Marbling in feedlot cattle: how nutrition and management shape the outcome

Why the question mattered to Australian feedlots#

By 2001 Australian cattle feeding programs had already moved further towards specific carcase outcomes than the equivalent industry in the United States, the paper notes, though increased participation by US feeders in branded beef programs and processor alliances was starting to close that gap. The paper argues that feeding cattle for extended periods to maximise marbling means juggling dietary energy intake against a web of variables that begin before the animal even enters the feedlot, continue through feedlot management, and are further shaped by market requirements at the other end.

At the time the paper was written, feedlot operators were also contending with younger cattle at entry, greater disease pressure, and high feed costs, all of which sharpened the need to secure marbling outcomes without blowing out the cost of production. The paper was written as a review, pulling together nutritional factors such as grain versus grass feeding, feed intake, days on feed and ionophores, alongside animal management factors including age, sex, background nutrition, supplementation, castration, health and hormonal growth promotant implants.

How the review of marbling in feedlot cattle was put together#

The paper is a workshop review rather than a single trial, and its evidence comes from citing a wide range of published feeding studies, mostly from North American research stations, alongside some contemporary Australian findings from the Cooperative Research Centre for Cattle and Beef Quality. Because it draws on so many separate experiments, the strength of any individual finding depends on the design of the study it originally came from, and George treats the material as a synthesis rather than presenting new data of his own.

The animal management studies referenced typically compare groups of steers or heifers managed differently before or during the feeding period, for example calf-fed versus yearling-fed cattle, or steers castrated at different ages, then measuring outcomes such as marbling score, carcase weight, dressing percentage, fat thickness and rib eye area at a common slaughter endpoint. This approach lets researchers separate the effect of age, weight or health status from other confounding factors, though as with any review, readers are relying on the original authors' own methods and statistics.

Grain, feed intake and the effect of restricting cattle#

Work by Williams and colleagues comparing grain and grass finishing systems found that cattle consuming grain diets had higher carcase marbling scores, higher USDA quality grade and more fat in soft tissue than grass-finished cattle. Australian research cited from the Cooperative Research Centre for Cattle and Beef Quality supported this pattern, finding grain-fed beef at the same carcase weight to be fatter than grass-fed cattle, with feedlot-finished cattle also scoring above pasture-raised animals for marbling.

On feed intake, the paper describes work by Berg and Butterfield describing nutrient partitioning as a hydraulic process, where available nutrients are directed first to maintenance and priority tissues, and only reach fat deposition once those higher priorities are satisfied. Burson and colleagues found that cattle fed sub-maintenance diets had the lowest fat thickness and kidney, pelvic and heart fat, while cattle given a concentrated ration across a run of 175 feeding days carried the greatest amount of both external and internal fat. Several later studies, including work by Hicks and colleagues, Hermesmeyer and colleagues and Rossi and colleagues, found that restricting or programming feed intake to improve efficiency repeatedly reduced marbling scores regardless of how many days the cattle were fed or how long the restriction period lasted. The paper draws the general conclusion that any form of intake restriction, whether from feedlot management or seasonal conditions, risks limiting how much marbling cattle can ultimately express.

Why extending days on feed has diminishing returns for marbling#

Increasing the number of days cattle spend on a high energy ration is described as the most common way to lift carcase marbling, and a series of serial slaughter studies cited in the paper, including work by Zinn and colleagues, Tatum and colleagues, Dolezal and colleagues, Williams and colleagues, Huffhines and colleagues, Duckett and colleagues and Van Koevering and colleagues, consistently found marbling deposition increasing with days on feed, though not in a straight line. Zinn reported that marbling score in calf-fed cattle kept climbing all the way out to 240 days on feed, while Williams and colleagues and May and colleagues found that pushing time on feed out from 84 to 112 days lifted marbling score further still, after which the response levelled off.

Duckett and colleagues found that intramuscular lipid content in the loin roughly doubled between 84 and 112 days on feed, but did not change between day 0 and day 84, or between day 112 and day 196. They attributed the increase to fat cells growing larger rather than increasing in number. Nash and colleagues used serial real-time ultrasound measurements and found the proportion of carcases grading USDA Choice rose from 20 per cent at day 84 to 80 per cent at both day 100 and day 120 on feed, illustrating how the timing of that response can shift quickly within a narrow window.

Age, backgrounding and creep feeding before the feedlot#

The paper describes how the age and maturity of cattle entering the feedlot, whether weaners at around nine months, yearlings at around one year, or older bullock-class cattle over 18 months and 370 to 450 kilograms, changes the management required to hit a given slaughter endpoint. Totusek found that older cattle at feedlot entry needed less time on feed to reach a grading endpoint and finished with heavier carcases as a result. Lunt and Orme compared weanling and yearling heifers slaughtered at the same weight and found yearlings more efficient, but weanlings carrying higher marbling scores and greater dressing percentages, with no difference in rib eye area.

A cloning study by Harris and colleagues separated the effects of age and feeding regimen using genetically matched clone pairs. Fed to a constant age of 16 months, calf-fed cattle spent 217 days on feed and finished heavier, carrying better dressing percentages and marbling than yearlings fed for only 93 days. When clone pairs were instead fed to a constant live weight of 528 kilograms, calf-feds still showed higher dressing percentages and greater external fat, but marbling scores similar to those of the yearlings, whose rib eyes were bigger and internal fat cover was lighter. At the extreme end of the age range, the paper notes that Angus and Charolais-cross cattle stop adding marbling once they reach roughly 700 days old, while Japanese Black cattle continue accumulating loin lipid up to nearly 1200 days of age.

Backgrounding studies by Burton and colleagues and Deering and colleagues placed Angus steers into five treatments ranging from early weaning straight onto feedlot rations at a young age of about three and a half months, through to extended dry wintering and grazing before feedlot entry at 17.4 months. At a constant fat thickness, early- and normally weaned cattle produced lighter carcases than backgrounded steers, but marbling score, rib eye area and USDA yield grade did not differ among the age treatments. Separately, Faulkner and colleagues found that creep feeding suckling calves reduced forage intake without affecting milk consumption, and although preweaning supplementation had no effect on later growing or finishing performance, it was linked to higher marbling scores attributed to greater overall fatness.

Castration timing, animal health and growth promotant implants#

Testosterone is described in the paper as prolonging muscle growth and delaying fattening, while oestrogen speeds physiological maturity and fat deposition. Champagne and colleagues found that castrating bulls at 2 or 7 months of age produced fatter carcases with higher marbling scores than castrating at 9 months or leaving cattle as non-castrates.

Animal health also mattered. The paper cites results from the Texas A & M Ranch to Rail program between 1993 and 2000 showing that cattle treated for respiratory disease had a lower incidence of carcases grading USDA Choice, down by between 12 and 17 per cent, and that most of the associated income loss, exceeding 100 dollars per head in 1999/2000, came from reduced liveweight performance and marbling rather than treatment costs and deaths. Gardner and colleagues, investigating finishing steer health, reported that carcase weight, growth rate, fat cover and marbling all suffered where respiratory disease had been treated, and that a lesion on the respiratory tract found at slaughter, whether active or inactive, was linked to lower marbling scores. Similar effects were reported by Roeber and colleagues across the full feeding period, and by Stovall and colleagues where the disease outbreak was limited to early days after cattle first arrived at the feedlot, although Roeber and colleagues found morbidity was lower in cattle that had gone through a preconditioning program before feedlot entry.

On implants, Duckett and colleagues found that steers implanted with oestradiol benzoate and trenbolone acetate had lower marbling scores than untreated controls, even though the actual quantity of fat in the loin was similar between groups, indicating the drop reflected increased muscling and larger muscle area rather than a true loss of intramuscular fat. A further study by Platter and colleagues found that marbling score fell progressively as the number of sequential implants administered through a steer's production life increased from one to four.

What this means for feedlot decisions#

Read across the whole body of evidence, the paper's central message is that marbling in feedlot cattle responds to a combination of nutritional consistency and management history rather than any single lever. Feeding an energy-dense grain ration without interruption, avoiding intake restriction, and allowing enough days on feed for the non-linear marbling response to run its course all featured as consistent themes across the cited trials. Backgrounding, castration timing, health status and implant use each shift the outcome in more specific, sometimes offsetting ways, such as implants improving muscling at some cost to marbling score.

We would treat this paper as a useful synthesis of established feedlot research rather than a source of new experimental proof, since its conclusions rest entirely on other groups' trials, several of them decades old and conducted under North American feeding conditions that may not map exactly onto Australian systems. For a fuller account of the biology behind how fat cells develop within muscle, readers of this summary may find it useful to compare it with the related summary on marbling in beef cattle, which covers the cellular side of the same process discussed in the wider Marbling Symposium collection. The proceedings sit alongside other feeding and carcase research gathered in the Beef CRC conferences collection, and further material of this kind can be located through the Livestock Library research index.

Sources and further reading#

• Trove library search: find a library that holds the paper
• Meat & Livestock Australia: red meat industry research and marketing body
• BREEDPLAN genetic evaluation: genetic evaluation system for Australian beef cattle
• Animal Genetics and Breeding Unit

Questions#

— The Livestock Library team