A study conducted by South Dakota State University (SDSU) researchers evaluated the impact additive combinations of growth-promotant technologies can have on beef carcass characteristics and tenderness.
This study evaluated four combinations of growth-promoting technologies: no technology, antibiotic treated, implant treated and beta-agonist treated. The treatments were designed to build upon each other with increasing amounts of technology. The no-technology group served as the control and received no antibiotics, beta-agonists, ionophores or implants.
The antibiotic-treated group was administered therapeutic antibiotics as needed, as well as monensin and tylosin during the finishing phase. The implant treated group was administered the antibiotic regimen and a series of implants, including a suckling calf implant, a moderate-potency initial feedyard implant and a high-potency finishing implant. The beta-agonist-treated group was administered the implant treatment regimen, and the beta-agonist ractopamine-HCl for the last 30 days before harvest. The four treatments were designed to represent different cattle feeding systems used in the U.S.
Methods
A set of 120 Angus-Simmental cross steer calves were allocated to one of the four treatments. There were three phases of this experiment: Phase 1, from the beginning of the experiment at branding through weaning; Phase 2, post-weaning through the beginning of the finishing phase, where the steers were fed in pens; and Phase 3, finishing phase when the steers were fed in an individual feed intake system through harvest.
The growing diet fed at the beginning of Phase 2 consisted of dry-rolled corn, grass hay, dried distiller’s grains with solubles, and limestone. The finishing diet fed at the end of Phase 2 and all of Phase 3 consisted of dry-rolled corn, wet corn gluten feed, grass hayand a vitamin and mineral supplement.
The steers were ultrasounded to predict harvest date at a common 12th rib backfat thickness of 0.6 inches, which resulted in two harvest groups. The no technology and implant treatments were harvested on the first harvest date and the antibiotic and beta-agonist treatments on the second harvest date.
The steers were transported to a packing plant and carcasses were tracked through the facility. Carcass data and a strip loin were collected from each carcass and transported back to SDSU. The strip loins were cut into New York strip steaks and used to measure tenderness.
Results
Minimal differences were observed between the no technology and antibiotic treatments or between the implant and beta-agonist treatments. Because of this, the results in this article will largely focus on the impact of implanted (implant and beta-agonist treatments) versus non-implanted (no technology and antibiotic treatments) cattle.
Steers that received implants had increased body weights compared to non-implanted steers through all phases of the experiment. Additionally, implanted steers had increased average daily gains and better feed conversion (feed:gain) than non-implanted steers.
The carcasses of implanted steers had heavier hot carcass weights than non-implanted steers. Ribeye area was largest in carcasses of steers from the implant treatment, the antibiotic treatment had the smallest ribeye area and the ribeye area of the no-technology and beta-agonist treatments was in the middle. Despite the differences in hot carcass weight and ribeye area, all treatments had similar yield grades, because increased hot carcass weights were offset by increased ribeye area in the yield grade equation. Carcasses of implanted steers had decreased marbling scores and fewer carcasses that graded USDA Prime compared to carcasses from non-implanted steers.
As expected, steaks from all the treatment groups improved in tenderness as they aged from seven to 21 days post-harvest. Additionally, steaks from non-implanted steers were more tender than implanted steers.
However, all of the treatments resulted in tenderness levels well below the threshold to be considered “very tender” by the American Society for Testing and Materials International. This means that while there were differences in tenderness among treatments, the average consumer would likely have a favorable eating experience from a tenderness standpoint with steaks from any treatment.
Conclusion
Implants were the most impactful technology to increase animal weight and hot carcass weight and resulted in the most-efficient feed conversion.
Implants reduced marbling scores and resulted in fewer carcasses grading USDA Prime.
Strip steaks from all treatment groups were well within parameters to be considered very tender.
This research was published across two articles in the open-access journal Translational Animal Science. — Christina Bakker, SDSU Extension meat science specialist
