Genetic parameters of three methods of temperament evaluation of Brahman calves 1

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1 Published November 21, 2014 Genetic parameters of three methods of temperament evaluation of Brahman calves 1 S. E. Schmidt,* D. A. Neuendorff, D. G. Riley,* R. C. Vann, S. T. Willard,# T. H. Welsh Jr.,* and R. D. Randel 2 *Texas A&M AgriLife Research and Department of Animal Science, Texas A&M University, College Station 77843; Texas A&M AgriLife Research, Overton 75684; Mississippi Agricultural and Forestry Experiment Station Brown Loam Branch Experiment Station, Mississippi State University, Raymond 39154; Department of Veterinary Integrative Biosciences, Texas A&M University, College Station 77843; #Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State 39762; and Department of Biochemistry and Molecular Biology, Mississippi State University, Mississippi State ABSTRACT: The objective of this study was to estimate the heritability of 3 measures of temperament in Brahman and Brahman-influenced calves (n = 1,209). Individual animal pen scores (PS) were determined by a trained observer who evaluated groups of 5 or 4 calves at a time for willingness to be approached by a human. Exit velocity (EV) was the rate (m/s) at which each calf exited a squeeze chute. Temperament score (TS) was calculated individually as (PS + EV)/2. Temperament was evaluated at 5 different times of record (28 d preweaning, weaning, 28 d postweaning, 56 d postweaning, and yearling). Contemporary groups (n = 34) comprised calves of the same sex born in the same season of the same year. There were an average of 36 calves per contemporary group and group size ranged from 3 to 78 calves. Average weaning age (186 d) ranged from 105 to 304 d. Calves were born from 2002 through Random effects included additive genetic and the permanent environmental variance. The fixed effects analyzed were age of dam, sex of calf, contemporary group, fraction of Brahman (2 levels: 1 and 0.5), age of calf at record, and weaning age. At weaning, the mean PS was 2.68 ± 0.1, the mean EV was 2.41 ± 0.1, and the mean TS was 2.48 ± 0.1. The PS was affected by fraction of Brahman (P = 0.034) and tended to be affected by age of dam (P = 0.06). The EV was affected by contemporary group (P < 0.001) and tended to be affected by weaning age (P = 0.074). Contemporary group affected TS (P < 0.001). All 3 methods of temperament evaluation were affected by time of record (P < 0.001). The regression coefficients for PS, EV, and TS were ± , ± , and ± m s 1 d 1 of age, respectively. Estimates of maternal genetic effects were always 0 and omitted from final models. Estimates of heritability were 0.27 ± 0.1, 0.49 ± 0.1, and 0.43 ± 0.1 for EV, PS, and TS, respectively. Estimates of permanent environmental variances as proportions of phenotypic variance were 0.33 ± 0.1, 0.23 ± 0.1, and 0.33 ± 0.1 for EV, PS, and TS, respectively. There appears to be sufficient additive genetic variance for selective improvement of temperament characteristics in Brahman cattle. Key words: Brahman calf, heritability, temperament 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION There is an increasing interest in improving animal temperament in the U.S. beef industry due to elevated awareness of its relationship with productivity 1 This study was supported, in part, by Texas A&M AgriLife Research, USDA-NRI-CSREES grant , and USDA SG The authors acknowledge the technical support of Andrew W. Lewis and Andrea N. Loyd. 2 Corresponding author: r-randel@tamu.edu Received December 10, Accepted April 14, and animal health as well as workplace and animal safety (Voisinet et al., 1997; Fell et al., 1999; King et al., 2006; Burdick et al., 2009). Temperament, defined as the reactivity of cattle to humans and novel environments (Fordyce et al., 1988), can be evaluated using a wide variety of both objective and subjective methods. A widely used subjective method of temperament evaluation adopted by several breed associations is the Beef Improvement Federation s (BIF) docility score, also referred to as a chute score, which has been shown to have a heritability of between 0.37 and 0.40

2 Genetic parameters of temperament 3083 in Bos taurus cattle (Beckman et al., 2005; Northcutt and Bowman, 2010). A weakness of the BIF docility scoring method, and others that rely on behavior displayed while confined in a working chute, is a weak correlation (r = 0.09, P = 0.46) with circulating cortisol concentrations (Curley et al., 2006). Furthermore, when compared with flight speed, chute score has a weaker correlation between repeated measures over time (Cafe et al., 2011). Chute scoring may also have a weaker association with productive traits. For example, chute score was not related to pregnancy rate, whereas exit score, another method of temperament evaluation, was negatively related to pregnancy rate following fixed time artificial insemination (Cooke et al., 2011). The objective of this study was to assess the potential for genetic selection of U.S. Brahman cattle to improve temperament using alternative methods of evaluation that are correlated with circulating cortisol. We hypothesized that these methods would have genetic parameters comparable to those estimated for the BIF docility score and offer an alternative for selecting temperament traits that relate more strongly to productive traits. MATERIALS AND METHODS All procedures were approved by the Institutional Animal Care and Use Committee of Texas A&M University (College Station, TX). Animals This study used records from 1,209 Brahman and Brahman-influenced calves (573 male and 636 female) born between 2002 and 2012 at the Texas A&M AgriLife Research and Extension Center in Overton, TX. Calves were born during both the fall (n = 217) and spring (n = 992) calving seasons. Average weaning age was 186 d and ranged from 105 to 304. The study population consisted of 1,015 pure Brahman (proportion of Brahman = 1) and 194 Brahman-influenced (proportion of Brahman = 0.5) calves. The Brahman-influenced calves were first-generation crosses between Hereford sires and Brahman dams. Temperament Evaluation This study used exit velocity (EV), pen score (PS), and temperament score (TS) to evaluate temperament records of calves at 5 different times of record: 28 d preweaning (n = 646), weaning (n = 1,148), 28 d postweaning (n = 562), 56 d postweaning (n = 487), and yearling (n = 80). Temperament records were not collected at every time of record for every contemporary group. However, all calves in a single contemporary group were evaluated for temperament at the same times of record. There were a total of 2,923 records of temperament evaluation. The EV was the velocity of a calf as it traversed a distance of 1.83 m after exiting a squeeze chute (Burrow et al., 1988; Curley et al., 2006). The time elapsed while crossing the specified distance was measured using 2 infrared sensors (FarmTek Inc., North Wylie, TX). The velocity was calculated as velocity = distance (m)/time (s) with EV presented in meters per second. An individual PS was assigned to each animal by a single trained evaluator as described by Hammond et al. (1996) and Burdick et al. (2013). The same evaluator scored every calf each year. Scores ranged from 1 (calm) to 5 (aggressive) and describe the animal s willingness to be approached by a human. Both PS and EV were evaluated at 28 d preweaning and at weaning in a setting where calves could hear their dams but not see them. The TS was calculated at each time of record for each animal as described by Burdick et al. (2010) and Hulbert et al. (2011). The formula for TS was (PS + EV)/2. The PS and EV were averaged with the intent of creating a new measure of temperament that compensates for the weaknesses of its wholly objective and subjective components. While PS is capable of evaluating the aggressive behaviors that concern producers, its subjective quality makes comparisons between evaluators and facilities difficult. In contrast, EV does not directly measure aggressive behaviors but does provide a more consistent general evaluation of temperament across different environments. Because PS and EV have similar ranges and distributions, they can be numerically averaged to calculate a TS. This provides a more useful measure of temperament to the cattle producer than either PS or EV alone. Estimation of Genetic Parameters and Statistical Analysis Data size and structure permitted only single-trait genetic analyses. Data were analyzed using an animal model with ASReml 3 (Gilmour et al., 2009). The single-trait repeatability model for EV, PS, and TS included year, season, sex of calf, dam age, proportion of Brahman (2 levels), time of record (5 levels), and their interactions. The final model did not include any interaction terms. Weaning age was modeled as a linear covariate. The pedigree included 1,373 animals, with 42 sires and 440 dams, 10 paternal grandsires, 17 paternal granddams, 31 maternal grandsires, and 200 maternal granddams in these equations. Random effects investigated included additive genetic, maternal genetic, and the permanent environmental variance. The final models for these traits included random animal and permanent environmental components. Characteristics of the data, particularly the numbers of records, did not permit appropriate estimation of other random components. Contemporary groups (n = 34)

3 3084 Schmidt et al. Table 1. Means for time of record Method of temperament evaluation Time of record Exit velocity, m/s Pen score 1 Temperament score 2 n Weaning 28 d 2.32 ± c 2.60 ± d 2.38 ± c 646 Weaning 2.41 ± b 2.68 ± c 2.48 ± b 1,148 Weaning + 28 d 2.50 ± a 2.87 ± ab 2.61 ± a 562 Weaning + 56 d 2.28 ± c 2.87 ± a 2.50 ± b 487 Yearling 2.14 ± c 2.51 ± ae 2.24 ± d 80 a e Means in a column that do not share a superscript differ (P < 0.05). Table 2. Probability values of F ratios for investigated fixed effects Exit velocity, Method of temperament evaluation Fixed effects m/s Pen score 1 Temperament score 2 Cow age Contemporary group < <0.001 Fraction of Brahman Time of record <0.001 <0.001 <0.001 Weaning age were constructed to best accommodate combinations of these fixed effects and comprised calves of the same sex and born in the same season of the same year. There was an average of 36 calves per contemporary group and group size ranged from 7 to 78 calves. Least squares means were calculated for the levels of significant fixed effects for each trait. Results were considered significant when P Exit Velocity RESULTS The mean EV for each time of record is presented in Table 1. The mean EV at 28 d preweaning (2.32 ± m/s) was less than the mean EV at weaning and 28 d postweaning (2.41 ± and 2.50 ± m/s; P < 0.05) but not significantly different from the mean EV at 56 d postweaning and yearling (2.28 ± and 2.14 ± m/s). The 28 d postweaning mean EV was greater than at all other times of record. Mean EV increased from 28 d preweaning until 28 d postweaning and then decreased through the yearling measurement. The EV was associated with contemporary group and time of record (P < 0.001) and tended to be related to weaning age (P = 0.074). Cow age, calf sex, and proportion of Brahman did not explain substantial variation in EV (Table 2). The regression coefficient of EV on calf age at weaning was ± m s 1 d 1. The h 2 and permanent environmental variance as proportions of phenotypic variance (c 2 ) were 0.27 ± and 0.33 ± 0.05, respectively (Table 3). Pen Score The mean PS for each time of record is presented in Table 1. The mean PS increased from 28 d preweaning (2.60 ± 0.137) to 56 d postweaning (2.87 ± 0.137). The PS was associated with fraction of Brahman (P = 0.034) and time of record (P < 0.001) and tended to be related to cow age (P = 0.06). The mean PS for each cow age group is presented in Table 4. Cows between 5 and 10 yr of age had calves with lower PS than 2- and 4-yr-old cows (P < 0.05) but not 3- or >10-yr-old cows. Pure Brahman calves had greater mean PS than F 1 Hereford- Brahman cross calves (2.914 ± vs ± ; P < 0.05). Pen score was not associated with contemporary group, weaning age, or sex of calf (P 0.06). The regression coefficient of PS on calf age at weaning was ± per d. The h 2 and c 2 of PS were 0.49 ± and 0.23 ± 0.05, respectively. Temperament Score The mean TS for each time of record is presented in Table 1. The TS increased from 28 d preweaning (2.38 ± 0.108) until 28 d postweaning (2.61 ± 0.109). Calves had a higher mean TS at the 28 d postweaning time of record than at any other (P < 0.05). Calves had a significantly lower mean TS at the yearling time of record (2.24 ± 0.125) than at any other (P < 0.05). The TS was associated with contemporary group and time of record (P < 0.001) but not with cow age, calf sex, or weaning age. The regression coefficient of TS on calf age at weaning was ± per d. The h 2 and c 2 of TS were 0.43 ± and 0.33 ± 0.054, respectively. DISCUSSION When evaluating replacement animals for temperament, consistency is crucial across time, evaluator, and facility to make subjective comparisons between contemporary groups. Objective methods remove the risk of evaluator bias and thus have an advantage over subjective methods. Some of these methods that have been investigated previously include EV, eye-white percentage visible during weighing (Core et al., 2009), and the number of movements an animal makes while confined in a chute (Waynert et al., 1999). Objective predictors of temperament include cannon bone dimensions and facial hair whorl placement (Lanier and Grandin, 2002; Grandin et al., 1995). Adamczyk et al. (2013) stated that while there is evidence that temperament can be improved through breeding, it is necessary to

4 Genetic parameters of temperament 3085 Table 3. Estimates of the regression coefficient of trait on calf age at weaning and estimates of h 2 and permanent environmental variance as a proportion of the phenotypic variance (c 2 ) Method of temperament evaluation Estimate Exit velocity, m/s Pen score 1 Temperament score 2 Regression on ± ± ± weaning age, m s 1 d 1 h ± ± ± c ± ± ± develop objective measures to compare breeding values of animals from within and between countries. Flight speed, measured in meters per second similarly to EV, is recognized as an objective measure of innate fear (Petherick et al., 2002) or reaction to handling (Kilgour et al., 2006). The consistency of EV over time, demonstrated by correlations between repetitions, and its correlation with serum concentration of cortisol have been well established (Müller and von Keyserlink, 2006; Curley et al., 2006; Burdick et al., 2011). Burdick et al. (2011) examined the evolution of EV between 21 d of age and 56 d postweaning in Brahman calves and found that the EV of temperamental calves increased at a faster rate compared with that of intermediate and calm calves. The regression on weaning age for all calves was ± m s 1 d 1, which is comparable to the calculated regression on weaning age in the present study of ± m s 1 d 1. Another finding of the present study is that EV increases as calf age increases until weaning and then decreases slightly, which is expected due to increased BW and thus greater mass to move quickly. Riley et al. (2010) observed an inverse relationship between EV and BW when measured at 28-d intervals between 7 and 19 mo of age. Increased flight speed has been associated with slower growth rate (Burrow and Dillon, 1997; Petherick et al., 2009b), reduced yield and increased the Warner-Bratzler shear force of meat (King et al., 2006), and reduced feed conversion efficiency (Petherick et al., 2002). However, other studies fail to relate flight speed to productive traits. At least 1 study found no association between EV and residual feed intake and growth in cattle with varying degrees of Brahman and Angus influence (Elzo et al., 2009). Hoppe et al. (2010) estimated a heritability of 0.11 for flight speed in Limousin calves and a heritability of 0.36 in Hereford calves. Benhajali et al. (2010) evaluated temperament at 5 and 7 mo of age in Limousin calves and estimated heritabilities between 0.11 and 0.31 for TS obtained from both the number of movements and the number of rush movements an animal made in the chute with a human Table 4. Mean pen score by cow age Cow age n Pen score 1 2 yr old ± a 3 yr old ± ab 4 yr old ± a 5 to 10 yr old 1, ± b >10 yr old ± ab a,b Means in a column that do not share a superscript differ (P < 0.05). standing in front for 10 s. The highest heritability was estimated for the number of movements in the chute at 5 mo of age. From this, it appears that the heritability of objective measures of temperament in Bos taurus cattle varies widely by both breed and the specific method of evaluation. Bos indicus and tropically adapted beef cattle have also been assessed for the heritability of temperament evaluated by objective methods. Prayaga et al. (2009) evaluated the genetic parameters of flight time (s 10 2 ), which was defined as the time an animal took to travel 1.7 m after leaving a chute, in Brahman and tropically adapted composite breeds of cattle. The estimated heritability was 0.17 for Brahman cattle and 0.31 for the tropically adapted composite breeds. Sant Anna et al. (2012) estimated a heritability of 0.26 of flight speed in Nellore yearling cattle. Burrow et al. (1988) estimated the heritability of flight speed at the time of weaning as 0.54 and a heritability of 0.26 for tropically adapted beef cattle at 18 mo of age. These results suggest that there may be differences in heritability of objective temperament traits between breeds of cattle, and therefore it may not be reasonable to make comparisons between studies in different breeds. It also appears that these methods of temperament evaluation have a moderate level of heritability. The estimated heritability of EV (0.27 ± 0.05) in the present study is within the range of results reported by other studies examining EV and flight speed in Bos indicus and tropically adapted beef cattle. It is also important to note that the current study is the first to estimate heritability of multiple temperament traits in the U.S. Brahman breed. Subjective methods of temperament evaluation, including the BIF docility score, do not offer the same reliability between evaluators that objective methods do but may be better for identifying temperament traits such as aggression. Hulsman Hanna et al. (2014) estimated a heritability of 0.23 in Nellore-Angus crossbred cattle for a subjective method of temperament evaluation performed at weaning. Cattle were scored on a scale of 1 through 9, with a score of 1 representing the calmest animals and a score of 9 representing the most temperamental, while separated from the group in an alleyway. The heritability estimated in the present study (0.49 ± 0.061) is greater,

5 3086 Schmidt et al. possibly due to breed differences or the fact that cattle were evaluated in groups of 4 to 5 rather than individually. Meagher (2009) suggested that subjective TS assigned by evaluators familiar with the animals add a beneficial dimension to the assessment of temperament. These evaluators combine an acquired understanding of the animal s behavior with prior experiences, which essentially allows scientists to gather years of data at once in their attempt to classify an animal s temperament. But although an evaluator that is familiar with the animals is uniquely capable of providing valuable insight, their interpretations may be inconsistent with those of other individuals. Le Neindre et al. (1995) tested Limousin heifers individually for docility between 10 and 11 mo of age. Seven different handlers were used to evaluate temperament, and there was a significant effect of handler on the outcome. This demonstrates a shortcoming of qualitative behavior assessments performed by different evaluators. In the present study, all PS were assigned by the same trained evaluator who was familiar with the cattle. Evaluation of restrained or nonrestrained cattle can be performed by trained evaluators who either passively observe cattle or approach the cattle. The evaluations can be performed individually or in groups, and a scaled score is typically assigned to stratify animals based on their observed response. Temperament assessments that evaluate general agitation and avoidance of humans are the most consistent under varying conditions, and those methods that use a forced approach are ideal (Adamczyk et al., 2013). This may partially explain the higher heritability of PS and TS compared to EV because the PS method involves the animal s willingness to be approached by a human. To assign the PS in the present study, the evaluator approached each animal individually and assessed its response. Subjective methods of temperament assessment are considered acceptable as long as they can be proven to be reliable and consistent. However, there are limitations of these methods because humans cannot be expected to fully understand every aspect of an animal s behavior. For this reason, they are typically validated against a measure such as a physiological stress marker, EV, or the frequency of a behavior or behaviors. Therefore, subjective measures of temperament evaluation should ideally be used in conjunction with other objective measures (Meagher, 2009). This supports the adoption of a holistic method of temperament evaluation, such as TS, that combines a subjective observation with an objective one. When animals are repeatedly handled, such as in the present study, there is concern that the results of temperament evaluation could be altered. Reduced chute scores and cortisol concentrations were associated with repeated handling in Brahman-influenced heifers (Cooke et al., 2009b). However, Riley et al. (2010) found no evidence of acclimation when EV was measured at 28-d intervals between 7 and 19 mo of age. Similarly, Petherick et al. (2009a) found that flight speed was not affected by the quality or quantity of handling cattle receive during a 12-mo backgrounding period, thus emphasizing that this measure of temperament is somewhat independent of environmental influences and therefore a good candidate for genetic selection. Furthermore, Cooke et al. (2009a) found that acclimation to humans through biweekly feedings did not affect temperament, as measured by chute score, PS, and EV, in Brahman-influenced cows. Burdick et al. (2010) used TS measured at 28 d before weaning to assign bulls to temperament classes. Temperamental bulls in that study had higher rectal temperatures both before and during transportation than bulls with intermediate or calm temperaments. Temperamental bulls also had higher cortisol and epinephrine concentrations than calm bulls both before and after transportation for 9 h. This shows that TS is capable of accurately assigning cattle to either temperamental, intermediate, or calm classifications and therefore may be useful as a selection tool. The present study is the first that has estimated genetic parameters of TS. It appears that TS has a high heritability, comparable to PS, in Brahman calves. Conclusion It appears that there is sufficient additive genetic variance for selective improvement of temperament characteristics in beef cattle. Furthermore, the methods of temperament evaluation assessed in the present study have comparable genetic parameters to established commonly used practices and may offer better consistency in evaluation between cattle operations. 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