It is no secret that beef slaughter weights have increased significantly in recent years – about 200 pounds on average since 1996 in fact. Several factors have influenced that trend, but mostly, cattle feeders have found that, in today’s market, it pays to feed cattle longer.

Marshall Streeter, PhD, a technical-services specialist with Merck Animal Health, outlined the reasons behind that trend during a recent Academy of Veterinary Consultants conference.

In the past, Streeter says, slaughter weights fluctuated based on market prices. Lately though, they have moved steadily heavier regardless of the markets. He trend is the same for steers and heifers. Dressing percentages have not changed much, but USDA Quality Grades have increased as longer-fed cattle are better able to reach their genetic potentials for marbling.

The genetic makeup of our beef herds has played a role, and packers generally have allowed heavier weights by shifting their threshold for heavyweight discounts. Perhaps the biggest factors though, are that growing numbers of fed cattle are sold on a carcass basis rather than live, which changes the ideal economic endpoint, as carcass gains remain cost effective later in the feeding period compared with live-weight gains.

About 75% of finished cattle in the United States are now priced on carcass, rather than live weight, Streeter says. That market favors hot carcass weight (HCW), yield and marbling. Toward the end of the feeding period, total gains end to drop off, but carcass gains during the final 60 days or so account for 75 to 90% of total gains during that period. If cattle are fed 21 days longer than their typical live-weight endpoint, and daily production costs remain the same, they probably are putting on profitable gains if sold on a carcass basis but losing money if sold on a live basis.

Dressing percentages also increase as cattle grow heavier. If we were to send 700-pound steers to slaughter, they probably would dress at about 58% yield, Streeter says, while a 1,400-pound steer will dress at around 64.5%.

On average, Streeter says, cattle marketed on a carcass basis should be fed about 60 days longer to reach their optimum economic endpoint compared with those sold on a live basis. The difference narrows somewhat during times of high feed prices. Generally, heavier carcass weights will more than compensate for any packer discounts for heavyweight cattle or Yield Grade 4s and 5s. Streeter acknowledges though, that the concept can be difficult for feedyard managers to explain to customers when reviewing closeout sheets.

At some point, of course, longer feeding periods could become an economic liability. In steers, too many heavyweight carcass discounts eventually limit time on feed, while in heifers, discounts for Yield Grade 4s and 5s are a limiting factor. Sorting cattle as they near their endpoints can, in some cases, help feeders minimize those problems.

Other factors such as risk of death loss and the relative price of replacement cattle also can affect the economics of feeding cattle longer. In general though, Streeter says daily value generation late in the feeding period is greater when cattle are marketed on a carcass basis, and grid discounts become less relevant at high base carcass prices.