For the last decade, at least, Paul Beck and colleagues have been studying how to best utilize byproduct feeds on cattle operations. Current economic conditions — with both expensive fertilizer and feed — mean it may be the right time to check the data again.

With growing cattle, “we must look at the value of what we're producing in relation to the cost of production,” said Beck, a University of Arkansas Extension animal scientist, at the Livestock and Forestry Branch Station field day outside Batesville, Ark., on April 15. “Right now, it's anyone's guess what next year's production will be worth. That's why there must be a lot of risk management to go along with what I'm going to talk about.

In 1996, Beck — who normally works at the university's Hope, Ark., station — began looking at the fertilizer rate in conjunction with the stocking rate. How much can the stocking rate increase for every unit of nitrogen put out?

“When we looked at that — with cheap fertilizer and values of gain around 50 cents (meaning every extra pound of gain put on the stocker calves was worth about 50 cents) — the most economically efficient rates were right at 200 pounds of N (220 pounds per ton/ammonium nitrate) and a stocking rate of about 2.5 calves per acre.”

Last fall, Beck redid those calculations. In the last two years, the value of gain “has gone up quite a bit for stocker cattle. In 2006, the value of gain was about 70 cents. In 2007, that number was around $1.07 per pound.”

When he plugged in the increased cost of N — 60 cents per unit — plus the increased value of gain, the actual stocking rate and fertilizer rates increased to 3.5-calves-per-acre and 300 pounds of N per acre, respectively. “That's counterintuitive to what most expect with high priced N fertilizer.”

Last year, Beck did a byproduct feed study at the Batesville station. Eighteen 2-acre bermudagrass pastures were used after receiving 100 pounds of N. Stocking rates of 1.5, 2 and 2.5 calves per acre were used.

“We fed no supplement, supplement equal to 0.3 percent of bodyweight, or 0.6 percent of bodyweight. The initial bodyweight on all pastures was 620 to 650 pounds.”

Total gain ranged from about 70 pounds to 150 pounds per calf. As for gain per acre, “as we added supplements and stocking rates, we increased our total gain per acre.

“And whenever we look at the cost of an additional pound of gain at the lower stocking rate, the lower supplementation costs about 60 cents per pound of gain. The higher supplementation rate, because performance wasn't increased much, cost about 80 cents per pound of gain.”

At the next higher stocking rate, when comparing the additional cost of gain from no supplement to 0.3 percent of bodyweight “still cost about 40 cents per pound of gain. Going up to 0.6 percent of bodyweight cost about 60 cents per pound of gain.”

With 2.5 calves per acre, the cost per pound of gain was about 74 cents (0.3 percent bodyweight) and $1.13 (0.6 percent bodyweight) per pound. Compared to unsupplemented calves at the lower stocking rate, the cost of additional gain was only 31 cents (for 2.5 calves per acre fed 0.3 percent bodyweight supplemental feed) and 56 cents per pound for 0.6 percent bodyweight supplemental feed.

“So, as we increase stocking rates, we can replace the forage with supplements. It depends on what the value of gain is relative to how much the supplement is costing. Right now, the gain is closer to 70 to 80 cents. We're still doing a little better with a higher stocking rate being fed a little more supplemental feed.”

A study from 2001 looked at fertilizer and stocking rates — 100 pounds of N per acre stocked with 2.5 calves per acre versus 167 pounds of N per acre stocked with 3.5 calves per acre. “Additionally, there was either no supplementation, 4 pounds per day of a blended wheat mid soybean hull supplement at the same stocking rate, or we increased the stocking rate by a third along with the supplemental feed.”

At the 100-pound N rate, there were unsupplemented calves stocked at 2.5 per acre and supplemented calves at 2.5 or 3 per acre.

At 167 pounds of N, there was a stocking rate of 3.5 and 4 calves per acre. Calves began at about 530 pounds.

Over the two-year test, at both fertilizer rates, average daily gain increased as supplemental feed was increased. At the lower fertilizer rate, “when we increased stocking rate and continued to feed, the average daily gain remained very similar to the lower stocking rate with supplement — right at 1.75 pounds per day.”

At the higher stocking rate with higher fertilizer level, there was a lower performance even though the supplement was provided. It was increased from the control “but we didn't make up the complete difference. As we added more calves, we increased the gain per acre. It went from 306 pounds of gain per acre up to about 550 pounds with the supplementation and higher stocking rate and 100 units of N.

“We went from about 417 with the higher fertilizer rate up to about 600 pounds with supplementation at the higher fertilizer rate.”

Cottonseed cake

Yet another study looked at replacing fescue hay with cottonseed cake. The cake is higher in fat than the normal cottonseed meal available the last few years.

The cake was fed at three rates: 0.3 percent, 0.6 percent and 1.2 percent of body weight “which equals about 2, 4, and 8 pounds per day, respectively. The calves started out at about 575 pounds. The ending body ended up at 721 pounds, 739 pounds and 759 pounds. The average daily gain — with the cake and also good quality hay (14 percent crude protein/63 percent TDN) was 1.83, 2.07 and 2.31 pounds.

“As we look at growing calves on alternate feedstuff, we can replace quite a bit of hay. But we can also pro-rate the amount of feed the calves get based on how much weight gain we need. If the work is with stocker cattle, we can provide a higher rate of feed. However, if we've got replacement heifers, we can feed the lower rate to get weight gains of about 1.5 to 1.75 pounds per day.”

Glycerin

What about glycerin — a byproduct in the production of biodiesel — as a supplemental feed? Glycerin is a three-carbon sugar the liver can convert for energy.

For cattle on forage-based diets, three studies have looked at such feed. The first is out of Wyoming looking at heifers fed an orchard grass hay. The supplement used was either 50 percent corn/50 percent soybean meal or replacing part of the corn with glycerin and a little corn gluten meal (to take the place of the protein from corn). That means there was about 15 percent crude glycerin in the supplement.

The supplement was fed at about 0.3 percent of bodyweight. So the percent glycerin of the total diet — “figuring the heifers were fed about 2.5 percent of their bodyweight as grass hay — was only at 1.5 percent. That's a very low percentage.”

The average daily gain from the corn supplement was about 2.67 pounds per day. From the glycerin it was 2.57 pounds per day.

In another glycerin study, Ken Coffey, University of Arkansas professor of animal science, worked with steers on wheat pastures. The steers began the 60-day trial weighing about 615 pounds. They were fed either corn at .25 percent bodyweight or glycerin at the same bodyweight level.

“This was glycerin alone - it was mixed with corn only for the first week to get them started on it. After that, the steers readily consumed the crude glycerin.”

The calves gained very well over the 60 days. “They went from around 615 pounds to around 840 pounds. The average daily gain was from about 3.7 pounds with the control and corn supplement to 3.4 pounds per day with the glycerin — not a big difference.

“Others say there could be a change in feedlot or dairy diets with (the inclusion) of glycerin. That's because they decrease intake — we're not sure why.”

Another Wyoming study looked at digestion with glycerin in a grass hay-based diet. The feed went from zero to 30 percent glycerin.

As the amount of glycerin is increased, “for 48 hours there's really no difference in total digestibility. Of course, glycerin is more digestible than hay. One difference, though, is the digestion rate decreased as more glycerin was added.”

On cows back in Hope, Ark., “we used some glycerin from Eastman (a biofuel plant in Batesville). We looked at corn, soybean hulls, wheat forage, and bermudagrass. In the dry matter digestibility, there wasn't much difference when we went from zero to 15 percent glycerin.”

The fiber digestibility of the corn and soybean hulls increased slightly as glycerin was added. However, the digestibility of the wheat forage and bermudagrass decreased slightly before increasing as glycerin was added.

“We also looked at the volatile fatty acid (VFA) production (a byproduct of fermentation in the cow), which is where cattle get most of their energy. Acetate is primarily produced in high forage diets. Propionate increases as concentrated supplements are added — or in cattle on higher grain diets. As you'd expect, as corn is added in different digestibility studies, that normally results in an increase in propionate and a decrease in acetate.”

A third important VFA is butyrate. “I've heard discussion that butyrate may be tied to the decrease in intake with feedlot and dairy diets as glycerol is added.”

Glycerin research as feed is just beginning. “I don't know where it'll go, but it is a byproduct that'll be available. If there's a (biofuel) plant close to your operation” glycerin is more likely to be an option. Because of its high-moisture nature, “it'll be more expensive to haul long distances. We're trying to figure out how to use it well.”