composite gel was the primary form of the lipid supplement
fed with the basal concentrate during the
experimental phase. During the control phase, unprotected
yellow grease (YG) was the lipid supplement
added to the concentrate. The YG diet with unprotected
lipid was used to allow the goats to return to
baseline with respect to FA composition of milk lipids.
In addition, the original intent of the study was to
measure oxidative stability of the milk lipid based on
hexanal and propanal concentrations. However,
methods could not be established in our laboratory.
The WPI gel preparations were added to the basal concentrate
immediately prior to each feeding. Particle
size of the gels was reduced prior to inclusion into the
concentrate using a cheese grater (Bradshaw International,
Rancho Cucamonga, CA, USA). The two lipid
sources were soya bean (S) oil and linseed (L) oil
(Table 2). Composites were formulated to yield a series
of feed supplements that only differed in their FA
composition (Tables 3, 4 and 5). The percentage of
lipid in the supplements was 61.3% WPI/S, 59.5%
WPI/SL and 59.6% WPI/L. The proportion of S and L
included in the gels was adjusted to yield gels with different
n-6 to n-3 ratios. Treatment variables consisted
of WPI gels containing (i) 100% S (WPI/S), (ii) a 1:1
(wt/wt) mixture of S and L (WPI/SL) and (iii) 100% L
(WPI/L).
Animals were housed in individual pens with rice
hull bedding and water free choice. Concentrate
mixes were fed at milking (05:00 and 17:00 hours).
Samples of each concentrate mix and the alfalfa hay
were collected during each phase. Dry matter was
determined at 100 °C for 15 h in a forced-air oven.
Samples were also air dried (approximately 26 °C). All
samples were ground through a 1 mm screen using a
Wiley mill (Arthur A. Thomas, Philadelphia, PA, USA)
and analysed for chemical composition Each WPI gel
was sampled using a core bore.
Yield of milk of each goat was recorded at each
milking, and milk samples were collected for analysis.
The evening milk sample was kept refrigerated