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ANIMAL GENETICS |
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* Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan;
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Faculty of Agriculture, Kobe University, Kobe 657-8501, Japan;
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Wagyu Registry Association, Kyoto 604-0845, Japan;
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Food Resources Education and Research Center, Faculty of Agriculture, Kobe University, Kasai 675-2103, Japan
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: beef cattle • direct genetic effect • genetic correlation • genetic variance • heritability • maternal effect
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Calves of Japanese Black cattle are weighed and traded at calf markets between 8 and 10 mo of age. Previous studies on calf market weight of Japanese Black cattle suggest the possibility of estimation of the maternal effect for early growth (Shimada et al., 1995
; Kitamura et al., 1999; Mukai et al., 2000). Mukai et al. (2000) indicated that there were considerable differences among 3 prefectures in (co)variance components and genetic correlations between direct and maternal effects for early growth traits. For simultaneous improvement of maternal ability and carcass traits, genetic relationships among these traits are necessary. However, relatively little is known about these genetic relationships (Mohiuddin, 1993; Koots et al., 1994; Splan et al., 2002).
The objective of this study was to estimate genetic relationships between direct and maternal effects for calf market weight and direct effects for carcass traits in Japanese Black cattle using field data collected in 2 prefectures.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Data
Data were collected from calf and carcass markets in Hyogo and Tottori prefectures and analyzed separately by prefecture. For calf market weight, birth year ranged from 1994 to 2002 in Hyogo and from 1988 to 2000 in Tottori. Records of twins and calves produced by embryo transfer were omitted. Only fattening animals with calf market weight were extracted from the carcass database and used for parameter estimation. These cattle were slaughtered from 1997 to 2003 in Hyogo and from 1991 to 2004 in Tottori.
The carcass traits analyzed were carcass weight (CW), ribeye area (RA), rib thickness (RT), subcutaneous fat thickness (SF), yield estimate (YE), beef marbling score (MS), meat color (MC), meat brightness (MB), meat firmness (MF), and meat texture (MT). All carcass traits were measured by official graders of the Japan Meat Grading Association according to the carcass grading standards (JMGA, 1988). Carcass traits except CW and YE are evaluated at the sixth to seventh rib section, and YE is calculated using CW, RA, RT, and SF as an indicator of salable meat proportion. The MS is a subjective measure of the degree of marbling, especially in the ribeye, and is categorized into 12 grades (from 0 to 3 with intervals of 0.33, and 4 and 5) according to the Beef Marbling Standard. Greater numbers indicate more marbling. The MC is evaluated using a 7-point Beef Color Standard (1 = bright, 7 = dark). Five-point scales are used to quantify MB (1 = very dull, 5 = very shiny), MF (1 = very loose, 5 = very firm), and MT (1 = very coarse, 5 = very fine).
Calf market and carcass datasets were integrated, and only the records from cow-calf production and fattening farms with at least 5 calf or carcass market records were used. Records were omitted if observations of each trait or ages (d), or both, at calf and carcass markets fell outside of the range of the mean ± 3 SD. Descriptive statistics of the traits analyzed after data editing are given in Table 1.
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, and means of covariates are found in Table 1
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and
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where subscripts 1 and 2 represent calf market weight and carcass traits, respectively, and y is the vector of records, ß is the vector of fixed effects, a and m are the vectors of direct and maternal genetic effects, f is the vector of farm effects, and e is the vector of residuals. X, Za, Zm, and Zf denote the incidence matrices relating y to ß, a, m, and f, respectively. For these models, assumed expectation and (co)variance structures are
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and
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where 
2ai, 2mi, 2fi, and 2ei stand for variances for additive direct genetic, maternal genetic, farm, and residual effects, respectively, for the ith trait, aiaj, aimj, and eiej for direct genetic, direct-maternal genetic, and residual covariances between the ith and jth traits, respectively. A and I denote the additive relationship and identity matrices, respectively.
Pedigrees were traced back to animals born in 1960 using pedigree information from the Wagyu Registry Association, and all available ancestors were included in calculation of the additive relationship matrix. As a result, the numbers of ancestors without records were 23,140 and 12,999 in Hyogo and Tottori, respectively.
Estimation of Variance and Covariance Components
Variance and covariance components were iteratively estimated by REML procedures (Patterson and Thompson, 1971; Henderson, 1984) using an expectation maximization algorithm (Dempster et al., 1977). Convergence criteria were set as (|| Di+1 || – || Di ||)/|| Di || <1.0e–6, where || || stands for the norm of matrix, and Di for the matrix of genetic (co)variance, farm (co)variance, or residual (co)variance at the ith iteration. For convergence, all random effects were required to meet the above criteria simultaneously. Standard errors of estimates of direct and maternal heritabilities and genetic correlations were calculated by formulas of Falconer (1989), as implemented by Carnier et al. (2000).
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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. In Tottori, cattle were younger at both calf and carcass markets than in Hyogo. In contrast, MS was greater in Hyogo, even though SF was less. A large difference in inbreeding coefficients was found, reflecting differences in breeding history and mating systems between prefectures. Breeding stock in Hyogo has been maintained as an almost closed population (Honda et al., 2001). Although data in this study were collected from commercial populations, all calves in the Hyogo datasets were produced by AI sires from the Hyogo breeding population. On the other hand, in the dataset of Tottori, the calves were produced by AI sires from various prefectures. The proportion of progeny produced by AI sires from the Tottori population decreased from 98.4% in 1988 to 75.8% in 2000.
Estimated genetic parameters for calf market weight are shown in Table 3. Variance components and heritability estimates for calf market weight are expressed as the average of 10 estimates obtained from 2-trait analyses with 10 carcass traits. Ranges of standard errors of individual direct heritability, maternal heritability, and genetic correlation between direct and maternal genetic effects from ten 2-trait analyses were from 0.03 to 0.04, 0.01 to 0.02, and 0.04 to 0.10, respectively. Mukai et al. (2000) reported estimates of direct heritability for calf market weight of Japanese Black cattle to be 0.25, 0.30, and 0.27 using field data from the Iwate, Gifu, and Kagoshima prefectures, respectively. The estimates in this study were similar to those reported estimates.
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. The estimate in Hyogo was lower than that in Tottori but similar to the estimate of 0.06 reported by Kitamura et al. (1999) using calf market weights of Japanese Black cattle in the Shimane prefecture.
Genetic correlations between direct effect and maternal effect were positive (0.17) in Hyogo and highly negative (–0.63) in Tottori. The estimates for calf market weight of Japanese Black cattle were also reported to be positive by Mukai et al. (2000) and Kitamura et al. (1999) and were consistent with our estimate in Hyogo. However, in Tottori, there was an antagonistic relationship between direct and maternal genetic effects. Shimada et al. (1995) analyzed body weights from birth to 6 mo in Japanese Black cattle from the National Agricultural Experimental Station and reported consistent negative direct-maternal genetic correlations (–0.70 to –0.32). Estimates of direct-maternal genetic correlations may be influenced by a negative dam-offspring environmental correlation (Koch, 1972; Baker, 1980), often known as fatty udder syndrome. However, in Japan, calves from poor milking cows are given more milk replacer and starter than calves from high milking cows (i.e., nutritional condition of calves from different cows tends to be similar and independent of milking ability in Japan). In such a case, dam-offspring covariance is expected to be small. Other possible reasons for negative estimates of direct-maternal genetic correlations may be additional variation between sires or sire x year interaction effects (Robinson 1996a,b; Meyer 1997). Robinson (1996b) stated that additional variation between sires might result from the importation of superior genetic material. As described earlier, because migration of breeding stock from other populations into Tottori tended to increase and changes in production systems may have occurred in Tottori, additional variation between sires or sire x year interaction effects are likely to have exaggerated the negative correlation in these data.
Fractions of phenotypic variance due to cow-calf production farm were estimated to be 16 and 17% in Hyogo and Tottori, respectively. It is expected that the feeding and management systems of individual caw-calf operators have a large effect on early growth of calf because the farmers try to enhance early growth to increase value at calf market.
Estimates of heritability for carcass traits, fractions of phenotypic variance due to fattening farm, and genetic correlations with direct and maternal effects for calf market weight are shown in Table 4. Estimates of heritability for carcass traits were moderate to high, ranging from 0.31 to 0.61 in Hyogo and from 0.32 to 0.53 in Tottori. Considerable genetic variation that can be utilized for genetic improvement seems to remain in both prefectures. Mukai et al. (1995) analyzed genetic relationships between growth traits measured during performance testing at a test station and carcass traits collected from field data in the Kagoshima prefecture. They reported estimates of heritability for carcass traits to be moderate (0.39) to high (0.55), similar in magnitude to our estimates. Variances attributable to fattening farm ranged from 2 to 14%. Generally, variance due to farm was not as large as genetic causes of variation.
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). This might contribute to the larger genetic correlations in Hyogo. Estimates of genetic correlations between direct effects for calf market weight and CW were highly positive in Hyogo (0.87) and Tottori (0.56). Mukai et al. (1995) also found that CW was highly correlated with weights during performance testing (0.87 to 0.95). Estimates of genetic correlations between maternal effect for calf market weight and direct effect for CW were also positive in both prefectures but lower than the corresponding direct-direct genetic correlations. Few literature estimates are available regarding genetic correlations between maternal genetic effects for early growth traits and direct effects for carcass traits. Using a multiple-trait animal model, Splan et al. (2002) estimated the genetic correlations between direct and maternal genetic effects for weaning weight and direct effects for carcass traits in crossbred cattle. They also reported large positive genetic correlations of direct effects for carcass weight with direct and maternal effects for weaning weight (0.70 and 0.61, respectively). Both RA and RT had positive genetic correlations with direct effects for calf market weight, but lower genetic correlations with maternal effects. However, estimates of genetic correlations of SF with direct and maternal effects for calf market weight were near zero and positive, respectively, in both prefectures.
Genetic correlations of MS with direct effects for calf market weight were estimated to be negative (–0.10) in both prefectures, whereas the correlations with maternal effects for calf market weight were 0.26 in Hyogo and 0.09 in Tottori. Mukai et al. (1995) also reported negative estimates of genetic correlations between direct effects for early weights and MS (–0.10 to –0.04), which are similar to our estimates. Splan et al. (2002) also reported a negative estimate of genetic correlation between direct effect for weaning weight and MS (–0.12) and a positive correlation between maternal effect for weaning weight and direct effect for MS (0.28). The magnitude of their estimates of genetic correlations was similar to those of this study. The positive genetic relationship between maternal effects for calf market weight and direct effects for MS is favorable from the viewpoint of improvement for both effects.
In Japan, consumers generally prefer meat color intermediate between bright and dark, corresponding to categories 3 or 4. In these data, one-half of the records for MC fell into category 4 in both prefectures. However, MC was found to be heritable and had genetic relationships with direct and maternal effects for calf market weight, except with the direct effect in Tottori. Although the magnitude of the relationships was small, attention should be paid to correlated response for MC with selection on direct and maternal effects for calf market weight.
For MB, MF, and MT, estimates of genetic correlations with calf market weight were similar to those involving MS in both prefectures. Hence, direct-direct genetic correlations and direct-maternal genetic correlations were low and positive in Hyogo, and were low negative and near zero in Tottori, respectively. This is not unexpected, as in the preliminary analyses, estimated genetic correlations among MS, MB, MF, and MT were very high, ranging from 0.93 to 1.00 in both prefectures. This may suggest that selection on calf market weight does not cause detrimental indirect effects on the meat characters, and, in addition, selection for MS would be expected to improve almost all meat qualities simultaneously in both prefectures.
Improved maternal ability is important to increase overall beef productivity, but records for estimating milking and nursing abilities are generally not available for beef cows because milk yield is not usually measured. In this study, it became clear that variances and covariances for such maternal effects could be estimated through calf market weight at about 8 to 10 mo of age. Because almost all calves are weighed at calf market, estimation of direct and maternal effects can be useful for evaluating maternal ability. Genetic parameters for calf market weight were different between Hyogo and Tottori, possibly due to differences in respective breeding and production systems. Therefore, genetic parameters for calf market weight should be estimated in each population under consideration. Furthermore, a negative direct-maternal genetic correlation for calf weight was estimated in Tottori. As a result, a breeding system should be planned carefully. Nomura and Shimada (1998) conducted a simulation study under negative direct-maternal correlation (–0.70) based on the genetic parameters for weight at 6 mo reported by Shimada et al. (1995). They demonstrated that an approach to mate selection as proposed by Toro and Silio (1992) was efficient in improving direct effects, while restricting maternal effects to zero change. Such an approach may be well suited for simultaneous selection in the Tottori population.
Direct and maternal effects for calf market weight were genetically correlated with carcass traits. Selection for increased direct genetic value for calf market weight would improve the traits concerning meat quantity. However, selection for direct genetic value for calf market weight would slightly decrease MS, whereas selection for maternal genetic value would result in increased MS. Thus, information obtainable from genetic evaluation of calf market weight should be considered in making breeding decisions, such as selection of breeding stock and mating schemes of AI sires with breeding cows.
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IMPLICATIONS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 Corresponding author: oyama{at}kobe-u.ac.jp
Received for publication December 13, 2005. Accepted for publication May 12, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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