Variable Sorghum Test Weight Has Little Impact on Cattle Rate of Gain

Lightweight sorghum has high protein; processing necessary.

Growing conditions this year resulted in grain sorghum with low test weights in parts of the High Plains, but studies conducted by Kansas State University Research and Extension indicate the grain is still suitable for cattle feed.

Sorghum less than 55 pounds per bushel is docked an increasing amount as test weight decreases, says Sandy Johnson, northwest area livestock specialist with K-State Research and Extension. One northwest Kansas elevator recently docked sorghum from 50.9 to 50 pounds by 12 cents and for each pound less than that, another five cents.

"Given that level of dockage at the elevator, a natural question is, what is the feeding value of low test weight grain sorghum?" said Johnson, who is based in Colby.

This question was addressed in growing and finishing steers at K-State's Southwest Research and Extension Center in Garden City.

In the growing trial, 35, 45, and 55 pounds-per-bushel grain sorghum was used in either a limit-fed high concentrate or full-fed high roughage diet, Johnson explains. Within a feeding level, average daily gain was not affected by sorghum test weight. Gain tended to decrease, however, with increasing test weight. Feed conversion in high concentrate steers was increased 11.4% compared to high roughage steers.

In the finishing trial, 35, 45, and 55 pound-per-bushel grain sorghum was processed by either dry-rolling or steam-flaking. After 124 days on feed, the average daily gain was similar for all test weights, Johnson says. Feed conversion was improved when the sorghum was steam-flaked, compared with dry-rolled sorghum. Cumulative feed conversion was similar for the dry-rolled treatments at all test weights. However, steers fed steam-flaked, 55 pounds-per-bushel sorghum had a 10.8% improvement in conversion compared to the average of all other treatments.

Carcass characteristics were not affected by sorghum test-weight differences, she says
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Another study at the K-State Agriculture Research Center in Hays compared 48 and 56 pounds-per-bushel grain sorghum in finishing steers. Feed consumption of steers fed the low-test sorghum was less and gain was slower than those fed normal sorghum. There was no difference in the net energy content of the two grains.

In light test weight sorghum, protein and fiber levels are increased, but starch content decreases as test weight declines, Johnson says. The higher protein content can be an advantage in ration formulation, especially for growing rations. Because of the smaller and variable seed size, fine processing is critical.

"These studies indicate the relative feeding value of 40- to 55-pound grain sorghum is similar," the animal scientist notes. Lower bulk density, however, increases transportation, handling and processing time and cost and requires more storage space per ton.

"These costs should be considered when determining the value of low test weight sorghum," Johnson says.

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