The carbon cost of poor animal health on the planet

And as is typically the case, the burden is highest for the poorest, with poultry production levels in low-income countries thought to be slashed by more than a fifth due because of disease.

But what does putting vets alongside farmers on the frontline of improving farm sustainability actually mean — and can it make enough of a difference in a global climate crisis to matter?

Two fronts

Poor livestock health hampers the sustainability of farms on two fronts.

The premature death of animals before they ever reach productivity means the energy and resources which go into producing and growing the animal are wasted, while sickness means energy which would typically go into food production is instead sapped up to fight off infection and disease.

Improving longevity — the length of time a production animal lives for — reduces the proportion of an animal’s life for which it is non productive.

Take the typical Irish dairy cow as an example; she will spend the first 60 days of her life on milk before weaning, and at least a further 16 months or more before she is bred.

During this time, the feed we are giving our heifer is mainly going into growing her frame and getting her ready for reproduction. Then the next nine months will see a growing proportion of this energy go into growing her calf. It’s only after that calf is born that the cow finally enters her productive stage, producing excess milk for human consumption.

It’s been well publicised recently that reducing her calving age to around 23 or 24 months means less unproductive time at the start of her life.

However, the same principle also applies to the other side of her life cycle - every additional lactation also further reduces the proportion of her life, which is unproductive, and the longer that cow is alive, the more productive she will be.

Essentially, a sick animal is not very productive — and a dead one even less so.

Yet maintaining good livestock health and tackling disease remains one of the biggest challenges for farmers on the ground.

Despite the millions — if not billions - thrown at livestock health research, shamefully, Rinderpest so far remains the only livestock disease ever globally eradicated.

While stamped out in these isles — for now — diseases like Foot and mouth, BSE, and African swine fever remain huge challenges overseas.

The burden to solve many of the most endemic diseases — for example, Johne’s Disease, IBR and BVD - remains on the industry.

However, Dr Ellen Hegarty explains managing these could have wider public good benefits.

“Vets have a huge role to play in advice around animal health and welfare, genetics and nutrition and all of these can contribute not only to improvements at farm level, but also improvements in farm emissions,” she said.

Eradicating BVD

However, while diseases like IBR and bovine TB remain significant challenges, sector-specific health plans, such as the National Johne’s Programme and Pig HealthCheck, have also made major recent gains in improving Irish livestock health.

It also certainly feels like the end is in

sight for Bovine Viral Diarrhoea, with Ireland now on the cusp of BVD-free status with the success of the first industry-led programme to tackle the disease.

BVD has as direct an effect on agricultural productivity as you can get — as infectious as the common cold, yet life-limiting, it causes animals to fail to thrive and usually die.

The frustrating thing about BVD is that most infected calves look perfectly healthy, meaning farmers can be reluctant to get them put down. But ultimately, most animals fail to survive past two years old, meaning the feed and resources which go into growing them to that stage are squandered.

And while persistently-infected animals make up a tiny minority, they play a very significant role in spreading the disease, meaning even more animals go on to carry the infection and develop symptoms.

“It’s not only the effects on these animals, it’s also the effect they have on the rest of the herd,” Dr Maria Guelbenzu, BVD and IBR programme manager at Animal Health Ireland, explained.

“When we have them in a group of calves, these persistently-infected animals are effectively mini ‘virus factories’, and when the rest of the cows get infected, what happens is that affects their immune system, and they become immunosuppressed.

“That then means the typical scour and pneumonia become really hard to treat, and so they become quite sick, they need more care. And that brings us to issues like antimicrobial usage, and also the social effects on the people looking after these animals.

“There is nothing more disheartening than having disease on your farm - I do feel for the unlucky farmers affected because it does take a toll, of course.”

BVD is particularly tricky to tackle as the virus can also cross the placenta meaning calves of infected cows are also typically infected and will later go on to spread the disease themselves — that’s if the virus doesn’t cause the calf to be aborted or born with significant deformities.

“The main environmental benefit of eliminating BVD is first on fertility, and having that effect in stock - failure and abortion - that is very important,” Dr Guelbenzu said.

“Because if we don’t have BVD, then we will use that a policeman rate, which means that we need fewer animals in total, and also increases the reproductive performance. So some of the measures in terms of reproduction is trying to get animals to reproduce that bit earlier, and things like that.

“The other key part, in terms of environmental benefits, is that healthier calves achieve higher growth rates, so there is less feed needed.”

There are now hopes that the BVD success story could be replicated for IBR. However, the project is still in the early stages and requires significant funding.

But with the planet in crisis, animal health gains a relatively easy way to reduce inputs; it could, in future, be presented as a different kind of ‘public good’.

“The healthier herd you have, the more sustainable industry we will have,” Dr Guelbenzu added. “It does pay all around; we know it pays on the economic side. And on the social side, I do feel for the unlucky farmers whose animals are affected by these diseases because it does take a toll.

“It doesn’t matter how good the nutrition you have, or your genetics are, if you have disease on your farm, you’re not going be as sustainable as you could be - having a healthy herd has to be our baseline.”

‘A vicious cycle’

The connection between animal health and climate change is a “vicious cycle”, which unchecked will only get worse, an American scientific study published in 2020 warned.

The paper lead-authored by Vanessa Ezenwa and published in the journal Trends in Ecology and Evolution explained that a warmed and wetter climate would not only increase animal infectious diseases, but those pathogens, would in turn, further exacerbate animal methane production.

And worryingly, the researchers behind the study estimated that pathogen-induced changes have the potential to increase livestock methane emissions by a staggering 50%.

The figure is based on recent studies of parasitic worm infections in sheep, which show that common parasites can elevate net methane emissions in animal production systems by increasing methane yield, reducing production efficiency, and increasing the time for animals to reach their production targets.

For example, while individual lambs and ewes infected with the gastrointestinal worm Teladorsagia circumcincta produced less daily methane on average than uninfected controls, methane yield per kilo of dry matter intake was 33% higher in parasitized lambs.

Infected lambs also gained weight at only 4% of the rate of uninfected lambs and would thus require more time to reach their target slaughter weight, resulting in greater lifetime methane production.

Likewise, in ewes, the combined effects of maternal weight loss and delayed weaning due to parasitism resulted in an 11% increase in methane emissions per kg of lamb liveweight gain.

It’s a concept backed up by other scientific sources, CIEL, the UK’s Centre for Innovation Excellence in Livestock, found that improved sheep productivity (through improved health and nutrition) greatly reduced total emissions by around 7%.

Similarly, moving to dairy cattle, a Norweigan study showed that cows infected with subclinical mastitis emitted up to 8% per kilo of milk produced than uninfected cows.

CIEL director Dr Elizabeth Magowan, who also leads Northern Ireland’s Agri-Food and Biosciences Institute, explained that improved animal health has the advantage of requiring fewer animals for the same level of output.

A recent report by the organisation states improving animal health could, in principle, lead to significant reductions in emissions intensity by, for example, improving the feed conversion ratio of individual animals and reducing the flock or herd breeding overhead (through improved fertility and reduced mortality).

The report recognised improved animal health as one of its preferred methods in terms of cost-benefit ratio for beef and dairy herds in particular.

“For dairy, beef and sheep systems, mitigations for improving production efficiency, through, for example, improved fertility, health and genetic gain, contributed significantly to reducing the carbon footprint and overall emissions. This often requires investment and system changes on farms,” Dr Magowan stated.

“Fewer animals with improved efficiency will result in more land being available for woodland or forestry, for example, capturing carbon within the farm. The scale of this carbon capture will depend on the nature of the afforestation or other strategies adopted, along with land type and location,” she said.

Key components of this include optimising calving intervals, replacement rates, and cow longevity, as well as better matching feed inputs to animal needs.

“It’s not a tug o’ war” — breeding for health traits

Recent research and modern technology, including pedometers, rumination-monitoring boluses and in-line milk recording, also make it possible to identify the earliest diseases often before visible symptoms emerge.

But could the next step be to breed cows which may not become sick in the first place?

Irish Cattle Breeding Federation (ICBF) geneticist Dr Siobhan Ring is one of the researchers behind the traits for TB and liver fluke resistance which are now incorporated into Irish breeding indexes.

The indexes allow farmers to actively choose sires which improve their calves’ resistance towards some of the most challenging diseases facing agriculture.

Health traits were first introduced into the dairy breeding indexes around 15 years ago, starting with lameness and mastitis. In 2019, the bovine TB resistance trait was introduced.

Dr Ring suggests the future could include the potential to predict the likelihood of a calf getting sick before it is even born.

As part of research carried out with Teagasc, she examined which diseases could be targeted through genetics.

“We looked at everything from BVD, TB, IBR, liver fluke or even the individual lameness causes, like white line disease, ulcers, etc. - so any trait you can think of potentially,” she said.

“For every single one of them, we could we realised that we could breed for resistance to them — and we found that we could breed animals that have less and less susceptibility for each of those individual diseases.”

But the most challenging aspect is staying on top of the latest data, she explains.

“What really limits us is, in the vast majority of cases, is to have data - and it’s not necessary to have huge volumes of data.

“It’s the collecting of routine, frequent data so that you can get the calves that are born on the year you’re working on.

“There’s no point in the evaluation using data from animals that were born two years ago — it needs to be updated all the time relevant to the calves that are being born now.” Her work currently uses data collected by the Department of Agriculture to pick up the family lines of cattle which are more susceptible to going down with TB — both in the factory or through the skin test.

“If pulled up two animals, one animal that’s really bad for TB, and another animal that’s got really good genetic merit in terms of TB, time and time, the animals that have the bad genetic merit go down far more often than those that have that good genetic merit.

“To put a number on it, it’s a 26% lower incidence of TB in those animals than those with poor genetic merit.”

Health traits are considered to have low heritability, meaning it can be difficult to pass the trait on. However, she explains that should not be a reason to pursue the gains which can be made.

“Fertility has a heritability of 3%, TB is 11% - more than nearly four times the heritability. So, in theory, we could make way more progress on TB if we really push the selection pressure on it; really effectively selecting the cows that we put forward for breeding,” Dr Ring said.

“These days, if a bull is not good for fertility, he’s out the door; he’s not going to be used. It’s the same approach needed essentially; if she’s not milking well, and she’s not going in calf, she’s going to be gone.

“So when you’re looking at all these things that you want, of course, farmers want good herd health, but it comes into priorities — it’s not a tug o’ war to breed for good health, we definitely can achieve it.”