Proceedings of the New Zealand Society of Animal Production. 1993,
53: 77-82
Proceedings of the New Zealand Society of Animal Production. 1993,
53: 77-82
In the first trial, the 20 cows were milk and blood sampled at 0630 h, 1030 h and 1430 h on 3 October and at 0630 h on the following day. Average metabolite concentrations in serum were within the ranges indicated by a regional laboratory as being normal for healthy cattle, but significant differences were associated with sampling time and among individual animals within this range. Blood and milk urea nitrogen (BUN and MUN) and blood beta hydroxybutyrate (BOH) concentrations increased by 1.82 ± 0.14, 1.37 ± 0.17 and 0.45 ± 0.04 mmol/l, respectively (mean change ± sed) from the first 0630 h sampling to the 1430 h sampling. Glucose and non- esterified fatty acid (NEFA) levels decreased by 1.03 ± 0.06 and 0.13 ± 0.03 mmol/l, respectively during this period. Albumin remained constant.
Average daily concentrations for each of these metabolites, except NEFA differed significantly in samples obtained from 12 animals over a period of 21 days from the 7 to 27 October 1991. The largest proportional changes in daily concentration were in BUN and MUN (ranging from 4.7 to 7.5 mmol/l).
Sampling regimes which could be used to identify factors contributing to sample variation will require the same representative portion of a herd to be sampled at the same time at frequent (daily) intervals in the case of BUN and MUN. Either blood or milk may be sampled as the concentrations of urea N were similar (5.64 ± 1.05 (sd) and 5.70 ± 1.10 mmol/l, respectively) and strongly correlated (R¾ = 96.6%). Daily sampling would be less critical for albumin, BOH, glucose and NEFA, but it should include the same animals being sampled at the same time of day.
Keywords: NZSAPAB; Metabolite; variability; dairy cow; pasture
