New Zealand Journal of
Agricultural Research abstracts
Effect of cow diet on free
fatty acid concentrations in milk
N. A. Thomson
W. C. Van der Poel
M. W. Woolford
Dexcel
Private Bag 3221
Hamilton, New Zealand
M. J. Auldist
Department of Primary
Industries
RMB 2460, Hazeldean Road
Ellinbank VIC 3821, Australia
Abstract Two
experiments were conducted: one during summer 1999 (Experiment 1,
180–200 days in milk (DIM)) and one in autumn 1999 (Experiment 2,
220–250 DIM), to examine the effect of pasture allowance on the
formation of free fatty acids (FFA) in milk from multiparous Jersey
cows. In Experiment 1, three treatments were investigated (n
= 15): fully fed on pasture (FFP) (pasture allowance 36 kg
DM/cow per day), restricted pasture (RP) (pasture allowance
23 kg DM/cow per day), and RP plus 5 kg DM/cow per
day of pasture silage (RP+S). Treatments were applied for 21 days.
Experiment 2 ran for 14 days and comprised two treatments, (n
= 15) FFP (pasture allowance 38 kg DM/cow per day) and a more
restricted pasture allowance (RP), of 16 kg DM/cow per day.
Milk samples for FFA analyses were collected by hand milking each cow
during the morning milking. The sample was split into three subsamples:
Sample 1 was fixed to prevent any further lipolysis (L0), Sample
2 had no additive (L24), and for Sample 3 air was drawn
through the sample for 4 min (D24). All samples were stored at
4°C for 24 h before being analysed for FFA
concentrations by the Bureau of Dairy Industries (BDI) method. A
restricted pasture allowance (RP) reduced milk yield by 14 and 36% in
Experiments 1 and 2, respectively. The feeding of silage to cows on a
restricted pasture allowance had no effect on milk yield. Pasture
allowance or supplementary feeding in Experiment 1 had no
effect on total FFA concentrations in L0, L24, or D24 samples. However,
the increase in FFA during 24 h, storage (L24–L0) was greater (P
< 0.001) for the RP and RP+S than the FFP treatments.
The restricted pasture allowance in Experiment 2 caused an increase in
total FFA concentrations in the L24 (P
< 0.001) and D24 (P
< 0.05) samples. The increase in FFA concentration
during storage (L24–L0) was greater (P
< 0.001) in milk from the RP treatment. In both trials,
the increase in FFA concentrations over 24 h between damaged
and undamaged milk (D24–L24) was similar for each treatment. The
greater increase in FFA concentration was in undamaged milk (L24–L0)
from the RP treatments. From this observation it is hypothesised that
the increase in FFA concentrations in milk due to underfeeding resulted
from an increase in the activity of lipoprotein lipase and not from an
increased susceptibility of the milk fat globule membrane to damage.
Overcoming a restricted pasture allowance by supplementary feeding of
silage had little effect on reducing the impact of a restricted
availability of summer pasture on milk yield or FFA concentrations.
Keywords free
fatty acids; bovine milk; pasture allowance; pasture silage
supplementation
A04102; Received 7 December
2004; accepted 16 June 2005; Online publication date 4 August 2005
New Zealand Journal of
Agricultural Research, 2005, Vol. 48:
301–310
0028–8233/05/4803–0301 © The Royal Society of New Zealand 2005
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