Effect of Zinpro 100® in a mineral mixture on gain and incidence of footrot in steers grazing native grass pastures

In a 3-year study, crossbred steers averaging 585 lb were allotted to groups given either a control or zinc methionine-supplemented mineral mixture while grazing burned native pastures in early summer. The steers were monitored for weight gain and incidence of footrot. The addition of 100 lb Zinpro 100® (50% zinc methionine) per ton of free-choice mineral mixture improved (P<.06) steer daily gain .08 lb. and reduced the incidence of footrot 55% (5.38 vs. 2.45%; P<.06). The gain benefit could not be attributed entirely to reduced footrot, but appeared to also have a nutritional basis.


Introduction
The incidence of footrot in cattle grazing native grass can range from 0 to 10%.Because these cattle are typically grazed in large pastures, treatment with injectable antibiotics also entails catching and restraining affected animals.Therefore, the best treatment is a preventative program.Zinpro 100 (zinc methionine) has been fed to feedlot cattle to reduce footrot and enhance performance.Therefore, our objective was to determine the influences of Zinpro 100® in a free-choice mineral mixture on weight gain and incidence of footrot in grazing cattle.

Experimental Procedures
In three consecutive years, two hundred and forty-one crossbred steers averaging 585 lb were weighed and allotted randomly in late April to eight pastures and offered either a Zinpro 100 or control mineral supplement.The two mineral treatments were rotated by year through the native grass pastures.After grazing for an average of 93 days, steers were gathered from the pastures in early morning and commingled in pens before final weights were obtained.The mineral mixtures were fed in open wooden boxes, and intake was recorded weekly.Compositions of the freechoice mineral mixtures are shown in Table 1.The steers were observed once each week for visible signs of footrot, typically lameness.Twenty-seven steers were removed from the study over the 3-year period for lump jaw, respiratory problems, death, or in response to hail that reduced the available forage in one pasture (12 animals).

Results and Discussion
Adding zinc methionine to the mineral supplement of steers grazing native grass improved (P<.06) daily gain .08 lb as shown in Table 2.The incidence of footrot was reduced (P<.06)from 5.38% in control steers to 2.45% in Zinpro-supplemented steers.
The average daily consumption of Zinpro 100 was 5.4 grams, or 2.7 grams of zinc methionine.This provided 540 mg of zinc in addition to 23 mg of zinc from the standard trace mineral pack, for a total of 563 mg/day of supplemental zinc.The control mineral mixture provided only 23 mg of zinc/day.Our best estimate of zinc provided by the grass is 226 mg/day, assuming 21 lb dry forage per day, 15.4 mg zinc/lb dry grass, and 70% zinc availability.Thus, total zinc consumption for the control steers averaged about 249 mg compared to about 789 mg for the Zinprosupplemented cattle.
The NRC zinc requirement for cattle is 30 ppm, or 286 mg/day.Therefore, zinc consumption by the control steers likely was 37 mg below NRC requirements, but steers offered the Zinpro mineral consumed almost 3 times the requirement.
Only a portion of the improvement in gain could be attributed to the lowered incidence of footrot.Cattle that had footrot gained 2.30 lb/day, whereas those not affected gained 2.76 lb/day.Multiplying that difference in gain by the percentages of steers that had footrot in the two mineral treatments only accounted for .013lb/day difference in gain.Therefore, the benefits of supplemental zinc methionine for steers grazing native grass pastures appear to be nutritional as well as therapeutic.

Table 2 . Effect of Zinpro 100 in a Mineral Mixture on Gain and Incidence of Footrot of Steers Grazing Native Grass
Means in the same row with unlike superscripts are different (P<.06).