The effect of implants on gain of steers and heifers grazing native The effect of implants on gain of steers and heifers grazing native grass grass

Appreciation is expressed to Mallinckrodt Veterinary, Inc. for partial funding; Frank Bills for 1 providing cattle; and Dr. Twig Marston and Dr. Kelly Kreikemeier for collecting carcass weights. Extension Livestock Specialist, Southeast Kansas. 2


Introduction
Implants have been used for years in grazing and feedlot cattle.With the variety of implants available, and differences in weight, grazing time, sex, etc., a number of implant strategies are possible.The objective of this study was to evaluate c ombinations of implants, sex, and length of grazing time in relation to cattle gain.

Materials and Methods
Trial I. Yearling steers (British Continental crossbred) were purchased in late winter and spring and were not implanted until being placed on native grass in April.Steers were allotted randomly to 1) Ralgrofi, 2) Ralgrofi Magnum , 3) Synovex Sfi, or 4) control (no implant) treatments.The steers grazed one burned native grass pasture for 81 days and were stocked at one steer per 2.5 acres.Steers had access to a fre e-choice salt-mineral mixture containing Rumensinfi (150 mg/hd/day).
The steers were shipped to the Brookover Ranch feedlot at Garden City and were all implanted with Revalorfi at days 1 and 60 during the 130-day feedlot.Carcass weights were collected for the steers at slaughter and live weights were determined by using a standard dressing percent of 64%.
Trial II.Yearling steers (British Continental crossbred) were purchased in the spring and were not implanted until being placed on native grass in April.The crossbred steers were allotted randomly to: 1) Ralgro, 2) Ralgro Magnum, 3) Synovex S, or 4) control (no implant) treatments.The ste ers grazed eight burned native grass pastures.All treatments were allotted equally to each pasture.One hundred fifty-four steers were grazed in four pastures (80 days) stocked at one steer per 2 acres.The other 10 6 steers were grazed in four pastures (110 days) stocked at one steer per 3 acres.Steers had access to a free-choice saltmineral mixture containing chlortetracycline (350 mg/hd/day).
The steers grazed for 80 d ays and then were shipped to Great Bend Feeders and fed for 136 days.They received the Revalor implants at days 1 and 60.C arcass weights were collected, and live weights were calculated as in Trial I.
Trial III.Yearling heifers (British Continental crossbred) were purchased in late winter and spring and were not implanted until being placed on native grass in April.The heifers were allotted randomly to: 1) Ralgro, 2) Synovex Hfi, or 3) control (no implant) treatments.All treatm ents were allotted equally to each pasture (stocking rate, one heifer per acre) and grazed for 88 days.Heifers had access to a free-choice salt-mineral mixture containing Rumensin (150 mg/hd/day).
Trial IV.Heifer calves (British Continental crossbred) were purchased in the spring and were not implanted until being placed on native grass in April.The heifers were allotted randomly to: 1) Ralgro, 2) Synovex Hfi, and 3) control (no implants) treatments.Heifers grazed burned native grass pastures at a stocking rate of one heifer per 4 acres for 147 days.Heifers had access to a free-choice saltmineral mixture containing Rumensin (150 mg/hd/day).
All implants were placed aseptically in the mid-third of the ear.Old implants were removed from the steers' and heifers' ears in all trials, but the stage of activity could not be determined.

Results
In Trial I involving 700 lb steers, all implanted steers gained faster on grass (Table 1, P<.02) than controls; however, no differences occurred among implants.The previous (grass) implant treatments had no effect on feedlot gains.
In Trial II (Tables 2 and 3) with 500 to 600 lb steers, no differences occurred among implant groups in pasture ADG, but all implanted steers gained faster (P<.01) than the nonimplant steers.Control steers that grazed for 80 days gained faster (P<.05) than Ralgro or Ralgro Magnum groups in the fe edlot after all steers were implanted with Revalor (Table 2).Consequently, weights of steers not implanted on grass were equal at slaughter to the average weight of the steers implanted on grass.
In Trial III (Table 4), no differences occurred in ADG among treatment groups for heifers placed on grass at 500 to 600 lb and grazing for 88 days.
In Trial IV (Table 5), no differences in ADG occurred among treatment groups of heifers grazing for 147 days.
The interaction between effects of implants on grazing cattle and on feedlot steers may be confounded with types of implants in both phases relative to cattle weight on grass, ADG, and length of time grazed.A clearer picture of how implanting cattle on grass interacts with implanting in feedlot cattle is needed to fully maximize the benefits of implants under both grazing and feedlot conditions.For 500 to 600 lb steers, not implanting on gra ss and implanting with Revalor in the feedlot may result in slaughter weights equal to those of steers implanted on grass and implanted with Revalor in the feedlot.

Table 2 . Effects of Implants on Steers Grazing Native Grass Pastures for 80 Days and Fed for 136 Days in a Feedlot
a,bMeans in the same row with unlike superscripts are different (P<.05).c,d

Table 3 . Effects of Implants on Steers Grazing Native Grass Pastures for 110 Days
Means in the same row with unlike superscripts are different (P<.01).