Meat-quality concerns

Increased feedyard performance and carcass composition is consistently recognized from the use of these repartitioning agents. However, there's universal concern about their effect on certain meat quality measures, especially tenderness, juiciness and flavor. Most of the concern is over zilpaterol, generally considered the more aggressive-acting of the two agents.

Intervet product managers say meat-quality research is “ongoing at several major universities” across the U.S. — with results to be released this summer. Floyd McKeith, University of Illinois-Urbana professor of meat science, was involved with the Intervet-sponsored experiments on meat quality but declined comment on any of his lab's findings due to confidentiality concerns.

Intervet product managers are just as mum on the soon-to-be released meat-quality research, only saying the meat-quality data will reflect positively on Zilmax in feedyard finishing rations. They direct cattle feeders to the U.S. Freedom of Information Act (FOIA) summary that's been published (www.fda.gov/cvm/FOI/141-258o08102006.pdf). See Table 2.

Earlier research in Mexico and corroborated by U.S. scientists reported that several values obtained for meat-quality variables from steers fed zilpaterol at recommended levels were within “normal ranges.” Concluding the study, Leonel Avendaño-Reyes, Instituto de Ciencias Agrícolas Universidad Autónoma de Baja California, says meat tenderness from animals treated with zilpaterol was classified as “intermediate.”

In the FOIA report, the Warner-Bratzler shear force analysis shows the values for steers finished with zilpaterol were within the normal ranges observed in the beef industry. While the Warner-Bratzler shear force was increased by the treatment, data from this study shows that meat tenderness values from the “control” steers and “treated” steers were both below the threshold levels of shear force.

Therefore, the report concluded that consumers wouldn't detect any difference in palatability. The slight increase in shear force values for the zilpaterol-fed steers may be partially due to an increase in the muscle fiber area, according to the FOIA report.

The quality issues regarding Optaflexx seem to be more satisfying to the industry.

Five years ago, Iowa State University food scientist Ken Prusa was among a cadre of scientists who coordinated eating-quality evaluations of cattle fed Optaflexx during the final stages of finishing. His tests were conducted using trained sensory panels and Warner-Bratzler shear force values.

Prusa says when Optaflexx was fed to cattle at the recommended “mid-range” dose, he saw no differences in meat quality compared with beef from control animals.

“This product comes from a totally different profile of compounds than the other beta-agonists that have been around,” he reports. “When fed responsibly, it works just like Elanco says it works — and like the FDA has indicated.”

Proceed with caution

Cleere, Prusa and Zinn issue a stern warning that all feed additives should be used exactly according to label instructions. In fact, they say not using products like zilpaterol and ractopamine as specified on the label can have serious negative effects — and negative implications to the industry.

They point out that feeding young cattle these products is not only off-label and ineffective, it's illegal. And, the adage of “more is not better” applies to these products.

“As cattle begin to mature, they tend to deposit more fat and less muscle,” Cleere explains. “Young, growing cattle won't respond to the repartitioning agents because most of their nutrients are already directed to protein/muscle synthesis rather than fat synthesis.”

Research shows the effect of ractopamine decreases after the first 35 days of feeding. After this, Cleere says, performance returns to prior levels and the animal's body essentially becomes desensitized to the active ingredients of the agent.

“Research trials have shown that feeding Optaflexx at higher levels shows little or no effect on animal performance or muscle deposition.”

Cleere also warns that Paylean is different from Optaflexx.

“Both products contain ractopamine hydrochloride — but at much different concentrations,” he says. “Remember, it's illegal to feed either product to species other than what's listed on the label.”

Table 1. Pooled Trial Analysis — Performance of cattle fed diets containing zilpaterol hydrochloride — main treatment effects

Claim variables	Zilpaterol hydrochloride, grams/ton (ppm) 90% DMa
	0 (0)	6.8 (7.5)	P valuec
Average daily gain	2.61	3.33	— d
Feed efficiency (feed-to-gain ratio)	7.59	5.71	— d
Carcass percent protein, %	13.38	14.10	<0.0001
Label panel variables
Dressing percentage, %	60.3	61.8	0.004
Hot carcass weight, lbs.	744.5	776.0	— e
Ribeye area, sq. in.	13.23	14.35	0.0001
Yield grade	2.81	2.52	0.005
12th rib fat thickness, in.	0.49	0.47	0.178
Marbling scoreb	4.62	4.31	— e
a Values are least squares means. b Marbling score of 4.00 = Small00, 5.00 = Modest00 as per USDA marbling scores. c Overall treatment effect d Significant gender by treatment interaction e Significant duration by treatment interaction
Source: U.S. Food and Drug Administration — Freedom of Information Summary NADA 141-258

Table 2: Pooled Trial Analysis — Summary of sensory panel evaluation and Warner-Bratzler shear force of strip loin steaks from cattle fed diets containing zilpaterol hydrochloride

Variables	Zilpaterol hydrochloride, grams/ton (ppm) 90% DMa
	0 (0)	6.8 (7.5)	P value
Overall tendernessb	6.48	5.83	0.001
Overall juicinessc	6.27	5.81	0.001
Flavor intensityd	6.56	6.30	0.002
Beef flavore	6.65	6.45	0.020
Off-flavorf	1.01	1.01	0.889
Warner Bratzler shear force, kg	3.29	4.01	<0.001
a Values are least squares means. b Tenderness scale (1 - 8) : 5 = Slightly tender; 6 = Moderately tender; 7 = Very tender c Juiciness scale (1 - 8): 5 = Slightly juicy; 6 = Moderately Juicy; 7 = Very juicy d Flavor intensity scale (1 - 8): 6 = Moderately intense; 7 = Very intense e Beef flavor scale (1 - 8): 6 = Moderately characteristic beef flavor; 7 = Very characteristic beef flavor f Off-flavor scale (1 - 5): 1 = None; 2 = Slight off-flavor, etc.
Source: U.S. Food and Drug Administration — Freedom of Information Summary NADA 141-258