0438 β-hydroxybutyrate and glucose concentrations in the blood of dairy calves

Abstract

This research was conducted to determine how blood β-hydroxybutyrate (BHBA) and glucose are impacted by age, time of day, voluntary starter intake, stress, weaning, and intake restriction in 1- to 9-wk-old calves and to see if either is an acceptable proxy for starter intake. Male Holstein calves were fed a 27% CP, 17% fat milk replacer at 660 g DM daily to weaning on d 42, along with free-choice starter (20% CP, 41% starch) and water. Jugular blood was sampled at 0800, 1200, and 1600 h and within 5 min of sampling BHBA and glucose concentrations were estimated using test strips (Nova Max® Plus meter, Nova Biomedical). Age effects were estimated by sampling blood weekly (d 6, 13, 20, 27, 34, 41, and 48). To determine vaccination stress, a Pasteurella vaccine was administered after blood sampling at 0800 h on d 36. Effect of voluntary starter intake was tested by selecting calves for low and high intakes (d 35 to 39) and sampling on d 40, 41, 43, and 44. Starter intake restriction was tested by restricting intake in 6 of 12 calves and sampling on d 60 and 61. Data were analyzed using several mixed model procedures (repeated measures, regression, etc.) in SAS. Time of day did not impact blood BHBA or glucose to wk 6, but did in wk 7 (P < 0.05). Blood glucose was greater (P < 0.05) in the first 5 wk compared with wk 6 and 7. Blood BHBA increased (P < 0.02; R2 = 0.28) and glucose decreased (P < 0.02; R2 = 0.23) with increasing starter intake. Blood BHBA declined (P < 0.05) due to vaccination but glucose was unaffected. Starter intake restriction reduced BHBA for 3 d (P < 0.05) and glucose for 2 d (P < 0.05) after intake restriction. Around weaning (d 40 to 44), BHBA and glucose increased (P < 0.05) with increasing starter intake. Blood BHBA was positively and glucose negatively related with starter intake; however, relationships were weak, variable, and impacted by time of day, stress, and intake restriction. Over 30% of calves tested ≤ 0.2 mmol/L BHBA when consuming > 1250 g/d of starter, and test strip increments were 0.1 mmol/L which represented > 25% of the mean blood BHBA concentration. In this study, neither blood BHBA nor glucose were an acceptable proxy for estimating starter intake.