In the last article, we looked at the history of declining dairy fertility. For those of you just joining us, a quick summary:
- It came hand-in-hand with increasing milk yield, but isn't directly caused by high production.
- It's difficult to monitor unless you collect data; unlike pasture growth, it's hard to 'see' pregnancies.
- Finally, the Australian dairy industry invested in two major initiatives in the late 1990s to turn the ship around.
The first initiative was the InCalf project, which we'll cover in the next issue.
The second initiative was the Daughter Fertility Australian Breeding Value (ABV), which was devised by dairy geneticists in 2003 and upgraded in 2013.
This was the first time farmers had the ability to pick bulls with daughters that were easier to get pregnant. Up until that point, farmers had to wait years before realising that a particular bull's daughters were no good and by then they'd stopped using it and were onto the next bull.
The ABV gave farmers a way of looking into the future to avoid accumulating these problem cows within their herds.
From my perspective as a dairy vet, I'd always recommended that farmers use the ABV, but found that not all of them had heard of it or trusted that it worked.
Some farmers were skeptical about whether you could make measurable progress in reproductive performance just using genetics, or whether Australian proofs were as reliable as international figures.
Over time, I started to question these things myself.
In 2016, I had the opportunity to complete a research master's thesis with the University of Melbourne dairy clinical resident program.
So, I decided to pursue validation of the Daughter Fertility ABV, using farm data that I could trust.
I collected records from 38 farmers who were identified as good record keepers, herd testers and early pregnancy testers with Rochester Veterinary Practice, in northern Victoria.
I interviewed them about the Daughter Fertility ABV to get a better understanding of farmer attitudes and opinions, and collected farm management data as well things like herd size, level of concentrate feeding and number of employees.
After the dust had settled, I found I had 86,974 cows with birthdates ranging from 1965 to 2017.
Some of our farmers had been keeping meticulous records for generations.
This included 438,578 pregnancy test and insemination records and 219,156 calving and lactation records.
Having such a large data set meant I was able to get results for both Holstein-Friesians and Jerseys.
The last year has been a whirlwind of writing code and wrangling statistics.
Related reading:
After months of analysis, I'm pleased to say that we can be confident that the ABV is associated with improved reproductive performance in both breeds.
For the Holsteins, one point of ABV was associated with a 2.6 per cent increase in the likelihood of submission, a 5.1pc increase in the likelihood of conception and a 5.7pc increase in the likelihood of calving in the first six weeks after calving start date.
For Jerseys, one point of ABV was associated with a 4.8pc increase in submission, a 6.5pc increase in conception and a 5.4pc increase in the likelihood of calving early.
These results are statistically significant with narrow confidence intervals and a p-value of less than 0.0001 or less than 0.001 for all measures.
The challenge is that artificial insemination sires only contribute half of their genetics to a new calf, and cows can have poor inherent fertility after decades of decline. Improving this will take time.
For the Holsteins, one point of ABV was associated with a 2.6 per cent increase in the likelihood of submission, a 5.1pc increase in the likelihood of conception and a 5.7pc increase in the likelihood of calving in the first six weeks after calving start date.
- Ee Cheng Ooi
On average, it took the herds in the study five years to increase their herd average daughter fertility ABV by 1.5 points.
Another finding of the study was that management is still an important part of improving fertility.
While one point of the daughter fertility ABV was associated with a 2.6pc increase in the likelihood of submission for Holsteins, being calved 65 days before mating start date was associated with a 71pc increase - a much larger impact.
However, we were pleased with this result and will continue to recommend to our farmers that they select bulls based on their daughter fertility ABVs preferably over 105 and certainly nothing below 100.
I'm not a geneticist and I don't sell semen, so I don't benefit commercially from the ABV.
But I do want to see the reproductive performance of my clients' herds continually improve and I'm satisfied that we have a useful tool to help achieve this.
Next up, we'll take a good look at the InCalf project.
*Ee Cheng Ooi is a cattle veterinarian and fertility researcher working with the animal health team at Dairy Australia. All comments and information discussed in this article are intended to be of a general nature only. Please consult the farm's vet for herd health advice, protocols and/or treatments that are tailored to a herd's particular needs.
This story first appeared on Australian Dairyfarmer
