Circulating beta-hydroxybutyrate concentration may be a predictive measurement for young cows that have a greater...

Timing of conception, which has been indicated to be negatively influenced by metabolic dysfunctions, can influence lifetime productivity within the cow herd. Therefore, our objective was to analyze the association of milk production, serum metabolites as an indicator of nutrient status, cow BW and BW change, and calf BW with timing of pregnancy in 183 spring-calving beef cows. Cows were retrospectively classified by timing of pregnancy as cows that were diagnosed pregnant by timed AI (TAI; = 118) or natural breeding (NAT; = 65). In addition, cows were grouped by age to represent young (3 to 4 yr old), mature (5 to 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. Weekly serum samples were composited by cow within 2 production periods: 1) prebreeding and 2) TAI to end of NAT. Cow BW and BCS did not influence ( ≥ 0.40) timing of pregnancy during the entire study. Similarly, calf BW at birth and weaning were not different ( ≥ 0.30) between timing of pregnancy groups. However, calf BW at weaning and calf value the subsequent year of the study were greater ( < 0.01) for TAI cows than for NAT cows. An age group × treatment interaction ( < 0.01) occurred for serum β-hydroxybutyrate (BHB). Serum BHB concentrations for mature and old cows were similar regardless of timing of pregnancy. However, serum BHB concentrations for young NAT cows were greater than for young TAI cows. In addition, serum NEFA exhibited ( = 0.04) a timing of pregnancy × sampling period interaction. Prebreeding serum NEFA concentrations were greater for NAT cows than for TAI cows. In contrast, serum NEFA concentrations during the NAT season were similar regardless of timing of pregnancy. Area under the curve of the receiver-operating characteristic curve for young cows' circulating BHB concentrations (0.66) was an acceptable predictor for pregnancy by TAI ( < 0.01). Results from this study indicate that only the young, postpartum beef cows during early lactation were susceptible to the measured metabolic dysfunctions of elevated blood BHB concentrations, which may have caused a delay in the timing of pregnancy.