Genetic and Environmental Parameters for Mature Weight and Other Growth Measures in Polled Hereford Cattle'

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1 Published December 11, 2014 Genetic and Environmental Parameters for Mature Weight and Other Growth Measures in Polled Hereford Cattle' K. D. Bullockz, J. K. Bertrand, and L. L. Benyshek Department of Animal Science, University of Georgia, Athens ABSTRACT: Variances and covariances were estimated for birth weight (B WT), weaning weight (WW), yearling gain (Y G), yearling weight (Y W), yearling height (YH), relative growth from birth to weaning (RGW) and weaning to yearling (RGY 1, 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 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, 230,.76,.89,.73, -.29, and.35, respectively, environmental correlations were.e,.43,.05,.40, 1.03,.32, and -.lo, respectively, and phenotypic correlations were.33,.32,.28,.46,.70,.oo, and.07, respectively. Key Words: Weight, Heritability, Correlation, Beef Cattle J. Anim. Sci : Introduction Recent selection practices in beef cattle have placed a large emphasis on increased growth. Considering the diverse management practices in the United States, this may not always be the best alternative in regard to the overall productivity of the cow herd. Maintaining reproductive efficiency in the herd should be of particular concern. Cows need to have adequate condition at parturition or be increasing in weight at mating to minimize the postpartum interval (Dunn and Kaltenbach, 1980). Therefore, it is necessary to ensure that the energy maintenance requirements of cows are met during the period between parturition and breeding. Two characteristics that influence the ability of a cow to meet maintenance nutrition requirements are milk production and BW (McMorris and Wilton, 1986; Montano-Bermudez et al., 1990). Although most beef 'This project was partially funded by the American Polled Hereford Association and the Georgia Exp. Sta. and was part of Hatch Project Present address: Anim. Sci. Dept., Univ. of Kentucky, Lexington Received September 4, Accepted February 15, breed registry associations provide EPD for milking ability, only one is producing EPD for mature size. Many researchers have reported mature weight heritability to be moderate to high (Brinks et al., 1964; Smith et al., 1976; DeNise and Brinks, 19851, which would indicate that mature weight could be changed genetically by selection. It is important to obtain the best estimates of population genetic and environmental variances for use in computing EPD. It is also necessary to understand the relationship between mature weight and other production traits. Therefore, the objective of this study was to compute genetic and environmental parameters for mature cow weight and other growth traits in Polled Hereford cattle. Materials and Methods Data. Field data records on 572,446 registered Polled Hereford progeny were obtained from the American Polled Hereford Association (APHA), Kansas City, MO. The data set included records for birth weight ( BWT), 205-d adjusted weaning weight (WW), 365-d adjusted weight (YW), 365-d adjusted hip height ( YH), and dam weights at weaning ( DW). Weaning weight, YW, and YH were adjusted to their 1737

2 1738 BULLOCK ET AL. Table 1. Number of records, sires, maternal grandsires, and contemporary groups represented for each trait Traita Record Sire MGS~ CGc Recordmd Skewd C h C d BWT 282,872 14,850 20,963 26,090 2, ww 503,250 24,133 31,708 52,058 2, YG 131,740 10,346 15,169 15,614 1, Yw 131,740 10,346 15,169 16,614 1, YH 27,110 2,821 4,473 3, RGW 278,189 14,812 20,836 29,739 2, RGY 131,740 10,346 15,169 15,614 1, abwt = adjusted birth weight (kg); WW = adjusted 205-d weight (kg); YG = 205- to 365-d gain (kg); YW = adjusted 365-d weight (kg); YH = adjusted yearling height (cm); RGW = relative growth rate from birth to weaning; RGY = relative growth rate from weaning to yearling. bmgs = maternal grandsire. CCG = contemporary group. dsires and CG included for mature weight in each of the two-trait analyses. respective constant ages using equations described in the Beef Improvement Federation ( ) guidelines. Age of dam correction factors for BWT and WW were additive age class corrections developed for the Polled Hereford breed and presently used in the APHA National Cattle Evaluation program ( NCE). From these weights, weaning to yearling gain ( YG) and relative growth rate from birth to weaning (RGW) and from weaning to yearling (RGY) were calculated. Weaning to yearling gain is simply the actual ADG from weaning to yearling multiplied by 160 d. The two relative growth rates were calculated as the natural logarithm of the final weight minus the natural logarithm of the initial weight divided by the period in days (Fitzhugh and Taylor, 1971). Contemporary group definitions for birth ( BCG), weaning ( WCG), and yearling ( YCG) were the same as those used in the NCE. Birth contemporary groups were formed from birth year, season, calf crop, and sex, and only single births were included. Weaning contemporary groups were formed from calf crop, weaning sex, birth type, creep or noncreep, weaning management group, weaning age group, and weaning weigh date. Yearling contemporary groups include WCG plus yearling calf crop, yearling sex, yearling management code, yearling management group, yearling age group, and yearling weigh date. Mature weight was calculated by fitting a quadratic with a plateau function: Plateau = A + B*IP + C*(IP)2 where A is the intercept, B is the linear regression coefficient, C is the quadratic coefficient, and IP is the inflection point, using iterative nonlinear procedures of SAS (1985). This function was fit to the entire data set and included BWT, WW, YW, and all DW. For this data set the plateau was 555 kg, A was , B was 1.43, C was , and the inflection point ( IP) was 1,506 d. If a cow had a measurement(s) past IP then the closest of these weights to IP was used as its mature weight (MW). If it only had a measurement before IP, the closest weight to IP was nonlinearly adjusted to the plateau (MW) using the coefficients and IP was computed when fitting the quadratic with a plateau function. The adjustment equation for these cows was as follows: MW = WT + 1, rIP - AGE] + [ (IP2 - AGE2)] where WT was the weight of the individual that was closest to IP and AGE was the actual age of the animal (days) when WT was recorded. Mature weight contemporary groups ( MCG) included the WCG of the cow and the WCG of the calf that was weaned at the time that the cow was weighed. This definition requires all cows in the same contemporary group to be the same age and under the same temporary environment. These restrictions were very stringent and created many single-sire and maternal-grandsire contemporary groups. After all traits were adjusted and calculated, records were edited for the following reasons: singlesire or maternal-grandsire contemporary groups, disconnected sires, and records that were more than 40% larger or smaller than their contemporary group mean. These editing procedures are the same as those used in the NCE of most beef breeds. The numbers of records, sires, contemporary groups, and maternal grandsires included in each analysis are presented in Table 1. Heritabilities and Correlations. Variance components were estimated using Henderson's (1980) new or simple method as extended by Bertrand and Benyshek (1987) and Bertrand and Kriese (1990). Mature weight was analyzed with each of the other traits (BWT, WW, YG, YW, YH, RGW, and RGY) in a two-trait model. A sire-maternal grandsire model was used to analyze the pre-mature measurements (BWT, WW, YG, YW, YH, RGW, and RGY) and MW was analyzed using a sire model. The model included the fured effect of contemporary group and random effects of sire, maternal grandsire (where appropriate), and

3 PARAMETERS FOR MATURE WEIGHT IN BEEF CATTLE 1739 error. From this analysis, additive direct, maternal, and error variances were calculated, as well as all possible covariances for each trait as described by Kriese et al. (1991). The heritability estimate for MW was an average of the estimates computed for the seven combinations. Genetic, environmental, and phenotypic correlations were calculated from the (cohariance component estimates, between MW and all other traits (BWT, WW, YG, YW, YH, RGW, and RGY). All heritabilities and correlations were calculated using the additive direct (co)variance component estimates where appropriate. Results and Discussion Defining Mature Weight. There are several procedures by which MW can be estimated. The most obvious would be an average of all weights taken on the animal after it has stopped growing ( MWA). This procedure does give an accurate assessment of MW; however, it limits the number of animals that can be used in a data set and it can be difficult to determine when an animal has stopped growing. Another approach and one that has been used in many studies (Fitzhugh and Taylor, 1971; Brown et al., 1972a; DeNise and Brinks, 1985) is the growth curve as described by Brody (1945): W, = A(l - Be-kt) where Wt is weight at time t, A is the asymptotic weight, B is the integration constant, and k is the relative growth rate. As with taking the mean of fully grown animals, to fit Brody s curve it is necessary to have records on the animal to a point when the animal is no longer growing (approximately 5 yr of age). When viewing the individual growth curves the weights seem to increase in a quadratic manner from birth to approximately 4 yr of age and then seem to level off. Therefore, another way to estimate MW is to fit a quadratic with a plateau: Mwp = A + B*MAGE + C*(MAGE)2 where MWP is the predicted MW, A is the intercept, B is the linear coefficient, C is the quadratic coefficient, and MAGE is the age at which the plateau is reached for each individual cow. The disadvantage of this method is the same as that for the previous two methods: actual MW are necessary. The advantage to this method, which is not available with the others, is that the point at which growth stops can be easily estimated (MAGE) as the age at which the curve reaches a plateau. With Brody s method an arbitrary percentage of the asymptotic weight is used to calculate the age at maturity (typically 98%). With each of these methods for determining MW only animals with records that extend past approximately 5 yr of age can be used in the analysis. Another problem is defining an accurate contemporary group for animals with multiple weights. Therefore, a method that allows animals that do not have actual mature records (> 5 yr) to be included in the analysis and that have a well-defined contemporary group would be advantageous. Benyshek and Marlowe (1973) used all cows with at least a 3-yr weight and adjusted cow weights according to age class. With this procedure all animals are included in the analysis but age differences within a class are not accounted for. If early weights are to be extended to a MW, it must be determined whether these earlier weights are correlated with the actual MW. Phenotypic correlations were computed between DW taken at 2, 3, and 4 yr with MWA. These correlations were.76,.83, and 37, respectively, which gives an indication of how accurately early weights predict true MW. As would be expected, correlations are larger as the animals get closer to 5 yr of age. This would justify using the weight closest to 5 yr as the weight used in the adjustment equation. The method of defining MW used in this study seems to address the problems associated with previously used methods. As long as a cow had a weight measurement at the weaning of its calf the cow was eligible for analysis. Another benefit of using a single weight measure and adjusting to a constant MW is that MCG could be accurately defined. Under varying environmental conditions a cow s mature weight can fluctuate drastically due to differences in body condition. However, body condition scores were not available in this data set. Another effect on a cow s mature size is her early life development. Therefore, defining MCG to account for these differences was imperative. These factors should be eliminated by including the cow s own WCG, as well as the WCG of its calf, when the cow s MW is recorded, in the MCG definition. These are very stringent requirements that require the cow to be raised under the same environmental conditions and raise her calf under the same environmental conditions as her contemporaries. When exposed to the same environmental conditions, variations in body condition should not be removed when measuring true mature weight differences. Heritabilities. Means, standard errors, and heritabilities for all traits are presented in Table 2. The heritabilities for BWT, WW, YG, and YW were.49,.24,.23, and.30, respectively. Using field data with Herefords Wilson et al. (1 986) estimated heritability for BWT and WW of.41 and.13, respectively. In other breeds, Massey and Benyshek ( 198 1) reported heritabilities of.16,.09, and.16 in Limousin; heritability estimates of.18,.34, and.33 were reported for Simmental by Benyshek and Little (1982); Alenda

4 1740 BULL 0 C K Table 2. Means and heritabilities for each trait - Traita nb X SE h2 312, ,603 30, ,704 6, Zd abwt = adjusted birth weight (kg); WW = adjusted 205-d weight (kg); YG = 205- to 365-d gain (kg); YW = adjusted 365-d weight (kg); YH = adjusted yearling height (cm); RGW = relative growth rate from birth to weaning; RGY = relative growth rate from weaning to yearling; MW = mature weight. bnumber records included in fl and SE, see Table 1 for number of records used to calculate h2. Values listed for X and SE were multiplied by lo5. dmean of seven estimates from each two-trait analysis (SE =,021. and Martin (1987) reported heritabilities of.46,.26, and.27 for Angus; and Winder et al. (1990) found that heritability estimates from Red Angus data were.46,.39, and.40 for BWT, WW, and YW, respectively. Thrift et al. (1981) reported heritability estimates of.45,.26,.47, and.32 for BWT, WW, YW, and YG in a selection study. The heritability of YH (h2 =.59) is in accordance with structural traits, which are typically highly heritable. High heritability estimates for hip height were also reported by Brown (1958) (h2 =.48) and Neville et al. (1978) (h2 = 54 and.75). The heritabilities for RGW and RGY were lower than those previously reported (h2 =.24 and.15, respectively). Fitzhugh and Taylor ( ) reported heritabilities of.47,.24, and.42 for the period of 6 to 12 mo, 12 to 18 mo, and 18 mo to maturity, respectively. Heritability estimates for relative growth rate seem to be somewhat dependent on the time period during which the weight is measured. Many of the heritability estimates reported previously for MW were in studies involving Hereford cattle; however, studies on MW involving Polled Herefords could not be found. Heritability estimates for MW in Hereford cattle reported were.75 and.73 (Brinks et al., 1962),.57 (Brinks et al., 19641,.57 (Fitzhugh and Taylor, 1971), -34 (Brown et al., 1972a),.39 (Brown et al., ,.57 to 1.00 (Benyshek and Marlowe, 1973),.55 (Smith et al., 1976),.44 (DeNise and Brinks, 19851, and.36 (Johnson et al., 1990). The heritability estimate for MW in the current study (h2 =.52) agrees with those reported. This is of particular interest considering that the data used to estimate MW heritability in this study included young cows (< 5 yr old). Correlations. Genetic, environmental, and phenotypic correlations between MW and the production traits are presented in Table 3. ET AL. Table 3. Genetic, environmental, and phenotypic correlations for all traits with mature weight Genetic Environmental Phenotypic Traita r r r BWT, kg w, kg YG, kg YW, kg YH, cm RGW oo RGY.35 -.lo.07 abwt = adjusted birth weight (kg); WW = adjusted 205-d weight (kg); YG = 205- to 365-d gain (kg); YW = adjusted 365-d weight (kg); YH = adjusted yearling height (cm); RGW = relative growth rate from birth to weaning; RGY = relative growth rate from weaning to yearling. The genetic correlations of BWT with MW (rg =.63) were similar to estimates reported by others. Brinks et al. (1964) reported genetic correlations of.61 and.68 between BWT and MW, whereas Smith et al. (1976) reported a value of 55. The genetic correlations between MW with WW, YG, and YW (rg = 30,.76, and.89, respectively) are higher than estimates reported by other researchers. Brinks et al. (1964) reported genetic correlation estimates of.40 and.41 for MW with WW and YW, respectively, and Smith et al. ( 19 76) reported genetic correlations of.60 and.80 for MW with 200-d and 396-d weights, respectively. Yearling hip height was highly correlated with MW (rg =.73). No other reports of YH-MW correlations could be found; however, Wilson and Northcutt ( reported genetic correlations between mature hip height and MW of.75. Genetic correlations involving MW with RGW and RGY seemed to be very dependent on the time periods involved, as were relative growth rate heritabilities. Fitzhugh and Taylor ( ) have suggested that relative growth rate was an indicator of maturity. They surmised that increased maturity at any age should increase relative growth rate before 12 mo. If early maturity is associated with smaller MW then relative growth rate before 12 mo should be negatively correlated with MW. This relationship with MW was observed for RGW (rg =.-.29); however, RGY (re =.35) showed the opposite relationship. The environmental correlation between MW and BWT (re =.15) is small and positive. This relationship seems reasonable because the time period between birth and maturity is so great that it seems unlikely that the environmental effects on BWT have a strong influence on the MW of the animal. Environmental correlation estimates for MW with WW and YW (r3 =.43 and.40, respectively) are larger than with BWT. It seems logical that the closer two weigh periods are to one another the more environmentally correlated the two traits would be. The environmental correlation between YH and MW was outside natural limits (rg = 1.03). This

5 PARAMETERS FOR MATURE WEIGHT IN BEEF CATTLE 1741 occurrence is not well understood; however, a large positive relationship may be possible. It seems likely that an environment that is conducive to early structural growth would lend itself to increased MW when the animal fully develops. Phenotypic correlations are presented in Table 3. The phenotypic correlations seem to be within normal limits. Phenotypic correlations tended to be lower than genetic correlations. Implications With increased selection emphasis being placed on growth in beef cattle it is important to understand what the effects are on other traits. One trait of importance is the mature weight of the cow herd. It seems that two of the traits that are typically selected for, high weaning and yearling weight, increase mature weight. The parameters estimated in this study could be used in the mixed-model procedures of the National Cattle Evaluation Program to compute genetic evaluations for mature cow weight. Having expected progeny differences for mature weight would provide producers with a valuable tool to manage cow size. Literature Cited Alenda, R., and T. G. Martin Genetic parameters and consequences of selection for growth traits in a beef herd selected for yearling weight. J. Anim. Sci. 64:366. Beef Improvement Federation BIF Guidelines for Uniform Beef Improvement Programs (6th Ed.). Raleigh, NC. Benyshek, L. L., and D. E. Little Estimates of genetic and phenotypic parameters associated with pelvic area in Simmental cattle. J. Anim. Sci. 54:258. Benyshek, L. L., and T. J. Marlowe Estimating heritability of Hereford cow weights. J. Anim. Sci. 36:854. Bertrand, J. K., and L. L. Benyshek Variance and covariance estimates for maternally influenced beef growth traits. J. Anim. Sci. 64:728. Bertrand, J. K., and L. A. Kriese Two methods for parameter estimation using multiple-trait models and beef cattle field data. J. Anim. Sci. 68:2310. Brinks, J. S., R. T. Clark, N. M. Kieffer, and J. R. Quesenberry Mature weight in Hereford range cows-heritability, repeatability, and relationship to calf performance. J. Anim. Sci. 21:501. Brinks, J. S., R. T. Clark, N. M. Kieffer, and J. J. Urick Estimates of genetic, environmental and phenotypic parameters in range Hereford females. J. Anim. Sci. 23:711. Brody, S Bioenergetics and Growth. Reinhold Publishing, New York. Brown, C. J Heritability of weight and certain body dimensions of beef calves at weaning. Arkansas Agric. Exp. Sta. Bull Brown, J. E., C. J. Brown, and W. T. Butts. 1972a. A discussion of the genetic aspects of weight, mature weight and rate of maturing in Hereford and Angus cattle. J. Anim. Sci. 34:525. Brown, J. E., C. J. Brown, and W. T. Butts. 1972b. Relationships among weights, gains and earliness of maturing in Hereford and Angus females. J. h im. Sci. 35:507. DeNise, R.S.K., and J. S. Brinks Genetic and environmental aspects of the growth curve parameters in beef cows. J. Anim. Sci. 61:1431. Dunn, T. G., and C. C. Kaltenbach Nutrition and the postpartum interval of the ewe, sow and cow. J. him. Sci. 51(Suppl. 2):29. Fitzhugh, H. A., Jr., and St. C. S. Taylor Genetic analysis of degree of maturity. J. Anim. Sci. 33:717. Henderson, C. R A simple method for unbiased estimation of variance components in the mixed model. Cornel1 Univ., Ithaca, NY (Mimeo). Johnson, Z. B., C. J. Brown, and A. H. Brown, Jr Evaluation of growth patterns of beef cows. Arkansas Agric. Exp. Sta. Bull Kriese, L. A., J. K. Bertrand, and L. L. Benyshek Age adjustment factors, heritabilities and genetic correlations for scrotal circumference and related growth traits in Hereford and Brangus bulls. J. Anim. Sci. 69:478. Massey, M. E., and L. L. Benyshek Estimates of genetic and environmental effects on performance traits from Limousin field data. J. Anim. Sci. 52:37. McMorris, M. R., and J. W. Wilton Breeding system, cow weight and milk yield effects on various biological variables in beef production. J. Anim. Sci. 63:1361. Montaxio-Bermudez, M., M. K. Nielsen, and G. H. Deutscher Energy requirements for maintenance of crossbred beef cattle with different genetic potential for milk. J. Anim. Sci. 68:2279. Neville, W. E., Jr., J. B. Smith, B. G. Mullinix, Jr., and W. C. McCormick Relationships between pelvic dimensions, between pelvic dimensions and hip height and estimates of heritabilities. J. Anim. Sci. 47:1089. SAS SAS User s Guide: Statistics. SAS Inst. Inc., Cary, NC. Smith, G. M., H. A. Fitzhugh, Jr., L. V. Cundiff, T. C. Cartwright, and K. E. Gregory A genetic analysis of maturing patterns in straightbred and crossbred Hereford, Angus and Shorthorn cattle. J. Anim. Sci. 43:389. Thrift, F. A., E. U. Dillard, R. R. Shrode, and W. T. Butts Genetic parameter estimates based on selected and control beef cattle populations. J. Anim. Sci. 53:57. Wilson, D. E., P. J. Berger, and R. L. Willham Estimates of beef growth trait variances and heritabilities determined from field records. J. Anim. Sci. 63:386. Wilson, D. E., and S. L. Northcutt Spring American Angus Association Sire Evaluation Report. American Angus Association, St. Joseph, MO. Winder, J. A., J. S. Brinks, R. M. Bourdon, and B. L. Golden Genetic analysis of absolute growth measurements, relative growth rate and restricted selection indices in Red Angus cattle. J. Anim. Sci. 68:330.