Xylanase Boosts Intake And Feedlot Growth Performance Physical chemical interactions and pH are the two most limiting factors affecting the rate of fiber digestion in the rumen. Rumen bacteria do not grow when the pH level is below 6.0. When the level is between 6.5 and 6.0, bacteria growth rate declines 14% per hour with each 0.1 decrease in pH. Optimal growth is achieved when pH is above 6.5.

A deficiency of fibrolytic enzymes in the rumen that break down the fiber can be partially overcome by enzyme supplementation. A study at the University of California's Desert Research & Extension Center evaluated the effectiveness of Fibrozyme (xylanase) in increasing rumen fiber digestion and boosting feed intake.

A group of 96 crossbred steer calves was used in a 64-day receiving trial with 16 pens of six head each. At the start of the trial the steers were implanted with Synovex-S. Half of the group served as controls, and the remainder of the calves received 7.5g of Fibrozyme top dressed on the ration at the twice-daily feeding.

At the end of the trial the supplemented steers had increased final weight 3%, average daily gain (ADG) 6% and dry matter intake 4.5% over the controls, according to Richard Zinn, who headed the research project. However, the Fibrozyme had no influence on the net energy value of the diet composed of 65% steam-flaked corn, 17% sudangrass hay, 5% alfalfa hay, 6% cane molasses, 4% yellow grease, trace mineralized salt, urea and limestone.

In analyzing the trial data, Zinn concluded xylanse will enhance runminal fiber digestion and dry matter intake and growth performance.

For more information contact Richard Zinn, University of California, at 760/356-3068 or e-mail razinn@ucdavis.edu.

There is a new product on the feedlot horizon that in feeding trials boosted average daily gain (ADG) and feed efficiency by 28% during the last six weeks of the feeding period. The best estimate is that it may be cleared and available for use by next year.

In a joint research project in Mexicali, Mexico, conducted by the University of California and a Mexican university, 140 crossbred steers averaging 820 lbs. were placed on a steam-rolled, wheat-based finishing ration. Half of the 14 pens of 10 head each were controls, and the other pens received 6 mg./kg., on an as-fed basis, of zilpaterol during the last six weeks of the finishing period.

Based on net energy intake, the control steers had an ADG of 99% of what was expected. The zilpaterol supplemented steers had an ADG 29% greater than expected. Steers receiving zilpaterol had an increase in average daily gain of 27% at 1.42 vs. 1.94 kg./day (3.13 vs. 4.28 lbs./day) and feed efficiency was 28% greater (6.08 vs. 4.37). However, there was no influence on dry matter intake for the supplemented steers.

The zilpaterol increased carcass weight by 4.5%, dressing percentage by 3.6% and the longissimus muscle area by 2.7%.There was no influence on kidney, heart or pelvic fat, fat thickness or marbling score. When adjusted to a constant carcass weight, zilpaterol increased gross primal cuts 1.7%, boneless closely trimmed primal cuts 2.9% and boneless closely trimmed retail cuts 3.2%.

The conclusion is that zilpaterol supplementation can have a marked beneficial effect on growth performance and carcass yield of feedlot steers. University of California's Richard Zinn, who helped conduct the study, points out enhanced growth performance accounts for 55% of the net economic value of zilpaterol supplementation that benefits the feeder. Meanwhile, increased carcass cutability accounts for 45% of the net value that benefits the meat packer and retailer.

Since up to one-third of the increase in weight gain is attributable to increased carcass yield, cattle finished on zilpaterol should be marketed on a grade and yield basis, Zinn says.

Zilpaterol chlorhydrate is a member of the family of compounds known as B-2-agonists. They enhance growth efficiency by stimulation of B-adrenergic receptors on cell surfaces. In muscle tissue they promote protein synthesis.

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