“It’s the maintenance that’ll kill ya,” your mechanic says when you find that “killer deal” on a classic sports car. The same could be said for some cow herds, as research increasingly shows that some genetic types require considerably more energy for maintenance than others, meaning higher production costs for each calf weaned.

Tom Jenkins, PhD, is a research animal scientist at the USDA’s Meat Animal Research Center, Clay Center, Neb. His primary research focus, he says, is on overall production efficiency in the cow herd. Feed efficiency is one component, but he notes that interactions between a number of other traits —fertility, milk, growth, survival — determine the ability of a cow to produce and wean a calf every year in a particular ranch environment. Management factors such as length of breeding season, stocking rates and feed availability during breeding and gestation also influence productivity.

Variable maintenance

Jenkins says he and other researchers at USMARC are trying to quantify what contributes to an efficient cow. He notes that maintenance energy requirements for the cow can differ considerably between different breeds and within breeds.

 Research has shown that about 73 percent of total feed costs for a cow are attributable to feed required for maintenance. About 20 percent goes to milk production and 7 percent for pregnancy, Jenkins says. Those studies also show that feed energy required for maintenance can vary by 25 percent or more among different types of cows. Differences in maintenance requirements, he adds, are associated with differences in body size and genetic potential for production.

Research has shown that maintenance requirements are correlated with peak milk production 10 to 13 weeks post-partum. Cows with the highest potential for peak milk production have the highest maintenance energy requirements throughout the production year.

Higher maintenance requirements in the cow herd have a large effect on overall production efficiency. Jenkins says animals with genetic potential for high growth and productivity could be at a disadvantage in more restrictive environments. Feed availability and body-condition score affect a cow’s ability to enter estrus after calving. Most cows with a BCS below 4.0 will not start cycling in time to conceive during a restricted breeding season, Jenkins says. So as feed becomes more limited, higher-maintenance cows are more likely to need additional inputs such as supplemental feed to maintain reproductive success.

USMARC researchers, Jenkins says, have conducted several studies to compare the maintenance requirements of cows within breeds and between breeds, and their abilities to convert feed to the weaning weight of their calves as well as how to utilize breed differences in designing breeding systems to maximize profit.

Early research showed, for example, that the Red Poll breed, not commonly used in modern beef production, has superior ability to reproduce in a limited-feed environment and at lower body-condition score. A composite breed developed at USMARC, MARC-III contains 25 percent Red Poll breeding.

Jenkins acknowledges the need for a balanced approach. Producers need cows that fit their environments, and in restricted environments this means cows that can provide good reproductive performance at lower body-condition scores.

Some cows can successfully wean a calf on significantly less feed than average and are more efficient overall, but they typically wean lighter calves. The challenge, he says, is to find the middle ground between cow efficiency and producing calves with enough weaning weight and overall quality to maintain profitability at sale time.

Structured mating

Toward that goal, researchers have tested structured mating systems, exploring how using differences in genetic potential for productivity traits can affect production efficiency and net income.

Because of environmental variation and the time involved, it is difficult to directly compare productivity between herds, so at the request of the NCBA a team led by researchers at Clay Center designed a large dynamic mathematical simulation model to compare the effect of strategic management decisions on productivity and net income. They evaluated four breeding systems — two straight-bred systems and two terminal-cross systems over a 10-year period. One straight-bred system used Angus sires with Angus cows, with genetic characteristics representative of those available in the mid 1990s. The other straight-bred system used moderately sized composite bulls and cows, using the MARC II four-breed composite.

The terminal-cross systems used Charolais bulls on either Angus cows or the MARC II composite cows. The model assumed the same feed resources for each herd and breeding system.

Production in each group naturally fluctuated from year to year, but on average, the composite system was slightly more productive and more profitable than the straight-bred Angus system. The composite breeding system, Jenkins says, offers retained heterozygosity, indicating the expected heterosis retained in the composite, at 76 percent of maximum, which accounts for much of the increased productivity.

Among the terminal-cross systems, the one using the moderately sized composite cows was more productive and profitable than the one with the Angus cows. (See table.) The primary reason here, Jenkins says, is that production efficiency benefited from the greater difference in growth characteristics between the Charolais bulls and composite cows. In the Charolais-Angus terminal cross, growth characteristics were similar between the two breeds.

Jenkins says that when breeds become too much alike, producers lose the advantage offered by using their differences in crossbreeding systems.

These studies show, he says, that predicted productivity and net income increased using maternal breeds with the same level of input as the straight-bred system, mostly due to retained heterosis. Benefits from use of terminal sires, he adds, are greatest when the breeds differ in growth potential. “All breeds,” he says, “do not need to be the same.”

Within breed differences

While mating systems utilizing differences between breeds can improve overall production efficiency, there also can be substantial differences in the way individual animals convert feed.

University of Missouri animal scientist Monty Kerley conducts research on feed efficiency and says a relatively new measure called Residual Feed Intake or Net Feed Intake is becoming a valuable tool for selecting cattle for better efficiency.

RFI, he says, compares an animal’s actual conversion of feed to gain with the expected rate. It is a measure of metabolic efficiency that is not confounded by rate of gain. In other words, a group of cattle in the same pen or pasture could have similar daily gains but large differences in feed intake.

Because RFI is not linked to growth, there are no clear physical indicators of the trait. In order to accurately measure RFI, researchers and, increasingly, seedstock producers need to use feeding systems that measure and record individual intake. The trait has moderate heritability, similar to carcass traits and growth, and some breeders have invested in the facilities as they work to identify lines of cattle that convert feed efficiently along with other desirable traits.

Kerley says the Beef Improvement Federation is developing standards for measuring and reporting RFI in breeding cattle.

Big differences

The variation between cattle can be substantial, Kerley says, as much as five pounds per day difference in dry-matter intake with the same performance. “It is a random trait,” he says, “because we have never selected for it.”

He cites a study in which University of Missouri researchers designed a test to measure forage intake of cows grazing fescue pasture. In dry cows, those with negative RFI consumed an average of 27.3 pounds of forage per day while those with positive RFI averaged 34.4 pounds per day, a difference of 21 percent. During lactation, the difference in intake narrowed to 11 percent, as the more efficient cows stepped up their intake somewhat. Average daily gains and body weights were similar across the group.

In a test on growing heifers, the animals in the top one-third for efficiency averaged -0.82 for RFI and consumed 12 percent less feed than the group average. The bottom one-third, with an average RFI of 1.25 consumed 23 percent more feed than the group average.

Feed efficiency, of course, is important in the feedlot, but the ability to select for RFI also will have tremendous value to cow-calf producers. Better feed efficiency could allow higher stocking rates, less supplemental feeding and, potentially, better reproductive performance in environments with limited feed.

RFI is a different measure than feed per gain, in that an animal with a good feed-per-gain ratio might also consume more feed than average. Feed conversion in that sense is linked to growth — some cattle with the best feed-per-gain ratios have the highest growth potential. Building that trait into a cow herd can result in big, high-maintenance cows. They might convert feed well but are inefficient nevertheless. Animals with negative RFI consume less feed than expected for their rate of growth. Cow-calf producers, then, should be able to use RFI ratings to select for efficiency while maintaining moderate-sized cows.

Kerley says that as more RFI information becomes available he expects breed associations to develop EPDs for the trait or include it in selection indexes. He reminds producers, though,
to stay committed to selecting for a balance of traits that create total value. A good approach, he says, will be to use selection pressure against the lower one-third in efficiency and selection for
the upper one-third.