was 18 November but that was entirely carryover cows. Subsequently if the carryover cows are removed from the data, the first mating for genuine spring calving cows effectively becomes 9 December and so their MSD is actually 9 December. That explains the significantly longer calving-MSD interval (due to the long VWP applied).
With the carryovers separated out, the stand out parameters now are:
- longer calving-MSD in spring as just described;
- very high Submission Rate in spring – this is to be expected in a fixed time AI synchrony program;
- typical Pregnancy Rates in both joinings;
- good First Service Conception Rates in both joinings;
- disappointingly high Not In Calf Rate in spring showing that the bulls have not performed well; and
- Carry-overs perform very well.
The unintentionally long Voluntary Wait Period applied in spring has had some effects:
- lengthened calvingMSD interval meaning cows have had a longer spell after calving which should improve their ability to get back in calf;
- has denied many cows the opportunity to conceive to the first mating on 18 November. That in turn would have resulted in a lower six week Pregnancy rate when measured from the true MSD on 18 November. The six week pregnancy rate in the table above is measured from 9 December to allow us to properly analyse how the synchrony program performed this season; and
- bulls have underperformed in spring, getting only nine cows in calf over a four week period.
Heifer management was excellent. Joining commenced three weeks earlier than for the cows and 97 per cent calved within three weeks – in other words they achieved a six week pregnancy rate of 97 per cent. Having an extra three weeks to clean up and cycle should help them conceive at the following joining.
- Continue with double OvSynch program for both joinings. Use a Voluntary Wait Period of 33 days between calving and first injection so that cows are mated no sooner than 60 days after calving. Cows will be Ultrasound pregnancy tested at 39 days and if not in calf are rejoined at 42 days with other cattle.
- Address bull power. InCalf recommends four bulls per 100 cows at MSD if synchrony is used. Subsequently approximately eight bulls are required for 200 cows at MSD. All eight bulls should be present for the expected date of returns, and then half rotated weekly.
- Continue with the nine to ten week joining period. Calving Induction is not used and carryover cows perform well so the decision is to keep split calving with two short joinings and carry empty cows over to next joining. From a fertility perspective – any cow that is carried over and fails to get in calf at the following joining should be earmarked for culling. From a production perspective this is sometimes hard to achieve.
- Future joinings will be analysed in a similar manner and plans revised. The Voluntary Wait Period may be reduced in future to 45 days (from calving – MSD).