Genetic parameters for cattle price and body weight from routinely collected data at livestock auctions and commercial farms

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1 Published December 4, 2014 Genetic parameters for cattle price and body weight from routinely collected data at livestock auctions and commercial farms N. Mc Hugh,* R. D. Evans, P. R. Amer, A. G. Fahey, and D. P. Berry* 1 *Animal and Bioscience Research Department, Animal and Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork, Ireland; School of Agriculture, Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland; Irish Cattle Breeding Federation, Highfield House, Bandon, Co. Cork, Ireland; and Abacus Biotech Limited, PO Box 558, Dunedin, New Zealand ABSTRACT: Beef outputs from dairy farms make an important contribution to overall profitability in Irish dairy herds and are the sole source of revenue in many beef herds. The aim of this study was to estimate genetic parameters for animal BW and price across different stages of maturity. Data originated from 2 main sources: price and BW from livestock auctions and BW from on-farm weighings between 2000 and The data were divided into 4 distinct maturity categories: calves (n = 24,513), weanlings (n = 27,877), postweanlings (n = 23,279), and cows (n = 4,894). A univariate animal model used to estimate variance components was progressively built up to include a maternal genetic effect and a permanent environmental maternal effect. Bivariate analyses were used to estimate genetic covariances between BW and price per animal within and across maturity category. Direct heritability estimates for price per animal were 0.34 ± 0.03, 0.31 ± 0.05, 0.19 ± 0.04, and 0.10 ± 0.04 for calves, weanling, postweanlings, and cows, respectively. Direct heritability estimates for BW were 0.26 ± 0.03 for weanlings, 0.25 ± 0.04 for postweanlings, and 0.24 ± 0.06 for cows; no BW data were available on calves. Significant maternal genetic and maternal permanent environmental effects were observed for weanling BW only. The genetic correlation between price per animal and BW within each maturity group varied from 0.55 ± 0.06 (postweanling price and BW) to 0.91 ± 0.04 (cow price and BW). The availability of routinely collected data, along with the existence of ample genetic variation for animal BW and price per animal, facilitates their inclusion in Irish dairy and beef breeding objectives to better reflect the profitability of both enterprises. Key words: body weight, cattle, genetic parameter, price per animal 2011 American Society of Animal Science. All rights reserved. J. Anim. Sci :29 39 doi: /jas INTRODUCTION Revenue from the sale of surplus animals is the primary source of on-farm income for Irish beef farmers. Some beef producers rear calves to weanling stage and, in doing so, aim for increased BW but more importantly seek to maximize the price received for the animal. Other beef producers sell cattle for finishing; they also aim for increased BW and maximum price. Cull cows sales also contribute to the overall profitability of beef production systems. Estimates of the genetic variation in price per animal as weanlings, postweanlings, or cows are lacking in the literature. Most international dairy breeding programs have historically selected for increased milk production (Miglior 1 Corresponding author: donagh.berry@teagasc.ie Received March 31, Accepted September 22, et al., 2005). However, beef output, such as young calves and cull cows, remains an important financial contribution to a dairy farm; van der Werf et al. (1998) reported that 10 to 20% of the gross income of a dairy farm is from the sale of calves and cull cows. Within Ireland there is a large interdependency between the beef and dairy herds. A large proportion of dairy females are mated to beef bulls, and a substantial proportion of the resulting crossbred females are used as dams within the national beef herd (Berry et al., 2006). The majority of dairy animals that are sold from the dairy herds and sired by beef and dairy sires are retained within Ireland and end up in specialized finishing herds that also finish weanlings purchased from beef herds. Possible breeding goal traits, which reflect beef revenue from beef and dairy enterprises, include price per animal, animal BW, and cull cow value. However, there is a paucity of studies that have attempted to quantify the genetic variation present in animal price, due mainly to a lack of available phenotypes. The aim of this study 29

2 30 was to estimate phenotypic and genetic parameters for animal BW and price per animal across different stages of maturity. MATERIALS AND METHODS Animal Care and Use Committee approval was not obtained for this study because the data were obtained from an existing database at the Irish Cattle Breeding Federation (ICBF) database, Bandon, Co. Cork, Ireland. The data originated from 2 main sources: BW and price data collected from livestock auctions and BW data collected from commercial farms. Data Editing A total of 2,967,791 BW and animal price records from 2,506,110 animals sold at 71 livestock auctions in Ireland between 2000 to 2008 were extracted from the ICBF database. Livestock selling auctions, from here on referred to as auctions, are permanent venues positioned around Ireland where farmers can purchase or sell livestock. As part of the national breeding program, progeny of test sires as well as commercial contemporaries are also weighed on commercial farms and these data are captured. A total of 875,874 records from 682,694 animals, between 150 and 600 d of age, collected from 32,089 herds between 2000 and 2008, were also available in this study; no price data were available on these animals. The data were divided into 4 distinct maturity categories, described later: calves, weanlings, postweanlings, and cows. To accurately estimate parameters, only animals sold individually at the livestock auctions were retained; 28% of the animals in the data set were sold in groups. Animals were discarded if their sire was unknown. Animals were also discarded if their sale price or BW were unknown, with the exception of calves where BW information was not available, but the price per animal was known. Progeny of dams calving greater than 22 mo from the median age within parity were discarded. Progeny of dams calving less than 18 mo of age were discarded. Animals retained had to have at least 66% of their breed fraction known; the mean breed fraction known varied from 89% (cows) to 93% (calves). Animals were subsequently classified into 7 main breed categories according to the dominant breed composition of the animal (proportion of each breed composition required in parentheses, along with breeds considered for inclusion within each category): purebred dairy animals (>90%, Holstein, Friesian, Montbeliarde, Normande, Norwegian Red, excluding Jerseys), purebred beef animals (>90%, Aberdeen Angus, Belgian Blue, Charolais, Hereford, Limousin, Simmental), dual-purpose dairy animals (33 to 66%, Montbeliarde, Normande, Norwegian Red), crossbred British beef animals (33 to 66%, Aberdeen Angus, Hereford), crossbred Mc Hugh et al. Continental beef animals (33 to 66%, Belgian Blue, Charolais, Limousin, Simmental), Jersey (33 to 66% Jersey), or other. Within each maturity category, price and BW records more than ±4 SD from the mean, within breed group, were discarded. This step was performed as an editing criterion only to remove possible outlier values; the individual breed proportion of each animal was included in the statistical model (described later). Because some animals go through auctions more than once in their lifetime, only the first recorded date in time for calves, weanlings, and postweanlings were retained; for cows the last recorded date in time was retained. Calves. In Ireland, calves from dairy herds are generally sold in livestock auctions from a couple days of age with the majority being sold before compulsory requirement of health testing at 6 wk of age (Mc Hugh et al., 2010). Not all calves are sold in livestock auctions, and some are sold privately among individuals; no data on these sales were available. In the present study, calves were defined as animals from dairy cows sold between 2 d of age and 12 wk of age. Calves are generally not weighed at livestock auctions, and therefore only individual calf price information was available for inclusion in this analysis. Calves were further categorized into 3 classes based on age at sale (percentage of calves in each age category in parentheses): 2 to 24 d (39%), 25 to 42 d of age (54%), and 43 to 84 (7%) d of age. Only calves sold between 2 and 450 were retained. Weanlings. Animals from beef cows are generally weaned at approximately 8 mo of age (Mc Hugh et al., 2010) at which time a large proportion are sold in livestock auctions. In this study weanlings were defined as animals sold between 6 and 12 mo of age from beef cows (i.e., dam breed proportion >66% beef) and were further divided into 2 age categories (percentage of weanlings in each age category in parentheses): 6 to 9 mo of age (64%) and 9 to 12 mo of age (36%). Only weanlings weighing between 150 and 900 kg and sold for between 200 and 1,200 were retained. On-farm BW records were also available on 17,673 weanlings from beef dams and with a known sire weighing between 150 and 600 kg; no price data were available on these animals. The BW data were included in the analysis as a separate trait but also combined with the BW data from the auction. Postweanlings. Postweanlings were defined as beef and dairy animals sold between 12 and 36 mo of age, and this included finishing steers, heifers, and bulls. Postweanlings were subcategorized into 2 age groups (percentage of postweanlings in each category in parentheses); 12 to 24 mo (79%) and 24 to 36 mo (21%). Postweanling data were limited to animals that weighed between 200 and 1,000 kg and were sold for between 200 and 1,500. On-farm weighing records were also available on 12,843 postweanlings weighing between 200 and 1,000 kg; no price data were available on these animals. The

3 Cattle price and body weight 31 BW data were included in the analysis as a separate trait but also combined with the BW data from the auction. Cows. Cows were defined as females that had calved at least once or were greater than 30 mo and less than 12 yr of age when sold. Only cows weighing between 300 and 1,000 kg and sold between 75 and 1,500 were retained. In Ireland, cows sold through livestock auctions include cull cows destined for slaughter, cows sold in calf, and cows not in calf when sold but that calved some time in the future (i.e., replacements). Accordingly, cows were classified both on their fate postsale and as a separate variable on the number of days since last calving. Fate postsale was categorized based on 4 possibilities. Where data on next calving were known, cows were grouped in days to next calving: less than 50 d, 51 to 100 d, 101 to 200 d, 201 to 300 d, and greater than 300 d. Cows that were destined for slaughter were grouped into 6 groups: cows slaughtered within 3 d postsale, 4 to 50 d, 51 to 100 d, 101 to 200 d, 201 to 300 d, and greater than 300 d. Cows that had not been allocated to any of the categories above but were sold within 280 d of the date of data extraction were allocated a separate code because their fate postsale could not be determined. Additionally, cows with no known fate postsale (i.e., did not calve again, were not slaughtered postsale, and were not sold within 280 d of the date of data extraction) were coded separately. Where cows calved again in their lifetime but were eventually slaughtered, fate postsale based on subsequent calving took precedence over fate postsale based on slaughter. Cows were also grouped on their days since last calving at the time of selling: less than 50 d postcalving, 51 to 100 d, 101 to 200 d, 201 to 300 d, and greater than 300 d. Females greater than 30 mo of age but with no recorded calving date were allocated a separate code. Contemporary Groups. For data originating from the auctions, 2 contemporary groups were defined: auction-date of sale and herd-year-season of sale. Where on-farm data were used, the contemporary group used was defined as herd-date of weighing. Herd-year-season of sale contemporary groups was generated using an algorithm described by Crump et al. (1997). This algorithm creates contemporary groups based on animals from the same herd that were sold in close proximity of time. In this study, animals from the same herd that were sold within 10 d of each other were grouped together. If the number of records in this immediately defined contemporary group was less than 8, then this contemporary group was merged with an adjacent group if the start date of one group and the end date of the other group were within 182 d of each other. An upper limit of 182 d was chosen for this study to retain a maximum number of records without compromising the purpose of defining contemporary groups. Across all contemporary group definitions, only records from contemporary groups with at least 5 records were retained. Final numbers per contemporary groups for each maturity group and across age groups are reported in Table 1. After all edits (including contemporary group edits) 24,513 calves, 27,877 weanlings, 23,379 postweanlings, and 4,894 cows remained with price or BW data or both (Table 1). The pedigree of each animal was traced back 4 generations, and the number of animals included in the pedigree for each maturity group is summarized in Table 1. Heterosis and recombination loss were calculated for each animal as n n sire + dam i i 1- åsire dam and 1- i i å, 2 i-1 i respectively, where sire i and dam i are the proportion of breed i in the sire and dam, respectively. Data Analysis Phenotypic and genetic variance components for animal price and BW, within each maturity group, were estimated separately using linear animal mixed models in ASREML (Gilmour et al., 2008); covariances between BW and price per animal within and across ages and sexes were also estimated using linear sire mixed models. Because price and BW information were available for the weanling, postweanling, and cow maturity categories, phenotypic and genetic variance components for price per kilogram were also estimated for these maturity categories. Fixed effects considered in all models, irrespective of maturity category, were as reported previously by Mc Hugh et al. (2010). These fixed effects included sex (male or female), age of animal at selling (continuous variable), the proportion of the 12 most common breeds (Aberdeen Angus, Belgian Blue, Charolais, Friesian, Hereford, Holstein, Jersey, Limousin, Montbeliarde, Normande, Norwegian Red, Simmental), calving ease (1 = no assistance/unobserved; 2 = slight assistance; 3 = severe assistance; 4 = veterinary assistance), whether the animal was born as a singleton or twin, heterosis (continuous variable), and recombination loss (continuous variable). Parity of dam (1, 2, 3, 4, 5, missing) and dam age in months relative to the median age within parity were also included as fixed effects. Breed proportion was treated as a continuous variable with a separate effect fitted in the models for each breed. When cow price was the dependent variable, cow parity number and cow age relative to the median age within parity were tested for inclusion in the models as described by Mc Hugh et al. (2010). When the dependent variable was weanling and postweanling price, the number of subsidies left to claim on the animal was also added as a fixed effect, and when cow price was the dependent variable, 2 variables describing a) the eventual fate of the sold cow

4 32 Table 1. Number of animals, contemporary groups (CG), herds, sires, dams, maternal grandsires (MGS), as well as the total number of animals in pedigree file for each maturity group and age groups within maturity group No. of CG Mc Hugh et al. Group and trait No. of animals Herdyear-season Date of sale or weighing No. of herds No. of sires No. of dams No. of MGS Pedigree Calf Price 24,513 2,769 1,064 1,325 2,975 20,771 2, ,729 <3 wk 9,545 2,161 1,235 1,140 1,961 8,561 1,697 3 to 6 wk 13,255 2,579 1,266 1,266 2,323 11,845 2,009 6 to 12 wk 1, , Weanling Price 10,304 1, ,329 7, ,980 6 to 9 mo 6,593 1,110 1, ,045 4, to 12 mo 3, , BW 27,877 2,532 2,491 1,380 2,861 19,124 2,871 99,009 6 to 9 mo 15,767 2,131 2,035 1,204 2,129 11,819 2,001 9 to 12 mo 12,110 1,903 1,885 1,090 1,921 9,698 1,965 Postweanling Price 16,317 2,202 1,357 1,582 2,909 14,716 2,961 93, to 24 mo 12,898 2,118 3,735 1,537 2,569 11,869 2, to 36 mo 3,419 1,020 1, ,105 3,260 1,049 BW 23,379 2,766 2, ,813 20,456 4, , to 24 mo 19,960 2,684 4,480 1,538 3,515 17,617 3, to 36 mo 3,419 1,020 1, ,105 3,260 1,049 Cow Price and BW 4, ,465 4,280 1,427 34,477 2 to 6 yr 2, ,682 1,020 6 to 14 yr 2, , and b) days since last calving were also included in the model. Due to large temporal variation in the market trends, standardization of price per animal was undertaken to account for the heterogeneity of residual variances across time. Before the estimation of variance components for price per animal, residuals from a fixed effects model with price per animal as the dependent variable and the aforementioned fixed effects included in the model (excluding contemporary groups) were standardized to the mean residual SD within the contemporary group of auction-date of sale. Standardized residuals were added back to the respective fixed effects solutions for each animal to generate a standardized price per animal. The variance components of the standardized price per animal and standardized price per kilogram are reported in the present study. Data on BW were not standardized. The univariate animal model used to estimate variance components was progressively built up to include a maternal genetic effect, a permanent environmental maternal effect, and a covariance between the direct and maternal components. The proportion of dams with greater than 1 progeny within maturity group were 15, 34, 11, and 14% for the calves, weanlings, postweanlings, and cows, respectively (Table 1). The log-likelihood ratio test between nested models was used to determine whether the addition of extra random components improved the fit of the data (Ferreira et al., 1999). Within each of the maturity groups, a series of bivariate analyses were undertaken using a sire model to estimate genetic correlations between animal BW and price (where available) as well as between sexes and between subgroups for age. With the exception of estimating the correlation between animal price and BW where animals had observations for both traits, there was no residual covariance between the 2 traits (e.g., an animal could not be both male and female). RESULTS The association between the fixed effects in the model and animal price are presented and discussed in detail elsewhere (Mc Hugh et al., 2010). In general, greater prices were paid for the older animals across maturity groups and especially for males. Irrespective of the maturity category, premium prices were paid for beef continental crossbred animals. The association between heterosis and price per animal was positive, and the size of the association increased with maturity category. Greater prices were paid for singletons, and the difference between price per animal paid for singletons and twins was greatest when sold as calves and weanlings. Across all maturity groups 76% of the animals were crossbred, although this varied from 49% (weanlings) to 91% (cows). The average heterosis for each maturity group was 0.62 for calves, 0.28 for weanlings, 0.46 for postweanlings, and 0.25 for cows. The average recom-

5 Cattle price and body weight 33 Table 2. Number of animals (n), mean (μ), and SD for the breed fraction of animals containing a proportion greater than zero for each breed across each maturity group 1 Calves Weanlings Postweanlings Cows Breed n μ SD n μ SD n μ SD n μ SD AN 5, , , BB 2, , , CH , , FR 18, , , HE 3, , , HO 24, , , , JE LM , , MO NO NR SI , , AN = Aberdeen Angus, BB = Belgian Blue, CH = Charolais, FR = Friesian, HE = Hereford, HO = Holstein, JE = Jersey, LM = Limousin, MO = Montbeliarde, NO = Normande, NR = Norwegian Red, SI = Simmental. bination across the maturity groups varied from 0.06 (weanlings) to 0.12 (cows). Most calves, postweanlings, and cows contained a proportion of Holstein; Charolais and Limousin contributed most to weanlings and postweanlings (Table 2). The annual genetic trend for price shows that prices increased for weanling and postweanlings and remained relatively constant for cows and calves (Figure 1). The annual genetic trend for BW (Figure 1) shows a decrease for cows and direct weanling BW but remained relatively constant for maternal weanling BW and postweanling BW. Calves Calves sold for an average price of 158 and the average age at sale was 28 d. Across different age groups and sexes, the genetic SD of total calf price varied from to 27.90, with greater genetic SD observed in female and younger calves (Table 3). The coefficient of genetic variation ranged from 8.3 to 19.5%, with greater values recorded in females and younger calves. The heritability across all calves was 0.34 ± 0.03, and the heritability estimates varied from 0.30 ± 0.05 to 0.45 ± 0.09 across sexes and calf age groups, with the exception of 0.09 ± 0.05 (calves aged 6 to 12 wk), although small numbers of animals (n = 1,713) were associated with this age group (Table 3). No significant maternal genetic variance and permanent environmental maternal variance were observed for calf price; maternal heritability across all calves was ± 0.006, and the maternal repeatability was ± The genetic correlation between male and female calf price across all calves was 0.44 ± The genetic correlations between price per animal at different ages were generally strong, ranging from 0.36 ± 0.19 (between calves aged 3 to 6 wk and calves aged 9 to 12 wk) to 0.98 ± (between calves 3 to 6 wk and 6 to 9 wk). Weanlings Price per Animal. Weanling price averaged 612, and the average age at sale of weanlings was 247 d. The genetic SD for weanling price ranged from to (Table 4). The coefficient of genetic variation for weanling price varied from 4.9 to 10.7%. Direct heritability for weanling price across all weanlings was 0.31 ± 0.05 and varied from 0.18 ± 0.06 to 0.59 ± 0.11 depending on the age group and sex under investigation (Table 4). Greater heritability estimates were associated with females (0.59 ± 0.11), although the SE were also larger. The maternal heritability and the maternal repeatability for weanling price were not different from zero. Across all weanlings, the maternal heritability was 0.03 ± 0.03 and the maternal repeatability was also 0.04 ± The correlation between female and male weanling price across all weanlings was strong (0.82 ± 0.06). The correlation between weanling prices across ages was strong (0.93 ± 0.18). BW. The average BW for weanlings sold through auctions was 303 kg; the average BW for farm recorded data was 350 kg. A strong genetic correlation existed between auction BW and on-farm BW (0.80 ± 0.02). Furthermore, the heritability for BW was similar irrespective of whether data were recorded in an auction (0.38 ± 0.03) or on farm (0.39 ± 0.07); the respective genetic SD were 22.7 and 27.1 kg. Mulder et al. (2006) reported that traits with a genetic correlation of 0.60 or greater in different environments could be treated as the same trait, although they could potentially be considered as genetically different traits. Therefore, BW data from both auction and on-farm weighings were combined and treated as 1 data set, and the results hereafter are based on the combined data set. Direct and maternal heritability estimates for the combined BW data are shown in Table 5. The direct

6 34 heritability of the combined data was 0.38 ± 0.03; however, when maternal effects were included in the model the direct heritability across all weanlings decreased to 0.26 ± 0.03, but varied across different ages and sexes when maternal effects were included in the model (Table 5). Maternal heritability estimates ranged from 0.04 ± 0.02 to 0.10 ± 0.02 and were different from zero across most age groups and sexes (Table 5). The maternal repeatability varied from 0.06 ± 0.03 to 0.19 ± 0.02 (Table 5). No significant genetic covariance was estimated between direct and maternal effects for weanling BW. Mc Hugh et al. The genetic correlation between BW in male and female weanlings was near unity (0.89 ± 0.01). The genetic correlation between weanling price and BW was strong (0.75 ± 0.04). Price per Kilogram. The average price per kilogram for weanlings sold through auctions was 1.84/ kg. The heritability estimates for price per kilogram were slightly less than the heritability estimates for price and BW for different ages and sexes (results not shown). Across all weanlings, the heritability for price per kilogram was 0.32 ± 0.04; the genetic SD was 0.11 /kg. Figure 1. Average EBV for (a) price in euro and (b) BW in kilograms with 1 SE represented on vertical bars each side of the mean across the year of birth of 2002 to 2008 for calves (- -), weanling direct (- -), weanling maternal (- -), postweanling (- -), and cows (- -).

7 Cattle price and body weight 35 Table 3. Number of records (n), mean price per animal in euro (μ), genetic SD in euro (σ g ), heritability (h 2 ; SE in parentheses), and coefficient of direct genetic variation (CV g ) for calves across all data (all animals), as well as within different sexes and age groups 1 Item Trait n µ σ g h 2 (SE) CV g All animals 24, (0.03) 16.3 Sex Female 7, (0.09) 19.5 Male 17, (0.04) 16.1 Age group <3 wk 9, (0.06) to 6 wk 13, (0.05) to 12 wk 1, (0.05) Maternal heritability and the maternal repeatability for calves are not reported here because they were not different from zero. Table 4. Number of records (n), mean price per animal in euro (μ), genetic SD in euro (σ g ), heritability (h 2 ; SE in parentheses), and coefficient of genetic variation (CV g ) for weanlings across all data (all animals), as well as within different sexes and age groups 1 Item Trait n μ σ g h 2 (SE) CV g All animals 10, (0.05) 7.4 Sex Female 4, (0.11) 10.7 Male 6, (0.06) 4.9 Age group 6 to 9 mo 6, (0.06) to 12 mo 3, (0.09) Maternal heritability and the maternal repeatability for weanling price are not reported because they were not different from zero. Table 5. Number of records (n), mean BW in kg (μ), genetic SD in kg (σ g ), direct heritability (h 2 d; SE in parentheses), coefficient of direct genetic variation (CV g ), maternal heritability (h 2 m; SE in parentheses), and the maternal repeatability (R m ) for weanlings across all data (all animals) and within different sexes and age groups Item Trait n μ σ g h 2 d (SE) CV g h 2 m (SE) R m All animals 27, (0.03) (0.01) a 0.12 (0.01) a Sex Female 11, (0.05) (0.03) a 0.12 (0.03) a Male 16, (0.05) (0.02) a 0.09 (0.03) a Age group 6 to 9 mo 15, (0.04) (0.02) a 0.19 (0.02) a 9 to 12 mo 12, (0.02) (0.02) 0.06 (0.03) a Maternal heritability and maternal repeatability significantly (P < 0.05) different from zero. Table 6. Number of records (n), mean price per animal in euro (μ), genetic SD in euro (σ g ), heritability (h 2 ; SE in parentheses), and coefficient of genetic variation (CV g ) for postweanlings across all data (all animals) and within different sexes and age groups 1 Item Trait n μ σ g h 2 (SE) CV g All animals 16, (0.04) 5.9 Sex Female 6, (0.09) 8.2 Male 10, (0.05) 5.4 Age group 12 to 24 mo 12, (0.04) to 36 mo 3, (0.12) Maternal heritability and the maternal repeatability for postweanling price are not reported because they were not different from zero.

8 36 Mc Hugh et al. Table 7. Number of records (n), mean BW in kg (μ), genetic SD in kg (σ g ), heritability (h 2 ; SE in parentheses), and coefficient of genetic variation (CV g ) for postweanlings across all data (all animals) as well as within different sexes and age groups 1 Item Trait n μ σ g h 2 (SE) CV g All animals 23, (0.04) 5.0 Sex Female 6, (0.09) 5.7 Male 16, (0.05) 4.1 Age group 12 to 24 mo 19, (0.04) to 36 mo 3, (0.13) Maternal heritability and the maternal repeatability for postweanling BW are not reported because they were not different from zero. Postweanlings Price per Animal. The mean selling price per animal for postweanlings was 633 at an average age of 578 d. The genetic SD for price per animal varied from to 48.30, with a greater value observed in females. The heritability for animal price across all data was 0.19 ± 0.04 (Table 6) and varied from 0.17 ± 0.04 to 0.39 ± 0.09 across ages and sexes (Table 6). The correlation between female price and male price across all postweanlings was 0.90 ± BW. The average BW of postweanlings recorded in auctions was 435 kg and was 485 kg when recorded on farm. Direct heritability estimates for BW was 0.25 ± 0.04 and 0.45 ± 0.05 for auction and on-farm BW data, respectively. The genetic correlation between BW measured in auctions and on-farm data was 0.69 ± In the present study, the 2 data sources were combined and treated as one. The combined results for auction and on-farm BW data are shown in Table 7. The direct heritability across all postweanlings was 0.25 ± 0.04 and varied from 0.17 ± 0.04 to 0.38 ± 0.09 across different ages and sexes (Table 7). The maternal heritability and maternal repeatability were not different from zero. The maternal heritability, estimated across all postweanlings, was 0.02 ± 0.05, and the maternal repeatability was 0.03 ± The genetic correlation between male and female BW was 0.59 ± The genetic correlation between postweanling price and BW was moderate to strong, 0.55 ± Price per Kilogram. The average price per kilogram for postweanlings was 1.45/kg. Across all data, the heritability for price per kilogram was 0.22 ± 0.04, and the genetic SD was 0.07 /kg. Cows Cows on average weighed 600 kg and sold for 559 (i.e., 0.93/kg of BW). Table 8 summarizes the heritability estimates for cow price and BW. Heritability estimates for cow price were moderately small, ranging from 0.09 ± 0.07 to 0.12 ± 0.11 across age groups. Maternal heritability and the maternal repeatability for cow price were not different from zero (0.005 ± 0.02 and 0.00, respectively, across all data). The genetic correlation between price per animal measured at the 2 age groups was 0.58 ± Heritability estimates for cow BW ranged from 0.19 ± 0.10 to 0.24 ± 0.12 across age groups (Table 8). Maternal heritability (0.03 ± 0.05) and the maternal repeatability (0.006 ± 0.02) for cow BW were not different from zero. The genetic correlation between BW measured at the 2 age groups was strong (0.97 ± 0.01). The genetic correlation between cow price and BW was 0.91 ± The heritability estimates for price per kilogram were consistent with the heritability estimates for price. Across all cows, the heritability was 0.06 ± 0.04, the genetic SD was 0.03/kg. Correlations Across Maturity Categories The genetic correlations between price per animal at different maturity categories were moderate to strong (Table 9) and varied from 0.34 ± 0.12 (calf and cow price) to 0.83 ± 0.48 (weanling and cow price). The genetic correlation between BW across different maturity groups varied from 0.16 ± 0.05 (weanling and cow weight) to 0.79 ± 0.03 (weanling and postweanling weight; Table 9). Table 8. Number of records (n), mean price per animal in euro and BW in kg (μ), genetic SD (σ g ), heritability (h 2 ; SE in parentheses), and coefficient of genetic variation (CV g ) for cows across all data (all animals) and within different age groups 1 Price BW Item Trait n μ σ g h 2 (SE) CV g μ σ g h 2 (SE) CV g All animals 4, (0.04) (0.06) 4.3 Age group 2 to 6 yr 2, (0.07) (0.10) to 14 yr 2, (0.11) (0.12) Maternal heritability and the maternal repeatability for cow price and BW are not reported because they were not different from zero.

9 Cattle price and body weight 37 Table 9. Genetic correlations (SE in parentheses) between price per animal and BW across and within the maturity categories Item Calf price Weanling price Weanling weight Postweanling price Postweanling weight Cow price Weanling price 0.52 (0.07) Weanling weight (0.03) (0.04) Postweanling price (0.04) (0.03) (0.09) Postweanling weight (0.07) (0.09) (0.03) (0.06) Cow price (0.12) (0.48) (0.07) (0.10) (0.06) Cow BW (0.10) (0.11) (0.05) (0.10) (0.05) (0.04) DISCUSSION When selling animals, the aim of dairy and beef farmers is to maximize the price per animal received. Although previous studies have documented significant genetic variation in BW (Bullock et al., 1993; Kaps et al., 1999; Pérez-Cabal and Alenda, 2003), to date the genetic variation that underlies cattle price has not been comprehensively investigated (Schierenbeck et al., 2008), especially for animals of different stages of life. Furthermore, the genetic correlations for price per animal across different stages of life have not been investigated. Therefore, the objective of this study was to estimate genetic parameters for animal BW and price per animal across different ages and sex. The present study clearly shows the existence of significant genetic variation in price per animal, as well as BW, across different stages of maturity and, because of their economic importance, justifies their inclusion in dairy and beef breeding objectives. Variance Components Direct heritability estimates for BW, in this study, were consistent with previous estimates in weanlings (Thrift et al., 1981; Bullock et al., 1993; Meyer et al., 1993) and postweanlings (Arnold et al., 1991; Bullock et al., 1993; Meyer et al., 1993). The direct heritability estimates for cow BW in the present study, albeit less than weanling and postweanling heritability estimates in the present study, were consistent with those previously reported in dairy cows (0.24 to 0.32; Ahlborn and Dempfle, 1992; Spelman and Garrick, 1997; Pérez- Cabal and Alenda, 2003). The existence of a significant maternal heritability for weanling BW but not in postweanlings and cows is also consistent with previous studies in crossbred beef cattle in the United States (Arango et al., 2002). The maternal heritability estimates for weanling BW in this study (0.04 to 0.10) were slightly less than those reported in previous studies (0.13 to 0.20; Meyer et al., 1993; Dodenhoff et al., 1998; Ferreira et al., 1999); these studies also estimated greater maternal heritability for birth BW. Birth weight of calves is generally reported soon after birth. However calves have little or no opportunity to suckle before BW is recorded, and therefore maternal effects such as dam milk yield are unlikely to have a large impact on the birth BW. Maternal heritability estimates for birth weight may therefore include possible intrauterine or epigenetic effects (Berry et al., 2008) or may be due to difficulty in the separation of the variance components due to data structure. The maternal heritability estimated for birth weight has been reported to be 0.10 to 0.14 (Meyer et al., 1993; Dodenhoff et al., 1998; Ferreira et al. 1999); therefore, the difference between maternal heritability for weaning and birth weight is 0.03 to 0.08, which is similar to the maternal heritability estimated for weanling BW in the present study. In contrast to BW, no previous heritability estimates for animal price have been reported with the exception of ram price (Maxa et al., 2009) and cow price (Schierenbeck et al., 2008), which corroborates estimates in the present study. Gengler et al. (1995) reported a heritability of 0.80 for price per kilogram; however, the heritability was estimated on performance-tested bulls, and the authors note that a bias may have occurred that favors superior lines when bulls were selected. The heritability estimates for animal price in the present study are similar to those for BW in the present study as well as other production traits such as milk yield (de Jager and Kennedy, 1987; Berry et al., 2002; Kadarmideen and Wegmann, 2003) and ADG (Hirooka et al., 1996; Albera et al., 2001; Crowley et al., 2010). The heritability estimates for price per animal in the present study are, however, greater than heritability estimates reported for subjective measures such as linear type traits in dairy cattle (Short et al., 1991; Pryce et al., 2000; Dechow et al., 2003) and beef cattle (Vesely and Robison, 1971; Gutiérrez and Goyache, 2002; Forabosco et al., 2005). Linear type traits would be expected to be related to animal value, especially muscularity traits in beef cattle. The coefficient of genetic variation for animal price in the present study was in most cases

10 38 not less than the coefficient of genetic variation for linear type traits. When coupled with the moderate to large heritability for price per animal and the routine availability of data on price per animal, greater genetic gain in animal price is expected over and above indirect selection using predictor traits such as linear scores. However, linear traits still remain important for the pedigree herds within Ireland because many of these animals will not be sold through the livestock auctions within their lifetime, and therefore early predictions of genetic merit for animal value may be possible by using linear scores. The larger CV for female price reflects the distinct difference in the end-market of females (i.e., replacement or slaughter). The genetic potential of replacements is likely to have a large bearing on the price per animal that purchasers are willing to pay for females. However, not all females are destined for herd replacements and some are retained for finishing, and hence a greater variation in price per animal is observed in females compared with males. A small amount of commercial females may also be sold for livestock competition, and farmers are willing to pay larger amounts for these animals. The greater heritability estimate for female calf price should be interpreted with caution, however, because fewer animals were within these categories, thus resulting in large SE. Genetic Correlations The genetic correlation between maturity categories for BW and price per animal were less than unity, suggesting they are genetically different traits. Although genetic correlations between price per animal and BW have not previously been reported in the literature, results from previous studies have shown that genetic correlations for dairy cow BW across lactation have been less than unity (Koenen and Veerkamp, 1998). Other studies have shown that the closer in time that measurements of traits are recorded, the stronger the genetic correlations (Koenen and Veerkamp, 1998; Dechow et al., 2001; Berry et al., 2002). Hence, correlations across nonadjacent maturity groups would be expected to be weaker than the correlation between adjacent maturity categories. Genetic correlation between BW across the different maturity categories were moderate to strong (0.16 to 0.79) and were generally greater than the respective phenotypic correlations reported by Mc Hugh et al. (2010), with the exception of the genetic correlation between weanling and cow BW, which was weaker in the present study (0.16 vs. 0.42, genetic and phenotypic correlation, respectively). Genetic correlations between prices across the different maturity categories were generally moderately strong (0.34 to 0.83) and were greater than the phenotypic correlations (Mc Hugh et al., 2010), with the exception of the correlation between postweanling price and cow price. Mc Hugh et al. Genetic merit for BW explained 30 to 83% of the genetic variation in price for weanlings, postweanlings, and cows, which was greater than the respective phenotypic analyses (Mc Hugh et al., 2010), where BW explained 10 to 55% of the phenotypic variation in price per animal. Nonetheless, the lack of unity genetic correlation between BW and price per animal suggests that factors other than genetic merit for BW and factors not accounted for in the model are associated with price per animal and may include factors such as animal color, muscle thickness, horn status, health, and body condition that have already been shown to be phenotypically associated with calf, steer, heifer, and bull price (Schroeder et al., 1988; Barham and Troxel, 2007; Troxel and Barham, 2007). Moderate to high heritability estimates coupled with large coefficients of genetic variation and the availability of routinely collected data on BW and price per animal clearly indicate that there is ample opportunity for selection on these 2 goal traits, and hence they can be included in national cattle breeding programs in Ireland both as selection criteria and as traits in the breeding objective to better reflect the on-farm profitability of dairy and beef enterprises. 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