It’s one of the best-kept secrets in dairy fertility: the fact that dairy cows with high milk protein percentages are more fertile than other cows.
It seems like such an unlikely thing – however, it’s not only true, but the relationship between milk protein concentration and dairy cow fertility has now been repeatedly proven by scientists all over the world. In fact, in the original Dairy Australia InCalf study, milk protein was found not only to be associated with fertility, it was one of the two factors most strongly correlated with dairy cow fertility – more so than things such as production levels, herd size or breed.
Strangely, there doesn’t seem to be a good reason why this is the case. Nobody knows exactly why the relationship exists. And, perhaps the most bizarre thing about the entire scenario? No one has taken more than a passing interest into this phenomenon. It’s a mystery that seems to fit better on a conspiracy theorist’s list rather than a highly reputable (and very attractively-featured!) fertility blog.
Rather than let this mystery stand through the mists of time, a small group of Australian researchers are determined to investigate it, seeking to turn it into a force for good that could be used to improve fertility and profitability on Australian dairy farms.
I spoke to one of these intrepid investigators, Dr Martin Auldist (Department of Economic Development, Jobs, Transport and Resources) about the current state of the project. Why is it important?
“Well, if we could have herds with more of these high protein cows in them, they would be extremely valuable animals because not only do they get in calf more easily, but they produce milk that is more valuable, given that we are paid twice as much for protein than we are for fat.”
This is why the impetus for this study has come from our shores rather than the American system, given that we get paid for milk solids rather than volume as is usual in the United States. Additionally, the phenomenon is also stronger in herds that produce more moderate levels of milk typical to the Australian pasture-based dairy industry.
With funding from DEDJTR, the team have managed to make a start on this topic. What have they accomplished?
“We’ve done two things: we’ve re-visited the InCalf data set, collaborating with Dr John Morton and Prof Jock Macmillan [two leading veterinary researchers] to go back and re-interrogate that database to try and get any leads on what’s causing the relationship. So there’s interesting information coming from that.
The other thing we did was look at some first lactation heifers here at Ellinbank [the DEDJTR dairy research centre], characterising them as high (average 3.3%) and low protein concentration (average 2.9%), then following them through a lactation to see if we can find any differences that can point us to how this relationship is happening. We measured physical parameters of the cows, like weight and condition, and some parameters in blood that might indicate differences in energy partitioning (i.e. whether cows are putting relatively more towards milk or body condition). Is there any difference between high and low milk protein concentration cows and if so what does that tell us?”
The outcomes of this experiment, led by young dairy scientist Meaghan Douglas, were presented at the Dairy Research Foundation Symposium earlier this year. You can read the paper here.
With my brain churning while Dr Auldist was talking, I thought I’d be a bit clever and put forward my own theory about how the phenomenon worked: perhaps it’s because cows in good body condition (with less negative energy balance) produce more protein in their milk. And, obviously, cows in better condition are easier to get pregnant! Mystery solved, right?
“That’s the first thing people say when they talk about what the possible mechanism might be. And it’s true, that might be part of the story. We found that cows with high milk protein were in better condition and produced less milk than cows with low milk protein. Concentrations of certain hormones and metabolites in the heifer’s blood also indicated there might be differences in the ways these groups were partitioning their dietary energy. Then, though, we looked at milk composition and the energy content of milk. We found virtually no difference between the high and low protein percentage cows. In other words the daily output of energy in milk was about the same. They appear to be putting their energy towards milk at the expense of body condition, but it’s not actually true when you look at the amount of energy in milk.”
Hmm, so it isn’t a simple relationship that is easily explained.
“Using data from the InCalf study we also looked at milk protein percentage not only in early lactation (when mating occurs in a seasonally-calving system), but all through lactation to see if it was related to fertility – and yes, no matter what stage of lactation you measure your milk protein concentration, it’s still related to fertility.”
This means that the association persists even after cows have recovered from negative energy balance and are in mid and late lactation. And, the final nail in the coffin of the early lactation energy balance theory:
“At the time heifers are mated, they’re not subjected to lactation-specific nutritional demands because they’re not lactating. Nevertheless the ease with which heifers get in calf is still significantly associated with their milk protein concentration when they do start lactation some nine months later. So, there’s plenty of evidence that it’s not all about negative energy balance in early lactation.”
Hmm, I might have to hold onto my day job for now…and leave the research up to the researchers. If the team could get their hands on further funding, I asked, then what potential applications could they foresee for farmers in the future?
“[Farmers could] use milk protein concentration as a marker for fertility and perhaps manage at-risk cows into extended lactation programs – if milk protein concentration is telling us they’ve got a low chance of getting in calf, then we won’t mate them right now. Milk protein concentration – as opposed to milk protein yield – might also be a useful consideration in breeding programs.”
“That’s where we’d like farmers to help us – if it’s something that is interesting to them, or if they can see value in it, they need to be saying so. We’re trying to get a handle on what controls this relationship and whether there’s opportunities to exploit it for the benefit of our dairy industry.”
If you’re interested in this research, a good place to start talking about it is here. Could you see a use for more information about milk protein and fertility? Would it influence your genetic selection choices in the future? Have you noticed that high milk protein percentage cows tend to get in calf a little easier? Write in and let us know in the comments below.