Beef Cattle Browsing – February 2008

Beef Cattle Browsing

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

February 2008

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.

As part of the voluntary National Animal Identification System (NAIS), the USDA-Animal and Plant Health Inspection Service released “A Business Plan to Advance Animal Disease Traceability” on December 12. As of December 31, USDA-APHIS estimates about 31% of U. S. premises have been registered under NAIS. The estimate for Texas is about 16%. One of the key elements of the business plan is target dates for progress. December, 2009 is the target to achieve the “ability to identify 70% of breeding animals to their premises of origin.” Note that this is 70% of the animals, not 70% of the  premises. It is estimated that roughly 20% of the beef cow operations in the U. S., those with over 50 head, have over 70% of the cows. So, the target could be reached by involving only the largest 20% or so of the operations. The complete business plan can be accessed at

The Temperature-Humidity Index (THI) is often used to assess heat stress. However, the index does not account for other important variables affecting stress, especially wind speed. Australian researchers developed a Heat Load Index (HLI) including temperature, humidity, and wind speed using data collected during eight summers on almost 18,000 feedlot steers. Breed-types included straight Bos taurus, Bos taurus crosses, Bos taurus-Bos indicus crosses, and straight Bos indicus. HLI thresholds were determined above which body temperature increased. So higher HLI equaled greater tolerance. HLI was:

  • highest for straight Bos indicus and lowest for straight Bos taurus
  • higher as amount of shade per animal increased
  • lower for animals showing clinical signs of sickness
  • lowest for black color, intermediate for red, and highest for white
  • lower as time on feed increased (apparently related to increased body fat)
  • lower as temperature of drinking water increased
  • lower as depth of manure in the lot increased

So, highest tolerance should be demonstrated in animals that are white-colored, healthy, straight Bos indicus with access to shade and cool water early in a feeding period on less manure depth. (J. Animal Sci. 86:226)

One way to measure the genetic selection being practiced in a breed over time is by selection pressure or intensity. Data from the American Simmental Association show what breeders have been selecting for since 1980. Selection emphasis has been consistently high for increased weaning and, even more, yearling weight. Initially, emphasis was for increased birth weight, no doubt unintentional as a result of selection for increased weaning/yearling weight without attention to birth weight. But there has been selection for decreased birth weight over the last several years. Emphasis has also been high for both direct and maternal calving ease. Less selection emphasis has been placed on increased marbling and there has been essentially no attention to selecting for improved yield grade. There has been consistent though relatively slight emphasis on decreasing milk, especially in recent years, realizing this is a relatively high-milking breed. Selection trends in other breeds would probably be similar, except for milk. (

Ractopamine hydrochloride (RAC, Optaflexx) is approved for feeding to confined cattle during the last 28 to 42 days before slaughter to increase rate of gain, feed efficiency, and carcass leanness. Based on limited data, the original application for approval to market the product indicated no effects on beef palatability. Colorado State University and Iowa State University researchers collaborated to study this subject more extensively using 420 weaned steer calves of British (BT), Continental-cross (CT), and Brahman-cross (BM) types. Strip loins were evaluated after aging for 3, 7, 14, and 21 days post-slaughter.

Feeding RAC resulted in decreased tenderness, both mechanical shear-force and taste panel, and the effect was greatest in BM. RAC also reduced taste-panel juiciness and beef flavor. There was no significant difference in tenderness between BT and CT, but tenderness was significantly lower for BM, especially with shorter aging. Longer aging increased tenderness, the effect being most pronounced for BM. Juiciness and beef flavor were highest for BT, intermediate for CT, and lowest for BM. (J. Animal Sci. 86:205)

Many cow-calf operations run multiple-sire breeding herds, where paternity is unknown and sires cannot be culled on the basis of performance of their calves. University of Nevada researchers investigated the accuracy and economics of DNA analysis to assess paternity in multiple-sire herds. The study included over 2000 animals from eight ranches. Herd size varied from about 50 to almost 700 cows. Paternity was identified with a high degree of accuracy. It was estimated that identification returned $1.71 per dollar of cost for bull culling rate of 20% and $2.44 for a culling rate of 30%. Also, returns per dollar increased as number of bulls in a herd decreased. (J. Animal Sci. 86:17)

The U. S. Meat Animal Research Center has been studying twinning for a number of years in what they call their twinning population. The base herd was established some 25 to 30 years ago with 96 cows of various breeds. All base cows had two or more twin calvings. Since then, female replacements have been selected over four to five generations for production of twin births. From 1994 to 2004, ovulation rate increased from 1.46 to 1.89, being higher in fall than spring breeding. There were more twins from bilateral ovulations than unilateral. Pregnancy rates were lower after cows produced twins or triplets. Cows with postpartum intervals less than 50 days had lower pregnancy rates than with intervals longer than 60 days. Fewer pregnancies were maintained to term with twins and, especially, triplets. In heifers, more fetal losses occurred with unilateral location than bilateral, but this was not true for cows.

Number of calves per parturition increased from 1.34 to 1.56, and there were more triplets than early in the study. There were 38% single births, 58% twins, and 4% triplets. Gestation length was 6.8 days shorter for twins and 12.7 days shorter for triplets, so birth weights were lower accordingly. Calving difficulty was higher with multiple births. Calf survival at birth was 97% for single, 89% for twin, and 70% for triplet, but beyond that there was no difference in survival to weaning. Total weaning weight per cow calving was 479 lb for singles, 722 lb for twins, and 832 lb for triplets. So, increased calf production from multiple births was accompanied by higher fetal mortality. There might be some opportunity for increased production with multiple births, but only under very high levels of management. (J. Animal Sci. 85:3228 and 85:3239)

University of Missouri researchers studied feeding behavior in cattle of differing feed efficiencies. The measure of efficiency was Residual Feed Intake (RFI). Two studies compared efficient (low RFI) and inefficient (high RFI) steers. Cattle were fed once daily at 8 am and had feed available at all times. In both studies there was no difference between the efficiency groups in initial weight, average daily gain, or final weight. There was no difference in eating rate, but more efficient steers ate fewer times in a day compared to less efficient (11.0 vs. 18.2 times/day in the first study and 14.5 vs. 17.6 in the second). So, total daily consumption was lower for the more efficient steers. About 65%-70% of daily consumption occurred between 9 am and 6 pm. Inefficient steers were more variable in their eating patterns. (J. Animal Sci. 86:180)

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