138 Sire Differences for Blood Urea Nitrogen (BUN) in Hereford Cattle

Abstract

Abstract Excess Nitrogen excretion is a growing concern worldwide within animal agriculture, and blood urea nitrogen (BUN; mg/dL) is known as a predictor of nitrogen excretion in cattle. The objective of this study was to determine sire differences in BUN within a population of Hereford steers. Steers (n = 74) were born between March and June of 2021 from a reference sire herd for The American Hereford Association in Western Nebraska. Sixteen different Hereford sires from The American Hereford Association reference sire program produced offspring used in this study. The steers entered an on-site feed intake unit and were fed a finishing diet consisting predominantly of corn, corn distiller grain, and corn silage. Animals were subjected to a 21-d warm-up period with a 55-d individual feed intake test period. Blood samples were collected on day 43 of the test period. Blood samples were then centrifuged to extract serum. The Urea Nitrogen (BUN) Colorimetric Detection Kit by Invitrogen was used for the assay. The average BUN concentration for all animals in this study was (0.492 ± 0.061 mg/dL). A generalized linear regression model was used to determine sire differences in BUN concentrations. Factors considered were sire and pen group. The sire with lowest least squared mean progeny BUN concentration estimate was (0.0362 ± 0.08 mg/dL; n = 4), and the highest was (0.605 ± 0.03 mg/dL; n = 7). Sire differences (P < 0.05; r2 = 0.36) were found to be important sources of variation as evidenced by its r2; however, pen group (P = 0.65; r2 < 0.05) appeared to have little impact on variation. The differences in sires indicate genetic differences could be leveraged to reduce excess nitrogen excretion in cattle populations.