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Beta-hydroxybutyrate concentration influences conception date in young beef cows in Tennessee
Selection for increased maternal traits like milk production in beef cattle may decrease reproductive efficiency due to increased metabolic load of lactation resulting in metabolic dysfunction. Therefore, our objective was to analyze the association of milk production, serum metabolites, cow BW change, and calf performance with time of conception in 183 spring-calving beef cows. Cows were classified by conception date as cows conceiving by timed-AI (TAI) or natural breeding (NAT). In addition, cows were grouped by age to represent young (3-and 4-yr-old), mature (5- and 6-yr-old), and old (7- to 9-yr-old) cows. Starting approximately d 30 postpartum, cow BW and BCS were recorded and blood samples were collected weekly through the end of breeding. Serum samples were aliquoted into pre-breeding and breeding composites then analyzed for metabolites. Cow BW and BCS did not influence (P > 0.40) conception date. Similarly, calf performance did not influence (P > 0.30) conception date. An age group × treatment interaction (P < 0.01) occurred for serum β-hydroxybutyrate (BHB). Serum BHB concentrations for mature and old cows were similar (P > 0.05) regardless of conception date. However, serum BHB concentrations for young NAT cows were greater (P < 0.01) than young cows conceiving at timed-AI. Serum non-esterified fatty acids (NEFA) exhibited (P < 0.05) a conception date × sampling period interaction. Pre-breeding serum NEFA concentrations were greater (P < 0.05) for NAT cows than TAI cows. Contrarily, serum NEFA concentrations during breeding were similar (P > 0.05) regardless of conception date. Serum glucose and urea N concentrations were not different (P > 0.23) between cows conceiving by timed-AI or natural service. Results from this study indicate that only the young, postpartum beef cows during early lactation were susceptible to metabolic dysfunctions and elevated blood BHB concentrations causing a delayed time to conception.
Keywords: beef cattle, β-hydroxybutyrate, conception time