Jennie Pryce - Breeding a better cow
Kat - This month I'm continuing my reports from the Genetics Society Spring Meeting, Breeding for Bacon, Beer and Biofuels, held up at the Roslin Institute in Edinburgh - birthplace of Dolly the Sheep. As we heard in the previous episode, selective conventional breeding has wrought huge genetic changes in the plants and animals that end up on our plates today - and then there's the new frontiers of genetically modified, or GM, organisms as well as the latest precision gene editing technology. Jennie Pryce, from La Trobe University in Australia, is bridging the gap between breeders and geneticists, in order to breed better dairy cows. I started by asking her to explain what farmers are looking for in the perfect milker.
Jennie - Modern breeding objectives which are, I suppose, things that include all the traits that are important for productivity in farms, they'll include a diverse range of traits. So obviously, milk production is very important because that's what farmers are paid for. But equally, it's very important that the have cows that can get in calf - to produce milk has have to calf every year, so that's obviously a very important trait. They're also interested in breeding for disease resistance, so resistance to mastitis, lameness and so on, and also, increasingly, feed efficiency. So, it's really incorporating all the traits that contribute to profitability but also with a view on animal welfare and sustainability for the future.
Kat - You mentioned feed efficiency. I don't often think about cows as being efficient. So, what's that about?
Jennie - So actually, what we've seen over the last 50 years or so is a massive improvement in efficiency. So, a cow that was around in the 1950s would produce, say, about 1700 litres of milk and the modern dairy cow produces somewhere about 7,000 litres of milk. The weight of cows hasn't increased that much which shows us that the efficiency has improved phenomenally. So, we reckon that it's somewhere in the region of doubling efficiency just through the breeding objectives that I described earlier so, selection for production primarily.
Kat - So, these cows are better at turning the food they eat into milk coming out the other side.
Jennie - Exactly, yeah and that's what we've achieved simply through selecting for production. But there are other opportunities as well. What we haven't known in the past is how much cows actually eat and we're actually able to measure that now, but only in very small populations, so research populations.
Kat - How do you go about figuring out how much cows eat and then how to incorporate that into breeding better cows?
Jennie - So, we actually measure, we weigh, exactly how much a cow would eat in a day and that's not a trivial matter. What we have is pretty high tech equipment that we use to measure each individual meal. if you like, that a cow eats. So, a cow will have an electronic ID in her ear and when she goes into this specially designed equipment, it will record her identification as well as the amount of food that she eats. We can calculate the average that she eats over a day or over several months if we want to.
Kat - So, you can look at all these different cows, you can see how much they're eating, how much milk they're producing. How do you then tie that back into their genetics and which are genetically the best cows?
Jennie - So, this is the absolutely fantastic thing that we now have this technology called genomic selection where we can use many genetic markers on each individual cow or bull that we're interested in and we marry that with the data that we have on feed efficiency, or feed intake to put it simply. And we look for patterns in terms of associations between those genetic markers and feed efficiency. Together, that tells us how good a particular animal might be in terms of its genetic potential for feed efficiency. So, the great thing about it is that we can translate information that we have in a research population and apply it to animals that have genetic markers or genotypes but don't actually have a measure of feed intake. That's incredibly powerful because all of a sudden, you can have that information available to a very large population of cows or bulls.
Kat - So basically, what you're doing is you're measuring the cows in your research population saying, okay, they have gene markers A, B, C, and D, they're very efficient these ones, and then you can go and look at totally unrelated bulls - breeding bulls - and go, they've also got A, B, C, and D. These are going to be the ones you want if you want to turn less food into more milk.
Jennie - Exactly. The principle is right. But in fact, in dairy cattle populations, there are a lot of relationships between individuals. That actually works to our advantage. So, if you like, the problem that they have in human genetics is that they don't have those relationships between individuals which makes it harder to get those genetic predictions in dairy cattle. Because we've used a few bulls as the sires of the next generations, it means that we can make those relationships a lot more easily.
Kat - Why is it important to have efficient cattle? What benefit is that for farmers?
Jennie - It's obviously important because feed is the largest variable cost on most dairy farms. So, if they can cut their feed bill, it's got to be a good thing. If you actually ask farmers, it's one of the main priorities in terms of traits that they'd really like to breed for, feed efficiency.
Kat - At the beginning of your talk, you showed a picture of a cow from the 1950s and a cow from today. They looked very, very different and you'd think that's some kind of weird mutant cow that's gone on there. but this is all the changes that we've seen in our cattle. They've all just been done by selective breeding overtime. Have there been any traits introduced by this breeding that while they've been good for farming have been negative traits for the cattle?
Jennie - Yeah. There's a few examples actually. One of the most important is the relationship between production and fertility. Back in the 1950s, right through to the '80s, when we were selecting primarily on production, mainly because we didn't have the data on the other traits that there was actually a deterioration in fertility. It was through the '90s into the 2000s that we started to realise that fertility in modern dairy cows was deteriorating quite rapidly. We needed to put a spot to that. At that point, there was a massive effort from around the world to develop breeding values for fertility, mastitis resistance and so on, so that we could broaden breeding goals to include not just production but also those traits that we want to guard against getting worse.
Kat - There's been quite a lot of talk recently about using some of the new gene editing technology. Obviously, there's a lot of talk about that. Do you think that the future of farming as well as involving breeding might involve at some point, genetically modifying animals whether that's dairy or for food?
Jennie - From my perspective, I think that there's still a lot of scope with the tools that we have currently. So, genomic selection, just using the same sort of principles that we've used in the past, but with smarter tools to enable us to identify the best animals for certain situations. So right now, I don't see a major role of gene editing or genetic modification in most dairy systems, but who's to say what would happen in the future.
Kat - That was Jennie Price, from La Trobe University.