University of Arkansas, Fayetteville Division of Agriculture
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Abstract

Objectives of this project were to evaluate polymorphisms in upstream elements of the lactate dehydrogenase B (LDHB) gene in crossbred dairy heifers (n = 27) and their effects on immune function and heifer growth when grazing endophyte-infected tall fescue. Two cultivars of tall fescue were utilized: Kentucky 31 (KY31), a wild-type endophyte-infected tall fescue, and HiMag 4 (HiMag), a domesticated non-toxic endophyte-infected tall fescue. Crossbred dairy heifers (Holstein × Jersey) were stratified by weight and randomly allotted to forage. The LDHB gene codes for one subunit of lactate dehydrogenase (LDH), an enzyme that catalyzes pyruvate to lactate and back to pyruvate. Forward primer used for amplification was 5’-ACACACCAGCAGCATCTCAG-3’ and reverse primer was 5’- GATAAGGGCTGCACGAAGAC-3’. The amplicon size for this LDHB primer set was 457 base pairs. Sequenced amplicons were aligned with Clustal2W for polymorphism detection and genotype assignment. Heifers that had a heterozygous genotype and grazed HiMag were heavier when compared with other heifer groups. Number of red blood cells and hemoglobin concentrations for heifers grazing KY31 were greater when compared to heifers grazing HiMag. Distribution of white blood cells was affected by LDHB genotype. Two dairy heifer management tools, stockpiled tall fescue and LDHB genotyping, were assessed in this study, both of which impacted heifer growth and immune function as assessed by blood cell differentials.

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