Concentrations of b-hydroxybutyrate in plasma (pBOH) and milk (mBOH) were measured post-partum (pp). Mean pBOH levels were highest in Weeks 3&4 pp (1.1 ± 0.1 mmol/L). Cows were grouped for length of post-partum anoestrous interval (PPAI) for the statistical analyses. Of those cows which required hormonal treatment because they were anoestrous at the planned start of mating, 77% had pBOH >1 mmol/L during Weeks 1&2 pp, compared to 52% of other cows (P < 0.1). Levels of pBOH alone could not predict the length of the PPAI (r2 = 2%). Logistic regression analyses confirmed age, calving live-weight and calving condition score as risk factors for prolonged PPAI. When these factors were considered with pBOH at Weeks 5&6 pp, a predictive relationship was found (P < 0.05). Levels of mBOH and pBOH were related (r2 = 0.68; P < 0.001). These results support negative energy balance in early lactation as a risk factor for prolonged PPAI, along with age and live-weight and body condition score at calving.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 205-207, 1999
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