Understanding cattle growth curves to hit carcase specifications

Why the question mattered to feeder steer buyers and finishers#

The paper was written for people buying and finishing feeder cattle who need a practical way to judge whether a given animal will reach market specifications for weight and fat depth. Gaden notes that most target markets centre on young growing steers, so weight and fat depth become the two factors that really determine readiness for sale.

Being able to explain why some cattle lay down fat sooner than others, and why some stay lean for much longer, helps buyers avoid paying for stock that will not suit the intended outlet, and helps finishers plan feeding programs that reach the right specification without wasted cost. The session formed part of the Armidale Feeder Steer School, and the broader set of papers from that event can be found in the Armidale Feeder Steer School collection within this index.

How the paper builds its growth model#

This is a workshop paper rather than a reported experiment. Gaden sketches an idealised growth path for a steer raised on adequate feed from birth onward, supported by two figures: one plotting overall liveweight against age, the other showing how the relative shares of fat, muscle and bone shift as the animal ages.

Rather than presenting new trial data, the paper pulls together accepted principles of livestock growth biology and applies them to everyday decisions about frame size, muscling, breed choice and feeding. Its usefulness lies in how plainly it lays out these relationships for a farmer audience, not in any new experimental finding.

The model splits the animal's life into three phases: the period before weaning, a growing-out phase that follows weaning, and a final finishing or maturing phase. Each phase is described by which tissue is being built, what feed quality the animal needs, and what kind of carcase results.

The three stages of growth and what happens in each#

In the first stage, from birth to weaning at around 6 to 7 months, building skeletal frame takes precedence while new muscle fibres are laid down and muscle mass climbs steadily; only small amounts of fat are stored. The calf depends on very high quality feed, chiefly milk from its mother, and at this point the carcase carries plenty of bone and muscle relative to fat, with a light gut. Meat from calves at this age is tender but lacks developed flavour.

The second stage, often called backgrounding or growing out, runs from weaning onward and sees skeletal growth continue while filling out muscle becomes the dominant process; fat remains a minor component. Gut size expands noticeably once the animal starts handling roughage after weaning, which holds dressing percentage down, while the carcase gains an increasing share of muscle relative to bone and delivers a high yield of saleable meat. Meat from vealers or yearlings in this stage is tender with more developed flavour, and animals carrying a little extra condition tend to eat better.

By the third stage, finishing and maturing, the skeleton has essentially stopped growing and every muscle fibre that will ever form has already been established, so any spare energy intake is converted into fat. That fat accumulates under the skin, between muscles and within muscle as marbling; the carcase becomes a larger share of total body weight so dressing percentage climbs, while the proportion of saleable meat falls as more trimming is needed to remove excess fat. Flavour peaks in the best cuts of a fully finished, mature steer, yet tenderness in the lesser cuts declines because connective tissue builds up with age.

Breed, sex and frame differences in cattle growth curves#

The paper describes how sex, frame size and muscling alter the shape of an individual's growth path. Heifers kept on the same feed as steers end up with somewhat less bone, markedly less muscle, and noticeably more fat cover; their growth tapers off sooner, so they reach their mature state earlier than steers do. Bulls, by contrast, build more bone and muscle and show little tendency to lay down fat, spend longer filling out muscle in the second stage, and carry more muscle once mature, which makes them slower to reach their final state.

Cattle with a large skeletal frame end up heavier at maturity and need extra time to get there, whereas smaller framed cattle reach a lighter mature weight sooner. Heavily muscled animals of a given frame size need extra time during the growing-out stage to develop their muscle fully, and end up carrying more muscle and less fat than average-muscled cattle of the same frame later in life, which effectively delays their finishing point. Lightly muscled cattle behave more like heifers, completing their muscle development sooner and at a lighter weight while channelling spare energy into fat instead.

The paper notes that combining a large frame with heavy muscling, as seen in breeds such as Charolais and Simmental, produces animals that mature very late, meaning they resist fattening while light and must reach substantial weights before they finish properly. British breeds generally carry a more modest frame and reach finishing condition at lighter to middling weights, although some have grown noticeably in frame and mature size over time. Breeds noted for strong muscling, such as Limousin, and smaller framed breeds such as Murray Grey, both deliver high-yielding carcases but within different weight ranges.

How nutrition changes outcomes at each stage#

The effect of feed quality on the growth path depends heavily on which stage the animal has reached. Feeding above basic requirements during the first stage lets a calf realise its full bone and muscle potential and may even allow some fat to accumulate, producing vealers that buyers seek out at 7-10 months while still leaving the animal able to grow on toward a heavy mature weight. Severe underfeeding during this same early stage, on the other hand, leaves lasting gaps in bone and muscle development that later good feeding cannot fully reverse, leading to carcases that end up lighter, less muscled and fatter than they should be. The paper specifically warns against buying lightweight weaners under 180kg for finishing, and flags that calves weaned early need particular care with their diet.

During the growing-out stage, feeding above requirement supports solid muscle gain along with some fat deposition, and the paper notes that most cattle destined for domestic and export table beef are slaughtered during this phase of life. Cutting back feed during this stage shrinks muscle fibre size, but as long as the calf had a sound start this effect proves temporary: once returned to good feed, cattle show catch-up growth, fat deposition is delayed a little, and the resulting carcase is leaner and higher yielding, a pattern the paper says finishers can turn to their advantage.

In the finishing stage, with skeletal and muscular development essentially complete, cattle gain or lose weight according to the feed on offer, with the change showing up mostly as a shift in body fat. Animals recovering from a period of poor condition rebuild muscle first, since no further muscle growth is needed, then direct any surplus into fat. Mature cattle finish readily once free of breeding duties, provided they remain sound, particularly in the mouth, and in good health. The paper observes that almost all steers are sold before reaching this final stage, leaving cull females and bulls as the main animals that pass through it.

Selecting cattle to a target maturity type#

Gaden cautions that choosing bulls purely by eye makes it very hard to breed toward a chosen maturity type, since the frame, muscle and fat cover visible on an animal owe as much to how it was raised as to its underlying genetics. This point is presented as a central limit on judging breeding stock from appearance alone.

The paper points to estimated breeding values generated through the BREEDPLAN evaluation system as a tool available across most breeds, letting producers refine selection for carcase yield, fatness, muscling and mature size by separating true genetic merit from the environmental variation that shapes how an animal looks at any one time.

We would treat this paper as a clear conceptual framework rather than a tested result, since it reports no trial data, measurements or statistical comparisons of its own; its value lies in organising established growth principles for practical decision-making rather than in demonstrating a new finding.

Matching genetics and nutrition to market specifications#

Market specifications are described mainly through age, sex, weight and fat cover, and the whole discussion of frame, muscling, breed and feeding in the paper is built around hitting these targets. Because weight and fat depth together decide whether cattle are ready for a given market, knowing where an animal sits along its growth path, and how its genetics and feeding will move it further along that path, becomes the practical tool for matching stock to what buyers want.

Gaden's closing point is that bringing genetics, nutrition and market demands together is a complex task precisely because all three keep shifting and interact with one another. Cattle of moderate frame carrying medium to heavy muscling come out as the most adaptable option, since with reasonable feeding they can deliver high-yielding carcases that suit almost every mainstream market, a conclusion relevant to readers browsing other papers in the broader Conferences community in this 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