New Zealand Journal of Agricultural Research abstracts
Variation in the characteristics of milkfat from pasture-fed dairy cows during
late spring and the effects of grain supplementation.
T. R. MACKLE
S. F. PETCH
A. M. BRYANT
M. J. AULDIST*
Dairying Research Corporation Ltd
Private Bag 3123
Hamilton, New Zealand
H. V. HENDERSON
AgResearch
Private Bag 3123
Hamilton, New Zealand
A. K. H. MACGIBBON
Food Science Section
New Zealand Dairy Research Institute
Private Bag 11 029
Palmerston North, New Zealand
Abstract Sources of variation in milkfat characteristics were
determined after approximately 115 days-in-milk for Friesian cows that had
calved in spring and grazed ryegrass-white clover pastures. Three groups each
of 15 multiparous cows were managed as separate herds. Each herd was subjected
to one of 3 management strategies: pasture only, pasture only during the
experimental period but previously supplemented with 2-3 kg/cow/day maize
grain, and pasture plus 3-4 kg/cow/day maize grain. During a 3-week period
beginning in November 1994, milk samples were collected twice-weekly from
individual cows and analysed for total milkfat, protein and lactose, fatty acid
profiles, and solid fat content (SFC). Repeat analyses were conducted on 39
samples to provide an estimation of analytical variation for fatty acid
profiles. Estimates of between-cow variation were greater than those of
within-cow variation for all parameters except fatty acids C6:0, C14:0, and
C18:2. Analytical variation was small. SFC at 10deg.C of milkfat from
individual cows was correlated significantly with total milkfat concentration,
the protein:fat ratio, and the proportions of fatty acids C16:0, C17:0, C17:1,
C18:1, and conjugated C18:2. Supplementing pasture with maize grain had minor
effects on the fatty acid profile of milkfat, but had no significant effect on
SFC. These data will enable increased efficiency of experimental design in this
research area, and detail the extent of the natural variation in milkfat
characteristics.
Keywords Milkfat; milk; cow; variation; nutrition; fatty
acids; solid fat content; pasture
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 349-359
0028-8233/97/4003-0349 $7.00/0 (c) The Royal Society of New Zealand
1997
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