Partitioning slaughter cattle drawn from separate paddocks on separate vendor declarations before consignment, and avoiding overnight lairage before slaughter were listed among a bunch of handy tips to help mitigate dark cutting in slaughter cattle offered to producers recently.

The University of New England’s Dr Peter McGilchrist told a producer audience last month that there were a number of methods to try to reduce dark cutting penalties in cattle sold weight and grade.

Dark cutting and high pH are among the most common causes of non-compliance among the 3.5 million carcases graded for Meat Standards Australia each year.

Nationally, dark cutting runs at about five percent of all carcases across the year, with some seasonal variance. Grainfed cattle have lower incidence of dark cutting than grassfed, because of nutritional input pre-slaughter, and having been better habituated to humans and activity, as part of the feedlot operations process.

Grassfed cattle average 8.7pc dark cutting across a typical yearly cycle, with variability year-to-year across the country, for seasonal reasons.

A small fuel tank

Dr McGilchrist provided a handy ‘Dark Cutting 101’ session during a Teys forum last month, re-stressing the importance of adequate glycogen in an animal’s system at time of slaughter, to produce enough lactic acid post-slaughter, in order to avoid high pH and dark cutting.

“We (both humans and cattle) can store only about 2pc of glycogen in our muscles – that’s it,” he said.

“The reason we can only hold 2pc glycogen is because it binds to water, and only 8pc of muscle weight is water. So the amount of water in our muscles limits the amount of glycogen we can store – we have only a small fuel tank,” he said.

A living animal uses that stored muscle glycogen to do physical work – whether it be through exercise or stress, via adrenaline.

“So we have to minimise both stress and exercise between when we muster cattle and their journey to the knocking box,” Dr McGilchrist said.

“But there are a whole heap of exercise and stressful occasions along that journey – including mustering, yarding, loading, trucking, unloading, lairage at the abattoir, and the journey to the knocking box.”

“Many of those cannot be avoided, but we can minimise the impact,” Dr McGilchrist said.

Avoiding the ‘danger zone’

At time of slaughter, cattle needed at least 1pc muscle glycogen remaining in order to avoid dark cutting, he said. Without it, each animal did not have enough ‘fuel in the tank’ to reduce pH to a great enough extent to avoid meat colour problems.

“So it’s only this difference between 1pc to 2pc (a full tank of glycogen) – that’s all the buffer zone we have to play with in this pre-slaughter period.”

“Start the journey at say, 1.2pc muscle glycogen, and by the time of slaughter, a whole bunch of them are going to cut dark, because of those various stressors and exercise. The further we can get away from the danger zone at time of muster, the better the outcome.”

“And to start that, they need adequate nutrition when leaving the paddock or yard, and then not burning through the whole glycogen reserve in that pre-slaughter period.”

It was impossible to tell whether an animal in the paddock had adequate glycogen ‘just by looking at it,’ but the best indicator was whether cattle were growing, or not, at time of muster, Dr McGilchrist said.

“If they are gaining weight, it means they are filling up the glycogen bucket first, and then laying down fat. But the problem is, fatness of an animal is no indication of glycogen level.”

Can the bucket be re-filled?

Responding to the question of whether cattle could be simply ‘re-fed’ after a stress event to raise glycogen before slaughter, he said glycogen in the muscle broke down at 11 micrograms/hour due to stress, but it could only be built back up (on really good feed) at 1 microgram/hour.

“What an animal breaks down in two hours, it takes 24 hours to put back,” he said. “Re-synthesis is much slower than what an animal can burn. Basically, it means we cannot replace glycogen at a fast-enough rate at the abattoir, through feeding.”

So what does the industry have against dark meat?

Dr McGilchrist said it was reasonably common among producers to simply dismiss dark cutting/high pH price penalties in their grids as ‘simply an excuse for processor discounting.’

“But in fact a beef processing plant wears about 70pc of the amount of money lost in discounting on farm cutting and high pH,” he said.

“It’s realty inefficient for our whole industry. None of us want any of these carcases … we grow these beautiful animals and put all the effort in – and if they cut dark it devalues the amount of money the industry can get from the consumer.”

Dark cutting meat was discounted in the market for a wide range of reasons, he said:

• It is more variable in tenderness
• Bacterial growth is more rapid being closer to neutral pH, impacting shelf-life
• Degree of ‘doneness’ when cooking changes
• Visual appearance.

Dr McGilchrist said high pH meat looked dark, because oxygen did not penetrate the muscle as far, and pH changed the structure of light reflectance.

“Some work to do”

With statistics showing 8.7pc of grassfed slaughter cattle processed across Australia each year cut dark, Dr McGilchrist suggested any producer whose annual slaughter turnoff figure was above 5pc ‘had some work to do.’

“Among grassfed cattle, we should aim as an industry to get down to 5pc or lower, aspirationally. We do have a problem in the grassfed industry, because every one of those dark-cutting carcases is losing the industry money,” he said.

Ten key interventions

Beyond on-farm nutrition to minimise those pre-slaughter glycogen losses, there was a number of things producers could do, involving gender, HGPs, mixing and drafting, breeds and age, selection for muscling, transport distance, washing of cattle (mostly grainfed cattle, for dag removal), and time in lairage.

“All of these things can have an additive effect, especially the closer your cattle are to the ‘danger zone’ (1pc) in terms of glycogen,” Dr McGilchrist said.

“We have to be aware of what can add a problem, assess what nutrition we think we have (glycogen stored), and then in some cases baby them in that period before we exit them.”

Here’s some key tips raised during Dr McGilchrist’s presentation:

Heifers

Heifers run about 2pc higher than steers (eg 6pc versus 4pc) in virtually every data set on dark cutting.

Why? On average, one in every 21 heifers will be cycling, meaning more activity (exercise or stress through being mounted or chased in the yard) in the pre-slaughter period.

Spaying (in states where it is permitted) is one solution. Another is reducing the amount of lairage involved. With a mob of heifers, the quicker they can be shifted from the paddock to the knocking box the better.

Mixing animals

Mixing animals had a big effect on dark cutting, because they had to socially re-rank and re-establish the hierarchy once mingled.

“That means putting strangers together in that last pre-slaughter period produces a lot of stress, and exercise, as animals follow each other around to work out who’s who,” Dr McGilchrist said.

For larger operators consigning multiple decks of cattle in the one shipment drawn from different paddocks, he suggested using separate vendor declarations.

“If you put them on two vendors decs, they legally have to be kept as two separate mobs – that’s the only way to ensure they remain separate, when the arrive at the plant.”

“Yes, it might cost a bit more time and admin, but it can deliver a better outcome,” he said.

Again, mixing strangers was a time issue. One interesting UK research study showed two mobs that were mixed produced 9pc dark cutters when processed after only three hours; after 24 hours the proportion grew to 27pc; while four separate mobs mixed pre-slaughter produced 45pc dark cutters after 24 hours.

Drafting

Sometimes, an entire mob cannot be shipped on a B-double load, for example, meaning pre-shipment drafting became inevitable.

“To be truly honest, we shouldn’t do it if we want to protect against dark cutting, but at times we have to,” Dr McGilchrist said.

“But that drafted mob will also socially re-rank, because some of them (perhaps including the king pin) have been left at home. So if we are going to draft before shipment, it’s best to do it either a month before, or as the cattle are being loaded onto the truck.”

“A month before gives them plenty of time to re-adjust to the new mob, while drafting onto the truck means there is less time to re-socialise. Do the draft a couple of days before, and they will spend the rest of the time re-jigging, not eating, exercising a lot and mucking around trying to re-establish the order.”

HGP

Dr McGilchrist said in all the MSA Australian data he had ever looked at, he had never found an effect on dark cutting from HGP. He hypothesised that this was because Australian users let the HGP payout period expire before time of slaughter.

Age

Older animals carried less glycogen in their muscle, and as a result were more likely to cut dark.

Dr McGilchrist’s own PhD student study showed that the risk of dark cutting increases once an animal reaches an ossification score around 200.

“Beyond that, there is an increased risk. Older cattle are also more stress-sensitive, and Wagyu and the dairy breeds also are,” he said. “They basically produce lactic acid slower than others, and have less glycogen, making them more prone to dark cutting.

“So we need really good stress management, if we are dealing with those type of animals pre-slaughter. In the same way, the older they are, the slower they produce lactic acid, meaning a long period is needed between the knocking box and grading to make sure they get down to ultimate pH.”

Muscling

On a similar theme, selecting for more highly-muscled animals was a good thing, when it came to dark cutting risk.

“We reduce the probability of cutting dark, as we get to more muscular animals,” Dr McGilchrist said.

Transport

Transport impact could not be avoided – apart from those rare cases where cattle might be fed in a feedlot beside a processing plant.

When a truck is moving, cattle were primarily focussed on staying on their feet, he said. That meant cattle tended to be calm, when moving, but when the truck stops, cattle can re-rank – even within their own small cohort in the crate.

“So stationary confinement during the transport phase is not a good thing,” Dr McGilchrist said.

“Drivers obviously have to stop to check the cattle, but we don’t want long periods of two, four, six or eight hours of stopping,” he said. For some reason, the same effect was not noted on rail consignments (Queensland maintains the only rail transport network for livestock), perhaps partly because trains don’t travel as fast, and there tended to be more space per animal.

Lairage

Ideally, we want as little time as possible in lairage at the abattoir, before slaughter, Dr McGilchrist said.

“In this country, we are a bit infatuated with overnight lairage,” he said.

“Why? Because we’ve always done it that way. But if we can reduce the amount of cattle held at the abattoir for excessive amounts of time, the better.”

Lack of feed during long periods of lairage also had an impact on stress.

‘Take a human away from food for 24 hours and they get hangry (hungry and angry). Why would cattle be any different?” he said.

“The further we get out in lairage time, the more that kicks in.”

Increasing time in lairage got more cattle closer to the glycogen ‘danger zone’ of 1pc, ramping up- the effect.

“So time in lairage is really important, if we think they are on the edge, in terms of glycogen –such as  any animals that have been drafted before transport, or off lesser quality pasture.”

Night-time lairage was less stressful than day-time.

WA trial on supplementation

A simple feeding study was carried out a few years ago, using a group of WA cattle producers whose previous year consignments had produced 10pc or more dark cutting.

Each producers’ consignment was divided into two, with a pasture paddock divided using an electric fence. One side of the paddock received a supplement comprising 2.5kg/day of a 14pc protein, 30mj energy pellet – not enough to produce acidosis, but enough to simply ‘top up’ then energy bucket. The supplement was fed for the final 14 days before consignment, but for bunk-weaned cattle, seven days would probably be enough, Dr McGilchrist said.

Dark cutting rates dropped to 3pc in the supplemented cattle, from 10pc the previous year, the trial showed.

“Supplementation works, when we think we are going to be close to the 1pc glycogen danger zone,” he said.

Additionally, there was an extra 3kg carcase weight in the supplemented mobs – essentially paying for the feed.

“So if we look at our paddock options when conditions aren’t great and simply being resigned to a train wreck (in dark-cutting terms), we can do something about it, by increasing energy intake over those last couple of weeks.”

Part of that management involved knowing your sale date, and developing a strategy based on pasture availability or supplement to match it, by increasing energy over the final couple of weeks.

“It’s too late, two days out, to think about intervention,” Dr McGilchrist said.

Water quality

Water quality is important for growth, because the more an animal drinks, the more it eats, and the more it grows, bumping-up glycogen levels.

“Water quality – particularly in the last few weeks before slaughter – helps reduce risk of dark cutting,” he said.

Habituation

Getting cattle habituated to humans – ‘training them to like us, or associate us with positive outcomes (eg feeding during weaning)’ also played a role in stress levels and dark cutting.

Dr McGilchrist said there were three overarching strategies in avoiding dark cutting:

• Filling the glycogen bucket through good nutrition (700g-1kg/day growth, ideally)
• Minimise stress and exercise on the way to slaughter
• “But the number one, foolproof way to avoid dark cutting is to sell them to somebody else, as feeders,” he said. “No more dark-cutters, ever, if you do that.”

He encouraged all producers to assess each slaughter consignment outcome for meat colour, and what might have changed.

“What was the feed like? How long were they on the truck? Were they co-mingled? You need to build that picture of your supply chain to make improvement.”

Questions

During questiontime, producers asked about same-day slaughter, and whether sending full or empty mattered.

“We used to be infatuated with curfews at trucking. But it’s just adding stress, and they are proper hungry by the time they get to the knocking box. As short a time as possible is best, Get them in, give them water, and let them go – an hour, two hours maximum,” was Dr McGilchrist’s advice.

Same-day slaughter

Another important research project involving MLA and a few feedlots explored the benefit of same-day slaughter.

“We can’t achieve it for all cattle, because a typical processor needs a quantity of animals on hand first-thing in the morning to get the day’s kill underway,” he said.

“But we certainly need to try to get a bigger percentage in that same day slaughter. If you have a lunchtime slot or an afternoon slot in that day’s kill, I would absolutely recommend (subject to transport distances involved) getting them to the plant that morning,” Dr McGilchrist said.

The other hidden advantage of same-day slaughter was carcase weight.

Some work last year with domestic-type cattle showed an extra 2.7kg carcase weight in animals slaughtered on day of delivery. That also benefited the processor, because they had an extra 2.7kg of meat to harvest from that animal, with the same fixed costs. Another trial using grainfed cattle in Queensland last summer produced a 4.7kg advantage in cattle slaughtered the same day as trucking.

Plant inspection

Dr McGilchrist was somewhat critical of the plant veterinary inspection process, where every animal has to be inspected by a vet, ante-mortem (before slaughter).

“Some plants are actually held to ransom by those vets,” he said. “They say, I will only do one ante-mortem inspection per day. Other plants have vets who will do as many ante mortem inspections as needed.”

“Those plants where only single inspections are carried out are holding the industry back – but we are trying to change that, working through the Federal on-plant vet inspection process,” he said.

Another question asked about any relationship between fat cover and pH/dark cutting.

“Across the whole MSA database, fat cover is a good indicator of nutrition,” Dr McGilchrist said.

“But on an individual animal basis, just because they have fatness does not mean their pH will be OK. They can be fat, but if their feed cuts out over the final month before slaughter, their glycogen is gone.”