Milestones in beef cattle genetic evaluation.

National beef cattle genetic evaluation programs have evolved in the United States over the last 35 yr to create important tools that are part of sustainable breeding programs. The history of national beef cattle genetic evaluation programs has lessons to offer the next generation of researchers as new approaches in molecular genetics and decision support are developed. Through a series of complex and intricate pressures from technology and organizational challenges, national cattle evaluation programs continue to grow in importance and impact. Development of enabling technologies and the interface of the disciplines of computer science, numerical methods, statistics, and quantitative genetics have created an example of how academics, government, and industry can work together to create more effective solutions to technical problems. The advent of mixed model procedures was complemented by a series of breakthrough discoveries that made what was previously considered intractable a reality. The creation of modern genetic evaluation procedures has followed a path characterized by a steady and constant approach to identification and solution for each technical problem encountered. At its core, the driving force for the evolution has been the need to constantly improve the accuracy of the predictions of genetic merit for breeding stock, especially young animals. Sensible approaches, such as the principle of economically relevant traits, were developed that created the rules to be followed as the programs grew. However, the current systems are far from complete or perfect. Modern genetic evaluation programs have a long way to go, and a great deal of improvement in the accuracy of prediction is still possible. But the greatest challenge remains: the need to understand that genetic predictions are only parameters for decision support procedures and not an end in themselves.

Genetic parameter estimates for carcass and yearling ultrasound measurements in Brangus cattle.

Carcass measurements of 12th-rib fat thickness (CARCFAT), longissimus muscle area (CARCLMA), and weight (CARCWT) on 2,028 Brangus and Brangus-sired fed steers and heifers, as well as yearling weights (YWT) and ultrasound measures of 12th-rib fat thickness (USFAT) and longissimus muscle area (USLMA) on 3,583 Brangus bulls and heifers were analyzed to estimate genetic parameters. Data were analyzed using a six-trait animal model and an average information REML algorithm. The model included fixed effects for contemporary group and breed of dam, covariates for age at slaughter or measurement, and random animal and residual effects. Heritabilities for CARCFAT, CARCLMA, CARCWT, USFAT, USLMA, and YWT were .27+/-.05, .39+/-.05, .59+/-.06, .11+/-.03, .29+/-.04, and .40+/-.04, respectively. Genetic correlations between CARCFAT and USFAT, CARCLMA and USLMA, and CARCWT and YWT were .69+/-.18, .66+/-.14, and .61+/-.11, respectively. The favorable and moderately strong genetic correlations between carcass measurements and similar yearling breeding-animal ultrasound measurements indicate that such measurements of 12th-rib fat and longissimus muscle area are useful in predicting genetic values for carcass leanness and longissimus muscle area. Selection using yearling ultrasound measurements of breeding cattle should result in predictable genetic improvement for carcass characteristics. Inclusion of yearling ultrasound measurements for fat thickness and longissimus muscle area should enhance national cattle evaluation programs.

Biceps femoris and rump fat as additional ultrasound measurements for predicting retail product and trimmable fat in beef carcasses.

One hundred ninety-eight steers of Angus and Hereford breeding were evaluated ultrasonically for fat thickness over the 12-13th rib (UFAT), fat thickness over the rump (URUMP), 12-13th longissimus muscle area (UREA), and depth of the biceps femoris (UROUND) before slaughter. Carcass measurements associated with the USDA yield grade were also obtained. Carcasses were fabricated into closely trimmed (.32 cm fat), boneless subprimals. Regression procedures were used to predict weight and the percentages of retail product and trimmable fat. Final weight (FINALWT) accounted for most of the variation when predicting kilograms of retail product and trimmable fat, with R2 values of .836 and .435, respectively. As single predictors URUMP and UFAT accounted for most of the variation when predicting the percentages of retail product and trimmable fat with R2 values of .244 and .220, respectively. Adding URUMP to equations that included FINALWT, UREA, and UFAT increased R2 values for percentage of retail product from .175 to .318 and for weight of retail product from .847 to .865, whereas the addition of UROUND did not appreciably increase R2 values for the same models. Adding URUMP and UROUND to the model of FINALWT, UREA, and UFAT to predict kilograms and the percentage of trimmable fat increased R2 values from .530 to .610 and from .254 to .360, respectively. Models using live-animal measurements to predict weight and the percentage of retail product gave R2 values equal to models using the actual measurements found in the USDA Yield Grade equation.

Effects of selection for scrotal circumference in Limousin bulls on reproductive and growth traits of progeny.

Nine pairs of Limousin bulls from nine contemporary groups were acquired, with each pair consisting of one large scrotal circumference (SC) bull and one small SC bull. Average adjusted yearling scrotal circumferences were 36.3 cm (SD 1.6 cm) and 28.5 cm (SD .9 cm) for large SC (LP) and small SC (SP) bulls, respectively. In addition to the phenotypic grouping, non-parent SC EPD were used to group bulls into high (HE, > .53 cm), average (AE), and low (LE, < -.61 cm) lines. Each bull was mated to a randomly assigned group of 15 to 20 Brangus x Hereford cows each yr for 1 to 3 yr. Birth weights, weaning and yearling weights and heights, and ultrasound measurements for backfat and ribeye measurements were taken on 407 progeny. Blood samples were collected on 210 heifer progeny when they averaged 11, 13, and 15 mo of age to determine whether they had reached puberty. When subjected to a breeding soundness exam (BSE), LP bulls scored higher (P < .01) for motility as well as total BSE score. The LP calves had heavier birth weights (P < .05) and greater testicular mass at weaning (P < .01) than SP calves. The HE and AE bull calves had greater (P < .02) testicular mass than did the LE bull calves. A greater (P < .05) percentage of HE heifers had reached puberty by the 11- and 13-mo measurements than either the AE or LE heifers. The HE heifers reached puberty at a younger age than AE (P < .01) or LE (P < .001) heifers. Selection using SC EPD was more effective than phenotypic selection in reducing age at puberty in daughters.

Evaluation of machine, technician, and interpreter effects on ultrasonic measures of backfat and longissimus muscle area in beef cattle.

Before slaughter, 44 Hereford-sired steers were measured ultrasonically for backfat (UFAT) and longissimus muscle area (ULMA) between the 12th and 13th ribs by three technicians (TECH) using two different machines (MACH) on two consecutive days (DAY). Each TECH interpreted (INT) his own images in addition to other TECH images. The absolute values of the difference between the 2 DAY's ultrasound measurements for ULMA (magnitude of LMAR) and UFAT (magnitude of FATR) were analyzed with a model including fixed effects of MACH and TECH with a random effect of steer and all interactions. For both magnitude of LMAR and magnitude of FATR, MACH x TECH was significant (P < .10). Correlations between the 2 DAY's measurements ranged from .36 to .90 and .69 to .90 for ULMA and UFAT, respectively. Simple statistics to quickly evaluate TECH and MACH were developed. Root mean squared errors (RMSE) and error standard deviations (ESD) between repeated measurements ranged from 3.89 to 11.32 and 3.93 to 11.34 cm2 for ULMA and .12 to .20 cm and .12 to .20 cm for UFAT, respectively. For accuracy, the absolute values of the difference between the ultrasound and carcass measurement for fat (magnitude of FATD) and longissimus muscle area (magnitude of LMAD) were analyzed with a model accounting for fixed effects of DAY, TECH, and MACH and a random effect of steer with all higher-order interactions. For magnitude of LMAD, TECH x MACH was a significant source of variation (P < .001). Also, a similar model was fit that included the fixed effects of TECH, MACH, and INT and a random effect of steer with all interactions. The MACH x INT interaction was found to be significant for magnitude of LMAD (P < .05). From this research, TECH and MACH differences do exist. Ultrasound is a valid means of measuring carcass traits in live steers if appropriate personnel and equipment are selected.

Comparison of live and carcass equations predicting percentage of cutability, retail product weight, and trimmable fat in beef cattle.

Forty-four Hereford-sired steers were measured ultrasonically for backfat and longissimus muscle area between the 12th and 13th ribs before slaughter and visually appraised for fatness, overall muscling, and frame. Carcass measurements associated with USDA yield and quality grades were measured and recorded. Carcasses were fabricated into closely trimmed, boneless subprimals at 1.27- and .32-cm fat trim levels. Cutability percentage (percentage of retail cuts from the cold carcass weight) and kilograms of retail product were defined three ways. The first definition included only retail cuts from the round, loin, rib, and chuck. The second included the above plus adjusted lean trim from the round, loin, rib, and chuck, and, finally, total retail product from the entire carcass. Kilograms (TOTFAT) and percentage (PERFAT) of trimmable fat were also calculated. Stepwise regression procedures were used for live and carcass trait model development predicting cutability percentages, kilograms of retail product, and trimmable fat. Fat measurements accounted for the largest portion of variation in cutability percentage and PERFAT. Weight measurements accounted for the major sources of variation in predicting kilograms of retail product and TOTFAT. Final models using live animal traits ranked the steers equally as well for cutability percentages as the original USDA cutability equation and stepwise, developed carcass equations (P > .10). Final models using live animal or carcass equations ranked the animals equally for kilograms of retail product yield (P > .10).

Development of an animal model for across-herd genetic evaluation of number born alive in swine.

An animal model and computer software were developed to conduct across-herd genetic evaluations using data from producers participating in the Sow Productivity Index program of the American Yorkshire Club. The final data set consisted of 61,596 litter records from 1986 to early 1990. The animal model included fixed contemporary group effects and random additive direct, service sire, permanent environmental, and residual effects. Additive genetic relationships among animals were included. A separate relationship matrix for service sires and their sires was also included. A data set similar to the Yorkshire field data was simulated to use in testing the animal model. The simulated data set consisted of 40 herds, each with 120 reproducing dams and either four or five sires. Six generations of simulated data were produced, resulting in 20,605 litter records. These records were then evaluated using the animal model for number of pigs born alive. Finally, correlations between the true breeding values from the simulation and the predicted breeding values were computed. The correlation between the 918 true and predicted sire breeding values was considerably lower for the animal model without a service sire effect than when it was included (.53 vs .74, respectively). However, the difference was cut in half (.66 vs .77) when only sires with greater than five daughter records were included. The high accuracy of the animal model with a random service sire effect indicates that the proposed model adequately accounts for the variation found in records for number of pigs born alive.

Genetic and environmental parameters for mature weight and other growth measures in Polled Hereford cattle.

Variances and covariances were estimated for birth weight (BWT), weaning weight (WW), yearling gain (YG), yearling weight (YW), yearling height (YH), relative growth from birth to weaning (RGW) and weaning to yearling (RGY), and mature weight (MW). Field records on 572,446 Polled Hereford cattle were analyzed. Because multiple dam weights were collected on a cow the MW used in the analysis was calculated using a nonlinear regression correction factor computed by fitting a quadratic with a plateau to the data. If the cow had an observation(s) beyond the inflection point (IP), the closest weight to that point was used. If the cow only had observation(s) before the IP the closest weight to that point was nonlinearly adjusted to the plateau. The IP for this data set was 1,506 d and the plateau was 554.7 kg. Heritabilities and genetic and environmental correlations were calculated from the appropriate (co)variances and phenotypic correlations were computed. Heritability estimates for BWT, WW, YG, YW, YH, RGW, RGY, and MW were .49, .24, .23, .30, .59, .24, .15, and .52, respectively. Genetic correlations between MW with BWT, WW, YG, YW, YH, RGW, and RGY were .64, .80, .76, .89, .73, -.29, and .35, respectively, environmental correlations were .15, .43, .05, .40, 1.03, .32, and -.10, respectively, and phenotypic correlations were .33, .32, .28, .46, .70, .00, and .07, respectively.

Animal model for genetic evaluation of multibreed data.

Extension of beef cattle genetic evaluation procedures to multibreed data sets is proposed as a way to allow inclusion of crossbred animals into current analyses and to provide comparisons between purebred animals of different breeds. Previous papers dealing with multibreed BLUP have proposed sire or sire-maternal grandsire models. Because current models used in the beef industry are predominantly of the reduced animal model form, models were developed for animal model and reduced animal model mixed-model evaluations that would account for fixed and random additive genetic effects, along with fixed and random nonadditive genetic effects for populations with heterogeneous means and variances.

Estimation of direct and maternal heritability and genetic correlation for backfat and growth rate in swine using data from centrally tested Yorkshire boars.

The purpose of this study was to estimate components of variance and covariance for backfat and growth rate in swine tested in central test stations in the United States. Data were collected from 26 central boar test stations from 1984 through 1990. The traits analyzed were backfat adjusted to a 104.5-kg basis and ADG adjusted to a 36-kg on-test weight. Records from 7,951 purebred Yorkshire boars were analyzed. Contemporary groups were defined as boars of a breed that were tested and sold as a common group in a test station. Variance components were estimated using a pseudo-expectation method with a multiple-trait, sire-maternal grandsire model. Direct heritabilities for backfat and ADG were estimated to be .56 and .24, respectively. Direct maternal effects were significant for both backfat and ADG; they accounted for 11 and 23% of the variance, respectively. The additive genetic correlation between backfat and ADG was approximately zero. Within this population of centrally tested Yorkshire boars, heritability seems to be high for backfat and moderate for ADG, with a significant maternal effect on each trait.

Comparison of real-time ultrasound and other live measures to carcass measures as predictors of beef cow energy stores.

Thirty-nine mature cows were divided into three condition groups on the basis of their subcutaneous fat thickness as determined by real-time ultrasound. A representative animal from each group was measured and slaughtered. The remaining cows with each group were stratified evenly into two groups with one group fed to gain weight and the other to lose weight. Several ultrasound and other live measures were taken every 4 wk and two animals per subgroup were randomly slaughtered. Carcass data were collected and one side of each carcass was boned, ground, mixed, and subsampled for fat and protein determination. Four regression equations were generated to predict percentage of fat (FAT), percentage of protein (PROT), total fat (TOTFAT), total protein (TOTPROT), total calories (CAL), CAL per live weight (CAL/WT), yield grade (YG), and marbling (MARB). The first equation used all live measures (SUB), the second equation used only objective live measures (OBJ), the third equation incorporated traditional live measures (EAS), and the fourth equation used only carcass data (CAR). Adjusted R-squares of the most appropriate equation using the SUB, OBJ, EAS, and CAR measurements were .82, .73, .82, and .82 for FAT; .82, .57, .61, and .66 for PROT; .89, .87, .86, and .85 for TOTFAT; .95, .95, .93, and .74 for TOTPROT; .93, .92, .91, and .90 for CAL; .83, .78, .83, and .82 for CAL/WT; .86, .86, .78, and .93 for YG; and .75, .70, .74, and .74 for MARB, respectively. It seems that condition score or ultrasound with other objective live measures is as accurate in predicting cow composition as carcass measures.

Evaluation of feed conversion in steers from a diallel of Simmental, Limousin, Polled Hereford, and Brahman beef cattle.

A total of 269 steers produced in a four-breed diallel mating design of Simmental, Limousin, Polled Hereford, and Brahman breeds were evaluated for the unadjusted and maintenance-adjusted total feed intake to total weight gain ratio. Time on feed ranged from 184 to 251 d. Covariate adjustments were made separately for age- and 12th rib fat-constant end points. Purebred, general combining ability, and maternal effects and heterosis were estimated. Effects of year, breed of dam, slaughter group, and days on feed accounted for most of the variation in feed conversion. Significantly higher unadjusted cumulative feed/gain ratios were found for steers from Brahman sires and for those from Simmental, Limousin, and Brahman dams. Adjustment to either fat- or age-constant values did not rerank breed groups, but a small reduction in the differences between these groups was detected for fat-constant efficiency. For maintenance-adjusted feed intake, progeny of Simmental and Limousin dams were less efficient than those of Polled Hereford and Brahman dams. Negative values for general combining ability, maternal effects, and heterosis would indicate less feed required per unit of weight gain. General combining ability for Polled Hereford crosses was negative and significant for cumulative feed/gain ratios, but no difference among dam breeds was found for the maintenance-adjusted ratio. Maternal effects for Limousin dams were positive and significant for all maintenance-adjusted ratios. Heterosis estimates for specific breed crosses were generally negative and ranged from -.87 to .22.

Genetic and environmental growth trait parameter estimates for Brahman and Brahman-derivative cattle.

Beefmaster, Brahman, Brangus, and Santa Gertrudis field data records were used to determine genetic and environmental parameter estimates using a multiple-trait, pseudo-expectation approach. Adjusted birth weight, 205-d weight, and postweaning gain records were analyzed for each breed. Also, Brangus weaning sheath and navel scores were both analyzed using a single-trait, pseudo-expectation method to determine genetic parameter estimates. Additive birth weight heritability (h2A) estimates ranged from .22 to .37 and maternal birth weight heritability (h2M) estimates ranged from .12 to .55. Estimates for 205-d weight h2A for the four breeds varied from .21 to .25, and 205-d weight h2M estimates ranged from .15 to .21. Postweaning gain h2A estimates ranged from .16 to .56. The genetic correlation between direct and maternal portions of birth weight was negative for all breeds. This was also true for the genetic correlation between direct and maternal portions of 205-d weight, except in Brahman cattle, for which it was .15. The genetic correlation between additive portions of birth weight and 205-d weight was large and positive in all breeds. A moderately positive correlation between 205-d weight and postweaning gain was found for all breeds except Santa Gertrudis, whereas the environmental correlation between these two traits was a small to moderately negative estimate in all breeds. Brangus weaning sheath and navel score heritabilities indicated that genetic change for the size and shape of the sheath and navel area is possible.

Estimates of genetic parameters for live animal ultrasound, actual carcass data, and growth traits in beef cattle.

Growth and carcass measurements were made on 2,411 Hereford steers slaughtered at a constant weight from a designed reference sire program involving 137 sires. A second data set consisted of ultrasound measures of backfat (USFAT) and longissimus muscle area (USREA) from 3,482 yearling Hereford cattle representing 441 sires. Restricted maximum likelihood procedures were used to estimate genetic parameters among carcass traits and live animal weight traits from these two separate data sets. Heritability estimates for the slaughter weight constant steer carcass backfat (FAT) and longissimus muscle area (REA) were .49 and .46, respectively. In addition, FAT had a negative genetic correlation with REA (-.37), weaning weight (-.28), and yearling weight (-.13) but positive with marbling (.19) and carcass weight (.36). Marbling was moderately heritable (.35) and highly correlated with total postweaning average daily gain (.54) and feedlot relative growth rate (.62). Heritability estimates for weight constant USFAT and USREA were .26 and .25, respectively. The genetic correlation between weight constant USFAT and USREA was positive (.39), indicating that in these young animals USFAT does not seem to be an indication of maturity. Mean USFAT measures and variability were small (.48 +/- .17 cm, n = 3,482). Results indicate that carcass fat on slaughter steers and ultrasound measures of backfat on young breeding animals may have different relationships with growth and muscling. These relationships need to be explored before wide scale selection based on ultrasound is implemented.

Age adjustment factors, heritabilities and genetic correlations for scrotal circumference and related growth traits in Hereford and Brangus bulls.

Field data records on 10,511 Hereford and 2,522 Brangus bulls between 330 and 430 d of age were analyzed to find age of calf and age of dam adjustment factors for yearling scrotal circumference. Age of calf adjustment factors were .024 cm/d for Hereford bulls and .041 cm/d for Brangus bulls. Sons of Hereford dams were adjusted to a 6- to 8-yr dam age basis by adding .7, .3, .2, .2 or .3 cm for dams 2, 3, 4, 5 or 8 or more years old, respectively. Age of dam adjustment factors for Brangus bulls were .8, .4, .3 and .2 for dams 2, 3, 4 or 8 or more years old, respectively. Variance and covariance components for yearling scrotal circumference and several growth traits were estimated within breed using multiple-trait models and pseudo expectations involving the solutions and the right-hand sides of the mixed-model equations. Additive heritability estimates for yearling scrotal circumference of .53 and .16 were found for Hereford and Brangus bulls, respectively. Maternal heritability estimates of .12 and .10 were found for Hereford and Brangus bulls, respectively. Genetic correlations between yearling scrotal circumference and other growth traits were positive for both sets of data indicating that selection for yearling scrotal circumference should not adversely affect other growth traits in either breed. Environmental correlation estimates between yearling scrotal circumference and adjusted birth weight and between yearling scrotal circumference and adjusted 205-d weight and adjusted 365-d height were positive and moderate in magnitude for both breeds.

Effect of preweaning nutritional management on yearling weight response in an open-herd selection program.

Records on 276 progeny were collected in the final 2 yr (1984 and 1985) of an 8-yr Hereford cattle selection project. Selection was practiced using the top sires from the American Hereford Association's National Cattle Evaluation based on yearling weight expected progeny difference. An unselected control line was maintained to monitor environmental change. One-half of each line was creep-fed during the preweaning period for the last 2 yr to evaluate genotype x environment interactions. Direct response to yearling weight selection averaged 28 +/- 8 kg. Correlated response to selection amounted to .057 +/- .028 kg/d in preweaning ADG, 14 +/- 6 kg in weaning weight, .085 +/- .033 kg/d in postweaning ADG, 4.6 +/- 1.5 cm in yearling hip height and 11.2 +/- 3.0 cm2 in yearling pelvic area. Yearling fat thickness and scrotal circumference were not significantly affected by selection. Significant effects of creep feeding were observed for yearling weight (15 +/- 3 kg), preweaning ADG (.067 +/- .012 kg/d), weaning weight (13 +/- 2 kg), yearling hip height (1.2 +/- .5 cm) and yearling fat thickness (.07 +/- .03 cm). Postweaning ADG, yearling pelvic area and yearling scrotal circumference were not affected by creep feeding. No significant genetic group x creep feeding effects were found for any of the traits analyzed, indicating calves genetically superior for growth did not gain any additional advantage from creep feeding.

Growth characteristics in crosses of Angus, Santa Gertrudis and Gelbvieh beef cattle.

A total of 343 calves (males and females) were evaluated for preweaning average daily gain, weaning weight (WW), feedlot average daily gain to slaughter (ADGF), slaughter weight (SW), pelvic height (PH), pelvic width, pelvic area, weaning conformation score (WS) and ratio of weaning weight to the dam's weight at weaning (R). Mating types included straight-bred Angus (A) and Santa Gertrudis (S), the reciprocal crosses of these two breeds and Gelbvieh (G) X Angus. Straightbred S and A X S crosses had the heaviest WW, followed by S X A and G X A crosses; straightbred A had significantly smaller WW than all other mating types. The crossbreds and the straightbred S had higher WS than straightbred A. The ratio of WW to cow weight was largest for S X A. The straightbred S and A X S crosses had significantly lower R values than the other mating types. Weaning weight per cow exposed, computed as the product of weaning rate and weight, indicated that straightbred A had an advantage over the other mating types (156.5 kg), whereas S and S X A were intermediate (147.9 and 147.6 kg, respectively) and A X S was lowest (128.9 kg). Feedlot gain was highest for A X S, though not significantly greater than for straightbred S or G X A. Straightbred A gained significantly less than other mating types except S X A. Straightbred A were found to be significantly smaller at slaughter than the other mating types. The S X A and G X A were intermediate; the straightbred S and A X S were significantly larger for SW.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of performance characteristics in a diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle. I. Growth, hip height and pelvic size.

Progeny of a diallel among Simmental, Limousin, Polled Hereford and Brahman breeds of cattle were evaluated over 5 yr for preweaning and postweaning growth, hip height and pelvic size. Calves from Brahman and Simmental dams had the highest preweaning gains and weaning weights, and those from Polled Hereford dams had the lowest (P less than .05). Differences in the availability of milk and postpartum compensatory gains in progeny of Brahman dams could have contributed to these results. However, calves from Simmental, Limousin and Polled Hereford dams had significantly greater feedlot daily gains than those from Brahman dams. Yearling hip height and pelvic area were lower for progeny of Polled Hereford dams, whereas calves from Simmental, Limousin and Brahman dams were not different for these traits. A series of linear comparisons among these four breeds using least-squares means to estimate general and specific combining ability and maternal effects found significant, negative maternal effects for Polled Hereford for preweaning gain and weaning weight. A positive maternal effect (P less than .05) for Limousin was found for feedlot gain. General combining ability and maternal estimates were significant and variable in most comparisons for yearling hip height and pelvic area. Heterosis estimates were positive and significant in all crosses with Brahman for preweaning gain, weaning weight, yearling weight, hip height and pelvic area. Significant, positive heterosis was also found in Polled Hereford crosses with Limousin and Simmental for preweaning gain, weaning weight and yearling weight.

Evaluation of performance characteristics in a diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle. II. Carcass traits.

Evaluations of steer and heifer progeny from a diallel mating design of Simmental, Limousin, Polled Hereford and Brahman beef cattle over 5 yr are presented. Traits evaluated included final weight, hot carcass weight, ribeye area, 12th rib fat thickness, marbling score, yield grade, dressing percentage and percentage of kidney, pelvic and heart fat. Progeny of Simmental sires were heavier at slaughter than those with Brahman sires (P less than .05), but no differences were found for carcass weight. Dressing percentage was higher for Limousin crosses compared with progeny of other sire breeds (P less than .05). Similar results were found for dam breeds, except that progeny of Limousin dams had heavier carcasses with a higher dressing percentage (P less than .05) than Brahman crosses. Crosses of Limousin and Simmental had larger ribeye areas (P less than .05) compared with calves of the other breeds. Progeny of Polled Hereford dams had higher marbling scores and were fatter than progeny of dams of other breeds (P less than .05). Heterosis estimates were significant for all Brahman crosses for final weight, carcass weight and ribeye area, but these contrasts were negligible for other traits. Estimates of general combining ability were positive and significant for Simmental for final weight, carcass weight, ribeye area and marbling score and were significant and negative for Limousin for final weight, fat thickness and yield grade. Maternal values were generally small.

A comparison of methods for ranking boars from different central test stations.

Data were received from 24 test stations on 3,999 boars tested in fall 1984 and spring 1985. In an effort to increase the connectedness between stations, one reference sire was selected to produce sons (reference boars) through artificial insemination to be tested in the different stations. Fifty-two reference boars were placed across 17 of the test stations. The performance traits analyzed were average daily gain (ADG) and backfat adjusted to 105 kg (ABF). The methods used to rank boars were: 1) individual record (ADG, ABF), 2) individual record deviated from the contemporary group mean, and 3/4) individual record plus performance of relatives (including/excluding reference boars) using expected progeny differences (EPD) estimated from a reduced animal model (RAM) statistical procedure. Ranks of boars using these four methods of genetic evaluation were compared using Spearman rank correlation methodology. The ranks of the boars changed significantly as the complexity of analysis increased for both ADG and ABF. Rank correlations between individual record and contemporary group deviations for ADG and BF were .47 and .20, respectively. Rank correlations between contemporary group deviations and RAM estimates of EPD for ADG and ABF were .53 and .41, respectively. These were significantly different from 1.0. However, there was no significant difference between rankings based on EPD including vs excluding the reference boars. The importance of rank changes coupled with the increased accuracy of these more complex evaluation methods strongly suggest that best linear unbiased predictors of genetic value be utilized in comparing boars in central test stations.