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ANIMAL GENETICS |
Animal and Dairy Science Department, University of Georgia, Athens 30602-2771
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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 • Growth • Maternal • Suspensory Score • Teat Score
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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; Lewis et al., 1990; Miller et al., 1999) in beef cattle. Milk yield in beef cattle can be effectively selected for through maternal genetic components of weaning weight (Diaz et al., 1992; Minick et al., 2001; Baker et al., 2003).
Some beef breed associations provide a scoring system for the evaluation of teat and udders. However, the relationship of udder scores with milk production and calf growth performance in beef cattle is unclear. In dairy cattle, several studies have examined the relationship between udder type traits and milk production with varying results. Long teats were associated with lower milk yield (Hickman, 1964; Freeman, 1976; DeGroot et al., 2002) and weaker, deeper udders (Short et al., 1991). Conversely, increased teat length (Harris et al., 1992; Brotherstone, 1994; Cruickshank et al., 2002), large teat diameter (Moore et al., 1981; Seykora and McDaniel, 1985; Seykora and McDaniel, 1986), loose foreudder attachment (Harris et al., 1992; Cruickshank et al., 2002; DeGroot et al., 2002), and pendulous udders (Freeman, 1976) were associated with higher milk yield.
The size and shape of a cow’s teats and udder can also limit a calf’s genetic potential for growth. Frisch (1982) reported an association between long teats and higher calf mortality due to the inability of a calf to nurse and concluded that the amount of milk a calf receives may depend on the size and shape of the dam’s teats. Likewise, Wythe (1970) reported that a pendulous udder and large teat size adversely affected calf nursing ability. The objectives of this study were to estimate genetic and environmental parameters for teat and udder suspensory score and to investigate the relationship of teat and udder suspensory score with calf growth traits and maternal genetic growth effects.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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. Each farm or ranch was responsible for evaluating cows for teat size and udder support. Teat score was a subjective assessment of the teat size and ranged from 0 (very large) to 50 (very small), and suspensory score was a subjective assessment of the udder support and ranged from 0 (very pendulous) to 50 (very tight). Teat size was a combination of length and circumference, with more emphasis on circumference when scoring (AGA, 1999).
Some cows in the dataset contained multiple score records within a few days, weeks, or months (less than 8 mo apart) of one another. If the scores were taken at parturition, then at least 9 mo should have separated a cow’s multiple-score records, unless it gave birth to twins or triplets. To decrease the bias when selecting first-parity records, cows with multiple scores within 280 d were removed. There was no information in the dataset pertaining to the rearing of multiple calves; therefore, cows that gave birth to multiple calves were removed. Thus, first-parity cows included in the analysis were required to 1) be at least 50% Gelbvieh, 2) have given birth to a single calf, 3) be 4 yr of age or younger at the time of measurement (parturition), and 4) be no younger than 548 d at the time of measurement (parturition). There were 9,202 first-parity cows that were 3 yr of age or younger at the time of conception; therefore, we believe that the inclusion of the 216 (2%) animals that conceived between 3 and 4 yr of age would not significantly alter the results presented in this paper. The format of the data was such that cows had a record for both teat and suspensory score. A total of 9,418 cows with teat and suspensory scores remained for analysis after editing. The number of sires, herds, and herd-years are shown in Table 1.
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). Weights recorded outside of their respective age range were considered missing.
The difference in weight between birth and weaning divided by weaning age was used to calculate WG. Similarly, YG was calculated as the difference between yearling and weaning weights divided by the difference in age between yearling and weaning. If a calf had a WW record, but no BW record, a standard BW of 39 kg for male or 36 kg for female calves (BIF, 1996a) was used to calculate WG. Calves that had missing BW, WW, and YW were not included in the analysis. Thus, a total of 19,119 calves with at least one growth record were included in the analysis, and 62,415 animals were included in the pedigree file. The number of sires, herds, and calf growth records for BW, WW, and YW is in Table 1
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Statistical Analysis and Computations
The udder score data evaluated on the cows were combined with the growth data measured on their corresponding calves for analysis. The following mixed model was used for the multiple-trait analysis of teat score, suspensory score, BW, WG, and YG:
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where yijklno was the observed teat score, suspensory score, BW, WG or YG for cow or calf n; HYi was the fixed effect of herd-year class i; MOj was the fixed effect of month of calving j; Ak was the fixed effect of age of cow (in years) at calving class k; Sl was the fixed effect of sex l of calf n (included only in the model for BW, WG, and YG); b was a fixed regression coefficient on percentage Gelbvieh (PG)ijklno of the animal in which the measurement was observed; un was the random additive effect of cow or calf n; mn was the random maternal genetic effect of cow n (included only in the model for BW and WG); pen was the permanent environment effect of cow n (included only in the model for BW and WG); and eijklno was the random residual term.
In matrix notation, the model could be expressed as:
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where y was the vector of phenotypic records, ß was the vector of systematic effects of order p, u was the vector of animal effects with order q, m was the vector of maternal genetic effects, pe was the vector of maternal permanent environment effects, and e was the vector of residual effects. Furthermore, X, Z, Zm, and W were the corresponding incidence matrices with the appropriate dimensions.
A Bayesian implementation via Gibbs sampling was adopted. Conditionally on the position parameter vector, 
= (ß', u', m', pe')', and the residual (co)variance matrix, R, the observed responses were assumed to be normally distributed:
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where R was a 5 x 5 matrix. Given that udder scores and growth traits were measured in different sets of animals, the residual covariances between those traits could not be inferred and hence were assumed as zero, leading to
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where
, 
, 
, 
and 
were the residual variances for teat score, suspensory score, BW, WG, and YG, respectively; 
eT,S was the residual covariance between teat and suspensory score; eBW,WG and eBW,YG were the residual covariances between BW with WG and YG, respectively; and eWG,YG was the residual covariance between WG and YG.
To ensure proper posterior distribution, the following prior distributions were assumed for the parameters in the model.
A normal distribution with mean 0 and a large variance was assumed as prior for the vector ß:
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Multivariate normal distributions were assumed as prior for direct additive and maternal effects:
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with
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where A was the relationship matrix of all animals in the pedigree file, G11 was a 5 x 5 (co)variance matrix of direct additive effects, G22 was a 2 x 2 matrix of maternal additive effects, and G12 was the matrix of genetic covariances between direct additive and maternal effects.
Multivariate normal distributions were assumed for the maternal permanent environment effects
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with
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where
and 
were the maternal permanent environment variances for BW and WG, respectively; and 
was the maternal permanent environment covariance between BW and WG.
For all parameters included in the dispersion matrices, R, G, and P, uniform bounded priors were assumed.
The joint posterior density was obtained by the product of densities in Expressions [1] through [4] and the dispersion parameters.
 | [5] |
defined only within the boundary of the dispersion parameters and the bounded priors.
The joint posterior distribution in Expression [5] was in closed form, and the conditional posterior distribution of all the parameters of the model can be derived as described by Jensen et al. (1994), with normal and scaled-inverted Wishart distributions for the position and dispersion parameters, respectively.
Convergence diagnostics were assessed using the method of Raftery and Lewis (1992) based on the first 25,000 iterations as implemented in the CODA software (Best et al., 1995). The required length of the burn-in period was always less than 7,000 iterations for all parameters. Thus, a total chain length of 75,000 iterations of the Gibbs sampler was run with a conservative burn-in of 25,000 iterations. The remaining 50,000 iterations were retained without thinning for post-Gibbs analysis.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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. A summary of the posterior means and SD for genetic and residual correlations of dam udder scores and calf growth traits is presented in Table 3.
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; Fuerst-Waltl et al., 1998; Van Dorp et al., 1998; Cruickshank et al., 2002; DeGroot et al., 2002), and teat score heritability in beef cattle that ranged from 0.16 to 0.22 (Sapp et al., 2003), depending on the number of score classes. The AGA considers teat score to be a subjective score of the teat size, where teat size is considered a combination of length and circumference. Luo et al. (1997) reported a heritability estimate for teat diameter of 0.38 in dairy goats based on a 50-point scale using an animal model and an estimate of 0.12 when a sire model was used. Heritability estimates of actual teat diameter measurements were 0.39 and 0.37 in Holsteins using a sire model and cow-dam regression, respectively (Seykora and McDaniel, 1985). Lin et al. (1987) reported actual front and rear teat diameter heritability estimates of 0.08 and 0.11, respectively.
Comparing the suspensory score in beef cattle with scores relating to suspension measurements in dairy cattle, such as foreudder attachment or udder cleft, would be difficult given the variation in the trait definitions as well as the training level or expertise of the classifiers. In dairy cattle, heritability estimates reported by Short et al. (1991), Cruickshank et al. (2002), and DeGroot et al. (2002) ranged from 0.19 to 0.37 and 0.13 to 0.29 for foreudder attachment and udder cleft, respectively.
The genetic correlation between teat and suspensory score was 0.95. This result suggests that the same genes might control both teat and suspensory score; however, research in dairy cattle indicates that teat and suspensory score are not the same trait. The genetic correlation between teat length and foreudder attachment in dairy cattle reported in the literature ranged from –0.13 to 0.31 (Short et al., 1991; Harris et al., 1992; Brotherstone, 1994; Gengler et al., 1997; Vukasinovic et al., 1997; Cruickshank et al., 2002; DeGroot et al., 2002). Likewise, the genetic correlation reported in the literature ranged from –0.10 to 0.21 (Short et al., 1991; Harris et al., 1992; Gengler et al., 1997; Cruickshank et al., 2002; DeGroot et al., 2002) and 0.11 to 0.31 (Brotherstone, 1994; Vukasinovic et al., 1997) between teat length with udder cleft and udder support, respectively. The differences in the level of expertise of the classifiers in the beef industry compared with those in the dairy industry may be a factor in the contrasting genetic relationship between teat size and udder suspension. Also upon observation of the data, 62% of the records had the same score for both teat and suspensory score, which may give a false impression of the genetic correlation. It seems that in this dataset, many producers evaluated the udder as a unit and then assigned teat size and udder suspension the same score, whereas the dairy classifier is more apt to score teats and suspension separately. However, the genetic relationship between teat size and udder suspension in dairy and beef cattle could also be dissimilar due to differences in trait definitions the dairy and beef industry use to describe udder suspension. Dairy cattle have different traits (foreudder attachment, udder cleft, and udder depth) that define specific areas or aspects of udder suspension. However, AGA scores overall udder suspension, which would include a combination of the above dairy traits to describe udder suspension, rather than each of the specific areas or aspects of the udder for suspension.
Calf Growth Traits
Direct heritability estimates of growth traits were moderate, whereas maternal heritability estimates were low. Estimates for direct and maternal heritability of BW were 0.39 and 0.09, respectively. Bennett and Gregory (1996) reported a direct heritability estimate for BW in Gelbvieh cattle of 0.38. MacNeil et al. (1998) reported direct and maternal heritability for BW in Hereford cattle of 0.28 and 0.16, respectively. Direct and maternal heritability estimates of WG were 0.27 and 0.14, respectively. Miller and Wilton (1999) reported heritabilities of 0.22 and 0.24 for direct and maternal components of weaning gain, respectively, in a multibreed beef cattle herd. The heritability estimate reported for YG was 0.21. Bennett and Gregory (1996) reported a 168-d postweaning gain heritability estimate for Gelbvieh cattle of 0.45.
The genetic correlations between direct BW with direct WG and YG were 0.40 and 0.32, respectively, suggesting that calves with genetics for increased prenatal growth also have increased genetic potential for growth to weaning and yearling. The correlation between direct BW and direct WG does not support the findings of Boggs et al. (1980) that BW had little effect on daily gain from birth to weaning. In contrast, Christian et al. (1965) reported a highly significant partial regression of ADG from birth to weaning on BW. The genetic correlation between direct WG and YG was –0.05. This indicates that direct WG had virtually no effect on direct YG, further suggesting that the level of growth from weaning to yearling did not depend on the level of growth from birth to weaning. Bennett and Gregory (1996) reported genetic correlations of 0.56 and 0.75 between direct effects of 200-d WW and 168-d postweaning gain in purebred and composite beef cattle, respectively. In Nelore cattle, the genetic correlation between direct WW and YW was 0.74 (Eler et al., 1995). Willham (1972) reported that decreased growth rate efficiency in the feedlot could occur if more milk was consumed by the calf than could be used for lean tissue growth, resulting in excess fat in the weaned calf. However, the slightly negative correlation between direct WG and YG may also be affected by the large amount of missing YG records (approximately 83%).
Genetic correlation estimates of direct BW with maternal BW and WG were –0.13 and –0.15, respectively. These correlations suggest that direct BW had a slightly negative effect on the maternal components of growth. Particularly, increased direct BW resulted in slightly decreased maternal WG or dam milk production. In contrast, Drewry et al. (1959) and Diaz et al. (1992) found positive effects of calf BW on dam milk production. Estimates of the genetic correlation of direct WG with maternal BW and maternal WG were –0.01 and –0.35, respectively. Previous research has shown a varying relationship between direct and maternal weaning gain. Miller and Wilton (1999) reported a genetic correlation between direct and maternal weaning gain of –0.35 in a multibreed herd. In contrast, Dodenhoff et al. (1999) reported a range of the genetic correlation between direct and maternal WW of –0.37 to 0.64 for 12 breeds of beef cattle. Bennett and Gregory (1996) reported –0.02 and 0.13 genetic correlations between direct and maternal 200-d weight for purebred and composite beef cattle, respectively. The maternal permanent environment correlation (SD) between BW and WG was 0.84 (0.06).
Dam Udder Scores and Calf Growth Traits
The genetic correlations of teat (suspensory) score with direct WG and maternal WG were 0.38 (0.31) and –0.47 (–0.55), respectively. The correlations between teat and suspensory score with direct WG indicate that cows with smaller teats or tighter udders have calves with more genetic potential for growth from birth to weaning. The correlations between teat and suspensory score with maternal WG indicate that as teats get smaller or udder suspension gets tighter, the maternal component of WG decreases. Previous research has shown varying genetic relationships between dam milking ability and calf WG. Lewis et al. (1990) and Miller et al. (1999) reported increased milk yield of the dam was associated with increased calf preweaning gain. Gleddie and Berg (1968) reported a phenotypic correlation with calf ADG from birth to weaning of 0.84 when milk yield was averaged from four test month measurements. Mallinckrodt et al. (1993) reported simple correlations between milk yield and WW of 0.40 and 0.36 in Polled Hereford and Simmental, respectively, whereas Lee and Pollak (2002) reported a negative genetic correlation between 120-d WW and daily milk yield measured at sequential intervals from calving to weaning. In beef cattle, the maternal component of WW (or WG, as reported in this article) is an indirect measurement of milk production of the dam. Thus, the results of this paper indicate that cows with smaller teats and tighter udders produced less milk and raised calves that had higher genetic potential for direct genetic WG.
Estimates of the genetic correlation between teat and suspensory score with direct BW were –0.18 and –0.06, respectively. The negative correlations of udder scores with direct BW suggest that cows with smaller teats and tighter udders have calves with slightly lower genetic growth potential for BW. An estimate of –0.16 was found for the genetic correlation between teat and suspensory score with maternal BW. The correlation between udder scores and maternal BW suggests that cows with smaller teats and tighter udders provide a slightly smaller maternal environment for prenatal growth. The correlations were low between dam udder scores and BW, but zero was not included in the high posterior density (95%) intervals. Although the genetic correlations are significantly different from zero, the practical implication of dam udder scores on direct and maternal BW of the calf may not be very large.
The genetic correlations of teat size, udder suspension, and weaning weight maternal with birth weight direct indicate a slight antagonistic relationship between dam milk production and calf prenatal growth. However, the relationship between calf BW and dam milk production is unclear in the literature. Lee and Pollak (2002) reported a negative genetic correlation (–0.16 to –0.08) for calf BW with dam milk production in Korean cattle. Mallinckrodt et al. (1993) reported a negative simple correlation (–0.05) between milk yield and BW in Simmental cattle and a positive correlation (0.24) in Polled Hereford cattle. Conversely, Drewry et al. (1959) reported significant intra-year correlations between BW of the calf and milk production of the dam. Likewise, Rutledge et al. (1971) and Diaz et al. (1992) reported positive effects of calf BW on milk production of the dam. Rutledge et al. (1971) and Diaz et al. (1992) speculated that increased BW of the calf and increased dam milk production could be due to an increased calf demand for milk that stimulates lactation or to a higher capacity of the calf to consume available milk. Sheldon (1984) suggested that increased placental lactogen secretion from heavier fetuses in turn stimulated increased milk production in the subsequent lactation.
Estimates of 0.09 and –0.01 were found for the genetic correlation between teat and suspensory score with direct YG. These correlations are small and close to zero, indicating that size of the teats and strength of the udder has virtually no effect on the direct component of YG. Lee and Pollak (2002) reported a genetic correlation of –0.17 between YW and daily milk yield from calving to 120-d postpartum. Miller et al. (1999) reported that postweaning growth was not significantly influenced by increased milk yield of the dam although the trend was negative. Lewis et al. (1990) reported postweaning effects of increased WW due to increased dam milk yield were small. Conversely, Clutter and Nielsen (1987) reported that calves of high-producing dams maintained 63% of the advantage in weaning weight through the postweaning feedlot period to slaughter.
Relationship of Breeding Values for Udder Scores and Maternal Weaning Gain
The Pearson correlations between predicted breeding values for additive teat and suspensory score with maternal WG are shown in Table 4. The Pearson correlation between predicted breeding values for additive teat (suspensory) score with maternal WG was –0.60 (–0.66). As pointed out in the previous discussion, the correlations suggest that animals with genetic potential for larger teats and more pendulous udders have an increased potential for milk production. However, increased milk production in beef cattle production has no benefit if a calf cannot obtain the milk. Frisch (1982) reported an association between long teats and higher calf mortality due to the inability of a calf to nurse and concluded that the amount of milk a calf receives may depend on the size and shape of the dam’s teats. Likewise, Wythe (1970) reported a pendulous udder and large teat size adversely affect calf nursing ability. Therefore, the additive predicted breeding values for teat score were separated into three categories. The first category, E1, contained the extreme 5,000 animals with predicted breeding values for larger teats. The third category, E2, contained the extreme 5,000 animals with predicted breeding values for smaller teats. The second category, M, contained all the remaining (52,415) animals that were not in either E1 or E2. Similarly, the additive predicted breeding values for suspensory score were separated into three categories: E1, M and E2.
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found that 27.9 and 38.1% of Brahman calves born to dams with long teats and very short teats, respectively, nursed without assistance. Similarly, Wythe (1970) reported that only 25.3% of calves born to dams with large udders nursed without assistance. Animals in the E2 category were those with the predicted genetic potential to have the smallest teats and tightest udders. Cows with extremely small teats or tight udders appear to have less genetic potential for milk production. Perhaps cows with extremely small teats and/or tight udders fail to produce enough milk to allow the calf to meet its full growth potential, which would again lead to less growth than expected and reduce the magnitude of the relationship between predicted breeding values of udder trait scores with maternal WG. Animals in the intermediate category were not in either extreme based on their predicted breeding values for either teat or suspensory score. Perhaps cows in this group generally produced enough milk to meet the growth potential of the calf and possess udders that do not hinder their calves’ ability to suckle; therefore, the correlations between predicted breeding values of teat and suspensory score with WG may be more reflective of the genetic relationship between udder scores and actual milk production. These results also suggest that it may be more beneficial for producers to select animals that have intermediate breeding values for teat and suspensory score in order to obtain a balance between increased milk production and accessibility of the milk by the suckling calf. |
Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Correspondence: Edgar L. Rhodes Center for Animal and Dairy Science (phone: 706-542-0965; fax: 706-583-0274; e-mail: rsapp{at}uga.edu).
Received for publication November 4, 2003. Accepted for publication April 16, 2004.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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  M. D. MacNeil and T. B. Mott Genetic analysis of gain from birth to weaning, milk production, and udder conformation in Line 1 Hereford cattle J Anim Sci, July 1, 2006; 84(7): 1639 - 1645. [Abstract] [Full Text] [PDF]
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