The effect of heterosis on pulmonary arterial pressure on beef cattle

Abstract Text:

ABSTRACT: Pulmonary hypertension can develop due to hypoxia-induced pulmonary vascular remodeling leading to right ventricular hypertrophy and edema, a condition known as brisket or high altitude disease (HAD). Pulmonary arterial pressure (PAP) is used at high altitude regions (>1,500m) as an indicator of an animal’s susceptibility to pulmonary hypertension and HAD.  Cattle located at altitudes greater than 1,500m with PAP measurements between 31 to 43 mm Hg are considered to have a low risk of developing HAD at most elevations. To date, there has been no reported research for the effects of heterosis on PAP and therefore, the objective of this study were to examine the effect of heterosis on PAP measurements. Classically, heterosis is most beneficial for survival and fertility related traits; therefore, we hypothesized that increased heterozygosity would decrease an animal’s PAP phenotype. Data collected from 2009 to 2015, was obtained from a multi-breed seedstock database with an average PAP measurement of 44.56±11.58, and a minimum and maximum of 32 and 149 mm Hg. Data included PAP records (n=2,001), PAP testing date, yearling management code, date of birth, sex and breed. A mixed animal model was used to estimate the effect of heterosis on PAP with the model containing degree of outcross and PAP age as covariates; and contemporary group (i.e. combination of PAP date and yearling management code)  and sex as categorical fixed effects. Animal was included as a random effect.  A 3 generational pedigree consisting of 9353 animals was used to estimate genetic parameters for PAP (h²=0.29±0.07). Breed effects were included as covariates of breed percentages for Angus, Red Angus, Charolais, South Devon, Gelbvieh, Simmental and “Other” breeds. The effect of breed on PAP had a range of 8.75 mm Hg. The estimated regression coefficient for PAP on heterosis was -0.02±1.31 mm Hg/percent outcross (P<0.155).  These results indicate that heterozygosity has no effect on PAP measurements, although other multi-breed populations should be examined.  As a result we would reject our hypothesis that an increase in heterosis would decrease PAP. 

Keywords: Pulmonary arterial pressure, heterosis, regression