SOURCES OF GENETIC VARIATION IN BEEF CATTLE 1. Larry V. Cundiff. U.S. Department of Agriculture

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1 SOURCES OF GENETC VARATON N BEEF CATTLE 1 Larry V. Cundiff U.S. Department of Agriculture Agricultural Research Service Roman L. Hruska U.S. Meat Animal Research Center Clay Center, NE ntroduction Grading up or straightbreeding to Shorthorns, Herefords and Angus was the dominant system employed in beef production from the late 1800's until the 1960's in the United States. Although most cattlemen had their favorite breed, the adage that "there is more variation within breeds than between breeds" was generally accepted as a truism among beef cattle breeders throughout this period. As Lush (1945) pointed out, stockmen were misled by this attitude into believing that genetic differences between breeds were "not real after all" or at least not very important. Recognition of the importance of heterosis from diallel crossing experiments conducted in the 1960's and interest in increasing output components of beef production, stimulated interest in crossbreeding to breeds with greater genetic potential for milk production, growth rate and mature size. As a result, a large number of breeds, introduced from Europe via quarantine facilities in Canada, became available to North American beef producers. nterest in the newly introduced breeds and in other breeds previously considered only for dairying coincided with the establishment of the Roman L. Hruska U.S. Meat Animal Research Center (MARC) in the late 1960's. The Germ Plasm Evaluation (GPE) Program was initiated in 1969 at MARC to characterize a broad spectrum of breeds that differed widely in genetic potential for growth rate, milk production, carcass composition and mature size. The purpose of this paper is to review results from the GPE program concerning genetic variation among breeds relative to that within breeds for bioeconomic traits important to beef production. ipresented at the National Breeders Roundtable, Poultry Breeders of America, St. Louis, MO, May 5-6,

2 Procedure The GPE Program has been conducted in four cycles. Table i shows the mating plan for Cycles,, and V. Topcross performance of 26 differemt sire breeds have been, or are being, evaluated in calves out of Hereford and Angus dams or calves out of F cross dams. These F cross dams were bred to Brahman, Devon and Holstein sires in Cycle and to Santa Gertrudis and Brangus sires in Cycle. Semen from the same Hereford and Angus bulls has been used throughout to produce a control population of Hereford-Angus reciprocal crosses in each Cycle of the program. n addition to the repeated use of semen from control Hereford and Angus bulls, new samples of Hereford, Angus, and Charolais bulls born since 1982 are being added in Cycle V to evaluate genetic trends within these breeds. To date, complete data are available only from the first three cycles of the program. Thus, this review will only include data from twenty sire breeds involved in the first three cycles of the program. Data presented were pooled over Cycles, and by adding the average differences between Hereford-Angus reciprocal crosses (HAx) and other breed groups (2-way and 3-way F crosses) within each cycle to the average of Hereford-Angus reciprocal crosses (HAx) over the three cycles. Data will be presented for nineteen F crosses (2-way and 3-way) grouped into seven biological types based on relative differences (X lowest, XXXXXX highest) in growth rate and mature size, lean-to-fat ratio, age at puberty and milk production (Table 2). The breed group means presented in this review are from previous reports for birth and weaning traits (Cycle l-phase" 1-2, Smith et al., 1976b_ 11-2, Gregory et al., 1978, -3, Notter et al., 1978a,b_ 111-2, Gregory et al., 1979a; 11-3, Anonymous, 1977), postweaning growth and feed efficiency of steers (1-2, Smith et al., 1976a; 1-3, Young et al., 1978a; 11-2, Cundiff et al., 1981; 11-3 Anonymous, 1978; 111-2, Cundiff et al., 1984), carcass and meat traits (1-2, Koch et al., 1976, Koch and Dikeman, 1977; 1-3, Young et al., 1978b; 11-2, Koch et al., 1979, Koch et al., 1981; 11-3, Anonymous, 1978; 111-2, Koch et al., 1982b), postweaning growth and puberty characteristics of heifers (1-2, Laster et al., 1976_ 1-3, Young et al., 1978b; 11-2, Laster et al., 1979; 11-3, Anonymous, 1978: 111-2, Gregory et al., 1979b) and reproduction and maternal performance of F cows (Cundiff et al., 1986a). Mean differences between breeds will be expressed in actual units and in standard deviation units for breeding value (ag - aph, where 75

3 the phenotypic standard deviation, ap, and heritability, h 2, were computed from paternal half sib analyses of variance of data from the GPE program (Koch et al., 1982a; MacNeil et al., 1984_ Cundiff et al., 1986b). Calving traits Results for gestation length are summarized in Figure. Means for F crosses are shown on the lower horizontal axis for F crosses. The spacing on the vertical axis is arbitrary but the ranking of biological types (separate bars) from the bottom to top reflect, generally, increasing increments of mature size. Breed rankings within each biological type are noted within each bar. n Figure, differences are doubled in the upper horizontal scale to reflect variation among pure breeds relative to a standard deviation change in breeding value lag = (a2p)(h2)] within pure breeds. Frequency curves, shown for Holstein, the average of Hereford and Angus, and Sahiwal reflect the distribution expected for breeding values of individual animals within pure breeds assuming a normal distribution (i.e., 68, 95 or 99.6_ of the observations are expected to lie within the range bracketed by the mean ± i, 2 or 3 standard deviations, respectively). The range for mean differences between breeds is estimated to be about 6.6 ag between Holstein and Sahiwal breeds. Bos indicus sired F crosses had significantly longer gestation length than Bos taurus sired breed crosses. Among Bos taurus breed crosses, gestation length tended to increase as size increased, except for Holsteins which had relatively short gestation length for their relatively large size. Genetic variation, both between and within breeds is considerable for gestation length. Results for birth weight are shown in Figure 2. Birth weight means ranged from as low as 69 b for Jersey sired topcrosses to as high as 91 ib for Charolais and Maine Anjou sired topcrosses. After adjusting to a purebred basis, the range between breeds is about 6.9 ag. Jersey's had especially light birth weights. Red Poll, Hereford and Angus sired topcrosses were 3.7 ag lighter than Charolais and Maine Anjou crosses. n one analysis of calving traits involving Bo ss taurus breeds (Cundiff et al., 1986b), breeds (B - 1/4 Vb, genetic variance between breeds) and sires within breeds (S - 1/4 Vg, the genetic variance within breeds) were both treated as random effects. Estimates of B and S were comparable for gestation length (B - 3.1, S - 3.3), while B was greater than S (B - 7.3, S = 2.1) for birth weight. Estimates of total heritability [4(B+S)/(4B+S+W)] 76

4 indicated that gestation length (.77) and birth weight (.79) were both under a high degree of genetic control. Consideration of the range of differences between and within breeds leads to the same conclusion (Figures and 2). Unfortunately, breeds siring the heaviest calves at birth experience more calving difficulty than breeds siring calves with lighter birth weights (Figure 3). The association between calving difficulty and birth weight was greater in two- and three-year dams in Cycle than in cows four years of age or older (Figure 3) in Cycles, and of the GPE program. Calving difficulty was in turn associated with increased calf mortality (Laster and Gregory, 1973) and reduced rebreeding performance of dams (i.e., conception rate was 16_ lower in females assisted at parturition than in females that were not assisted, Laster et al., 1973). Feed Efficiency Feed efficiency from weaning to different slaughter endpoints are summarized in Figure 4. Feed efficiency (b TDN per ib live weight gain) was evaluated for replicated pens (2 pens per sire breed group per year). Thus, heritability could not be computed for individual steers and breed group differences are not shown in Og units. Steers sampled from each pen were slaughtered serially in 3 or 4 slaughter groups per year spaced at about 28 to 36 days between intervals. Linear and quadratic regression procedures were used to estimate changes in live weight, feed consumption and carcass composition associated with time on feed. These estimates were in turn used to adjust efficiency to different time, weight and carcass composition endpoints. Choice of interval of evaluation or endpoint greatly influenced rankings among breeds for feed efficiency from weaning to slaughter. Steers from faster gaining breed groups characterized by larger mature size were more efficient to time and especially to weight endpoints. The breed differences to a weight constant endpoint were especially large because fewer days and less total feed were required for maintenance of faster gaining breed groups compared to slower gaining breed groups. However, feed efficiency to a marbling endpoint corresponding to USDA choice quality grade was not favorably associated with size. Breed groups with the greatest propensity to deposit marbling in the fewest days tended to be most efficient to the grade endpoint. However, if differences in carcass composition are considered, the larger, leaner breed groups still produced more retail product per unit of feed cost than breed groups of smaller size even to a 77

5 grade constant endpoint (Smith, 1976). Carcass and Meat Characteristics Retail Product. Throughout the GPE program, we have obtained closely trimmed_boneless retail product, i.e., steaks and roasts (trimmed to.3 in of external fat and boneless except for the short loin and rib roasts) and lean trim (trimmed and processed into ground beef with 259 fat content based on chemical analysis) from the right side of each carcass. n the first three cycles of the program, these data were obtained at Kansas State University under the direction of Dr. Michael E. Dikeman. n Cycle V of the program these data are being obtained in our own laboratory, with Dr. Dikeman still collaborating to assure continuity with previous cycles of the program. Recently, in the GPE program we have obtained data on retail product with two levels of trim. After weights for closely trimmed retail product from each wholesale cut are recorded, retail cuts are trimmed to 0 in outside fat and made entirely boneless. The fat trim removed between the closely trimmed (.3 in) and zero trimmed (.0 in) accounted for 4.69 of the side weight of yield grade i cattle and from 5.3, 5.5 and 5.59 of the side weight of yield grades 2, 3 and 4 cattle, respectively (Crouse et al., 1988). Thus, there is a high degree of association between closely trimmed and zero trimmed retail product, especially in cattle of yield grades 2, 3 and 4. n this presentation, variation in growth and distribution of muscle will be assessed as reflected by variation in growth and distribution of closely trimmed retail product. Results for retail product growth to 458 days of age are summarized in Figure 5. Steers sired by bulls of breeds with large mature size produced significantly more retail product than steers sired by bulls of breeds with small mature size. The breeding value of the heaviest Jersey is not expected to equal that of the lightest Chianina and the heaviest Hereford and Angus would only equal the lightest Chianina in genetic potential for retail product growth to 458 days. The range for mean differences between breeds is estimated to be about 5.7 ag between Chianina and Hereford or Angus steers and about 8.2 ag between Chianina and Jersey steers. Genetic variation, both between and within breeds is considerable for this important measure of output. When both between and within breed genetic variation are considered, the range in breeding value from the smallest Jersey steers to the heaviest Chianina steers is estimated to be 180 kg, or 889 of the overall mean. About 78

6 half of the variation among breeds in retail product at 458 days of age is associated with variation in carcass weight and half is associated with composition or percentage of the carcass accounted for by retail product (Figureo6). Marbling. Degree of marbling (i.e., deposits of fat interspersed in muscle) in the twelfth rib cross-section of the rib eye muscle is currently the primary determinant of USDA quality grade among carcasses of cattle of the same age. Traditionally, marbling has been emphasized because it was believed to be associated with palatability characteristics of meat. Some studies have shown a positive relationship between marbling and palatability characteristics, especially sensory panel ratings for tenderness or Warner-Bratzler shear force, while others have shown a very low or nonexistent relationship (Smith et al., 1984). Significant genetic variation exists between and within breeds for propensity to deposit marbling (Figure 7). Again, the range for differences between breeds is about equal to the range for breeding value of individual animals within breeds for marbling. Within breeds, variation in marbling was highly heritable (.40). However, it is much easier to use information on variation among breeds than within breeds for marbling because of the difficulty of measuring marbling levels in live bulls and heifers used for breeding. Also, heritability of breed differences is high (approximately 100P), provided the breed means are estimated with an adequate sample to average out errors of sampling individual animals within breeds. The tendency for progeny from individual animals to regress to their own breed group mean is much greater than any tendency to regress to the mean of all cattle. Unfortunately, breeds that rank highest for retail product percentage rank lowest for marbling (Figure 8). Similarly, high negative genetic correlations have been found within breeds between marbling and retail product percentage. Thus, only limited opportunity exists from between breed selection or from within breed selection for genetically increasing marbling without increasing fat trim and reducing retail product percentage. This antagonistic relationship between retail product percentage and marbling, or between USDA yield grade and USDA quality grade has deterred the substitution of breeds to those that excel in leanness and yield grade from those with lower yield grades but higher USDA quality grades. 79

7 Marbling and Palatability. Concern with the antagonism between marbling and retail product percentage is justified to the extent that a certain amount of marbling is required to ensure palatability of the retail product. Sensory, panel evaluations of uniformly cooked loth rib steaks from about 1,230 steers produced in the GPE program are summarized in Table 3. High levels of acceptance were found for steaks from all Bos taurus breed groups when the steers were fed and managed alike and slaughtered at 14 to 16 months of age. n these studies, sensory scores were assigned on a 9 point scale from i - extremely undesirable (e.g., extremely tough), 5 - acceptable, up to 9 - extremely desirable (e.g., extremely tender). Average taste panel scores and Warner-Bratzler shear determinations for tenderness did tend to improve as marbling increased when comparisons were at the same age, but the change was very small. Although, breed groups differed significantly in average marbling scores and in percentage of carcasses that had adequate marbling to grade USDA Choice or better, average sensory panel evaluations of tenderness, flavor and juiciness were acceptable for all breed groups. However, variation in sensory panel tenderness scores (see standard deviations, Table 4) tends to be greater in cattle with low levels of marbling than in cattle with high levels of marbling (Koch et al., 1988). This in turn leads to greater risk of at least some steaks having less than acceptable tenderness at low levels of marbling. n Bos taurus sired cattle with a slight degree of marbling (USDA Select), 39 of the steaks were scored as less than acceptable (sensory panel scores of <5) in tenderness. n Bos taurus sired cattle with moderate or greater degrees of marbling (USDA high Choice or Prime), 09 of the steaks were scored as less than acceptable (i.e., 1009 had scores _ 5). Sensory panel scores for steaks from Bos indicus sired steers were lower for tenderness than those from Bos taurus sired steers, even at the same degree of marbling. Caloric Density of Retail Product. Dairy processors have developed and effectively marketed products with a similar range in caloric content to that found between Chianina and Jersey steers. Low fat milk (29 fat content) contains 209 fewer calories per one cup serving than regular milk (3.59 fat content). Similar ranges can be achieved in beef products by fabrication and marketing of totally-trimmed retail cuts. The key to production of low calorie beef products is total trimming. Fat contains 225 calories per ounce. Caloric content of totally-trimmed beef varies depending on the level 80

8 of intramuscular fat (marbling) in the lean. Composition and estimates of caloric content in oz portions of uncooked longissimus (rib eye) muscle with different USDA quality grades and degrees of marbling are shown in Table 5. Muscle with a slight degree of marbling (USDA Select quality grade, formerly USDA Good) is about 3.7_ fat and contains about 40 kcal per ounce. Muscle from carcasses grading USDA Choice range from about 4.7 to 9.3_ fat and contain about 43 to 51 kcal per ounce. Muscle from carcasses in the USDA Prime grade range from about 9.2 to fat and contain 52 to 60 kcal per oz. Breed group means for calories originating from the lean, intra-muscular fat, and inter-muscular fat components of 00 gram (3.5 oz) uncooked portions of retail product are presented in Table 6 (Cundiff, 1986). External and inter-muscular fat (averaging 20.6_ over all breeds) accounted for a much greater proportion of total fat in the retail product than intra-muscular (i.e., marbling) fat (averaging 4.0_). Variation among breeds was important for both percentage of external and intra-muscular fat (range 2.6 percentage units) and for percentage of inter-muscular fat (range of 3.2_). On the average, a i00 gram portion of uncooked retail product containing a total of 280 kcal, would have 83 kcal originate from protein (29.7_), 34 kcal originate from intra-muscular fat (12.2_) and 163 kcal originate from external and inter-muscular fat (58.3_). Caloric content of retail product is markedly reduced by total trimming of visible fat. Total trimming will obviously favor production of carcasses with a higher percentage of retail product and less fat trim. Caloric content of totally-trimmed portions (lean and intra-muscular fat only) contained an average of 117 kcal. For totally-trimmed retail product, the range among F breed groups was 14 kcal (ii for Chianina crosses to 125 kcal for Jersey crosses). Since topcross comparisons estimate only half of the difference between breeds, estimates of the range between F crosses can be doubled to estimate the range between pure breeds--28 kcal or from about 99 kcal for Chianina to 127 kcal for Jersey steers. Significant opportunity exits to breed and produce cattle which will provide for two types of beef: i) lean beef that is low in fat and caloric content more suited to customers seeking to limit dietary intake of saturated fats, and 2) highly marbled beef that is well suited to the gourmet food trade where customers are more concerned about the risk of serving or 81

9 consuming an occasional steak with less than acceptable tenderness than they are about the risk of consuming too much fat. Reproduction and Maternal Traits n each cycle, all F cross produced were retained to evaluate age and weight at puberty and reproduction and maternal performance through 7 or 8 years of age. The females were produced in the spring, weaned at about seven months of age, developed in a drylot during their first winter, and placed on improved pasture at about 13 months of age. They were maintained on improved pastures until their evaluation of reproduction and maternal performance was completed at 7 or 8 years of age. Supplementary grass hay and alfalfa hay was provided (about i to 13 kg/cow daily) during the winter months. The females were bred to produce terminal cross calves by unrelated sire breeds in the spring (March and April). Age and WeiEht at Puberty. Genetic variation among breeds relative to that within breeds for age and weight at puberty is shown in Figures 9 and i0, respectively (Cundiff et al., 1986a). Heifers sired by bulls of breeds with large mature size (e.g., Charolais, Chianina) tended to be older and heavier at puberty than heifers sired by bulls of breeds with smaller mature size (Hereford, Angus). However, the relationship between mature size and age at puberty can be offset by associations with milk production. Breeds which have been selected for milk production appear to reach puberty earlier than breeds of similar mature size and retail product that do not have a history of selection for milk production (e.g., Simmental, Holstein, Brown Swiss, and Gelbvieh versus Charolais and Chianina). Also, it appears that the Bos indicus breeds (Brahman and Sahiwal), which exceeded all other breeds in age at puberty, have been subjected to selection pressures that set them apart from Bos taurus breeds in age at which they exhibit their first estrus. The range between Bos taurus breeds of 6.3 ag forage at puberty and 7.0 ag for weight at puberty exceeded that expected for breeding value of individuals within breeds (6 ag). The breeding value of the oldest (or heaviest) Jersey is not expected to equal that of the youngest (or lightest) Charolais (or Chianina or Limousin) in age (or weight) at puberty. Both between and within breed sources of genetic variation were large and important for age or weight at puberty. Although age at puberty differed significantly among breeds, conception rate in yearling heifers did not differ consistently between breed groups 82

10 reaching puberty at the oldest ages from those breed groups reaching puberty at the youngest ages (Laster et al., 1976; Young et al., 1978b; Laster et al., 1979; Gregory et al., 1979a). For example, conception rate of Brahman and Sah_wal cross heifers was very high in spite of their older age at puberty. The heifers in all breed groups were grown and developed under dry lot conditions on a moderately high energy diet (about 2.2 Mcal ME per kg) and conception rate was not limited by variation observed among breed groups in age at puberty. t has been shown that heifers developed more slowly on diets with lower energy density, exhibit puberty at significantly older ages and have lower conception rates than heifers developed more rapidly when exposed to breeding as yearlings (Wiltbank et al., 1966, 1969; Ferrell, 1982). Reproduction. Breed group means for calf weaned expressed as a percentage of cows exposed to breeding are summarized in Figure ii. Heritability of calf crop weaned is known to be very low; however, differences between breeds are not expressed in standard deviations because reproduction rate has a binomial distribution rather than a normal distribution. Only the most extreme differences in calf crop percentage born and weaned are statistically significant (about 4_ for comparisons in the same cycle and 6.0_ for comparisons in different cycles). The F cows by Bos taurus breeds of large size and low genetic potential for milk production (Charolais, Chianina, Limousin), large size and high genetic potential for milk production (Brown Swiss, Gelbvieh, Holstein, Simmental and Maine Anjou), moderate size and low to moderate genetic potential for milk production (Hereford-Angus, Red Poll, Devon), small size and high genetic potential for milk production (Jersey), and moderately large and moderately high genetic potential for milk production (South Devon, Tarentaise, Pinzgauer) did not differ significantly from each other in calf crop percentage born or weaned. Results from other experiments have indicated that if added nutrient requirements of cows of large size and higher milk production potential are not met, the intervals from calving to first estrus increase and conception rates decline (e.g., Deutscher and _iteman, 1971; Kropp et al., 1973; Holloway et al., 1975a). The F cows in each cycle of the program have been run together on one feeding regime. The relatively high reproduction rate even for biological types with large size and high milk production potential indicates that the nutritional regime provided at MARC has been 83

11 adequate to meet requirements for growth, maintenance, and lactation, even of the most productive groups. Milk Production. Breed group means for milk production (mean of three estimates based on calf weights before and after nursing obtained on a sample of 18 cows per breed group at 3 and 4 years of age) are shown in Figure 12 (Cundiff et al., 1986a). Among Bos taurus sired F cows, breeds which have a history of selection for milk production (Jersey's excelled in milk production, followed by Simmental, Gelbvieh, and Brown Swiss, then by Tarentaise, Pinzgauer and Red Poll) produced higher levels of milk than breeds which do not have a history of selection for milk production (Charolais, Limousin, Chianina and Hereford-Angus). Maine Anjou F cows produced relatively low levels of milk considering their history of selection for milk production. When breed group differences are doubled in the upper horizontal scale to reflect variation among pure breeds relative to a standard deviation change in breeding value within pure breeds, indications are that additive genetic variation between breeds is about equal to that within breeds for milk production. Weaning Weight. Breed group means for weaning weight per calf weaned are summarized in Figure 13. The range in differences between F cow means for weaning weight per calf weaned (Devon to Holstein) was about 2.2 ag (Cundiff et al., 1986a). n Figure 13, differences between F cross means (i/4g + /2g M) are adjusted to a purebred basis (gl + gm). On a purebred basis, the range in differences between breeds (5.3 ag) is nearly as great as that expected among individuals within breeds (6 ag). Results for weaning weight per calf weaned show strong associations with estimates of milk production (Figure 12) and with genetic potential for growth of the F cows. Weaning weight per calf weaned for F cows by sire breeds of large size and low genetic potential for milk production (Charolais and Chianina) exceeded that for F cows by sire breeds of moderate size and low genetic potential for milk production (Hereford-Angus and Devon), but not by as much as F cows by sire breeds of large size and high genetic potential for milk production (Brown Swiss, Gelbvieh, Holstein, and Simmental). Weaning weight per calf weaned for F cows by sire breeds of large size and low genetic potential for milk production (Charolais and Chianina) were comparable to that for F cows by sire breeds of moderately large size and moderately high genetic potential for milk production (South Devon, Tarentaise, 84

12 Pinzgauer). Breed group means for weaning weight per cow exposed to breeding are also summarized in Figure 14. n general, rankings for weaning weight per cow exposed, to breeding correspond closely to those for weaning weight per calf weaned. Output was greatest for Zebu (Brahman and Sahiwal) and large size dual purpose breeds (Gelbvieh, Brown Swiss, Maine Anjou and Simmental). Output of dual purpose breeds with intermediate size (Pinzgauer, Tarentaise and South Devon) was intermediate to that of Hereford-Angus F crosses and larger-higher milking dual purpose breeds (Gelbvieh, Brown Swiss, Maine Anjou and Simmental). Output of Limousin and Charolais cross cows was similar to that of Hereford and Angus crosses. Extra growth rate of progeny out of Charolais cross cows was offset by a relatively higher calf crop percentage weaned for Hereford-Angus cross cows (Figure i). Output of Chianina crosses was high relative to Hereford-Angus, Limousin and Charolais crosses due to relatively high calf crop percentages and weaning weight. Output of Jersey crosses exceeded that of Hereford-Angus crosses by about 4 percent reflecting higher milk production. The higher milk production of Red Poll crosses and weaning weights of progeny out of Red Poll F cross cows was offset by a lower calf crop weaned, so that differences between Red Poll and Hereford-Angus F cross cows were small for 200-day weight per cow exposed. Cow Weight. Breed group means for cow weights at 7 years of age are Shown in Figure 15. Mean weights of F cows by sire breeds of large size and low genetic potential for milk (Charolais and Chianina) exceed those of F cows by sire breeds of large size and high milk production (Brown Swiss, Gelbvieh, Holstein, and Simmental). Results for condition scores indicated that at least part of this difference in weight was accounted for by differences in fatness of the cows. Mean weights of F cows by sire breeds of large size and high genetic potential for milk production (Brown Swiss, Gelbvieh, Holstein, Simmental) were higher than those of F cows by sire breeds of moderate size and low genetic potential for milk production (Hereford-Angus and Devon). The variation among and within breeds in mature weight is vast and highly heritable (Cundiff et al., 1986a). f the range of differences between F crosses is doubled to reflect differences between breeds (8.1 ag), the range is somewhat greater than that expected for breeding value of individuals within breeds (6 ag). n any given environment the mature weight of cows can 85

13 be determined with reasonable precision by the breeds chosen and by the breeding value of individuals used within breeds for growth rate and mature size. The question becomes, what is the optimum mature weight for any given environment? Heavier cow weight increases output per head from the production system when cows are sold; however, heavier cow weight also increases nutrient requirements per head for maintenance of the cow herd. Ferrell and Jenkins (1984) have estimated daily maintenance requirements of 130, 129, 145, and 160 kcal/kg "75 for mature Angus or Hereford, Charolais, Jersey, and Simmental sired F cows out of Hereford and Angus dams. Thus, increases in output associated with increased size tend to be offset by increases in feed requirements for maintenance, so that differences in efficiency are small (Marshall et al., 1976; Bowden, 1980; Cundiff et al., 1983; Jenkins and Ferrell, 1983). ncreases in output of progeny weight associated with increasing increments of milk production of dams appear to be more than offset by increased feed requirements for lactation (Holloway et al., 1975b; Cundiff et al., 1983; Jenkins and Ferrell, 1983). The key to efficient production is synchronizing the genetic potential for mature weight and milk production with the feed resources which can be provided most economically. Conclusions The variation that exists in biological traits of economic importance to beef production, including carcass leanness, is vast and under a high degree of genetic control. The range for differences between breeds was comparable in magnitude to the range for breeding value of individuals within breeds for most bioeconomic traits important to beef production. Thus, significant genetic change can result from 'selection both between and within breeds. Between breed differences are more easily exploited than genetic variation within breeds because they are more highly heritable. Also, use of genetic variation within breeds is often complicated by difficulties of measurement for characteristics such as carcass and meat traits, age at puberty, and milk production. Breeds can be selected to optimize performance levels for important bioeconomic traits with a high level of precision much more quickly than intrapopulation selection. However, breeds that excel in output should not necessarily be substituted for breeds with less genetic potential because of trade-offs resulting from antagonistic relationships among traits. Breeds (and sires) 86

14 that excel in retail product growth potential also: i) sire progeny with heavier birth weights and increased calving difficulty; 2) produce carcasses with lower marbling but very acceptable meat tenderness; 3) tend to reach pubertyoat an older age; and 4) generally have heavier mature weight. Heavier mature weight increases output per cow, but also increases nutrient requirements for maintenance. Thus, differences in output tend to be offset by input differences for maintenance and lactation so that differences in life cycle efficiency are generally small. Because of trade-offs resulting from antagonistic genetic relationships among breeds, it is not possible for any one breed to excel in all characteristics of economic importance to beef production. Nor is it possible to expect simultaneous improvemen_ in all characteristics from intrapopulation selection since similar relationships exist within breeds. Use of crossbreeding systems that exploit complementarity by terminal crossing of sire breeds noted for lean tissue growth efficiency with crossbred cows of small to medium size and optimum milk production provide the most effective means of managing trade-offs that result from genetic antagonisms. Progeny produced by terminal sire breeds which excel in genetic potential for retail product growth potential produce carcasses with lower levels of marbling and totally-trimmed retail cuts with lower fat and caloric content. Terminal crosses are especially well suited for marketing opportunities for low fat or low caloric beef with acceptable palatability characteristics. Maternal breeds mated to provide female replacements can be selected to optimize milk production and size in the cow herd. f marbling is also considered in selection of maternal breeds, the steers produced from matings required to produce female replacements can be well suited to marketing opportunities for the gourmet food trade where the risk of occasional steaks with unacceptable tenderness must be minimized. References Anonymous Germ Plasm Evaluation Program Progress Report No. 5. U.S. Meat Animal Research Center, Agr. Res. Serv., U.S. Dept. of Agr., ARS-NC-55. Anonymous Germ Plasm Evaluation Program Progress Report No. 6. U.S. Meat Animal Research Center, Agr. Res. Serv., U.S. Dept. of Agr., ARM-NC-2. Bowden, D. M Feed utilization for calf production in the first lactation by 2-year-old F crossbred beef cows. J. Anim. Sci. 51: Campion, D. R., Crouse, J. D. and Dikeman, M. E Predictive value of USDA quality grade factors for cooked meat palatability. J. Food Sci. 87

15 40: Grouse, J. D., Cundiff, L. V., Koch, R. M. and Dikeman, M. E Closely vs. totally trimmed retail product yields of carcass beef. J. Anim. Sci. 67(Suppl. i). (Abstract in press.) Cundiff, L. V The effect of future demand on production programs biological versus product antagonisms. Proceedings Beef mprovement Federation. Department of Animal Science, North Carolina State University, Box 7621 Raleigh, NC pp Cundiff, L. V., Ferrell, C. L. and Jenkins, T. G Output/input differences among F cows of diverse biological type. J. Anim. Sci. 57(Suppl. i):148. (Abstr.) Cundiff, L. V., Gregory, K. E., Koch, R. M. and Dickerson, G. E. 1986a. Genetic diversity among cattle breeds and its use to increase beef production efficiency in a temperate environment. Proc. 3rd World Congr. on Genet. Appl. to Livestock Prod. Lincoln, NE, USA. X: Cundiff, L. V., MacNeil, M. D., Gregory, K. E. and Koch, R. M. 1986b. Between and wlthin-breed genetic analysis of calving traits and survival to weaning in beef cattle. J. Anim. Sci. 63: Cundiff, L. V., Koch, R. M., and Gregory, K. E Characterization of biological types of cattle. (Cycle ) V. Postweaning growth and feed efficiency. J. Anim. Sci. 58: Cundiff, L. V., Koch, R. M., Gregory, K. E. and Smith, G. M Characterization of biological types of cattle. (Cycle ) V. Postweaning growth and feed efficiency of steers. J. Anim. Sci. 53: Deutscher, G. H. and Whiteman, J. V Productivity as two-year-olds of Angus-Holstein crossbreds compared to Angus heifers under range conditions. J. Anim. Sci. 33: Ferrell, C. L Effects of postweaning rate of growth on onset of puberty and productive performance of heifers of different breeds. J. Anim. Sci. 55: Ferrell, C. L. and Jenkins, T. G Energy utilization by mature, nonpregnant, nonlactating cows. J. Anim. Sci. 58: Ganong, W. F Review of Medical Physiology, 8th ed. Lange Medical Publications, Los Altos, CA. pp Gregory, K. E., Cundiff, L. V., Smith, G. M., Laster, D. B. and Fitzhugh_ H. A. Jr Characterization of biological types of cattle - Cycle :. Birth and weaning traits. J. Anim. Sei. 47:1022-i033. Gregory, K. E., Laster, D. B., Cundiff, L. V., Smith, G. M. and Koch, R. M. 1979a. Characterization of biological types of cattle - Cycle :. Growth rate and puberty in heifers. J. Anim. Sci. 49: Gregory, K. E., Smith, G. M., Cundiff, L. V., Koch, R. M. and Laster, D. B. 1979b. Characterization of biological types of cattle Cycle :. Birth and weaning traits. J. Anim. Sci. 48: Holloway, J. W., Stephens, D. F., Whiteman, J. V. and Totusek, R. 1975a. Performance of three-year-old Hereford, Hereford x Holstein and Holstein cows on range and in drylot. J. Anim. Sci. 40: Holloway, J. W., Stephens, D. F., Whiteman, J. V. and Totusek, R. 1975b. Efficiency of production of 2- and 3-year-old Hereford, Hereford x Holstein and Holstein cows. J. Anim. Sci. 41: Jenkins, Z. G. and Ferrell, C. L Estimated production efficiencies of crossbred cows. J. Anim. Sci. 57(Suppl. 1):154. (Abstr.) Koch, R. M., Crouse, J. D., Dikeman, M. E., Cundiff, L. V. and Gregory, K. E Effects of marbling on sensory panel tenderness in Bos taurus 88

16 and bo ss ndicus crosses. J. Anim. Sci. 67(Suppl. i). (Abstract in press.) Koch, R. M., Cundiff, L. V. and Gregory, K. E. 1982a. Heritabilities and genetic, environmental and phenotypic correlations of carcass traits in a population of diverse biological types and their implications in selection programs. J. Anim. Sci. 55: Koch, R. M. and Dikeman, M. E Characterization of biological types of cattle. V. Carcass wholesale cut composition. J. Anim. Sci. 45: Koch, R. M., Dikeman, M. E., Allen, D. M., May, M., Crouse, J. D. and Campion, D. R Characterization of biological traits of cattle. ll. Carcass composition, quality and palatability. J. Anim. Sci. 43: Koch, R. M., Dikeman, M. E. and Crouse, J. D. 1982b. Characterization of biological types of cattle (Cycle ).. Carcass composition, quality and palatability. J. Anim. Sci. 54: Koch, R. M., Dikeman, M. E. and Cundiff, L. V Characterization of biological types of cattle. V. Carcass wholesale cut composition. J. Anim. Sci. 53: Koch, R. M., Dikeman, M. E., Lipsey, R. J., Allen, D. M. and Crouse, J. D Characterization of biological types of cattle Cycle :. Carcass composition, quality and palatability. J. Anim. Sci. 49: Kropp, J. R., Stephens, D. F., Holloway, J. W., Whiteman, J. V., Knori, L. and Totusek, R Performance on range and in drylot of two-year-old Hereford, Hereford x Holstein and Holstein females as influenced by level of winter supplementation. J. Anim. Sci. 37: Laster, D. B., Glimp, H. A., Cundiff, L. V. and Gregory, K. E Factors affecting dystocia and effects of dystocia on subsequent reproduction in beef cattle. J. Anim. Sci. 36: Laster, D. B. and Gregory, K. E Factors affecting dystocia and effects of dystocia on subsequent reproduction in beef cattle. J. Anim. Sci. 37: Laster, D. B., Smith, G. M., Cundiff, L. V. and Gregory, K. E Characterization of biological types of cattle (Cycle ).. Postweaning growth and puberty of heifers. J. Anim. Sci. 48: Laster, D. B., Smith, G. M. and Gregory, K. E Characterization of biological types of cattle. V. Postweaning growth and puberty of heifers. J. Anim. Sci. 43: Lush, J. L Animal Breeding Plans. owa State University Press. Marshall, D. W., Parker W. R. and Dinkel, C. A Factors affecting efficiency to weaning in Angus, Charolais and reciprocal cross cows. J. Anim. Sci. 43: NAS Body Composition in Animals and Man. National Academy of Sciences, Publ Washington D.C. p. 23. Notter, D. R., Cundiff, L. V., Smith, G. M., Laster, D. B. and Gregory, K. E. 1978a. Characterization of biological types of cattle. V. Transmitted and maternal effects on birth and survival traits in progeny of young cows. J. Anim. Sci. 46: Notter, D. R., Cundiff, L. V., Smith, G. M., Laster, D. B. and Gregory, K. E. 1978b. Characterization of biological types of cattle. V. Milk production in young cows and transmitted and maternal effects on preweaning growth of progeny. J. Anim. Sci. 46: MacNeil. M. D., Cundiff, L. V., Dinkel, C. A. and Koch, R. M Genetic 89

17 correlations among sex limited traits in beef cattle. J. Anim. Sci. 58: Smith, G. C., Carpenter, Z. L., Cross, H. R., Murphey, C. E., Abraham, H. C., Savell, J. W., Davis, G. W., Berry, B. W. and Parrish, F. C. Jr Relationship of USDA marbling groups to palatability of cooked beef. J. Food Qual. 7: Smith, G_ M Sire breed effects on economic efficiency of a terminal-cross beef production system. J. Anim. Sci. 43: Smith, G. M., Laster, D. B., Cundiff, L. V. and Gregory, K. E. 1976a. Characterization of biological types of cattle.. Postweaning growth and feed efficsency of steers. J. Anim. Sci. 43: Smith, G. M., Laster, D. B., and Gregory, K. E. 1976b. Characterization of biological types of cattle.. Dystocia and preweaning growth. J. Anim. Sci. 43: Wiltbank, J. N., Gregory, K. E., Swiger, L. A., ngalls, J. E., Rothlisberger, J. A. and Koch, R. M Effects of heterosis on age and weight at puberty in beef heifers. J. Anim. Sci. 25: Wiltbank, J. N., Kasson, C. W. and ngalls, J. E Puberty in crossbred and straightbred beef heifers on two levels of feed. J. Anim. Sci. 29: Young, L. D., Cundiff, L. V., Crouse, J. D., Smith, G. M. and Gregory, K. E. 1978a. Characterization of biological types of cattle. X. Postweaning growth and carcass traits of three-way cross steers. J. Anim. Sci. 46: Young, L. D., Laster, D. B., Cundiff, L. V., Smith, G. M. and Gregory, K. E. 1978b. Characterization of biological types of cattle. X. Postweaning growth and puberty of three-breed heifers. J. Anim. Sci. 47:

18 TABLE i. SRE BREEDS USED N GERM PLASM EVALUATON PROGRAM Cycle Cycle Cycle Cycle V ( ) ( ) ( ) ( ) F crosses from Hereford or Angus dams (Phase 2) Hereford Hereford Hereford Hereford a Angus Angus Angus Angus a Jersey Red Poll Brahman Longhorn S. Devon Brown Swiss Sahiwal Salers Limousin Gelbvieh Pinzgauer Galloway Simmental Maine Anjou Tarentaise Nellore Charolais Chianina Shorthorn Piedmontese Charolais Gelbvieh Hereford 3-way crosses out of F dams (Phase 3) Hereford Angus Angus Brahman Brangus Devon Santa Gertrudis Holstein Pinzgauer ahereford and Angus sires, originally sampled in 1969, 1970 and 1971, have been used throughout the program. n Cycle V, a new sample of Hereford and Angus sires produced after 1982 are being used and compared to the original Hereford and Angus sires. 91

19 TABLE 2. BREED CROSSES GROUPED NTO SX BOLOGCAL TYPES ON THE BASS OF FOUR MAJOR CRTERA a Growth Lean rate & to Age mature fat at Milk Breed group size ratio puberty production Jersey (J) X X X XXXXX Hereford-Angus (HA) XX XX XXX XX Red Poll (R) XX XX XX XXX Devon (D) XX XX XXX XX South Devon (Sd) XXX XXX XX XXX Tarentaise (T) XXX XXX XX XXX Pinzgauer (P) XXX XXX XX XXX Brangus (Bn) XXX XX XXXX XX Santa Gert. (Sg) XXX XX XXXX XX Sahiwal (Sw) XX XXX XXXXX XXX Brahman (Bm) XXXX XXX XXXXX XXX Brown Swiss (B) XXXX XXX_X XX XXXX Gelbvieh (G) XXXX XXXX XX XXXX Holstein (Ho) XXXX XXXX XX XXXXX Simmental (S) XXXXX XYOtX XXX XXXX Maine Anjou (M) XXXXX _XXX XXX XXX Limousin (L) XXX XXXXX XXXX X Charolais (C) XXXXX XXXXX XXXX X Chianina (Ci) XXXXX XXXXX XXXX X alncreasing number of X's indicate relatively higher values. 92

20 TABLE 3. BREED GROUP MEANS FOR FACTORS DENTFED WTH MEAT QUALTY Warner- Sensory panel scores c Percent USDA Bratz_er shear v Breed group Marbling a choice (b) Tenderness Flavor Juiciness Chianina-X Limousin-X Brahman-X Gelbvieh-X Sahiwal-X Simmental-X Maine-Anjou-X i0.i Tarentaise-X Charolais X Brown Swiss-X Pinzgauer-X South Devon-X Hereford-Angus-X Red Pol-X Jersey-X amarbling: 8 - slight, ii = small, 14 = modest, 17 - moderate. bshear force required for a in core of cooked steak. CTaste panel scores: 2 = undesirable, 5 = acceptable, 7 m moderately desirable, 9 = extremely desirable. 93

21 94

22 TABLE 5. COMPOSTON AND CALORC CONTENT OF L. DORS (RB EYE) MUSCLE WTH DFFERENT DEGREES OF MARBLNG (i OZ UNCOOKED PORTON) Chem. Fat a Protein b Quality Total grade Marbling % kcal % kcal kcal Fat free Standard Practically devoid Standard Traces Select Slight Choice Small Choice Modest Choice Moderate Prime Slightly abundant Prime Moderately abundant Prime Abundant achemical fat, % (M) where M = 5 for traces, 8 for slight,... and 17 for moderate degrees of marbling (Campion et al., 1975) and fat contains 9.3 kcal per gram (Ganong, 1977). blean is 27% protein (NAS, 1967) and protein contains 4.1 kcal per gram (Ganong, 1977). 95

23 TABLE 6. BREED GROUP (F CROSS) MEANS FOR CALORC CONTENT OF RETAL PRODUCT, i00 g (3.5 OZ) UNCOOKED PORTON (Cundiff, 1986) Lean ntra- nter- Lean & intraprotein muscular muscular Total muscular fat Breed group kcal fat, kcal fat, kcal kcal only, kcal Jersey-X Hereford-Angus-X Red Pol X South Devon-X Tarentaise-X Pinzgauer-X Sahiwal-X Brahman-X Brown Swiss-X Gelbvieh-X Simmental-X Maine Anjou-X A Limousin-X i Charolais-X Chianina-X iii Range (R)

24 VARATON BETWEEN AND WTHN BREEDS Ho HA Sw , HO BM G S t,,,a B. Sg L---LJ PSdT 8m Sw J GESTATON LENGTH, DAYS Figure 1. Breed group means (lower axis) and genetic variation between and within breeds (upper axis) for gestation length (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. VARATON BETWEEN AND WTHN BREEDS le trg _ $.7r9 --u--el "BG S M TS4 P RHAO J 40 _ BRTH WEGHToLB Figure 2. Breed group means (lower axis) and genetic variation between and within breeds (upper axis) for birth weight (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. 97

25 22 MA le C 16 Si E e 6 2 J HA 4 R T s O OF,, n t a n n ' n t Kg _ BRTH WEGHT(Kg) Figure 3. Breed of sire means for calving difficulty versus birth weight for Hereford and Angus females calving at 4 years of age or older (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. TON/UNT OF GAN N OFFERENT NTERVALS OF' EVALUATON [KS _ n., CLG C 0 L C L C_ MA in n-r-! T G 8S,S MAG 8S S MAS; P D r----! r- B'Sa 8r Sa Sa _ SO T SOP T SOP T [ G r----- '_ R HA R,M, R J J J CONSTANT V_GHT OONSTAK" A_B.JNG CONSTANT Figure 4. TDN/unit gain in different intervals of evaluation (adapted from Cundlff et al., 1986a). See Table 2 for abbreviations. 98

26 VARATONBETWEEN AND WTHN BREEDS J HA Ci _2.Scrg - %": 5.7 rg _% , P _T Rp DHA _ RETAL PRODUCT WEGHT, 458 DAYS(LB) Figure 5. Breed group means (lower axis) and genetic variation between and within breeds (upper axis) for weight of retail product at 458 days (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. VARATON BETWEEN AND WTHN BREEDS J HA Ci Y.6-_ 5.2 _ N J B GMHoS L-J Sw Bm Be S9, e lar 0 Sd P T C L Ci t " * * ' " ' RETAL PRODUCT, % Figure 6. Breed group means (lower axis) and genetic variation between and within breeds (upper axis) for retail product as a percentage of carcass weight at 458 days of age (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. 99

27 VARATON BETWEENAND WTHN BREEDS CZ HA J _-- 3.1=,g _Z.2o'q"_ ?. - 0! Z 3 4 S _t_$m8 _, 0 /t0 _A 4._ Z _ 16 7 MARBLNG SCORE Figure 7. Breed group means (lower axis) and genetic variation between and within breeds (upper axis) for marbling score (adapted from Cundiff et al., 1986a). See Table 2 for abbreviations. 14.MODEST RELATONSHP BETWEEN MARBLNG SCORE AND RETAL PROOUCT(_ t_j n- O U MOOEST- _J 12.SMALL.SMALL HAe R O =_,osma'l - %S em, ec G % 9.StlGNT + el e RETAL PRODUCT(%) e_ Figure 8. Breed group means for retail product percentage versus marbling score at 458 days of age (adapted from Koch et al., 1976, 1979, 1982b). See Table 2 for abbreviations. to0