IMPLANT EFFECTS ON CARCASS COMPOSITION AND MEAT QUALITY AS AFFECTED BY DIET

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1 IMPLANT EFFECTS ON CARCASS COMPOSITION AND MEAT QUALITY AS AFFECTED BY DIET P. L. McEwen 1 and I.B. Mandell 2 1 Department of Animal & Poultry Science, Ridgetown College - University of Guelph 2 Department of Animal & Poultry Science, University of Guelph Summary Implant effects on carcass composition and meat quality as affected by diet were examined in 108 Charolais crossbred steers. Cattle were fed either an 87% whole shelled corn ration or one containing 81% cracked corn and 12.5% corn silage. Steers were randomly assigned to four implant treatments (a non-implant control, Ralgro, Revalor-S or Synovex-S). Implanted cattle outgained the non-implanted control resulting in heavier carcass weights as days on feed and dressing percentages were similar across all four implant treatments. Fat partitioning was altered using implants with increased deposition of subcutaneous fat (% of rib dissection) and decreased deposition of intermuscular fat (% of rib dissection) and intramuscular fat (% in the longissimus) versus non-implanted cattle. Lean colour was not affected by implant treatment. Laboratory assessment of meat tenderness was generally not affected by implant treatment with the exception of higher shear scores in cattle implanted with Ralgro. Most carcass and meat quality traits were similar between diets with the exception of fat partitioning. Intermuscular and chemical fat depositions were greater in cattle fed the cracked corn and corn silage diet. A decreased available energy content for the whole corn diet was probably the primary reason for these observed differences. Introduction Anabolic implants are commonly used in beef cattle production throughout North America due to their beneficial effects on improved growth performance. Our 1996 study published in Beef Research Update (McEwen et al., 1996) evaluated the effects of growth implants and diet on growth performance and carcass merit. The effects of implant and diet on meat quality were not evaluated. Therefore the primary objective for this study was to determine the effects of implant on meat quality. A second objective was to determine if meat quality differences were present for two corn based diets comparing whole shelled corn versus cracked corn and corn silage. Materials and Methods One hundred and eight Charolais crossbred steers were purchased at Ontario livestock sales for use in the study. Cattle were randomly allotted to 18 pens (6 head per pen) equipped with Calan feeders to enable accurate determination of dry matter intake. The steers were implanted with Synovex-S and then initially used in an 84 day growth performance trial where five corn silage hybrids were evaluated. The cattle were then adjusted over a three week period to either one of two finishing diets; an 81% cracked corn, 12.5% corn silage ration supplemented with a 56% crude protein, vitamin-mineral supplement (6.5% of ration dry matter) or an 87% whole shelled corn ration supplemented with the 56% crude protein supplement (13% of ration dry matter). Both rations satisfied industry guidelines for crude protein, vitamin and mineral levels. Steers were also randomly assigned to four implant treatments (non-

2 implanted control, Ralgro, Revalor-S and Synovex-S) in the finishing trial with at least 13 head per implant /ration combination. Cattle were slaughtered after achieving an ultrasound backfat reading of 6 to 8 mm. This slaughter endpoint was chosen based on American studies which indicate that approximately 7 mm of backfat is needed for optimal palatability. All cattle were slaughtered at a commercial abattoir which employed high voltage electrical stimulation. Carcasses were federally graded 24 hours after slaughter and then a primal rib was obtained from each carcass for further processing at the University of Guelph. The 10th-12th ribs were separated into muscle, bone, and subcutaneous, intermuscular, and body cavity fat to determine yields of dissectible lean, fat and bone. Ribeye steaks from the 10th to 12th rib were aged for 7 days prior to being frozen. A steak from the 12th rib was used for chemical fat analysis to determine intramuscular fat content. An adjacent steak was used for Warner-Bratzler shear evaluation of beef tenderness. Muscle colour was measured on freshly cut surfaces 24 hours and 7 days after slaughter using a Minolta Chroma Meter with data collected in the CIE, L* a* b* scale. Results and Discussion Use of implants significantly increased carcass weights (Table 1) due to higher rates of gain versus the non-implanted, control. Dressing percentages were similar across treatments averaging 56%. Days on feed were similar between control and implant treatment groups with the exception of Revalor implanted cattle being marketed approximately 15 days earlier. Use of implants altered fat partitioning with greater amounts of subcutaneous fat (% of rib dissection) and lower amounts of intermuscular fat (% of rib dissection) and intramuscular fat (% in the longissimus). Percentage intermuscular fat was greater in Revalor-implanted cattle than cattle implanted with Ralgro or Synovex. Implant effects on meat quality have been a concern for the beef industry. While past studies have found increased incidence of dark cutters using specific implants, this was not a problem in the present study. Subtle differences in calorimetric measurements for redness and yellowness in lean colour were found between implant treatment groups both at 24 hours and 7 days post-slaughter. However, these differences would not be readily apparent to the human eye. Luminosity was not affected by implant treatment. Warner-Bratzler shear scores were used to evaluate treatment differences in beef tenderness by measuring the peak force required to shear across the muscle fibres. Shear scores were similar between control and implanted cattle. Since a high shear score is associated with less tender meat, lower shear scores for Synovex- versus Ralgro-implanted cattle suggests increased tenderness for cattle implanted with Synovex. Taste panel work would help determine if the observed increase in shear (muscle fibre) strength for Ralgro equated to a less desirable tenderness rating. Most carcass composition and meat quality traits (table 2) were not influenced by diet. Fat and bone yields (%), lean colour and shear measurements were similar for both diet groups while intermuscular and chemical fats were higher for the cracked corn/corn silage diet. A more digestible energy source (cracked corn) and a 9 kilogram advantage in carcass weight (more mature) are possible reasons for these observed differences.

3 Significance to the Industry At the present time a primary goal for the beef industry is to produce a high quality consistent product. Meat portions displayed at the supermarket should be visibly appealing to the consumer. Adequate levels of marbling or intermuscular fat should be present to add moisture and taste to the cooked product. A consistently tender product (higher priced cuts) should also be a fundamental goal for the beef industry to stimulate consumer demand. Differences in meat quality were observed between implant treatments. Chemical fat percentages were reduced when the three implant treatments were compared to the nonimplanted group. Significant implant differences were observed for shear strength. Higher scores were noted for the Ralgro implant when they were compared to Synovex-S. Future taste panel work would help clarify the importance of this result. The effects of implant and diet on meat quality should be further investigated as differences were found in this preliminary study. Acknowledgments The authors are grateful for trial help (Mark Cameron) and financial support from Ralston Purina Canada, Inc. and the cooperation of Better Beef Ltd. The authors are indebted to personnel in the Meat Science Laboratory at the University of Guelph for their assistance. We are also grateful to Gary Brien and his staff at the Ridgetown Beef Center for their care and feeding of the cattle.

4 Table 1. Implant Effects on Carcass Composition and Meat Quality Implant Trait Control Synovex-S Ralgro Revalor-S SE 1 Days on Feed Hot Carcass Weight (kg) Grade Fat (mm) Bone Yield from Rib Dissection (%) Fat Yield from Rib Dissection (%) Fat Partitioning - Subcutaneous (%) Intermuscular (%) Body Cavity (%) Chemical Fat (%) L Value (luminosity), hours after slaughter a Value (redness), hours after slaughter b Value, 24 hours after slaughter L Value, 7 days after slaughter a Value, 7 days after slaughter b Value, 7 days after slaughter Warner-Bratzler Shear (kg/cm 2 ) Standard error.

5 Table 2. Diet Effects on Carcass Composition and Meat Quality Diet 2 81% Cracked Corn 87% Whole 12.5% Corn Silage, Shelled Corn Trait 6.5% Supplement 13% Supplement SE 2 Days on feed Hot carcass weight, kg Grade fat, mm Bone Yield from Rib Dissection (%) Fat Yield from Rib Dissection (%) Fat Partitioning - Subcutaneous (%) Intermuscular (%) Body Cavity (%) Chemical Fat (%) L Value (luminosity), 24 hours after slaughter a Value (redness), 24 hours after slaughter b Value (yellowness),24 hours after slaughter L Value, 7 days after slaughter a Value, 7 days after slaughter b Value, 7 days after slaughter Warner-Bratzler Shear (kg/cm 2 ) Diets contained 56% crude, vitamin-mineral supplement 2 Standard error