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.
Mysterious lake monster… or the missing link between milk protein and fertility?
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?
Martin Auldist, research scientist and intrepid investigator
“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.
We already know that body condition has a big impact on fertility. Regular scoring is key to managing this.
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?
Unfortunately not.
“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.
“We found that cows with high milk protein … produced less milk than cows with low milk protein.”
This statement puzzles me.
First, does “milk” mean volume (litres), or does it mean milk solids. Or does it it mean protein solids.
Presuming it means litres, I notice often that better fed cows lift litres and lift, or least maintain, protein %, so produce more protein kg. Poorly fed herds seem to have lower protein % and vice versa, at any lactation stage. I watch many herds from year to year and if fed better they seem to lift protein %
I know cows have a certain protein percent “bred” into them, but whatever that percentage is, I presume if she is fed at a higher level, ( I don’t mean fed more kg DM, I mean fed more energy) she will produce more protein.
So….better fed cows have higher protein % and are more fertile?
Perhaps I am reading the research badly, and a high protein % cow means she is “classified” as a high protein percent cow and is more fertile, rather than “feed her better” to lift her protein % and she becomes more fertile.
Hi Frank, thanks for your comment. I had a read and passed it on to Martin, who said he’d like to address it himself. So, I’ll refrain from pre-empting him – but it’s a good question and I’m glad you asked it.
Hi Frank,
In this context, by ‘milk’, Eee Cheng was referring to milk volume. Most studies (including ours) have shown that, over large numbers of cows, on average high milk protein% cows have lower milk volumes. Importantly, many factors affect milk volume, and there are many high milk protein% cows with high milk volumes and many low milk protein% cows with low. Nevertheless, over large numbers of cows, this relationship is almost always evident in amongst the scatter.
This milk volume-milk protein % relationship would be due to both genetic and non-genetic factors. For example, just looking at the genetic factors, we know that if we selected sires solely on milk volume (not that anyone should or would), we know that we would reduce milk protein% due to changed herd genetics, and if all else was unchanged, we would see this as reduced vat milk protein%.
Changing direction slightly, our research has clearly shown that the milk protein%-reproductive performance relationship is not due to the higher milk volume amongst
low milk protein% cows being the cause of their generally poorer repro performance. (Again, we say ‘generally’ because plenty of cows with low milk protein% get in calf quickly and plenty of high milk protein% cows have very poor repro performance. Nevertheless, on average, within Holsteins, the high milk protein% cows have better reproductive performance relationship. Virtually every study globally that has looked for this relationship has seen it.)
Your points re effects of increasing energy intake on milk protein% are central to the research questions. When we first saw the milk protein%-reproductive performance relationship, we thought it was partly due to reduced negative energy balance in early lactation causing both higher milk protein% and improved reproductive performance. This may well be true but our research is showing us that there is more to this relationship than that. For example, through better feeding we might shift a cow’s milk protein % by 0.1% to 0.3% but in our study data, we’re seeing milk protein% varying from less than 2.5% to over 4.0%. Some of this range will be due to differing genetics but we suspect that some of the rest is also due to non-genetic factors. We need to know what these non-genetic factors are as some of them may also improve repro performance.
So frustratingly, there are more questions than answers so far. But we think our research is going to help narrow down the questions so the next set of questions get us closer to the answers. One thing that is clear is that this is a powerful relationship – cows with high milk protein% have, on average, much better reproductive performance and if we can capture this through better genetics and/or management, we would expect to see really nice increases in reproductive performance.
John
Interesting – our younger heifers have no worries getting in calf – and I looked back on 15 months of herd test, where 1st lactation heifers have tested as an average – 3.32%P to 3.77%P – predominantly Holsteins too.
Hi Jess – yes, it *is* interesting, isn’t it? I wonder how your results look across the rest of the herd as well. It’s tough to do a statistical analysis without time and data, but it’s interesting to keep an eye on the trends and see how well they match your experiences.
Hi Jessica,
In one of our studies, we only used those heifers that got in calf as yearlings; we then compared their calving dates and that’s when we say that those with high milk protein% early in their first lactation had calved earlier. This relationship is weaker in first calvers than older cows (weaker than effects of liveweight and body condition at the yearling mating, for example) and so you would probably need a lot of heifers to see it (although we saw it with only 900 or so Holstein first calvers). Plenty of those with low milk protein% early in their first lactation had calved earlier and plenty of those with high milk protein% early in their first lactation had calved a bit later. But in amongst that scatter, there was the relationship.
This is important as it provides one more piece in the jigsaw – it shows that part of the milk protein %-reproductive performance relationship is at work in the yearlings, so negative energy balance in early lactation is not the full story. And the fact that this relationship is stronger in second and higher cows than first calvers tells us that some parts of the relationship are due to lactational factors.
John