Beef Cattle Browsing – December 2006

Beef Cattle Browsing

Editor: Dr. Stephen Hammack, Professor & Extension Beef Cattle Specialist Emeritus

December 2006

This newsletter is published by Texas AgriLife Extension – Animal Science. Media, feel free to use this information as needed and cite Texas A&M University Beef Cattle Browsing Newsletter, Dr. Steve Hammack.

We know that the environment can significantly affect production, especially in extensively managed situations. But exactly how do various environmental factors affect reproduction? University of Nebraska researchers analyzed 10 years of records from British-Continental cows managed in southeast Nebraska. Cows averaged 7 years of age and the average number of cows/year was 182. Breeding started in late May and lasted to about August 1 with approximately 25 cows/bull. Environmental variables that significantly influenced pregnancy rate were: average daily temperature (AT), minimum daily temperature (MT), wind speed (WS), and temperature-humidity index (THI). THI was calculated as (0.8 X temperature) + [(% relative humidity/100) X (temperature – 14.4)] + 46.4. MT had more effect on pregnancy rate than AT. Pregnancy tended to decrease with higher MT and THI and lower WS. Amount of solar radiation had little effect. Optimum MT was approximately 55 to 59 degrees F., increasing as the 60-day breeding season progressed. Optimum THI was 68. Reductions in pregnancy rate were likely to occur if MT exceeded 62 degrees and THI exceeded 73. At least for British-Continental cows, whenever night time temperatures start staying above 60 degrees reproduction may decline. (J. Animal Sci. 84:3415)

Ractopamine, marketed as Optaflexxfor cattle and Paylean for swine, enhances lean growth. Some research has shown that swine fed ractopamine were more active, had higher heart rates, and needed more time and physical contact to be moved. Colorado State University and Elanco Animal Health researchers wanted to know if there were similar effects in cattle. They studied 420 steers of British, Continental-British, and Brahman-British inheritance, feeding 10 steers per pen sorted by weight within type. Half the pens got 200mg ractopamine/steer/day for the last 28 days before slaughter and half were controls. While being weighed at the end of the 28-day period, steers were evaluated for entry force score (degree of force needed to load into the chute), chute entry speed score, chute behavior score, and chute exit speed score. There were no significant treatment differences in entry force, chute behavior, or exit speed. Treated steers did enter the chute slightly faster. Continental-British steers required more force to get into the chute and British steers exited the chute slower. There were no significant differences among types in entry speed or chute behavior. Ractopamine appears to have no important effects on behavior of feedlot cattle. (J. Animal Sci. 84:3410)


We know that aging of beef generally improves tenderness. But does it make any difference what the beef is? Colorado State University researchers evaluated tenderness of 17 individual muscles from both Select and upper 2/3 Choice carcasses. Carcasses were selected randomly 16 times over a 7-month period at a large packing plant. Two days after slaughter, aging of boneless subprimal cuts was initiated at 35-36 degrees F. Tenderness determinations (Warner-Bratzler shear force) were made before aging commenced (2 days post-slaughter) and then of aged samples at 4, 6, 10, 14, 21, and 28 days after slaughter. At 2 days, Choice muscles averaged 1.08 lb lower shear force (more tender) than Select. Aging increased tenderness of all muscles. However, aging effects were more pronounced in Select; at 28 days, Choice averaged only 0.62 lb more tender. Aging response was more rapid in Choice; of total tenderness measured at 28 days, an average of 85% had occurred by 14 days in Choice, compared to an average of only 68% in Select. The effect of aging on tenderness varied greatly for different muscles; in general, the toughest muscles (at day 2) improved most by aging. The authors concluded that “if postmortem aging is managed with respect to individual muscle and quality grade, certain Select muscles may be able to be substituted for analogous premium Choice muscles in commercial merchandizing systems”. (J. Animal Sci. 84:3387)

How reliable is genetic information on parents in predicting response in progeny? University of Kentucky and University of Florida researchers collaborated in reviewing 31 research studies comparing predicted and actual changes in body weight (birth, weaning, yearling), carcass characteristics (weight, marbling, fat thickness, ribeye area, and percent lean) and maternal/reproductive factors (milk, total maternal, and scrotal circumference). Actual progeny differences for body weight generally agreed closely with those predicted by sire EPD. In fact, progeny response in yearling weight tended to be greater than predicted, especially if yearling weight was the primary factor for sire selection. Sires with high carcass EPD tended to sire progeny that were also high, compared to those sired by low-EPD sires. Sires with high milk EPD and/or total maternal EPD sired daughters with higher milk production, producing heavier calves. Sires with high scrotal-circumference EPD sired daughters that reached puberty earlier than those by sires with low scrotal-circumference EPD; however, there was no difference in pregnancy rate. The authors noted that the relationship between sire EPD and actual progeny difference should be greater with proven sires of high EPD accuracy compared to young, untested sires with low accuracy, especially when herd size and number of sires is small. (Prof. Animal Sci. 22:413)

USDA recently posted a Draft User Guide for NAIS. The following was copied from

“As part of the ongoing NAIS development process, we have completed a Draft User Guide for NAIS and are requesting comments on the document. The Draft User Guide is the most current plan for the NAIS and replaces all previously published program documents, including the 2005 Draft Strategic Plan and Draft Program Standards and the 2006 Implementation Strategies. The NAIS Draft User Guide provides valuable information on how producers can participate in the voluntary NAIS if they so choose, how participation would benefit them, and how the system is being implemented. Comments on the Guide are being accepted through January 22, 2007.”

Note the statement “participate in the voluntary NAIS if they so choose”. This seems to remove speculations about making NAIS compulsory as a national program. States could still enact, or not enact, whatever programs they might wish.

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