More zinc not necessary

More is not necessarily better when it comes to feeding zinc, say New Mexico researchers.

Researchers allotted 108 yearling crossbred steers to 90% concentrate finishing diets containing three different levels of supplemental zinc: 20, 100 and 200 ppm (in the form of zinc sulfate). The National Research Council (NRC) dietary recommendation for zinc is 20 to 40 ppm.

The steers were slaughtered after 112 days on feed. There were no significant differences in average daily gain or feed efficiency. However, there was a slight decline in dry matter intake as zinc level increased. There were no important differences in any carcass traits.

Researchers concluded that increasing supplemental zinc above NRC recommendations has no benefit on carcass characteristics and that extremely high levels may reduce feed intake.

For more information contact Glenn Duff at the Clayton Livestock Research Center, 505/374-2566.

Feeding supplemental Vitamin D3 for five to 10 days prior to slaughter improves beef tenderness, say Oklahoma State University researchers.

In the first of two experiments, 118 steers were supplemented with 0 or 5 million IU of vitamin D3 per head per day for five days prior to slaughter. In the second experiment, 44 steers were supplemented with 0 or 711/42 million IU of vitamin D3 per head per day for 10 days prior to slaughter.

After slaughter, a loin steak from each carcass was removed and aged for either seven, 14 or 21 days prior to a shear force tenderness evaluation.

In experiment one, steers supplemented with vitamin D3 were 12.6% higher than unsupplemented steer in blood plasma calcium concentration. After seven days of aging, steaks from supplemented steers were 6.6% lower (more tender) in shear force and the number of tough steaks was 21.8% lower. After 14 and 21 days of aging, there were no significant differences in tenderness.

In experiment two, vitamin D3 supplementation resulted in 18% lower shear force values after seven days of aging and reduced the number of tough steaks by 23.3% and 22.5% after 14 and 21 days of aging, respectively.

In experiment two, where vitamin D3 was fed at a higher level for a longer period of time, the effect on toughness was extended beyond seven days of aging. For this reason, the researchers concluded that optimum dosage levels and times for vitamin D3 to reduce shear force of the loin and other muscle groups remain to be pinpointed.

For more information contact J. Brad Morgan, Oklahoma State University, at 405/744-6062.

Are feeder cattle sorting systems feasible? Canadian researchers set out to answer that question by evaluating 1,031 yearling steers in three Alberta feedlots using two sorting systems.

Alberta Agriculture and University of Saskatchewan researchers evaluated the two systems for their ability to improve carcass backfat uniformity. System 1 (MSI sorting system) used initial weight, frame score and muscle score to hypothetically group cattle into five "predicted days on feed" (PDOF) groups. System 2 (Oltjen scoring system) used initial weight, rump height, backfat thickness, feeding inputs and a computer model of cattle growth to hypothetically group cattle into five PDOF groups.

Each system was compared with the traditional system of visually sorting cattle at slaughter time. Steers were identified for slaughter when they reached the weight and condition desired by the feedyard manager.

The MSI system reduced the variability in slaughter weight by 14.3%, but had no effect on the variability in carcass backfat thickness. The change in predicted net return resulting from the MSI system ranged from -$4.09 to $8.82 per head slaughtered. The Oltjen system ranged from -$3.65 to $11.55 per head.

Researchers concluded further research is needed to determine the actual effect of sorting systems on feed efficiency, carcass quality and net return.

For more information contact John Basarab, Lacombe Research Center, Alberta, Canada, at 403/782-8032.

"Research Roundup" is compiled by Kindra Gordon, 612/851-4671 (Kindra _Gordon@intertec.com).