J. Anim. Sci. 2002. 80:1716-1724
© 2002 American Society of Animal Science
Evaluations of genotypexenvironment interactions of beef bulls performance-tested in feedlot or pasture
J. F. Baker1,
R. C. Vann2 and
W. E. Neville, Jr.
Coastal Plain Experiment Station, University of Georgia, Tifton 31793-0748
1 Correspondence:
P.O. Box 748 (phone: 229-386-3367; fax 229-386-3219; E-mail:
jfbaker{at}tifton.cpes.peachnet.edu.
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Abstract
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Purebred Angus (n = 96) and Polled Hereford (n = 96) bull calves sired by bulls of either low or high yearling weight performance lines were assigned to either creep-fed or non-creep-fed treatment before weaning for four calf crops. For each breed, after weaning in the fall, half of the calves within each of the four groups were fed a high concentrate diet for 189 d after weaning in a feedlot and the remainder were put on winter temporary pastures (rye or ryegrass) followed by summer grazing on pearl millet and bermudagrass pastures for 329 d after weaning. Dependent variables were ADG for various intervals and the complete test period, weight, height and scrotal circumference at periodic intervals, and weight per day of age at regular intervals during the test. The model included breed, performance line, sire nested within breed and line, year, age of dam, preweaning treatment, postweaning treatment, and two- and three-factor interactions. Age of calf was included as a covariate for weight, height, and scrotal circumference measurements. Line and breed differences generally were significant for weight but not for height. The interaction of primary interest (line by preweaning treatment by postweaning treatment) was not significant. The high growth performance line gained faster than low growth performance line for all intervals and were 45 kg heavier by 189 d after weaning. Preweaning treatment did not affect postweaning ADG but did affect weight per day of age. Creep-fed calves were heavier than non-creep-fed calves and maintained this advantage during the postweaning treatment periods in both the feedlot and pasture. Both preweaning treatment groups had similar ADG after weaning. Angus were 23 kg heavier at weaning than Polled Herefords; however, breed weight means were similar by 16 mo of age. In summary, bulls from different selection lines for growth were identified in feedlot and pasture when adjustments were made for prior management effects. The lack of significant interactions in these data indicates that central test station data, appropriately adjusted, are useful for ranking bulls on genetic merit for growth in feedlot and on pasture.
Key Words: Beef Bulls • Growth • Performance Testing
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Introduction
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Selection of beef bulls for use in commercial and purebred herds utilizes various criteria such as growth measurements, visual appraisal, and EPD. Postweaning gain tests have been a useful method to compare bulls under standardized conditions. These gain test programs have several features that permit valid comparisons for genetic merit assuming that differences due to nongenetic preweaning conditions do not influence the final ranking for genetic merit for growth. A study was designed to determine the extent to which preweaning management affects postweaning test performance and, if it does, to determine procedures to minimize these effects on identification of genetically superior bulls. A second objective of this study was to determine whether sire rankings based on postweaning progeny performance are affected by diets of diverse energy density such as those based on concentrate vs forage. This study also evaluated the length of the postweaning test period that is needed to identify genetically superior bulls under concentrate (feedlot) and roughage (pasture) types of testing.
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Materials and Methods
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Purebred Angus (n = 96) and Polled Hereford (n = 96) bull calves sired by bulls with either low or high growth performance were assigned to either creep-fed or non-creep-fed treatment at approximately 2 to 3 mo of age. Following weaning in the fall, half of the calves in each preweaning group were randomly assigned to either a high concentrate diet for 189 d or a forage-based system of winter temporary pastures (rye or ryegrass) followed by summer grazing on pearl millet and bermudagrass pastures for 329 d. The research protocol and facilities were approved annually by the University of Georgia Animal Care and Use Committee (IACUC #A1999-10079-0).
The rationale for this study was based on previous results of 25 yr of postweaning gain testing. Bull calves from the Angus and Polled Hereford herds at this location had been evaluated for about 25 yr prior to initiation of this project. The top-gaining bulls from each test were then used when they were 2 yr old. The sires of the bull calves evaluated for this study were all selected based on individual gain performance without use of EPD. The sires for this study were all selected within line after completing the standard high-concentrate feeding program. The average performances of the high and low line sires used in the production of the calf crops are presented in Table 1
. Each year three of the highest- and three of the lowest-performing bulls of each breed were retained until they were 2 yr old for breeding to cows of their respective breed. The bulls were replaced each year to produce the four calf crops evaluated in this study. The cows’ individual performance was not considered in the mating plans. However, replacement heifers had not been retained from low-performance sires, so all females in the study were sired by bulls that had previously been selected from among the faster-gaining bulls. Age of breeding females was balanced as nearly as possible among breeding units within breed.
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Table 1. Least square means and standard errors of the average performance of the high- and low-line sires of each breed used in production of calf crops
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Before the start of the breeding period, four similar breeding groups of 20 to 25 cows were formed within each breed. Two groups were bred during the usual 80- to 85-d breeding period to two high-gain-performance bulls and the other two groups to two low-gain-performance bulls in individual sire groups on pasture. The third bull selected from each performance line was used only as a replacement in the event of infertility, injury, or death. After calving, cows within each breed were divided into four similar management groups with the provision that each group contain half the male progeny of high-gain-line sires and half the male progeny of the low-gain-line sires. During the last 75 to 90 d of the nursing period, calves from one group of cows were provided creep feed on pasture and calves from the other group of cows were not creep fed. Access to the creep feed was on an ad libitum basis; the feed was a mixture of rolled corn (75%), rolled oats (15%), and cottonseed meal (10%). Trace minerals and salt were provided in loose form in a mineral feeder.
Weaning occurred each year in early September. A schematic of the experimental design is presented in Table 2. Thus, for each breed at weaning, four groups of bull calves of equal number were used for postweaning treatments each year of the four year study. The genetic and environmental diversity at weaning produced by this procedure was assumed to be similar to that present among bulls submitted by cattle producers for testing at central test stations.
After weaning, bulls assigned to the feedlot were randomly assigned to one of four pens by treatment but blocked on previous treatment and fed a high concentrate diet (rolled corn 78.8%, peanut hulls 15%, soybean meal 4.8%, trace mineral salt 0.8%, and calcium carbonate 0.6%). Bulls were allowed to consume the diet on an ad libitum basis. Bulls on pasture were managed as a single group and grazed on a forage system of winter temporary pasture (rye or ryegrass) followed by summer grazing on pearl millet and bermudagrass. In each of the two postweaning treatments calves were weighed initially at 21 d after weaning and subsequently at 28-d intervals (49, 77, 105, 133, 161, and 189 d after weaning). Bulls in the feedlot treatment were fed for 189 d after weaning, which is longer than current programs in the southeastern United States. The longer time period was used to determine the length of the postweaning test period that is needed to identify superior bulls for growth rate. Bulls on the forage-based diet were on treatment through 329 d after weaning and were weighed at 217, 245, 273, 301, and 329 d after weaning.
Pertinent data collected included BW, hip heights, and scrotal circumference. Dependent variables included daily gains for the complete test period and specific segments of the test period, BW, heights, weight per day of age, and height per day of age at specific dates during and at the end of the test. The ADG and BW per day of age at regular periods after weaning were added together to create a simple phenotypic index. The index value was used to rank bulls similar to systems used in centralized bull evaluation programs. Fixed effects in the statistical models included breed, performance line, preweaning treatment, and postweaning treatment. The two-, three-, and four-factor interactions evaluated were as follows: breed x line, breed x preweaning treatment, breed x postweaning treatment, line x preweaning treatment, line x postweaning treatment, preweaning treatment x postweaning treatment, breed x line x preweaning treatment, line x preweaning treatment x postweaning treatment, and all four factors. The three-way interaction of line x preweaning treatment x postweaning treatment was considered to be the interaction of most importance. The least squares means and standard errors for the traits measured up to 189 d after weaning were obtained from the four-factor interaction (breed x performance line x preweaning treatment x postweaning treatment). Random effects included in the model were year, sire nested with breed and line, and age of dam. Maternal grandsire was included in early analyses but was not significant and was deleted from final analyses. The PROC MIXED procedures (SAS Institute, Inc., 1999, Cary, NC) were used for the statistical analyses.
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Results and Discussion
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Pre-weaning Performance
The mean age at weaning was 229 d. There were no significant differences in age at weaning between the breeds, performance lines, preweaning treatments, or postweaning treatments. Breed was a significant source of variation for birth weight, weaning weight, ADG from birth to weaning, weight per day of age, and scrotal circumference at weaning. The performance line was also a significant source of variation for BW at weaning, ADG from birth to weaning, weight per day of age, hip height at weaning, and scrotal circumference at weaning. The creep-fed and non-creep-fed bulls were significantly different for weaning weight, ADG, and weight per day of age at weaning but similar for hip height and scrotal circumference at weaning. No significant two-way or three-way interactions were detected for weaning weight, weaning hip height, weaning scrotal circumference, weaning weight per day of age, weaning hip height per day of age, or weaning ADG.
The Polled Hereford bull calves were heavier (P < 0.003) at birth (35.9 ± 0.5 vs 33.8 ± 0.5 kg, respectively) than the Angus bull calves regardless of their performance line. However, this advantage in birth weight was not maintained to weaning. The Angus bull calves were (P < 0.001) heavier at weaning (257 ± 3 vs 229 ± 3 kg, respectively) and had a greater (P < 0.0009) weaning weight per day of age (1.10 ± 0.01 vs 1.01 ± 0.01 kg/d of age, respectively) compared to the Polled Hereford bull calves. Breed of calf did not (P > 0.10) affect hip height at weaning (109 ± 0.3 and 108 ± 0.3 cm) or weaning hip height per day of age (0.471 ± 0.004 and 0.479 ± 0.004 cm/d of age). Angus bull calves had greater (P < 0.001) scrotal circumference at weaning (22.9 ± 0.3 vs 21.3 ± 0.3 cm, respectively) and ADG (0.95 ± 0.01 vs 0.85 ± 0.01 kg, respectively) than Polled Hereford bull calves. In agreement with these results, Bailey and Lawson (1989) reported that compared to Angus bulls, Hereford bulls were heavier at birth and grew more slowly to weaning but grew faster after weaning.
Bull calves sired by sires of the high yearling performance line were heavier (P < 0.001) at weaning (255.4 ± 4.2 vs 230.5 ± 3.8 kg, respectively) and had greater weaning weight per day of age (1.11 ± 0.01 vs 1.00 ± 0.01 kg/d of age, respectively) and greater ADG to weaning (0.95 ± 0.01 vs 0.85 ± 0.01 kg, respectively) than bull calves sired by the sires of the low yearling performance line. In addition, the bull calves from the sires of the high performance line had greater (P < 0.001) hip heights at weaning (110 ± 0.4 vs 107 ± 0.3 cm, respectively), greater hip heights per day of age at weaning (0.485 ± 0.004 vs 0.464 ± 0.004 cm/d of age, respectively), and greater scrotal circumference at weaning (22.6 ± 0.3 vs 21.6 ± 0.3 cm, respectively) compared to bull calves from sires of the low performance line.
Bull calves that received creep feed had (P < 0.001) greater weaning weights (253.6 ± 2.7 vs 229.2 ± 3.0 kg, respectively), greater weight per day of age at weaning (1.11 ± 0.01 vs 1.00 ± 0.01 kg/d of age, respectively), and greater ADG to weaning (0.95 ± 0.01 vs 0.85 ± 0.01 kg, respectively) than bull calves not provided creep feed. Creep feeding did not (P > 0.07) affect weaning hip heights (108.8 ± 0.3 and 108.2 ± 0.4 cm), hip height per day of age at weaning (0.480 ± 0.004 and 0.470 ± 0.004 cm/d of age), or scrotal circumference at weaning (22.5 ± 0.26 and 21.7 ± 0.29 cm).
Growth Analyses from Weaning Through 189 d After Weaning
Breed, performance line, preweaning treatment, and postweaning treatment effects were significant sources of variation for BW and weight per day of age at 49, 77, 105, 133, 161, and 189 d after weaning. The two-, three-, and four-factor interactions were not significant for BW or weight per day of age at any measurement point after weaning.
Angus bull calves had greater BW (Table 3P < 0.04) and weight per day of age (Table 4P < 0.03) than Polled Hereford bull calves (Tables 5 and 6) through 189 d after weaning. Bulls by sires from the high performance line had greater (P < 0.001) postweaning ADG for all measurement intervals (Tables 4 and 6) and greater weight per day of age (P < 0.001) than bulls sired by bulls from the low performance line (Tables 4 and 6). Bulls that were creep-fed continued to be heavier (P < 0.003) and had greater (P < 0.001) weights per day of age after weaning through 189 d (Tables 4 and 6) than non-creep fed-bulls. Bulls that were fed high-concentrate diets during the postweaning treatment period had greater (P < 0.001) weight gains and weight per day of age than bulls fed forage-based diets. Bulls fed high-concentrate diets after weaning had faster ADG (P < 0.001) than bulls fed forage-based diets (Tables 4 and 6). Breed was an important (P < 0.01) source of variation for ADG (Tables 4 and 6) at 49 and 77 d after weaning but was not important (P < 0.12) thereafter through 189 d after weaning. Preweaning treatment and breed differences were less important (P > 0.07) for the index by 131 d after weaning. The use of a combination of ADG and weight per day of age index to rank bulls would seem to be influenced by preweaning management beyond the time when ADG is no longer significantly influenced by preweaning management. It may therefore be important for centralized bull performance testing programs to consider the importance of length of test when deciding on the ranking procedures. The genetic line and postweaning treatment were important (P < 0.001) through 189 d after weaning for the index trait (Tables 4 and 6). Schoeman and Jordaan (1998) observed significant changes in rank when bulls were evaluated on both forage and feedlot conditions. In their study bulls were first evaluated for gain in a feedlot and then switched to a forage diet. In the present study the interaction between performance line and postweaning treatment was not significant for ADG, BW, weight per day of age, or the index. Schoeman and Jordaan (1998) concluded that forage diets and high-concentrate diets should be considered as two independent traits for selection programs.
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Table 3. Body weight, hip height, and scrotal circumference least square means and standard errors for bull calves from the Angus genetic line
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Table 4. Average daily gain, weight per day of age, and index least square means and standard errors for bull calves for the Angus genetic lines
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Table 5. Body weight, hip height, and scrotal circumference least square means and standard errors for bull calves for the Polled Hereford genetic line
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Table 6. Average daily gain, weight per day of age, and index least square means and standard errors for bull calves for the Polled Hereford genetic lines
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Several investigators have reported that the herd of origin or preweaning treatment had a significant effect on weights and ADG, especially within the first 4 wk after weaning (Amal and Crow, 1987; Rahnefeld et al. 1987; Liu and Makarechian, 1993). The results of the present study support these findings of other investigators, in that as the numbers of days on-test increased the effect of preweaning treatment on ADG declined. Preweaning treatment had significant effects on ADG at 49 d after weaning but not by 77 d after weaning. However, preweaning treatment effects continued to be important (P < 0.001) for BW and weight per day of age through 189 d after weaning. In a study by McClave and Dietrich (1988) the statistical comparison of first-order and second-order models indicated that herd of origin or preweaning treatment had an effect (P < 0.05) on weight gain from d 0 through d 133, which is much longer than findings of other studies in the literature that weight gain within the first 4 wk on test is affected by preweaning treatment (Cundiff et al., 1975; Tong et al., 1986; Amal and Crow, 1987).
Preweaning treatment was important (P < 0.02) for hip heights (Tables 3
and 5) at 49, 77, and 105 d after weaning, which reflects the larger size at weaning of the creep-fed bulls. However, for measurements at 133, 161, and 189 d after weaning, preweaning treatment did not significantly affect hip heights. During the first 105 d of the postweaning period, the creep-fed bulls had greater (P < 0.02) hip heights than non-creep-fed bulls. Bulls by sires of the high performance line had greater (P < 0.001) hip heights than bulls sired by bulls of the low performance line. Breed of bull did not significantly affect postweaning hip heights (Tables 3 and 5, P > 0.09).
Postweaning scrotal circumference at d 49 (Tables 3 and 5) had a significant two-way interaction (breed x line; P < 0.04); however, no other significant two- or three-way interactions were detected for scrotal circumference at 105, 131, 161, or 189 d after weaning. This breed x line interaction was caused by the fact that the Hereford bulls of the low performance line had a significantly smaller scrotal circumference at this weigh period than all other groups. At d 105, 131, 161, and 189, Angus bulls had greater (P < 0.04) scrotal circumference than Polled Hereford bulls, and the bulls of the high performance line had greater (P < 0.002) scrotal circumference than the bulls of the low performance line. Creep feeding did not significantly affect scrotal circumference during the postweaning treatment period. Bulls that were fed high-concentrate diets during the postweaning treatment period had greater (P < 0.009) scrotal circumference than bulls fed the forage-based diets after weaning. Scrotal circumference was positively correlated with BW at the end of a feedlot test (Makarechian et al., 1984; Bourdon and Brinks, 1986). Because BW at the end of a feeding test affects scrotal circumference (Makarechian et al., 1984; Bourdon and Brinks, 1986) and BW is a function of birth weight, preweaning and postweaning growth rate, and age, all of which influence testes development, it is not surprising that the calves fed the high-concentrate diet in this study had greater scrotal circumference than bulls fed the forage-based diet.
Growth Analyses from 189 d Through 329 d After Weaning
Forage-fed performance programs for bulls in Georgia and other southeastern states involve lengthier evaluations than high-concentrate programs. Therefore, producers must consider the higher feed costs with high-concentrate programs and longer ownership costs with forage programs. Breed did not significantly affect BW, weight per day of age, ADG, or the index trait at any measurement between 189 and 329 d after weaning, except breed effect was significant for ADG from weaning to 301 and 329 d postweaning. Performance line was significant for all traits except scrotal circumference (Tables 7 and 8). Interactions (breed x performance line, breed x preweaning treatment, performance line x preweaning treatment, and breed x performance line x preweaning treatment) were not significant for any variable measured or calculated from 217 to 329 d after weaning.
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Table 7. Body weight, hip height, and scrotal circumference least square means and standard errorsfor bull calves from both breeds on the forage based postweaning treatment
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The influence of creep feed continued to be important (P < 0.01) for BW and weight per day of age. Those bulls that had received creep feed were heavier and had greater weight per day of age (Tables 7 and 8; P < 0.002) than those not creep-fed. The creep-fed calves had greater BW than the calves not receiving creep feed throughout the study, and this is illustrated in Figure 1. The BW differences between those receiving creep feed and those that did not declined from weaning to 189 d after weaning for those that were on the high-concentrate diet. Standard errors for the differences in Figure 1 ranged from 8 to 10 kg. Tests of significance for the difference being greater than zero indicated that only the low performance line on high-concentrate diet at 133, 161 and 189 d after weaning and the high performance line on high-concentrate diet at 189 d postweaning were not different from zero. The differences between BW for those bulls on the forage diet were significantly greater than zero throughout the postweaning evaluation period.
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Figure 1. Difference between BW least square means of creep fed and not creep bulls by performance line and postweaning management at regular intervals. (High line = high-performance line, Low line = low-performance line, Concentrate = high concentrate diet postweaning, Forage = forage based diet postweaning).
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Breed differences for BW (Table 7), weight per day of age (Table 8), or the index (Table 8) were not important (P > 0.25) during this phase of the study. However, breed was important (P < 0.003) for ADG from weaning to 301 and 329 d (Table 8) after weaning. The Hereford bulls were now gaining faster than the Angus (0.75 ± 0.02 kg/d vs 0.69 ± 0.02 kg/d, respectively, for ADG from weaning to 329 d after weaning). Bulls from sires of the high performance line continued to have greater (P < 0.001) hip heights (Table 7) than bulls from sires of the low performance line. Preweaning treatment did not significantly affect hip heights during the forage-based diet treatment period. Angus bulls had greater (P < 0.001) scrotal circumference than Polled Hereford bulls. However, creep feed and performance line did not significantly affect scrotal circumference during this treatment period.
Conclusion
Regardless of breed type, the bulls from sires of the high performance line were heavier and gained faster than the bulls from sires of the low performance line. Creep feeding produced heavier calves at weaning, and these calves continued to maintain this weight advantage after weaning despite slower postweaning gains (Figure 1). The effect of creep feeding on ADG after weaning was not important after 49 d following weaning. However, effects of creep feeding continued to influence weight per day of age and BW to 329 d. The index of ADG plus weight per day of age was influenced by preweaning treatments for growth performance evaluations until 133 d after weaning. At weaning, Angus bull calves were heavier than Polled Hereford bull calves; however, by 16 mo of age the mean BW for the two breeds were similar. During the later part of the postweaning treatment the Polled Hereford bulls had faster gains than the Angus bulls. In agreement with the results of this study, Bailey and Lawson, (1989) reported that Hereford bulls were heavier at birth and grew more slowly to weaning but more efficiently thereafter, and their carcasses were smaller in proportion to empty live BW than those of Angus bulls. In conclusion, bulls from different performance lines for growth were distinguished when adjustments were made for prior management effects. The lack of significant interactions in these data indicate that central test station data, appropriately adjusted, are useful for ranking bulls on genetic merit for growth in feedlot and on pasture.
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Implications
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Centralized off-farm postweaning gain programs continue to provide educational and marketing opportunities for beef cattle seedstock producers. However, these performance records are not usually included in national evaluation programs because of single-animal contemporary groups. In this study the lack of important genotype x environment interactions implies that producers can be satisfied that bulls can be correctly ranked for postweaning gains in either a high-concentrate diet performance trial or forage-based feeding program.
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Footnotes
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2 Current address: CMREC, Mississippi State Univ., 1320 Seven Springs Rd., Raymond 39154. 
Received for publication July 2, 2001.
Accepted for publication January 22, 2002.
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Literature Cited
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Amal, S., and G. H. Crow. 1987. Herd of origin effects on the performance of station-tested beef bulls. Can. J. Anim. Sci. 67:349–358.
Bailey, C. B., and J. E. Lawson. 1989. Rate and efficiency of gain in Hereford and Angus bulls from lines selected for rapid growth on high-energy and low-energy diets. Can. J. Anim. Sci. 69:161–172.
Bourdon, R. M., and J. S. Brinks. 1986. Scrotal circumference in yearling Hereford bulls: Adjustment factors, heritabilities and genetic, environmental and phenotypic relationships with growth traits. J. Anim. Sci. 62:958–967.
Cundiff, L. V., K. E. Gregory, and C. R. Long. 1975. Genetic variation among and within herds of Angus and Hereford cattle. J. Anim. Sci. 41:1270–1280.[Abstract/Free Full Text]
Liu, M. F., and M. Makarechian. 1993. Factors influencing growth performance of beef bulls in a test station. J. Anim. Sci. 71:1123–1127.[Abstract]
Makarechian, M., A. Farid, and R. T. Berg. 1984. Relationships between growth parameters, and scrotal circumference in young beef bulls. Theriogenology 22:667–674.
McClave, J. T., and F. H. Dietrich, II. 1988. Model building: Testing portions of a model. In: Statistics. 4th ed. pp 872–887. Dellen Publishing Co., San Francisco, CA.
Rahnefeld, G. W., H. T. Fredeen, R. M. McKay, G. M. Weiss, J. E. Lawson, and J. A. Newman. 1987. Genotype x Environment interactions for postweaning growth performance of backcross bulls. Can. J. Anim. Sci. 67:359–370.
Schoeman, S. J., and G. F. Jordaan. 1998. Animal x nutritional regime interaction in postweaning growth traits of young bulls. In: Proc. 6th World Cong. Genet. Appl. Livest. Prod. Armidale, NSW, Australia. 23:267–270.
Tong, A. K. W., J. A. Newman, and G. W. Rahnefeld. 1986. Pretest herd effects on station performance test. Can. J. Anim. Sci. 66:925–935.
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Abstract
Introduction
