Title: BEEF CATTLE RESEARCH UPDATE
Author: Animal Science
Last saved by: John Doyle
Company: Michigan State University

Animal Science Staff Paper 445
File 19
November, 2002

BEEF CATTLE RESEARCH UPDATE

November, 2002

Harlan Ritchie, Steven Rust, Daniel Buskirk, and Joel Cowley
Beef Cattle Specialists, Department of Animal Science
Michigan State University
East Lansing, MI 48824

Following are reviews of research projects recently reported at scientific meetings or in scientific publications.  Please feel free to use as you see fit.

BREEDING/GENETICS

Effect of Selection for High Marbling vs. High Percent Retail Product

	Montana State Univ. scientists initiated a long-term study to compare progeny of sires having high EPDs for marbling vs. those having high EPDs for percent retail product (% RP).  Also, one sire was used that had high EPDs for both marbling and % RP.  Steer calves were assigned to one of two treatments: implants (Revalor^®) vs. no implants, and were slaughtered at about 14 mos. of age.  Carcass results from the first calf crop are presented in Tables 1 and 2.

Table 1.  Effect of Implant Status on Carcass Traits
Trait | Implant | No implant
Carcass wt, lb | 693 | 659
Ribeye area, sq in | 10.7 | 10.6
Backfat, in | .49 | .48
Yield grade | 3.3 | 3.2
Marbling scoreª | 4.7 | 5.7
% Prime | 3 | 13
% Premium Choice | 13 | 42
% Low Choice | 38 | 26
% Select | 48 | 19
ª4.0=Slight°; 5.0=Small°; 6.0=Modest°.

Table 2.  Effect of Sire Type on Carcass Traits
| Sire type
Trait | Marbling | % RP | Marb. + % RP
Carcass wt, lb | 683 | 689 | 665
Ribeye area, sq in | 10.5 | 10.8 | 10.6
Backfat, in | .51 | .48 | .49
Yield grade | 3.4 | 3.2 | 3.2
Marbling scoreª | 5.3 | 4.4 | 5.9
% Prime | 16 | --- | 20
% Premium Choice | 30 | 24 | 40
% Low Choice | 38 | 27 | 40
% Select | 16 | 49 | ---
ª4.0=Slight°; 5.0=Small°; 6.0=Modest°.

	As shown in Table 1, implanted steers had greater carcass weights, less marbling and lower quality grades.  The significant differences in Table 2 were the lower marbling scores and lower quality grades for calves sired by high % RP bulls.  The only other major difference was the lower carcass weight of the marbling + % RP sire group.  However, this could likely be a result of having only one sire represented in this group.  Based upon the first year’s data, the author concluded that the use of EPDs for carcass traits can be useful in hitting specific market targets.  She also noted that using high % RP sires gave results that were similar to the use of implants (K.C. Davis. 2002. Montana Nutrition Conf.)

Effect of Residual Feed Intake on Efficiency, Growth, and Body Composition

	Feed efficiency has been traditionally defined as feed conversion ratio (lb feed DM per lb gain).  Recent research has shown that selection pressure for improved feed conversion ratio in growing-finishing cattle will enhance growth rate but increase mature cow weight.  Consequently, selection for feed conversion ratio in young cattle will likely increase maintenance feed costs in the cow herd and not necessarily improve overall biological efficiency of beef production.  

	Research in Australia and Canada recently revealed that selection for residual feed intake (actual feed intake minus expected feed intake) is a moderately heritable trait that appears to be genetically independent of growth and body weight.  In this study, Texas A & M researchers individually fed 169 crossbred steers, measured weight and feed intake for 77 days, calculated residual feed intake (RFI), and estimated composition with ultrasound.

	RFI was not correlated with avg. daily gain, final weight, ribeye area or intramuscular fat, but was correlated with feed intake, feed/gain, and backfat.  Comparisons between low and high RFI steers are shown in Table 1.  Compared to high RFI steers, the low RFI steers (high net feed efficiency) were significantly lower in RFI, feed intake, feed conversion ratio, rump fat, and approached significance in backfat.

Table 1.  Composition of steers with low and high residual feed intake.

Item

Low RFI
 (high net feed eff.)

High RFI 
(low net feed eff.)

Initial wt, lb | 543.5 | 540.2
Final wt, lb | 716.6 | 713.8
RFI, lb/day | -2.16** | 1.94
ADG, lb/day | 2.25 | 2.25
Feed intake, lb/day | 17.5 | 21.1
Feed conversion, lb DM/lb gain | 7.91** | 9.71
Ultrasound measures: | |
Backfat, mm | 3.96 | 4.23
Rump fat, mm | 3.89* | 4.24
Ribeye area, sq in | 8.19 | 8.26
IMF fat, % | 2.84 | 2.89
*  Statistically significant (P < .05)
**Statistically significant (P < .01).

	The authors stated that increased leanness of low RFI steers may have contributed to their improved feed efficiency, but given that the magnitude of this difference in composition was minimal, it is likely that other physiological factors (e.g., maintenance requirements, feeding activity and behavior, and protein turnover) were involved (Carstens et al. 2002. Proc. Western Section, ASAS, 53:552). 

Combining Live Animal Data and Carcass Data Improved Accuracy
of Breeding Values for Traits Related to Carcass Yield

	Scientists at the Lethbridge, Alberta Research Centre obtained live weight (LW) and real time ultrasound (RTU) measures of ribeye area (REA) and fat thickness (FT) on a total of 404 yearling bulls and 514 yearling heifers from three calf crops.  Measures of carcass weight (CW), REA, and FT were also obtained on a total of 235 steers from these same calf crops.  Estimated breeding values (EBV) were initially determined for CW, REA, and FT using only the steer carcass data.  EBV were also determined for LW, REA, and FT using live animal RTU data from the yearling bulls and heifers.  Carcass and live animal data were also combined to determine EBV in a full animal model.  Following is a summary of their results.

•	EBV from the carcass data model were less accurate than those from the live animal data model.
•	Adding live animal RTU data to the carcass model increased the average accuracy of carcass trait breeding values by 91, 75, and 51% for CW, REA, and FT, respectively.
•	Rank correlations among breeding values were lower when estimated solely with carcass data vs. RTU data.

The authors concluded that the addition of live animal data to carcass data for genetic evaluation 
of carcass traits is expected to result in EBV that are more accurate for potential replacements (Crews and Kemp.  2002.  J. Anim. Sci. 80: 1809).

Concentrations of the Hormone IGF-1 Were Not Associated with Postpartum Follicular Development Among Various Genotypes of Cows

	An extended period of postpartum anestrus (failure to return to estrus on schedule) results in an extended calving season and loss of reproductive efficiency.  Numerous studies on hormone changes during postpartum anestrus have been conducted over the past several decades.  One hormone found to change during this period is insulin-like growth factor-1 (IGF-1).  In a 2-year study, Oklahoma State Univ., USDA, and Univ. of Florida researchers hypothesized that differences in IGF-1 concentrations among various genotypes may be associated with differences in return to estrous cyclicity in postpartum cows.  Serum concentrations of IGF-1, body condition score (BCS) and body weight (BW) were determined between weeks 2 and 9 postpartum.  As a measure of return to cyclicity, rectal ultrasound was used to determine days postpartum to first medium sized ovarian follicle (6-9 mm) and first large (≥ 10 mm) follicle.  

•	Averaged across genotypes, BCS decreased significantly from week 3 to week 6 postpartum, and BW decreased significantly from week 2 to week 9 postpartum.
•	IGF-1 concentrations were greatest in Brahman (B); lowest in Angus (A), Charolais (C) and A x C; and intermediate in A x B and B x C cows.
•	Average no. of days to first medium follicle and first large follicle did not differ among genotypes.
•	Serum IGF-1 correlated significantly with BCS but not with days to first large follicle.
•	Cows that lost BCS postpartum had lower serum IGF-1 concentrations.
•	Cows that calved with adequate BCS (≥ 5) had greater IGF-1 concentrations than those with inadequate BCS, but days to first medium and large follicle did not differ.

The authors concluded that serum IGF-1 concentrations differed among genotypes and were
associated with BCS but not with days to first medium or large follicle in postpartum beef cows (Spicer et al. 2002. J. Anim. Sci. 80: 716).

A Sperm Enzyme May be the Factor that Triggers Fertilization

	British scientists, Larman and Swann, University College of London, claim to have identified an enzyme, PLC-zeta, in sperm that is 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 hrs., 78% of the injected eggs had reached the two-cell stage of development.  Within 96 hrs., 62% had reached the blastocyst stage, “suggesting they were developmentally competent,” said Larman.  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.  However, these approaches are very hit-and-miss.  Larman says that, armed with the factor that has been so thoroughly tried and tested by nature, parthenogenesis could eventually become routine and reliable (FASS TRACK news, July, 2002.)

COW-CALF

Exposure to Ammoniated Wheat Straw as Suckling Heifer Calves 
Improved Their Performance as Mature Cows

	In an interesting study to determine the effects of exposure to ammoniated wheat straw (AWS) early in life on performance later in life, Utah State Univ. researchers allotted 32 mature cows (5 yrs.) to two groups:  1)  exposed (EXP) to AWS for 66 days as suckling calves; 2) not exposed (NEXP) to AWS as suckling calves.  Cows had free access to AWS during a 150-day wintering period for 3 consecutive yrs.  They were supplemented with alfalfa hay to meet increasing protein and energy requirements from late gestation through early lactation.  For all 3 yrs., yearly average body wt. and condition scores were significantly higher for EXP than NEXP cows.  Postpartum interval to rebreeding was shorter for EXP cows for 2 out of the 3 yrs.  EXP cows also produced more milk than NEXP cows during yrs. 1 and 2.  This study supports the results of previous research with other ruminant species which revealed the importance of exposing animals at an early age to dietary regimens they may encounter later in life, particularly if those regimens are likely to be challenging, such as low-quality forages.  The authors recommended that producers consider previous exposure to low-quality forages when considering using such forages to reduce feed costs (Wiedmeier et al. 2002.  J. Anim. Sci. 80:  2340.

Processing Barley Dramatically Improved Starch Digestibility in Older Cattle

	Montana State Univ. researchers studied the effects of animal age and barley processing method on diet digestibility.  Angus crossbred cows (31 mos. old) and their newly weaned calves were allotted to whole vs. rolled barley treatments.  Cows received 5.5 lb barley, 0.4 lb protein supplement, and 7.5 lb grass hay per day.  Calves were fed 2.53 lb barley, .4 lb protein supplement, and 11.2 lb hay per day.  Processing method did not affect organic matter, protein, or fiber digestibility.  Age influenced organic matter and protein digestibility (calves > cows) but did not affect fiber digestibility.

	The most important effects were those of processing method and age on starch digestibility.  Rolling did not affect starch digestibililty in calves but dramatically improved it in cows (71.4% for rolled vs. 23.3% for whole).  There was no difference in starch digestibility between cows and calves consuming rolled barley, but when whole barley was fed, there was a large difference in starch digestibility (73.7% for calves vs. 23.3% for cows).  The authors concluded that processing of barley is clearly necessary for mature cows (Rainey et al. 2002. Montana Nutrition Conf., Bozeman, MT.)

Weight Required to Change Body Condition Scores in Angus Cows

	Clemson Univ. researchers analyzed the records on Angus females to determine the weight change necessary to change body condition scores (BCS) at five time periods:  precalving, postcalving, prebreeding, postbreeding, and midgestation.  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 adjust cows to a BCS of 5 are shown in Table 1 (Spitzer et al. 2002. J. Anim. Sci. 80: 2031).

Table 1.  Weight needed to adjust BCS to a body condition of 5 (average of five time periods)
Body condition score | Weight change needed (lb)
2 | 150
3 | 110
4 | 46
5 | 0
6 | -53
7 | -112
8 | -161

Early Versus Normal Weaning in a Sub-Tropical Environment

	Research has demonstrated that early weaning has some definite advantages under certain circumstances (e.g., drought) in temperate regions of North America.  Florida scientists recently conducted an early weaning study at the Range Cattle Research Station in South Florida, where forages are high yielding but of limited quality for supporting reproduction performance of young lactating cows.  Fall-born calves on Braford and Brangus 3-yr-old dams were allotted to either an early weaning (EW; 84 days, Jan. 23) or a normal weaning (NW; 196 days, Aug. 1) treatment.  Following EW, all cows were returned to bahia-grass pastures for 112 days and supplemented with 5 lb/cow/day of a molasses supplement.  EW calves were maintained on rye grass pastures and fed supplemental grain at 1% of body weight daily.  NW calves remained with their dams on the bahia-grass pastures until they were weaned.  Results are summarized in Table 1.

Table 1.  Early versus normal weaning in a sub-tropical climate.
| Treatment
Item | EW | NW
Calf wt at 84 days, lb | 200.0 | 192.1
Cow condition score at 84 days | 3.90 | 3.88
Calf ADG, day 84 to 196 days, lb | 1.90** | 1.48
Cow wt at 196 days, lb | 1074** | 982
Cow condition score at 96 days | 6.25* | 4.50
Cow pregnancy rate, % | 89.5* | 50.0
Cow calving interval, days | 391* | 412
*Statistically significant (P < .05).
**Statistically significant (P < .01)

	As shown in Table 1, EW calves gained significantly faster from 84 days to 196 than NW calves.  EW dams were significantly heavier and in better body condition at 196 days than NW dams.  This improvement in body condition was associated with a significantly higher pregnancy rate and shorter calving interval.  These results indicated that EW works just as well or better in a sub-tropical climate compared to a temperate climate (Arthington and Kalmbacher.  2002.  J. Anim. Sci. 80 (Suppl. 1): 101).

STOCKER/FEEDLOT

Comingling and In-Weight had Significant Effects on Health,
Feedyard Performance and Carcass Quality

	Data on 70 pens (202 head/pen) of feeder calves from seven states were analyzed by Montana State Univ. researchers 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 to 290 days.  After weaning, calves were backgrounded an average of 69 days with a range of zero to 135 days.  Feedyard in-weight averaged 719 lb and ranged from 456 to 891 lb.  The pens were on feed for an average of 167 days and had an average daily gain of 2.95 lb.  Morbidity increased 7% when calves were comingled in the feedyard compared to those not comingled.  Calves that entered the feedlot at heavier weights had less mortality, higher average daily gains, greater carcass weights and a higher percent of Choice carcasses than those entering at lighter weights.  The authors stated these results indicated that comingling and in-weight were critical to health, feedlot performance and carcass quality (Fennewald et al. 2002. Montana Nutrition Conf., Bozeman, MT).

Deposition of Marbling Was Accelerated at a Set Body Weight

	Recently, there has been considerable interest in determining if and when there is a point at which marbling is accelerated in feedlot cattle.  In a Univ. of Missouri trial, Angus crossbred steers (774 lb) were assigned to three treatment groups, representing a weight at which they would enter the feedlot (800, 900, or 1000 lb).  Before entering the feedlot, they were grazed on pasture and supplemented to achieve a gain of 1.75 lb/day.  In the feedlot, they were measured ultrasonically for intramuscular fat (marbling) every 28 days until they were harvested at approximately 1250 lb.  There were no differences between treatments in daily gain on pasture or in the feedlot.  Using broken-line statistical analysis, the authors determined the breakpoint at which deposition of intramuscular fat began to increase.  Regardless of weight at feedlot entry, the breakpoint for increased intramuscular fat accretion rate was calculated as 64% of mature body weight in these steers.  The authors indicated this type of information could enhance beef production efficiency by more accurately hitting a quality grade window and avoid overfeeding.  They stated that further research is needed to determine the marbling breakpoint values for other breedtypes that vary in frame size and mature weight (Carter et al. 2002. Prof. Anim. Sci. 18: 135).

Evaluating the 1979 USDA Standards for Feeder Cattle Frame Size and Muscle Thickness

	There has been concern in the industry that the U.S. Standards for Grades of Feeder Cattle, adopted in 1979, do not adequately categorize today’s cattle population.  A Colorado State Univ. study was conducted to determine the live weight at which large-, medium-, and small-framed feeder steers and heifers attain a degree of finish associated with a carcass quality grade of Low Choice and to examine the relationship of muscle thickness to carcass yield grades.  

•	Frame size effectively predicted finished weight at a marbling endpoint of Small°°(Low Choice) for both heifers and steers.
•	For steers, the Small/Medium frame intersect was 1111 lb, and the Medium/Large intersect was 1272 lb.  For heifers, these intersects were 1014 lb and 1147 lb, respectively.  These weights are greater than the weight specifications in the 1979 USDA standards.  
•	Evaluation of 1979 muscle thickness score (1 = thick; 2 = moderate; 3 = thin) revealed they were related to ribeye area but not to yield grade.
•	An alternative muscle thickness scheme, using four classes rather than three, was effective for stratifying cattle according to eventual difference in yield grade.

The authors indicated these results suggest that the 1979 USDA grade standards are no longer adequate for describing today’s feeder cattle population (Grona et al. 2002. J. Anim. Sci. 80:560).

Zinc Proteinate Supplementation Improved Performance of Finishing Steers

	In a growing-finishing trial to compare organic vs. inorganic sources of zinc, North Carolina State Univ. scientists allotted 60 individually-fed Angus and Angus x Hereford steers (542 lb) to four treatments; 1)  control, no supplemental zinc (Zn); 2)  zinc oxide (ZnO); 3) Zn proteinate-A; 4)  Zn proteinate-B.  Treatments 2, 3 and 4 provided 25 parts per million (ppm) of supplemental Zn.  Steers were fed a corn silage-based diet during the 84-day growing phase and a high corn diet during the finishing phase.  During the growing phase, all three Zn supplements significantly increased ADG over the Controls.  In the finishing phase, steers fed Zn proteinate tended to gain faster and more efficiently than ZnO or Control steers.  Zinc proteinate steers had significantly heavier hot carcass weights and slightly higher dressing percentages than control or ZnO steers.  Zinc supplementation, regardless of source, significantly increased quality grade, yield grade, marbling and backfat over Controls.  Soluble concentrations of Zn in ruminal fluid were significantly higher in steers fed Zn proteinate than those fed ZnO.  The authors concluded that Zn proteinate may improve performance of finishing steers above that observed with inorganic Zn supplementation (Spears and Kegley.  2002.  J. Anim. Sci. 80:  2747).

Feeding Melengesterol Acetate Failed to Suppress Reproduction Activity in Yearling Feedlot Bulls

	When administered to male humans and monkeys, progestins have been shown to suppress libido and sexual behavior.  In beef cattle, the orally active progestin melengesterol acetate (MGA) is routinely used to suppress estrous behavior in feedlot heifers.  In a Univ. of Kentucky study, crossbred bull calves (317 days of age) were fed 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, thereby making them more suitable for finishing and subsequent harvest.  Luteinizing hormone (LH) and testosterone concentrations were characterized 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). 

CARCASS/MEAT SCIENCE

Steaks from Dark Cutting Carcasses Were Significantly Tougher than 
Steaks from Normal Carcasses

	Dry, firm, dark cutting (DFD) beef is undesirable because of its unattractive appearance and because it is more susceptible to microbial growth.  However, the effects of DFD on beef palatability are not well defined and there is disagreement among studies on this subject.  Researchers at South Dakota State and Ohio State Universities conducted a study to evaluate the impact of DFD on the 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 percent greater, respectively, than those of normal steaks.  Likewise, sensory panel tenderness scores were significantly lower for steaks from DFD carcasses.  Furthermore, 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).

An Online Video Image Analysis System More Accurately 
Predicted Carcass Cutout Yields than Online USDA Graders

	Colorado State Univ. researchers used 296 steer and heifer carcasses to evaluate the accuracy of four different methods of predicting fabricated yields of closely trimmed subprimals:  1) whole yield grade numbers assigned by USDA graders online at chain speed (10-12 seconds/carcass); 2) yield grades assigned offline to the nearest 0.1 by expert USDA graders at a comfortable rate of speed; 3) a video image analysis system, “Computer Vision System” (CVS), to estimate carcass yield at chain speed; 4) CVS measured ribeye area in conjunction with expert grader estimates of the remaining yield grade factors (fat thickness, carcass weight, and % KPH fat).  Accuracies of the four systems were 39, 67, 64, and 65%, respectively.  The authors concluded that prediction models using the CVS estimates—either alone or combines with some human grader estimates—more accurately predicted carcass cutout yields than did yield grades assigned by online graders (Cannell et al. 2002. J. Anim. Sci. 80: 1195).