Diurnal variation in blood plasma metabolites and insulin of
lactating dairy cows grazing pasture and supplemented with a high-lipid
supplement either once or twice a day
N.A. THOMSON, K. SINGH AND J.K. KAY
Dexcel, Private Bag 3221, Hamilton
E-Mail:
NZSAP 2003 Abstract No. 26
Proceedings of the New Zealand Society of Animal Production
63: 107-111
The experiment determined the diurnal variation of a blood
plasma hormone and three metabolites (insulin, glucose, NEFA and
triglyceride) and how these varied with different frequencies of
supplementary feeding. Twenty-four cows in early lactation (DIM 81
± 20) were divided randomly into three treatments; grazed pasture
only and pasture supplemented with 2 kg/cow/day of ruminally protected
oilseed supplement (metabolisable energy 19 MJ/kg DM) either once a day
after morning milking or twice a day after morning and afternoon
milking. On day 12 of the experiment, 12 cows (4 cows/treatment) were
jugular catheterised and commencing at 1600 h, blood sampled at 2-hourly
intervals for 24 h. This protocol was repeated for the remaining 12 cows
on day 13 Concentrations of the selected blood plasma hormone and
metabolites varied diurnally (P<0.001). The difference between the
average peak and nadir concentrations over the 24 hours were 54%, 66%,
224% and 63% for plasma insulin, glucose, NEFA and triglyceride
respectively. Feeding the lipid supplement increased blood plasma NEFA
(P<0.01), and triglycerides (P<0.001) but had no effect on
insulin, or glucose concentrations. Frequency of supplementary feeding
influenced (P<0.05) the diurnal variation of NEFA but not, insulin,
glucose, or triglyceride. Concentrations of NEFA, glucose, and
triglyceride were variable between 0600 h and 1000 h and stabilised
between 1600 h to 2000 h. Plasma insulin concentrations were low and
stable between 0400 h to 0800 h. Consideration of diurnal variation and
the stability of the blood plasma components measured led to the
recommendation that the best time to blood sample for insulin is between
0400 - 0800 h and for glucose, NEFA, and triglyceride, between 1600
2000h.
Keywords: NZSAPAB;
diurnal variation; plasma insulin; plasma glucose; plasma NEFA;
plasma triglyceride
Last Updated 8/07/2004
