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D Didn’t Stop Toughening

Purdue University researchers evaluate effects of vitamin D supplementation with Zilmax.®

Zilmax® (zilpaterol hydrochloride) is often fed at the end of finishing periods because of its favorable effects on performance and carcass leanness, but there are often unfavorable effects on tenderness. Supplemental vitamin D3 has been shown to improve tenderness. A study was conducted to see if feeding D long-term (165-day finishing period) or short-term (last 13 days before slaughter) would improve tenderness with or without Zilmax. Results were:

Unfortunately, feeding D either long-term or short-term had no effect on tenderness, except for a tendency for slight improvement when Zilmax was fed and steaks were aged 21 days.

As expected, feeding zilpaterol resulted in higher feed efficiency, carcass weight, dressing percent and ribeye area, and decreased fat thickness, numerical yield grade, marbling and tenderness. Across Vitamin D treatments, marbling of Zilmax-fed cattle averaged Small23 and cattle not fed Zilmax averaged Small46. This may seem like a small difference, but when the average is near the minimum of Small00 for Choice not much difference can be important. That was true in this study since Zilmax-fed cattle averaged 54% low-Choice and higher and cattle not fed Zilmax averaged 72% low-Choice and higher.

A difference of 54% vs. 72% Choice is certainly large. Not feeding Zilmax increased the percent grading Choice by 18 percentage points not 100, i.e., grade could not be improved for every carcass by eliminating the product. On the other hand, average carcass weight in this study was 856 pounds (lb.) for those fed Zilmax and 824 lb. for those not fed the product. That difference of 32 lb. applies to the entire group. Using a Choice-Select spread of $10 per hundredweight (cwt.) carcass and applying that to the 32 lb. results in average total carcass value of $1,673 per head for those fed Zilmax and $1,625 per head for those not fed the product, even though the latter graded much better.

NOTE: This does not account for any effect if some carcasses qualified for premium programs such as Certified Angus Beef® (CAB®), but also does not account for benefit from differences in feed efficiency. All variables should be accounted for, as is done by knowledgeable cattle feeders.

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Editor’s Note: Stephen Hammack is professor and extension beef cattle specialist emeritus for Texas A&M University and editor of the Beef Cattle Browsing electronic newsletter in which this article was first published. The newsletter, available at
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