There has been recent interest in the use of organic trace minerals in the diets of domestic animals. Studies with feedlot receiving and finishing diets have shown improved performance and reduced morbidity when organic zinc complexes were included in the rations. Effects on the performance of grazing stockers where morbidity is expected to be low have been more variable.
In two previous years at the Mountain Research Station we have tested organic trace minerals and there have been trends toward improved growth rate, but in neither year were the differences significant. It is difficult to answer producer's questions about whether feeding this type of mineral is recommendable to local stocker grazers. The present study evaluated Zinc Methionine which was substituted for zinc oxide to provide the same amount of total zinc in the mineral mix (Table 1).
Materials and Methods
The study was conducted during the summer of 1994 at the Mountain Research Station at Waynesville, NC. Eighty-four head of 4 cwt M-1 steer calves which included Angus, Angus cross and exotic crosses were purchased from local graded stocker cattle sales. The calves were backgrounded in the barn by the methods required by the Western North Carolina Preconditioned Feeder Cattle Program using a mixed feed with hay offered free choice. The cattle were turned out to pasture after a 28 day confinement period and were allotted to treatments on May 5 based on a weight taken in the morning. A second weight was taken the morning of May 6, and the calves were sorted into six equivalent groups based on breed type and estimated age. Initial weight was approximately 604 lbs.
Each group continuously grazed an improved mountain pasture of approximately 12 acres. Pastures were a mixture of bluegrass, fescue, orchardgrass, white clover and other minor species. Each week, the animals were rotated around the six pastures to minimize pasture effects. When the cattle were moved, the mineral feeders were weighed, moved with the cattle, and fresh mineral supplement was added.
Cattle were weighed each 28 days throughout the trial, with two consecutive morning weights at the end of the trial on September 8 and 9 making for a total of 126 days on test. At the initial, 56-day and final weighing, a blood sample was taken from the jugular vein of six calves in each group to evaluate plasma zinc and copper levels.
Results and Discussion
Results of the trial are presented in Table 2. Calves consumed 2.48 and 2.53 oz/head/day over the course of the study for the control and zinc methionine supplements, respectively. This resulted in a zinc intake of approximately 240 mg/day with 192/day mg from zinc methionine in the experimental mineral. The recommended rate is between 150 and 300 mg/head/day so we were in the range targeted for intake in this study. The cost of the mineral program was $4.41/head for the control groups and $5.42/head for the experimental groups.
There was no effect of zinc source on the performance of the cattle, although there was a slight trend of about .1 lb of ADG in favor of the zinc methionine (P=.14). There was no difference in the blood analysis for copper or zinc at any of the sampling dates. There were several cases of pink eye during the trial, but there were no other health problems with the cattle.
The Bottom Line
This trial is similar to trials conducted in the past where there was no significant effect of supplementing zinc methionine for grazing stocker cattle. Because feeding this supplement does not result in a predictable improvement in performance in this system it is not strongly recommended at the current time. It maybe recommendable in the future when we have a better understanding of when it may be predicted to give a significant response.
|Table 1. Mineral supplements used in the grazing trial.|
|Control, %||Zn-Met, %|
|Vitamin ADE Premix **||2.5||2.5|
|Selenium Premix (1%)||0.52||0.52|
|Zin Pro 100||-||2.7|
|** Provides 100,000 I Vitamin A/lb|
|12,500 I Vitamin D/lb|
|600 I Vitamin E/lb|
|Table 2. Mineral intake performance and economic analysis.|
|Mineral cost, $/50 lb bag||$11.20||$13.70|
|Mineral intake, oz/day||2.48||2.53|
|Mineral cost, $/head||$4.41||$5.42|
|Total gain, lb/head||179.4||192.0|
|Average daily gain, lb/day||1.42||1.52|
|Actual increased return||-||$5.29|
|Table 3. Blood levels of zinc and copper on the three sampling days.|
|Plasma zinc, ppm|
|Plasma copper, ppm|