Beef Cattle Browsing – May 2010

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

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.

McDONALD’S AND FREE-RANGE EGGS
The Humane Society of the United States, a McDonald’s stock holder, has proposed purchasing five percent of the company’s eggs from cage-free sources. The company has rejected the proposal on the grounds that there is not enough scientific evidence to do so and that cage-free systems may increase risk of infectious disease. (Texas Cattle Feeders Association newsletter, 4/16/10)

EFFECT OF ZILMAX® ON COMPOSITION AND PALATIBILITY
Effects of feeding Zilmax® (zilpaterol hydrochloride, ZH) were reported in two recent research papers. In one study, almost 12,000 steers from seven studies were fed ZH. Compared to controls, ZH-fed steers produced carcasses with heavier (P<.05) weight of the major subprimal cuts. In addition, the percentage of carcass weight was higher (P<.05) for the tenderloin, strip loin, and top sirloin butt. ZH-feeding increased (P<.05) total saleable yield by 1.76 percentage units, and reduced (P>.05) fat trim % by 0.58 units and bone % by 1.10 units.

In the other study, ZH-feeding had no significant effect on taste panel flavor score of strip loin steaks aged 14 days but decreased (P<.05) tenderness and tended (P<.10) to reduce juiciness and overall palatability. In steaks aged 21 days, tenderness, juiciness and overall palatability were reduced (P>.05) and flavor score tended (P<.10) to be reduced.

These results confirm the tradeoff from ZH feeding of higher lean yield but lower eating satisfaction. (J. Animal Sci. 88:1809 and 88:1817; New Mexico St. Univ., Oklahoma St. Univ., Texas A&M Univ., Texas Tech Univ., West Texas A&M Univ., Intervet/Schering-Plough Animal Health)

LONG-TERM PERFORMANCE OF COWS IN ARID CONDITIONS
Growth and reproductive data were collected from a Brangus herd from 1972 to 2006. Over 2600 records were analyzed from 525 spring-calving cows. The herd was maintained in the New Mexico Chihuahuan desert, where long-term precipitation averaged 9.21 inches/year.

Over the course of the study, there was gradual improvement in percent of yearling heifers pregnant, number calving as twos, and first rebreeding percent. Birth, weaning, and yearling weights tended to increase early, decrease slightly, and then increase in the later years. Fall cow weight (in Body Condition Score 5) increased from about 900 lb to 1100 lb in 1997 and then decreased slightly. Pregnancy percent of cows decreased during the first half of the study and then increased slightly. So, as cow weight increased, pregnancy percent tended to decline. A maturing rate index was calculated for cows. This index was negatively related to age at first calving and calving interval, that is, early-maturing cows tended to be more fertile. Early-maturing, small- to moderate-sized cows appeared to perform best under these conditions. (J. Animal Sci. 88:1891; New Mexico St. Univ. and Colorado St. Univ.)

GRASS-FED VS GRASS-SUPPLEMENTED VS FEEDLOT
A group of 72 steers (out of British-cross cows and sired by Angus, Charolais, or Brangus bulls) were weaned and maintained for 90-days on a forage-based ration. At that time, the steers were divided equally by breed cross into the following treatment groups for finishing to an estimated 0.25 inch fat thickness, the amount found to be possible in previous studies at this location before forage growth limited weight gain:

• ryegrass grazing only (control)
• grazing plus 0.5% body weight whole shelled corn fed daily
• grazing plus 1.0% body weight whole shelled corn fed daily
• grazing plus 1.5% body weight whole shelled corn fed daily
• grazing plus 2.0% body weight whole shelled corn fed daily
• drylot on high-concentrate ration.

Results were as follows:

Treatment effects on the traits tabled above were all significantly different (P<.05), except for marbling (P<.12). Increasing the amount of corn supplementation tended to decrease days on feed and increased ADG, dressing percent, hot carcass weight, and numerical Yield Grade (decreased leanness). The only statistically significant effects on palatability traits were that beef flavor score trended higher as amount of corn increased (P<.001) with the highest value for drylot-fed, which also had the highest tenderness and juiciness ratings. All groups fell into the Select USDA Quality Grade.

The fat end-point in this study of 0.25 inches is roughly half or less of what would usually be obtained with high-concentrate feeding, which would not have been possible with grass finishing. Extending fat thickness to industry norms would have resulted in higher Quality Grade for high-concentrate feeding. Grass-finishing and high-concentrate finishing are difficult to compare. They are different systems designed to produce different end products. At this point, the industry generally makes better use of grass and grain by separating into growing and finishing phases. (J. Animal Sci. 87:2690; Auburn Univ.)

REPRODUCTIVE TRACT SCORE TO PREDICT FERTILITY AND PRODUCTION
Reproductive Tract Score (RTS) involves rectal palpation of the reproductive tract and ovarian structures. RTS was evaluated one day before onset of breeding in 272 Bovelder heifers (a South African Bos taurus-Bos indicus combination breed) and related to measures of fertility and production. RTS was positively related (P<.01) to pregnancy rate during 50 days of AI, calf weaning weight, and pregnancy rate the next year and negatively related (P<.01) to days to calving. The authors concluded that RTS in virgin heifers should be a good predictor of lifetime production. (J. Animal Sci. 87:1934; Univ. of Pretoria, South Africa)

GENETICS OF HEIFER REBREEDING
In this study, records were available from 417 females born from 1976 to 1994. The females were Hereford and Tarentaise purebreds and F1, F2, and ¾ crosses of the two breeds. Across breed types, 72% of heifers rebred as 3-year-olds. Rebreeding percent was highest for F1s and lowest for ¾ bloods. Heritability ranged from 0.08 to 0.14, depending on how it was calculated. This is similar to many other measures of fertility or reproduction. So, while there is a genetic component to heifer rebreeding, it is so low that selection response for the trait would be very slow. (J. Animal Sci. 86 Supple. 1: 191; Montana St. Univ. and Colorado St. Univ.)

NATURAL VS CONVENTIONAL FEEDING
A group of 41 Angus heifers initially averaging 594 lb were fed in a conventional feeding system with an 85% corn-based diet containing Rumensin®, Tylan®, and MGA and implanting with Revalor® I-H at 30 and 120 days on feed or a “natural” system with no drugs or implants. The following traits were statistically different (P<.01-.03):

Days on feed, dry matter intake, feed efficiency, fat thickness, marbling, and Yield Grade did not significantly differ (P>.31 for all traits). Since conventional-fed gained more but did not consume significantly more, their feed efficiency would be higher. The natural group graded 100% Choice or Prime compared to 90.5% for the conventional group (P<.17). Conventional heifers carcass value was $944.96 compared to $910.24 for natural (P<.27). (J. Animal Sci. 85 Supple. 2: 137; Purdue Univ.)

SHOULD WE RETURN TO “GREENER” PRODUCTION SYSTEMS?
It’s hard to read a weekly mass-circulation magazine or watch television without encountering some “expert” (or not) blasting “factory farming” of livestock and advocating, if not demanding, a return to simpler, cleaner, more ethical production systems. A recent research paper compared typical dairy systems from 1944, when management was largely pasture-based, and typical 2007 management. Compared to the 1944 system, to produce the same amount of milk the modern system needed only 21% as many animals, 23% as much feedstuffs, 35% as much water, and 10% as much land. In addition, for the same amount of milk the modern system produced only 24% as much manure, 43% as much methane, and 56% as much nitrous oxide and had a carbon footprint only 37% as large. Comparison of grass-fed beef production and current management systems has yielded similar results. (J. Animal Sci. 87:2160; Univ. of Georgia)