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item Riley, David
item Chase, Chadwick - Chad
item WEST, R
item OLSON, T
item Hammond, Andrew - Andy
item Coleman, Samuel

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2003
Publication Date: 11/30/2003
Citation: Riley, D.G., Chase, C.C., Pringle, T.D., West, R.L., Johnson, D.D., Olson, T.A., Hammond, A.C., Coleman, S.W. 2003. Effect of sire on mu- and m-calpain activity and rate of tenderization as indicated by myofibrillar fragmentation indices of brahman steaks. Journal of Animal Science. 81:2440-2447.

Interpretive Summary: Brahman cross cows are widely known for their excellent reproductive and maternal ability in the hot, humid regions of the world, but cattle with any visible indication of Brahman inheritance are frequently discounted at market, because of their reputation for poor meat quality and tenderness. Calpains, including mu-calpain and m-calpain are naturally occurring enzymes that are responsible for the physical breakdown (tenderization) of beef muscle tissue after slaughter. Calpastatin is a naturally occurring enzyme that inhibits or restrains the activities of mu- and m-calpain, and hence tenderness. Beef from Brahman cattle has been shown to have higher levels of calpastatin activity than beef from other breeds, and this may be the reason for lower tenderness. Myofibril fragmentation indices are measures of the physical breakdown of muscle fibers after slaughter, and are indications of tenderness. The degree of inheritance for calpain activities or the tenderization associated with aging are unknown. Sire influence on calpain activities and on tenderness associated with aging (as indicated by myofibrillar fragmentation indices) was assessed in Brahman steaks. A mathematical function representing the change over 21 days of aging in myofibrillar fragmentation indices was created, and three parameters of that function were estimated, representing 1) ultimate tenderness, 2) the difference between initial (at day one) and ultimate tenderness, and 3) the rate of change in tenderness. Results indicated sires influenced mu-, but not m-calpain activity. There appear to be large sire differences in the rate and change of tenderness (as indicated by myofibrillar fragmentation indices) associated with aging. These may be indicative of genetic control over these traits/processes, which would represent unique opportunities for improvement of tenderness by selection of parents based upon these parameters.

Technical Abstract: The objective of this study was to assess sire influences on postmortem enzyme activity related to tenderness of Brahman steaks, and on the rate and extent of tenderization associated with aging of Brahman longissimus. Brahman calves (n = 87) were sired by 9 bulls, and were born, weaned, fed, and slaughtered in central Florida. Traits evaluated include mu- and m-calpain activity, calpastatin activity, myofibrillar fragmentation indices (MFI) after 1, 7, 14, and 21 days of aging, percentage raw and cooked lipids, Warner-Bratzler shear force after 7, 14, and 21 days of aging, and sensory panel rating of tenderness, juiciness, and connective tissue amount after 14 days of aging. Data were analyzed using a model with sire, sex, year, and slaughter group (calves of the same sex slaughtered on the same date) as fixed effects, and adjusted to a constant adjusted backfat thickness. Sire effects were significant for mu-calpain activity, calpastatin activity, d-14 MFI, and d-14 shear force. Measures of tenderness and palatability were generally moderately to strongly correlated (both simple and residual correlations) with calpastatin and m-calpain activity. Myofibrillar fragmentation index residuals (adjusted for all model components except sire) after all aging periods were fitted using nonlinear regression to the exponential curve MFIi = k0 + k1 exp{k2 t} + e, where t represents aging in days, k0 is ultimate MFI after aging, k1 is the difference between initial and ultimate MFI, and k2 is the rate of increase in MFI. Sires had different estimates and combinations of estimates, which were used to plot MFI change with time. These curves visually differed for sires, and suggested that postmortem tenderization extent and rate differ as well. Use of a combination of these estimated parameters in a selection/carcass sorting program represents an alternative consideration for tenderization improvement programs.