Effect of body condition at calving on milkfat composition of
Friesian heifers during the first ten weeks of lactation
N.A. THOMSON, M.O. BRYANT, A. CHAND, A.K.H. MacGIBBON AND L.M.
CHAGAS
Dexcel, Private Bag 3221, Hamilton
E-Mail:
NZSAP 2002 Abstract No. 11
Proceedings of the New Zealand Society of Animal Production 62:
38-41
The effects of live weight and body condition score (CS) at
calving on milksolids production has been well documented. The effects
of CS at calving on detailed composition of milk, the physical
characteristics, or, product quality are largely unknown. Milkfat yield,
fatty acid profile (FAP), solid fat content (SFC) of milkfat during the
first 10 weeks of lactation were monitored for Friesian heifers with a
pre-calving CS of 4.1 (LCS) or 5.2 (HCS). Once calved, all heifers were
grazed as one herd and offered pasture ad libitum. Composition
and characteristics of milkfat were determined at four, six, and 10
weeks postpartum. At four weeks postpartum the HCS heifers, produced 23%
more (P<0.001) milkfat, lost 59% more (P<0.001) live weight and CS
declined 30% more (P<0.05) than did LCS heifers. Associated with
these changes were compositional changes in milkfat. CS at calving had
no effect on milkfat concentration. HCS heifers produced milkfat with
lower concentrations (P<0.01) of de novo synthesised fatty
acids (C4:0-C15:1) and higher (P<0.01) concentrations of preformed
fatty acids. Concentration (mg/100 mg milkfat) of oleic acid (C18:1)
was higher: 27.4% c.f. 24.8%, s.e.d. 0.94 (P<0.001) for HCS compared
with LCS heifers. Milkfat from HCS heifers was softer, SFC at 5°C
(55% c.f. 59%, s.e.d. 1.2, P<0.01) than from LCS heifers. Six weeks
postpartum, the differences in FAP persisted but changes in live weight
and CS were small compared with the first four weeks of lactation. Ten
weeks post calving both groups were gaining live weight, but although
differences (P<0.01) in live weight, CS, and daily milkfat yield
persisted, no differences in FAP or SFC were found. These results show
that differences in pre-calving live weight and CS cause differences in
the composition and characteristics of milkfat. Milkfat from HCS heifers
was more desirable (softer and higher in unsaturated fatty acids) than
from LCS heifers. These differences disappeared once the two heifer
groups were in positive energy balance by 10 weeks postpartum.
Keywords: NZSAPAB;
calving condition score; early lactation; liveweight change;
characteristics of milkfat; composition of milkfat
Last Updated 30/07/2002
