After a year writing columns for the Australian Dairyfarmer, I'm yet to touch on the topic that's closest to my heart. I'm talking about dairy fertility. This is partly because it's so complicated too complicated for a single article.
But with the forbearance of my readers (and editor), I'd like to indulge in a series focused on herd reproductive performance, covering the history of our fertility issues, genetic improvement, management of reproduction and the interplay between fertility and data. Hold onto your hats, friends it's going to be a wild ride.
In the late 20th century, farmers all around the world focused on increasing milk production through two mechanisms by feeding and by breeding. They were wildly successful. In 1989, the average annual milk production per cow was 2848 litres in Australia. In 2017, this rose to 6070 litres more than doubling in just 28 years.
Unfortunately, it wasn't until the 1990s that farmers noticed that their herds had a worsening fertility issue. This isn't surprising unlike grass, which will (hopefully) visibly grow within a week if you throw urea on it, it can take months or even years to see a response to change in reproduction. The second problem is that there are so many environmental factors that influence fertility, it's easy to dismiss a blip in one year or two, especially if you're not collecting data or keeping an eye on historic trends.
A move to split calving in response to poor fertility is logical. However, if this has had a negative impact on profitability, then that's not good.
As time passed, farmer concerns grew. In response, the Dairy Research and Development Corporation (now Dairy Australia) commissioned what is now known as the InCalf study, confirming that fertility in the national dairy herd was declining. Although the exact causes are somewhat controversial, the decline has been implicated as an unintended consequence of single-trait selection for milk production.
This doesn't mean that high production directly causes infertility. There are high-producing dairy cows that are able to get in-calf without issue. However, it has been proven that there is a negative genetic correlation between the two traits, which means that selecting for one without considering the other leads, over time, to poor reproductive outcomes.
I should add that there are other contributing management, environmental, physiological and genetic factors, but let's not get too far into these things for now.
Once confirmed, the second question became: what could be done about this?
Firstly, farmers needed a way of assessing fertility when picking artificial insemination bulls. To do this, geneticists devised a measurement for the inherent fertility of a bull's daughters not an easy thing to do. This resulted in the creation of the Daughter Fertility Australian Breeding Value in 2003, with an improved multi-trait version released in 2013. We'll talk about this in further detail in the next column.
Secondly, genetic improvement is slow and incremental so a shorter term solution needed to be pursued. The InCalf extension program helps farmers improve fertility using management changes. Eight key management areas have been identified that influence overall herd performance, including: calving pattern, heifer management, heat detection, body condition and nutrition, transition cow management and health, AI technique, genetic selection and bull management.
Unfortunately, like pretty much everything in farming, being good at one or two of these things isn't enough and yet, trying to improve everything at the same time is impossible. We'll talk about diagnosing a fertility issue and how to prioritise your focus more in later articles.
Thirdly, and unofficially, farmers changed the way they farm. According to the NatSCAN reproductive database, in 1997, 86 per cent of the herds were seasonal calving, with 8pc split and 6pc year-round. In 2016, this had changed to 30pc seasonal, 47pc split and 22pc year-round herds. NatSCAN is a sample of the national dairy herd not all farms are included in it. However, it is one of the best reproductive datasets we've got.
It's no surprise that farmers are great at adapting to changing situations and a move to split calving in response to poor fertility is logical. However, if this has had a negative impact on profitability, then that's not good. It also doesn't stop a downward decline in fertility if anything, it makes it worse, because a cow with poor fertility can be carried over multiple seasons until its gives birth to another cow with poor fertility.
Split calving also makes it easy to slide a fertility issue on the backburner, because it hides the impact that poor reproductive performance can have on a system on cow longevity and involuntary culling, on fewer cows at peak production, a mismatch between peak production and pasture growth, on lower genetic gain, and the cost of rearing replacements.
There are plenty of split calving farms with good-enough reproductive performance who are happy with their system, but farmers who are dissatisfied with their herd's fertility might be interested in taking steps to improve it.
If this sounds like you, then follow me down the rabbit hole in future issues as we explore the fascinating world of dairy fertility.
*Ee Cheng Ooi is a cattle veterinarian and fertility researchers 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
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