← FAT Research Library

📅 Prepared March 3, 2026  |  🔄 Revised May 2, 2026

✍️ Dirk Adams

⌛ 7 min read

FAT RESEARCH SERIES — ECONOMIC CONCENTRATION / BEEF

Grass-fed cattle are structurally older at slaughter, almost never graded, and completely unscreened for the maturity characteristics that determine tenderness. The consumer has no way to know what they’re getting — and the current system has no mechanism to fix it.

The Hidden Variable in Your Grass-Fed Steak

Most consumers buying grass-fed beef are focused on what the animal ate. Was it truly grass-fed? Was it pasture-raised? Were hormones or antibiotics involved? These are important questions. But there is a question almost nobody — not consumers, not most retailers, and not even many producers — is asking: How old was the animal when it was slaughtered, and what does that age mean for the tenderness and eating quality of the meat?

Age matters enormously for beef tenderness. As cattle mature, the collagen in their muscles undergoes a process called cross-linking, forming heat-stable bonds that make meat progressively tougher. This is not a subtle effect. It is the primary biological mechanism behind the well-established relationship between animal maturity and meat toughness. The conventional beef industry accounts for this through the USDA grading system, which evaluates carcass maturity as a core component of quality grade. But grass-fed beef largely exists outside that system — and the consequences for the consumer are significant.

Why Grass-Fed Cattle Are Older at Slaughter

The fundamental issue is growth rate. Cattle finished on grain in a feedlot gain weight rapidly — typically 2.5 to 4.0 pounds per day on high-energy rations — and reach slaughter weight at 14 to 20 months of age. Grass-finished cattle gain weight much more slowly, at 1.5 to 2.5 pounds per day, and typically are not ready for slaughter until 24 to 30 months of age. Some larger-framed breeds finished on grass can take even longer.

A 2024 South Dakota State University Extension review confirmed this range, noting that in grass-fed systems, cattle are often slaughtered between 1,000 and 1,200 pounds at 24 to 28 months of age. That is 6 to 14 months older than the typical grain-finished animal. And this additional age is not merely a bookkeeping detail. It has direct, measurable consequences for the collagen structure of the animal’s muscles.

The Science of Collagen Cross-Linking and Age

Meat scientists have thoroughly documented the relationship between animal age and beef toughness. The mechanism involves collagen, the most abundant structural protein in muscle. As cattle age, the collagen fibrils in their muscles form trivalent cross-links — primarily a compound called pyridinoline — that are heat-stable and do not break down during normal cooking.

Research published in the Journal of Animal Science confirmed that concentrations of pyridinoline are positively correlated with both Warner-Bratzler shear force (the standard laboratory measure of toughness) and animal age at slaughter. Earlier research had recommended that to avoid the toughening effects of aged collagen, animals should ideally be slaughtered between 12 and 18 months — a window that grain-finished cattle comfortably fit within but that grass-finished cattle almost always exceed.

“To avoid the effect of aged collagen and obtain the most tender beef, animals between 12 and 18 months should be used.”

Bailey (1972); Shimokomaki et al. (1972), as cited in McCormick, Reciprocal Meat Conference

Critically, it is not just chronological age that matters — it is the animal’s growth pattern. Periods of slow growth or nutritional stress accelerate the maturation of collagen cross-links relative to the animal’s chronological age. This is particularly relevant for grass-fed cattle, where seasonal forage quality fluctuations, winter feeding on low-quality hay, and drought conditions can create stop-and-start growth patterns. A grass-fed animal that experienced a winter on coarse hay followed by rapid spring growth may have collagen maturity that exceeds what its birth certificate would suggest.

As the U.S. Premium Beef cooperative noted in a November 2024 report, research has shown that periods of low growth rate increase the maturity of collagen and advance bone maturity more rapidly. Grazing during a drought, for example, would include both coarse forages and slow growth rate — a combination that pushes physiological maturity ahead of chronological age.

The Grading Gap: Why Nobody Knows How Old Grass-Fed Beef Is

In the conventional system, the USDA grading process provides a built-in maturity check. When a carcass is presented for grading, USDA Agricultural Marketing Service graders evaluate the ossification of bone and cartilage in the vertebrae, the color and texture of the lean, and dentition — all of which serve as proxies for physiological age. Maturity is classified on an A-through-E scale, with A maturity corresponding to approximately 9 to 30 months of age and B maturity to 30 to 42 months. Only A and B maturity carcasses are eligible for the consumer-facing quality grades of Prime, Choice, and Select.

But USDA quality grading is voluntary. It is a fee-based service that processors request and pay for. And most grass-fed beef processors — especially the small and very small plants that handle the majority of direct-to-consumer grass-fed beef — do not request it.

The reasons are straightforward. The USDA grading system is built around marbling as the primary quality signal, and grass-fed carcasses, being leaner, almost invariably receive low quality grades. Small-scale producers who pasture-raise usually do not participate in grading because the standards are built around what grain-fed beef should look like, which virtually guarantees a low score for grass-finished carcasses. Producers rationally opt out of a system that would label their premium product as Standard or worse.

Compounding Factors: Why Grass-Fed Is Particularly Vulnerable

The age problem does not exist in isolation. Several characteristics of grass-fed beef production compound the tenderness risk.

Less marbling to buffer against toughness. Intramuscular fat (marbling) acts as a natural tenderizer. Even when collagen is somewhat cross-linked, abundant marbling can compensate by providing juiciness and a perception of tenderness during chewing. Grass-fed beef, by definition, has less marbling. So the one factor that might partially offset increased age — high intramuscular fat — is precisely the factor that grass-fed cattle lack.

Intermittent growth on seasonal forage. Unlike feedlot cattle that receive a consistent high-energy ration every day, grass-fed cattle are subject to seasonal fluctuations in forage quality and quantity. A calf born in March that goes through its first winter on stockpiled fescue or medium-quality hay may experience weeks of sub-maintenance growth before recovering on spring pasture. Each period of slow growth advances collagen maturity disproportionately.

Breed mismatch. Many grass-fed producers use the same cattle genetics suited for feedlot finishing — large-framed Continental breeds or Continental crosses that are slow to mature on forage diets. These animals may not reach finished condition until 28 months or later. Simmental calves finished on grass need to be held over another winter, reaching slaughter at 24 to 26 months, while most tropical cattle breeds take 30 months or more.

Small-plant processing limitations. Many grass-fed cattle are processed at small state-inspected or custom-exempt plants that lack the infrastructure, carcass grading cameras, or USDA grader access that larger plants have. These plants may not perform any systematic maturity assessment, and the dentition checks used for OTM (over 30 months) classification at large federally inspected plants are tied to export verification programs that small plants rarely participate in.

What “Over 30 Months” Means — and Why It Matters Here

In the conventional packing industry, carcasses determined to be over 30 months of age (OTM) by dentition — the presence of three or more permanent incisors breaking the gumline — face significant discounts and operational restrictions. The most recent USDA LM_CT169 report shows OTM discounts ranging from $10.00 to $40.00 per hundredweight, with a weighted average around $16.68/cwt. OTM carcasses are also excluded from all export programs (because major importing countries like Japan and South Korea restrict beef to under-30-month animals) and lose eligibility for premium branded programs like Certified Angus Beef.

The 2022 National Beef Quality Audit, the most comprehensive benchmark study of the U.S. fed cattle population, found that 2.6% of fed steer and heifer carcasses were classified as 30 months of age or older by dentition. The U.S. Premium Beef cooperative reported in November 2024 that this percentage is trending upward — their Kansas grid cattle averaged 2.52% OTM in fiscal year 2024, up from 2.13% the prior year — driven by longer days on feed and heavier target weights across the industry.

These OTM classifications occur in feedlot cattle that are typically 18 to 22 months old at slaughter. The issue is that dentition is a physiological indicator, not a chronological one. Cattle older than 20 to 24 months have an increased risk of being classified as OTM by dentition even if their true chronological age is under 30 months.

Now consider: if conventionally fed cattle at 18 to 22 months are seeing 2.5% OTM rates, what would the OTM rate be for grass-fed cattle harvested at 24 to 30 months? The answer is almost certainly much higher — but we do not know, because these carcasses are not systematically screened. This is the transparency gap at the heart of the problem.

What Can Be Done? Six Approaches to Close the Gap

The tools to address this problem already exist. They are simply not being applied to the grass-fed sector. Here are six approaches, ranging from what is available today to what would require industry or regulatory change.

1. USDA Certified Tender / Very Tender Program

This is the most immediately available and arguably the most powerful tool. USDA’s Agricultural Marketing Service launched a Tenderness Verification Program in 2012 that certifies beef cuts based on objective slice shear force (SSF) or Warner-Bratzler shear force (WBSF) testing — not marbling, not maturity score, but actual measured tenderness. Beef must achieve a WBSF score of 4.4 kg or an SSF score of 20.0 kg, with no artificial tenderization permitted. This is an outcome-based standard that is entirely agnostic to feeding system. A grass-fed processor who adopted this program could certify their product as tender based on science, not marketing claims — and screen out the carcasses that even extended aging cannot rescue.

2. Age and Source Verification Through Traceability

USDA AMS already administers Process Verified Programs (PVP) that allow producers to make verified age claims using birth-to-harvest traceability through electronic ID tags. A grass-fed brand could implement documented age records and guarantee that no animal over a specific age threshold — say, 26 or 28 months — enters their supply chain. This does not require USDA grading. It requires a documented chain of custody, which organizations like the American Grassfed Association could potentially incorporate into their certification standards.

3. Genetics Matched to Grass-Finishing

Moderate-framed, early-maturing British breeds — Angus, Hereford, Shorthorn, Red Angus — finish on grass faster than large-framed Continental or tropical breeds. Selecting genetics that reach finished condition at 20 to 24 months rather than 28 to 32 months on grass is likely the single highest-leverage production decision a grass-fed operator can make for tenderness outcomes.

4. Mandatory Maturity Screening for Ungraded Beef Sold as Whole Cuts

This would require a regulatory change — mandating that any beef sold as intact muscle cuts (steaks, roasts) at retail undergo some form of maturity assessment, regardless of whether the producer opts into the full quality grading system. Currently, an ungraded 36-month-old grass-fed carcass can be broken into steaks and sold to a consumer at a premium price with zero maturity information. This is a consumer protection gap, not merely a quality assurance gap.

5. Extended Aging as Standard Practice

Research consistently demonstrates that extended wet-aging (28 to 42 days postmortem) significantly reduces shear force values even in older-maturity carcasses, by allowing natural enzymatic degradation of myofibrillar proteins. While extended aging cannot fully compensate for severe collagen cross-linking in very mature animals, it meaningfully reduces the variability problem. A grass-fed brand that systematically aged every carcass 28+ days and then applied shear force testing would be combining two complementary quality assurance tools — time and measurement.

6. Ossification Assessment Decoupled from Quality Grade

Camera grading systems already installed in large plants (such as the VBG2000) can assess ossification and predict tenderness independently of the marbling-based quality grade. There is no technical barrier to deploying this capability in smaller plants or through a mobile/regional service. A consortium of grass-fed processors could share access to a maturity-assessment service that evaluates only what matters for their product — physiological maturity and predicted tenderness — without running their carcasses through a grading system designed for grain-finished beef.

What the Consumer Should Know

If you are buying grass-fed beef — especially whole cuts like steaks and roasts rather than ground beef, where tenderness differences are largely moot — here is what the current system does not tell you:

The animal’s age at slaughter is almost certainly unknown to the retailer and unverifiable by you. No maturity assessment was performed on the carcass unless it went through full USDA grading (which most grass-fed beef does not). The beef may be from an animal that was 22 months old or 34 months old, and the eating quality difference between those two endpoints can be dramatic — especially in a lean carcass with minimal marbling to compensate.

This is not an argument against grass-fed beef. It is an argument for the same kind of transparency in the grass-fed sector that the USDA grading system (imperfectly) provides for conventional beef. Consumers paying a premium for grass-fed product deserve to know not just what the animal ate, but whether the meat on their plate will be tender enough to enjoy.

References

1. USDA AMS. “Carcass Beef Grades and Standards.” ams.usda.gov.
2. USDA AMS. “LM_CT169: 5-Area Weekly Weighted Average Direct Slaughter Cattle.” ams.usda.gov.
3. Mayer et al. “National Beef Quality Audit 2022.” Translational Animal Science, 2024.
4. U.S. Premium Beef. “Understanding Over 30 Month Carcasses.” USPB Update, Nov 2024.
5. Roy et al. “Collagen cross-link concentrations.” Meat Science, 110:109-117, 2015.
6. Bruce et al. “Meat quality and intramuscular collagen.” Meat Science, 2021.
7. McCormick. “Collagen in Meat Tenderness.” Reciprocal Meat Conference, Vol. 47.
8. SDSU Extension. “Grass-Fed Beef: Understanding Terminology.” extension.sdstate.edu, 2025.
9. SDSU Extension. “USDA Beef Quality Grades.” extension.sdstate.edu, 2024.
10. USDA. “Try A Little Tenderness.” usda.gov, Dec 2024.
11. USDA AMS. “Certified Tender or Very Tender.” ams.usda.gov.
12. USDA AMS. “Grass Fed Program for Small Producers.” ams.usda.gov.
13. OK State Extension. “Finishing Beef Cattle On The Farm.” extension.okstate.edu, 2021.
14. Penn State Extension. “Grass-Fed Beef Production.” extension.psu.edu.
15. Cheung and McMahon. “Back to Grass.” Stone Barns Center, 2017.
16. Polkinghorne et al. “Ossification score.” Meat Science, 2015.
17. Modern Farmer. “Demystifying USDA Beef Grades.” 2013.

Written by Dirk Adams

Additional References

1. USDA AMS. U.S. Standards for Grades of Carcass Beef. www.ams.usda.gov.
2. Bonny, S.P.F., et al. Meat Science 120 (2016): 62-74. pubmed.ncbi.nlm.nih.gov.
3. Daley, C.A., et al. “A Review of Fatty Acid Profiles in Grass-Fed and Grain-Fed Beef.” Nutrition Journal 9 (2010): 10. pmc.ncbi.nlm.nih.gov.
4. USDA FSIS. “FSIS Guideline on Substantiating Animal-Raising Labeling Claims.” 2024. www.fsis.usda.gov.