J. L. Williams, J. K. Bertrand, I. Misztal and M. LukaszewiczAngus cattle

Genotype by environment interaction for growth due to altitude in United States

doi: 10.2527/jas.2011-43652012, 90:2152-2158.J ANIM SCI 

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2152

Key words: altitude, beef cattle, genotype by environment interaction, growth, survival

ABSTRACT: The objectives of this study were to determine if sires perform consistently across alti-tude and to quantify the genetic relationship between growth and survival at differing altitudes. Data from the American Angus Association included weaning weight (WW) adjusted to 205 (n = 77,771) and yearling weight adjusted to 365 (n = 39,450) d of age from 77,771 pure-bred Angus cattle born in Colorado between 1972 and 2007. Postweaning gain (PWG) was calculated by sub-tracting adjusted WW from adjusted yearling weight. Altitude was assigned to each record based upon the zip code of each herd in the database. Records for WW and PWG were each split into 2 traits measured at low and high altitude, with the records from medium altitude removed from the data due to inconsistencies between growth performance and apparent culling rate. A binary trait, survival (SV), was defi ned to account for censored records at yearling for each altitude. It was assumed that, at high altitude, individuals missing a yearling weight either died or required relocation to a lower altitude predominantly due to brisket disease, a condition com-mon at high altitude. Model 1 considered each WW and PWG measured at 2 altitudes as separate traits. Model

2 treated PWG and SV measured as separate traits due to altitude. Models included the effects of weaning con-temporary group, age of dam, animal additive genetic effects, and residual. Maternal genetic and maternal per-manent environmental effects were included for WW. Heritability estimates for WW in Model 1 were 0.28 and 0.26 and for PWG were 0.26 and 0.19 with greater val-ues in low altitude. Genetic correlations between growth traits measured at different altitude were moderate in magnitude: 0.74 for WW and 0.76 for PWG and indicate possibility of reranking of sires across altitude. Maternal genetic correlation between WW at varying altitude of 0.75 also indicates these may be different traits. In Model 2, heritabilities were 0.14 and 0.27 for PWG and 0.36 and 0.47 for SV. Genetic correlation between PWG measured at low and high altitude was 0.68. Favorable genetic correlations were estimated between SV and PWG within and between altitudes, suggesting that calves with genetics for increased growth from wean-ing to yearling also have increased genetic potential for SV. Genetic evaluations of PWG in different altitudes should consider preselection of the data, by using a cen-soring trait, like survivability to yearling.

Genotype by environment interaction for growth due to altitude in United States Angus cattle1

J. L. Williams,* J. K. Bertrand,* I. Misztal,* and M. Łukaszewicz*†2

*Animal and Dairy Science Department, University of Georgia, Athens 30602-2771; and †Institute of Genetics and Animal Breeding, Jastrzębiec, 05-552 Magdalenka, Poland

© 2012 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2012.90:2152–2158 doi:10.2527/jas2011-4365

INTRODUCTION

Genetic predictions for growth are based on the performance of the progeny of a sire in a number of environments and do not necessarily refl ect his true merit in any single environment (Bourdon, 2000). Brisket disease, also known as high altitude disease, occurs frequently in domestic cattle less than 1 yr of

age at altitudes above 1,524 m and is a noninfectious cardiac pulmonary condition characterized by edema in the brisket and lower body (Gjermundson, 2000). Approximately 1.5 million cattle in the United States are raised at high altitude and 5% of annual death loss-es in these areas have been attributed to brisket disease (Holt and Callan, 2007). These fi gures translate into an annual loss of 75,000 cattle worth more than $60 million. In a review by Kelly and Janzen (1986), the incidence of morbidity in North American feedlots was estimated at between 15% and 45% and the mortality rate was at most 5.6%. Studies have used pulmonary arterial pressure as an indicator trait for susceptibility

1The authors thank the American Angus Association for supplying the data used in this study.

2Corresponding author: marekl@uga.edu Received June 13, 2011.Accepted January 12, 2012.

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Genetics of US Angus growth across altitudes 2153

to brisket disease given that increased blood pressure is a refl ection of a restriction in blood fl ow (Holt and Callan, 2007). Investigating the genetic relationship between pulmonary arterial pressure and growth, Shirley et al. (2008) concluded that selecting for growth at low alti-tude would increase pulmonary arterial pressure scores and susceptibility to brisket disease. Hence, producers raising cattle in high altitude environments and basing their selection decisions on pooled predictions may not obtain the performance they expect when the majority of the offspring of a sire are maintained at low altitude.

The objectives of this study were to determine if growth and survival can be considered the same traits due to altitude and to quantify the genetic relationship between growth and survival at differing altitudes.

MATERIALS AND METHODS

Performance data in this study were obtained from an existing database; therefore, Animal Care and Use Committee approval was not sought.

Data

Growth records for weaning weight (WW) ad-justed to 205 and yearling weight adjusted to 365 d of age according to BIF Guidelines (BIF, 2002) were ob-tained from the American Angus Association (AAA; St. Joseph, MO). Records were from purebred Angus cattle born between 1972 and 2007 in Colorado. Postweaning gain (PWG) was calculated by subtracting adjusted WW from adjusted yearling weight. Contemporary groups were defi ned based upon herd, process date, lot identi-fi cation, management code, and sex resulting in 3,920 unique groups each containing an average of 20 indi-viduals. Contemporary groups represented by a single sire as well as individuals with an age of dam greater than 12 yr were not included in analyses. In addition, analyses were limited to large herds with more than 200 animals represented in the data. Zip code information provided by AAA referred only to the herd location at weaning; thus, zip codes pertaining to yearling herds were unavailable for those individuals changing herds from weaning to yearling. Animals in this situation were removed from the data because an appropriate altitude could not be assigned in this case.

Colorado has been the focus of a number of stud-ies investigating brisket disease due to its very diverse geography. The eastern half of the state is considered high plains and ranges between 900 and 1,830 m in alti-tude whereas the western half is comprised of the Rocky Mountain range and has an altitude of 1,830 to 3,658 m. Performance records were assigned an altitude based upon the zip code associated with each herd in the data-

base. Altitudes associated with records in the data ranged from 914 to 2,743 m, spanning over some 1,800 m. Three altitude classes (low, medium, and high), each comprising 600 m, were initially formed and WW and PWG records were categorized based on these altitude classes. The low altitude class consisted of herds located at altitudes ranging from 914 to 1523 m, medium at altitudes rang-ing from 1,524 to 2,133 m, and the high altitude class in-cluded herds elevated from 2,134 to 2,743 m.

Hence, the low altitude group of herds originated entirely from both the Colorado eastern high plains and altitudes considered safe, from the brisket disease point of view. Similarly, the high altitude herds were all located in the Rocky Mountains. It was only the medium altitude herds that were scattered over the 2 sub-regions. However, the performance of cattle at the medium altitude appeared least in terms of growth, paralleled by the least culling rate, and we were unable to reconcile management prac-tices or environmental circumstances that would explain these 2 seemly contradictory observations. It is important to note that the zip codes provided by the AAA, which were used to identify altitude for each observation, cor-responded to the mailing address on fi le and may not nec-essarily refl ect where the cattle are actually maintained. This means that observations appearing to come from me-dium altitude may actually be from a greater altitude and perhaps explain low mean WW and PWG from medium altitude. Therefore, we decided to include only low and high altitude data in the present study.

Weaning weight and PWG measured at low and high altitude were coded as WWL, WWH, PWGL and PWGH, respectively. There were 142 sires in common among PWG measured at the 2 altitudes and 204 sires in common among WW measured at each altitude to allow for accurate estimation of the correlations between the traits measured at each altitude.

A trait measuring survival (SV) at each of the 2 altitudes (SVL and SVH) was developed to account for censoring or the presence or absence of yearling weights among animals in the same weaning contem-porary group. Individuals in the data with yearling weight observations were coded as 2 (survive) whereas animals missing a yearling weight were coded either 1 (not survive) or 0 (missing). Animals coded as miss-ing were members of a weaning contemporary group in which none of their contemporaries possessed a yearling weight, and were assumed to belong to a herd that did not routinely report yearling weights. Individuals coded as not surviving were in a weaning contemporary group where some individuals had a yearling weight reported. It was assumed that these animals either suffered heart failure and died or required relocation to a lower altitude due to brisket disease. After edits, a 5-generation pedi-gree fi le of 135,158 animals was extracted.

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Williams et al.

Models and Analyses

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Genetics of US Angus growth across altitudes

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RESULTS AND DISCUSSION

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Genetics of US Angus growth across altitudes 2157

Coeffi cients of heritability for SV at different alti-tudes are high and reach 0.47 for SV at the low altitude (Table 6). Treating SV as a categorical as opposed to a continuous trait would likely be the cause of high herita-bility estimates as the variability on the underlying scale is better accounted for (e.g., Urioste et al., 2007). It is also apparent that selection for survivability can be very effi cient, regardless of the altitude.

Estimates of the genetic correlation (Table 6) between PWG and SV measured at the same altitude were positive and reached a moderate magnitude of 0.62 between PWG and SV at high altitude. Calves with genetics for increased growth from weaning to yearling also have increased ge-netic potential for SV within an altitude. However, the correlation between PWGL and SVH can be considered accidental as it is low and of high SE, which may support the above mentioned conclusion of Shirley et al. (2008). The majority of research focusing on the genetics of bris-ket disease centers on pulmonary arterial pressure as an indicator trait for susceptibility to brisket disease given that increased blood pressure is a common symptom of the disease. Schimmel and Brinks (1982) reported a strong negative correlation of −0.46 between postwean-ing ADG and pulmonary arterial pressure suggesting that as producers select bulls for increased gain they are also indirectly selecting for decreased susceptibility to brisket disease. These fi ndings agree nicely with those reported here for PWG and SV indicating selection for greater gains, especially at greater altitudes, will also lead to bet-ter SV (reduced susceptibility).

Posterior mean genetic correlation between SV at each altitude was 0.47 (Table 6) which, from the point of view of Robertson (1959), implies that quite different genetic qualities are required for calves to stay at dif-ferent altitudes. Although brisket disease, which in the current paper is believed to be the main component of the between-elevation difference in the line-up of cull-ing causes, can occur at altitudes of less than 2,134 m, the greatest incidence tends to occur above this altitude (Will and Alexander, 1970) and may explain why the ge-

netic ability to survive at high altitude differs genetically so much from survivability at altitudes beneath 1,524 m.

A very strong assumption made in this study was that animals missing yearling weights were either moved to lower altitudes or died of heart failure, both of which were associated with brisket disease. Disposal codes for calves at weaning would help in identifying the reason for an animal leaving the herd. In addition, measures of pulmonary arterial pressure on all individuals in the dataset could have assisted us in our assumption that animals leaving the herd at weaning were susceptible to brisket disease. Herd zip codes that refl ect the exact location of the cattle when performance was measured could have also been very useful in assigning WW to the correct environment.

In conclusion, genetic correlations between direct effects for WW and PWG measured at low and high altitude indicated evidence for GxE and suggested that sires may rerank in their performance across altitude. Selection for greater BW gains from weaning to yearling would be expected to increase SV, especially at greater altitudes. The results presented here also suggest that ge-netic evaluations of PWG in different altitudes should account for preselection of the data, by using a censor-ing trait, like survivability to yearling.

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PWGL PWGH SVL SVHPWGL 0.27 (0.02) 0.68 (0.07) 0.33 (0.06) 0.12 (0.08)PWGH 0.14 (0.02) 0.14 (0.19) 0.62 (0.07)SVL 0.47 (0.02) 0.47 (0.20)SVH 0.36 (0.03)

1SD in parentheses

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