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Education ?

Medical School Score Rankings
University of Utah (1999)
Diagnostic Radiology
Top 50%

Awards & Distinctions ?

American Board of Radiology

Affiliations ?

Dr. Johnston is affiliated with 5 hospitals.

Hospital Affiliations



  • Baylor All Saints Medical Centers
    1400 8th Ave, Fort Worth, TX 76104
    Top 25%
  • Medical Center Of Arlington
    3301 Matlock Rd, Arlington, TX 76015
    Top 50%
  • Tops Comprehensive Breast Center
  • Memorial Medical Center
  • Texas Health Fort Worth
  • Publications & Research

    Dr. Johnston has contributed to 1 publication.
    Title Genetic and Phenotypic Variance and Covariance Components for Feed Intake, Feed Efficiency, and Other Postweaning Traits in Angus Cattle.
    Date April 2002
    Journal Journal of Animal Science

    Records on 1,180 young Angus bulls and heifers involved in performance tests were used to estimate genetic and phenotypic parameters for feed intake, feed efficiency, and other postweaning traits. The mean age was 268 d at the start of the performance test, which comprised 21-d adjustment and 70-d test periods. Traits studied included 200-d weight, 400-d weight, scrotal circumference, ultrasonic measurements of rib and rump fat depths and longissimus muscle area, ADG, metabolic weight, daily feed intake, feed conversion ratio, and residual feed intake. For all traits except the last five, additional data from the Angus Society ofAustralia pedigree and performance database were included, which increased the number of animals to 27,229. Genetic (co)variances were estimated by REML using animal models. Direct heritability estimates for 200-d weight, 400-d weight, rib fat depth, ADG, feed conversion,and residual feed intake were 0.17 +/- 0.03, 0.27 +/- 0.03, 0.35 +/- 0.04, 0.28 +/- 0.04, 0.29 +/- 0.04, and 0.39 +/- 0.03, respectively. Feed conversion ratio was genetically (r(g) = 0.66 ) and phenotypically (r(p) = 0.53) correlated with residual feed intake. Feed conversion ratio was correlated (r(g) = -0.62, r(p) = -0.74) with ADG, whereas residual feed intake was not (rg = -0.04, r(p) = -0.06). Genetically, both residual feed intake and feed conversion ratio were negatively correlated with direct effects of 200-d weight (r(g) = -0.45 and -0.21) and 400-d weight (r(g) = -0.26 and -0.09). The correlations between the remaining traits and the feed efficiency traits were near zero, except between feed intake and feed conversion ratio (r(g) = 0.31, r(p) = 0.23), feed intake and residual feed intake (r(g) = 0.69, r(p) = 0.72), and rib fat depth and residual feed intake (r(g) = 0.17, r(p) = 0.14). These results indicate that genetic improvement in feed efficiency can be achieved through selection and, in general, correlated responses in growth and the other postweaning traits will be minimal.

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