Beef carcass fat colour: what drives yellow fat in Australian cattle

Why fat colour matters to the beef trade#

Appearance counts heavily in how consumers judge beef, and fat colour is one of the first things a buyer notices on a carcass or in a display cabinet. The paper notes that yellow fat is less acceptable than white fat in both the domestic and export trade, and carcasses showing it are typically diverted to the lower-priced manufacturing market rather than sold as prime cuts.

The Japanese market was singled out as particularly strict, specifying a requirement for white fat in the Australian beef it imports. That commercial pressure is what gave the study its practical purpose: understanding what causes yellow fat so that producers and processors can manage it, rather than simply discovering it after the animal is already on the rail.

The paper explains that the yellow pigment responsible is a carotenoid, mainly beta-carotene, a precursor of vitamin A that builds up within fat cells. The more carotenoid present, the more intense the yellow colouring becomes. Diet, inheritance, age, which fat depot is examined, chilling conditions and processing method had all previously been identified as factors affecting fat colour, according to earlier work the authors cite.

How the study measured 622 carcasses#

The researchers collected data from 622 beef carcasses during eleven visits to five Victorian abattoirs over an autumn/winter period, covering operations ranging from small domestic meatworks to large export plants. This breadth of sites was intended to capture the range of cattle types that actually move through Victorian processing in a normal season.

Objective colour was measured with a Minolta CR200 chromameter at the P8 site, the same rump location used for fat depth measurement under AUS-MEAT definitions. Three measurements were taken on each hot carcass after washing and averaged, recorded in the CIE-Lab colour space, with the b value used throughout the analysis because it specifically measures yellowness.

Every carcass was also given a subjective score using a six-point chart with accompanying photographs, originating from work in Western Australia, running from white at one end to very yellow at the other. Carcasses with blood splash, bruising, air bubbles in the fat, or less than three millimetres of fat depth at the P8 site were excluded, to keep the measurement reliable.

Cattle were deliberately drawn from four nutritional backgrounds: domestic feedlot beef on grain for 70 to 100 days, export feedlot beef on grain for a longer period destined for Japan, grass-fed beef off autumn/winter pasture in southern Australia, and milk vealers. Breed, sex, dentition (used to estimate age) and hot carcass weight were also recorded for each animal.

Objective measurement versus the eye of the grader#

The mean b* value across the sample was 11.24, and it explained 46% of the variation in the subjective fat colour scores given by the photographic chart, a relationship the authors describe as statistically significant but weaker than they had hoped. Most carcasses, 80.6% of the sample, fell into fat colour scores 2 and 3, equivalent to creamy-white to cream fat, and very few scored 5 or higher, the yellow to very yellow end of the chart.

The authors suggest the modest strength of the link between the instrument reading and the human score may reflect inaccuracies in the subjective assessment system itself, rather than a shortcoming of the chromameter. They point to Murray and colleagues, who reported a much tighter correlation, r = 0.96, between chromameter readings and subjective meat colour using a five-point scale for meat colour rather than fat colour, suggesting that instrument-based measurement has real potential to standardise grading if the human reference scale can be sharpened.

This gap between objective and subjective assessment is one of the more practically important findings of the study. If fat colour grading is going to influence price, as the paper makes clear it already does in some markets, the industry needs a dependable, repeatable way of scoring it, and a chromameter reading is more consistent than a grader's eye against a printed chart, even if the two do not always agree. The same tension between instrument reading and visual scoring also runs through meat colour and shelf life, which looks at colour stability in meat rather than fat.

Diet, age and sex: the main drivers of beef carcass fat colour#

For the British breed cattle that made up the bulk of the sample, a stepwise multiple regression found significant effects of nutritional category, dentition (age), sex, and interactions between hot carcass weight and dentition and between sex and dentition, all at P<0.001. Together this model accounted for 63% of the variation in fat yellowness in British breeds, a considerably stronger fit than the subjective-objective comparison.

Feedlot cattle consistently had lower, whiter b values than grass-fed cattle or milk vealers. The paper reports mean b values for the four nutritional groups, with the grass-fed group at 13.8 and milk vealers at 9.0 sitting well above both feedlot groups, and the export feedlot group, fed grain for longer than the domestic feedlot group, showing a lower value again than the domestic feedlot group. This pattern is consistent with the idea that extending time on grain keeps reducing yellow colour.

Sex and age effects were also clear. Female cattle had yellower fat than steers across all dentition categories: the gap between predicted female and steer b* values ran to roughly three units through the younger age groups before narrowing sharply, to around one unit, in the oldest animals recorded (those with eight permanent incisors). Those oldest cattle, overall, carried higher, yellower b* values than any of the younger dentition groups, which were themselves broadly similar to one another.

Breed added a further, independent effect (P<0.001) when the full data set was analysed. In the second-oldest dentition category, b* values were 8.5 for British breeds, 17.4 for Channel Island dairy breeds, 15.1 for other dairy breeds and 11.5 for European breeds; in the oldest category these had risen across the board, to 20.7, 28.1, 24.1 and 11.1 respectively. Dairy breeds, in other words, carried noticeably yellower fat than British or European beef breeds, and this gap widened with age.

Reading the results against earlier New Zealand work#

The authors compare their findings with earlier New Zealand research by Morgan and colleagues. Their own data supported that earlier finding that aged dairy-breed cattle are the group most likely to produce extremely yellow fat, visible here in the high b* values recorded for Channel Island, British and other dairy breeds carrying eight permanent incisors.

On sex, however, the two studies disagreed. Morgan and colleagues reported little difference in fat colour between the sexes, whereas this study found female cattle consistently yellower than steers of the same breed across every dentition category measured. The paper does not attempt to explain this discrepancy beyond reporting it, leaving open whether it reflects genuine biological difference, sampling differences between the two studies, or something about how the Australian cattle population was structured.

The grain-feeding result matched expectations set by earlier Canadian and American studies cited in the paper, including work by Forrest and by Dinius and Cross, who had shown that time spent on grain progressively whitens fat because grain carries much less beta-carotene than pasture. The Victorian data extended this by comparing two feedlot durations directly within the same sampling frame, strengthening confidence that the effect holds under Australian conditions and processing practice.

What the sampling design could and could not separate#

The authors are candid about confounding in their sample, a point worth weighing carefully. Older male cattle and those with the longest time on grain tended to have heavier hot carcass weights; most carcasses in the oldest dentition category were female, while most in the next category down were male; domestic feedlot cattle were all recorded in a single dentition category; and milk vealers appeared only in the youngest dentition group.

This pattern, the paper notes, mirrors how cattle are actually presented for slaughter in Victoria, so the confounding is realistic rather than an artefact of poor sample selection. It does mean that some of the apparent effects of sex, age, weight and nutritional background are entangled with one another, and the authors say the results need to be interpreted carefully as a result, even though they consider them meaningful.

That honesty about the sample's structure is, in our judgement, the main limitation to keep in mind when applying these findings. The regression approach used, with its reported interaction terms, goes some way to separating these effects statistically, but a design where every nutritional category, age group and sex combination was represented in balanced numbers would allow more confident, independent estimates of each factor's true contribution to beef carcass fat colour. A similarly structured, industry-wide sampling approach underlies the Information Nucleus lamb production project, which drew on commercial flocks across multiple sites to reach broader conclusions.

Practical implications for producers and processors#

The paper's own figures give some reassurance for the industry overall. Because the domestic market was reported to accept fat colour scores of 1 to 3, corresponding to b values of 1 to 18, and the Japanese market scores of 1 to 2, corresponding to b values of 1 to 11, and because most carcasses in this sample fell within the creamy-white to cream range, the authors conclude that the great majority of the cattle sampled would not have been discounted on fat colour grounds.

Where risk concentrates is at the margins: aged cattle, particularly of dairy breeds, finished on pasture rather than grain. The practical lever identified by the study is straightforward in principle, feeding grain for longer reduces yellow fat colour, with the effect still building at the longest durations examined. The authors flag further investigation of dietary manipulation in the weeks or months before slaughter as warranted, specifically with growing Japanese and Pacific rim export markets in mind.

For anyone assessing carcasses against market specifications, the gap between chromameter readings and subjective scoring found here is also worth factoring in: a visual score against a printed chart and an instrument reading will not always tell quite the same story, even though both are measuring the same fat. This study sits within a wider body of carcass work carried out under the banner of the ASAP conference proceedings collection, which gathers many such industry-funded trials from the same era.

Sources and further reading#

• Australian Association of Animal Sciences: successor to ASAP
• Trove library search: find a library that holds the paper
• Meat & Livestock Australia: red meat industry research and marketing body
• Feedipedia animal feed database: an open-access database of animal feeds

Questions#

— The Livestock Library team