While we know that implants improve gains and efficiency in steers and heifers at all production stages, most of the research on implant response has been conducted on steers. New data however, could improve our understanding of implant use in feedyard heifers.
During the recent Cattle Feeders Business Summit hosted by Merck Animal Health, Merck nutritionist Marshall Streeter, PhD, outlined some of the research conducted in preparation for release of a new heifer implant, Revalor XH. The new heifer implant, due to hit the shelves sometime this summer, The extended-release implant is similar to Revalor XS, except formulated for heifers, providing up to 200 days of payout without a need to re-implant. In each implant, six of the 10 pellets are coated with a polymer that provides extended release of the active ingredients.
In his presentation to cattle feeders, Streeter outlined several trials researchers conducted during the approval process for the new implant, results of which provide some general insights into implanting feedlot heifers.
Prior to implant trials, researchers conducted a series of “serial harvest” studies exploring growth and carcass characteristics of heifers fed varying lengths of time. Several results were what we might expect; marbling scores improve with more time on feed, as do the percentage of heifers reaching USDA Yield Grade 4 or 5. Performance late in the feeding period can be very good, when evaluated on a carcass basis. Streeter outlined the concept of “carcass transfer,” which is the proportion of live gain captured as carcass gain. In the heifers in these trials, 80% to 90% of late-feeding gains transferred to carcass weight. For heifers fed longer than normal, discounts for Yield Grade 4 and 5 are more likely than discounts for heavyweight carcasses. Streeter says these results suggest cattle feeders can efficiently extend the feeding period for heifers, capturing the benefits of a 200-day implant program.
In a series of implant trials, researchers compared Revalor XH against control cattle receiving no implants and against other heifer-implant programs. In tests against non-implanted control cattle, heifers implanted with Revalor XH finished with an average hot carcass weight advantage of 59 pounds over a 191-day finishing period. Advantages in average daily gains and feed efficiency were fairly steady through the feeding period for implanted cattle, with only slight reductions in marbling scores.
Other trials compared a single Revalor XH implant with re-implant programs including Revalor 200 followed by Revalor 200 at 100 days – a relatively aggressive implant program – and against Revalor IH followed by Revalor 200 at 90 days.
Notably, a single Revalor XH implant contains 200 mg of trenbolone acetate and 20 mg estradiol. Revalor 200 contains the same levels of each hormone, while Revalor H contains 140 mg of trenbolone acetate and 14 mg estradiol. So, either of the re-implant programs delivered a significantly higher total dosage of hormones.
In these trials, performance was similar in each of the implant groups. Marbling scores were somewhat higher in the Revalor XH groups compared with the re-implant programs, while Yield Grades also were slightly higher. These results suggest traditional re-implant programs for heifers might deliver higher levels of hormones than needed for an optimal response. By eliminating the need for a second implant, the extended-release product reduces labor requirements, animal stress, disease exposure and other challenges associated with re-implanting.
Also Streeter points out that for each of the implant programs, compared with non-implanted controls, the total growth advantage was around one-half to two-thirds that typically seen in implant trials with steers. The response in heifers is economically beneficial, but this result has implications for feeders producing cattle for natural or non-hormone-treated beef programs. Since the response is lower, Streeter says, cattle feeders could consider selecting heifers for those specialized programs while keeping steers in conventional management systems using implants. This would reduce some of the opportunity cost incurred when feeders withhold implants to qualify cattle for those programs.