Administration of growth-promoting implants and days on feed affected allometric growth coefficients, fabrication yields, and economic returns of serially harvested beef steers
Wesley, Kaitlyn Renee
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The objective of the first part of this study was to quantify differences in fabricated primals, subprimals, and carcass components of implanted and non-implanted steers. Steers (n = 80; initial BW 271 ± 99 kg) were paired and randomized to harvest date (d 0, 42, 84, 126, 168, 210, 252, 294, 336, 378). Individuals were randomized to treatment of CON (negative control) or REV (Revalor-XS; Merck Animal Health; Madison, NJ on d 0 and 190). One side of each animal was fabricated after a 48 h chill into primals, denuded subprimals, lean trim, trimmed fat, and bone; weights were recorded individually. Data were analyzed via mixed models. Implants increased cold side weights (CSW) 7.7%, bone yield 4.9%, and red meat yield 8.5% (P < 0.03), with no differences in fat yield (P = 0.78). Brisket and foreshank primals were increased 6.9% and 7.2%, respectively (P ≤ 0.02) from implanted cattle. Chuck primals from REV steers were 8.4% heavier, with similar trends in the arm roast, flat iron, petite tender, chuck eye roll, and mock tender (P ≤ 0.02). Rib primals of REV steers were 5.2% heavier, and the ribeye roll and rib blade meat showed an increase (P ≤ 0.04). Plate primals did not differ between treatments (P = 0.13). However the inside skirt, outside skirt, and outside skirt as % CSW were heavier (P ≤ 0.04) from REV steers. Loin primals from REV steers were 7.0% larger, along with the striploin, tenderloin, top sirloin butt, top sirloin butt cap, and bottom sirloin tri tip subprimals (P < 0.01). The flank primal of REV steers was 8.6% heavier, bottom sirloin flap and flank steak were also heavier (P ≤ 0.04), and the elephant ear tended to be heavier (P = 0.08). Round primals from REV steers were 6.3% heavier, and the top round, eye of round, bottom round, and knuckle were all heavier (P ≤ 0.03) than CON. Length of feeding period notably affected weights for all primals with exception of the chuck, loin, and several components of the sirloin. Fat as % CSW increased at 0.043% per day, whereas bone and red meat yield decreased at -0.013% and -0.023% per day, respectively. These data indicate implanted steers are more likely to have heavier side weights, higher bone yield, and increased red meat yields. Additionally, heavier primals and subprimals were observed in implanted steers. The objective of the second section of this study was to quantify allometric growth coefficients of non-carcass and carcass components of implanted or non-implanted Charolais × Angus steers in relation to empty body weight (EBW). Steers (n = 80; initial BW 271 ± 99 kg) were paired, randomized to harvest date (d 0-42-84-126-168-210-252-294-336-378), and individuals within pairs were randomized to CON (negative control) or REV (Revalor-XS on d 0 and 190) treatments. Weights (g) of non-carcass and carcass components were log transformed and consolidated to arithmetic means by treatment and harvest date. Growth coefficients were calculated using the allometric equation Y=bXa, which when log transformed is represented as Y=b+aX where Y= log(non-carcass or carcass component), X= log(EBW), a= log(slope), and b= log(intercept); the empty body grows at a rate of 1. Treatment outcomes were compared via independent t-test. Tendencies for faster growth of REV steers were detected in non-carcass components between treatments in the kidney (P = 0.06) and lungs/trachea (P = 0.09). Non-carcass components with lowest growth coefficients included small intestine (0.02), large intestine (0.12), and brain and spinal cord (0.13). However, kidney-pelvic-heart fat (2.01) accumulated at more than 2 times the rate of the empty body, whereas cod fat (1.42) and GIT fat (1.61) grew faster than the empty body. Growth coefficients were greater (P < 0.01) for REV in two carcass components (chuck eye roll, eye of round), whereas CON was greater (P < 0.01) in one component (flank steak). Although not different (P > 0.62), growth coefficients of carcass primals were numerically greater for REV steers with exception of the rib. All primals except the round (0.81) and foreshank (0.87) exhibited growth coefficients greater than the empty body (flank, 1.47; plate, 1.45; brisket, 1.18; rib, 1.18; loin, 1.04; and chuck, 1.03). Conversely, pectoral meat (0.19), bottom sirloin flap (0.56), heel meat (0.59), sirloin tip (0.66), and mock tender (0.69) subprimals all exhibited growth coefficients notably less than the empty body. Although not different, total lean was deposited more quickly in REV steers (0.95 vs 0.88; P = 0.45), whereas total fat (2.17 vs 1.98; P = 0.35) and total bone (0.92 vs 0.75; P = 0.29) were faster growing for CON steers. These data indicate total body fat exhibited the greatest growth coefficients compared to empty body. Whereas, there were minimal differences in growth coefficients of steers in regards to treatment. The objective of the third section of this study was to compare the profitability of finished steers produced and processed in either a non-hormone treated (NHTC) or traditional implant program and marketed at various end points. Steers (n=80; Charolais×Angus) were paired by genetic group, estimated finished body weight, frame score, and d to target BW. Pairs were randomized to harvest date (d 0-42-84-126-168-210-252-294-336-378) and individuals within pairs were randomized to CON (negative control) or REV (Revalor-XS on d 0, 190). Live, carcass, subprimal, non-carcass drop, and overhead prices were consolidated from USDA Mandatory Price Reports and industry contacts. Data were analyzed via mixed models. Initial cost varied (P < 0.01) between treatments as CON steers demanded premiums for NHTC and source verification. Feed costs were similar, and total production costs tended to be greater for CON (P = 0.09). Cattle marketed live or in the beef were of greater (P < 0.01) value for REV, as no premium was offered for NHTC steers. Quality grade adjustments tended to discount REV more heavily (P = 0.06), yield discounts tended to be greater for CON (P = 0.10), and weight based grid adjustments were unaffected by treatment (P = 0.53). Adjusted carcass value favored CON steers (P < 0.01) due to the NHTC premium. When sold on a live, in the beef, or grid basis, neither treatment yielded positive return. All variables with exception of initial cattle cost were different across DOF (P < 0.01). Non-carcass drop values were greater (P = 0.03) for REV. Boxed beef values were greater (P < 0.01) for CON. Processor net returns were calculated by difference in revenue (boxed beef plus non-carcass drop) and expense (overhead [-$190/carcass] plus procurement of the grid purchased carcass). Net return for processors was similar between treatments (P = 0.65). These data indicate implanted steers returned greater revenue when marketed on a live or in the beef basis, whereas NHTC steers returned more value when marketed on a grid basis, although neither treatment was profitable. Additionally, there was no difference between treatments in regards to the profitability of beef processors.