The following reports were published in Michigan State University's “Beef Cattle Research Update,” Animal Science Staff Paper 445, November 2002.
Clemson University researchers have provided information on the weight required to change body condition scores in Angus cows. The Clemson researchers analyzed records on Angus females to determine the weight adjustment necessary to change body condition scores (BCS) at five time periods: precalving, postcalving, prebreeding, postbreeding, and midgestation.
|Body condition score||Weight change needed (lbs.)|
The number of observations totaled 3,912. Only BCS 2 through 8 were analyzed, as there were no recorded observations of BCS 1 or 9. Weight changes varied across time periods. The overall weight adjustments to change cows to a BCS of 5 are shown in Table 1. (Spitzer et al. 2002. J. Anim. Sci. 80: 2031)
Commingling and in-weight had significant effects on health, feedyard performance and carcass quality, according to results of a Montana State University study. Data on 70 pens (202 head/pen) of feeder calves from seven states were analyzed to determine the effect of certain parameters on health, feedlot performance and carcass quality.
Age at weaning averaged 220 days with a range of 148-290 days. After weaning, calves were backgrounded an average of 69 days with a range of 0-135 days. Feedyard in-weights averaged 719 lbs. and ranged from 456-891 lbs. The pens were on feed for an average of 167 days and had an average daily gain (ADG) of 2.95 lbs.
Morbidity increased 7% when calves were commingled in the feedyard compared to those not commingled. Calves that entered the feedlot at heavier weights had less mortality, higher ADGs, greater carcass weights and a higher percent of Choice carcasses than those entering at lighter weights. (Fennewald et al. 2002. Montana Nutrition Conf., Bozeman, MT)
A sperm enzyme may be the factor that triggers fertilization. British scientists at University College of London claim to have identified an enzyme, PLC-zeta, in sperm that's capable of initiating fertilization without the need for the sperm itself (“parthenogenetic reproduction”).
Using eggs from mice, they injected PLC-zeta into the eggs. Within 24 hours, 78% of the injected eggs had reached the two-cell stage of development. Within 96 hours, 62% had reached the blastocyst stage, “suggesting they were developmentally competent,” one researcher said. These success rates are similar to those achieved with in vitro fertilization.
There are other parthenogenetic techniques already in use for in vitro fertilization of livestock that involve injection of sperm extracts or strontium ions, but they're very unreliable. Armed with the factor that has been so thoroughly tried and tested by nature, parthenogenesis could eventually become routine and reliable, the researcher said. (FASS TRACK news, July 2002)
Deposition of marbling was accelerated at a set body weight in a University of Missouri trial. Missouri researchers attempted to determine if and when there's a point at which marbling is accelerated in feedlot cattle.
Angus crossbred steers (774 lbs.) were assigned to three treatment groups representing a weight at which they would enter the feedlot (800, 900 or 1,000 lbs.). Before entering the feedlot, they were grazed on pasture and supplemented to achieve an ADG of 1.75 lbs. In the feedlot, they were measured ultrasonically for intramuscular (IM) fat (marbling) every 28 days until harvesting at about 1,250 lbs.
There were no differences between treatments in ADG on pasture or in the feedlot. Using broken-line statistical analysis, the authors determined the breakpoint at which deposition of IM fat began to increase.
Regardless of weight at feedlot entry, the breakpoint for increased IM fat accretion rate was calculated as 64% of mature body weight in these steers. The authors say this type of information could enhance beef production efficiency by more accurately hitting a quality grade window and avoid overfeeding.
Further research is needed to determine the marbling breakpoint values for other breed types that vary in frame size and mature weight. (Carter et al. 2002. Prof. Anim. Sci. 18: 135)
Feeding melengesterol acetate (MGA) failed to suppress reproduction activity in yearling feedlot bulls. University of Kentucky researchers fed crossbred bull calves (317 days of age) a daily dose of 0, 0.5, 1.0 or 2.0 mg MGA for 99 days to determine if MGA could suppress the sexual behavior of young feedlot bulls to make them more suitable for finishing and subsequent harvest.
In male humans and monkeys, progestins suppress libido and sexual behavior. In beef cattle, the orally active progestin MGA is routinely used to suppress estrous behavior in feedlot heifers.
The researchers characterized luteinizing hormone (LH) and testosterone concentrations on days 8, 36, 63 and 92. Mounting behavior was assessed on days 15, 43, 71 and 99.
Overall, feeding MGA had little or no effect on hormone concentrations or mounting behavior. The authors concluded that these results fail to support the hypothesis that progestins suppress sexual behavior or fertility in beef bulls. (Imwalle et al. 2002. J. Anim. Sci. 80: 1059)
Steaks from dark cutting carcasses were significantly tougher than steaks from normal carcasses. Dry, firm, dark (DFD) cutting beef is undesirable because of its unattractive appearance and greater susceptibility to microbial growth. The effects of DFD on beef palatability, however, aren't well defined and there's disagreement among studies on this subject.
South Dakota State University and Ohio State University researchers conducted a study to evaluate the impact of DFD on palatability of eight different muscles from the hindquarter of normal and DFD carcasses. DFD strip loin, top sirloin and top round steaks had shear force values that were 46%, 33% and 36% greater, respectively, than those of normal steaks.
Likewise, sensory panel tenderness scores were significantly lower for steaks from DFD carcasses. And steaks from DFD carcasses had more off-flavor comments by panelists than steaks from normal carcasses.
The authors concluded that, because of poor palatability, dark cutters should be excluded from USDA Prime, Choice and Select grades and from premium beef marketing programs. (Wulf et al. 2002. J. Anim. Sci. 80: 1895)
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