Abstract :
The objective of this experiment was to examine the effects of dietary n-3 or n-6 fatty acid (FA) supplementation on blood FA,
metabolite and hormone concentrations, follicle size and dynamics and corpus luteum (CL) size. Reproductively normal heifers
(n524) were individually fed diets of chopped straw and concentrate containing either (i) no added lipid (CON; n58); (ii) 2%
added fat as whole raw soya beans (WSB, n-6; n58); or (iii) 2% added fat as fish oil (FO, n-3; n58). Following oestrous cycle
synchronisation, blood samples were collected at appropriate times and intervals for the measurement of hormones, FAs and
metabolites. On days 15 and 16 of the cycle, animals were subjected to an intravenous oxytocin challenge and prostaglandin F2a
(PGF2a) response, measured as venous concentrations of 13,14-dihydro-15-keto PGF2a (PGFM). Dry matter intake and average daily
gain were similar among treatments ( P.0.05). Plasma concentration of linoleic acid was highest on WSB ( P,0.05), while
eicosapentaenoic (EPA, n-3; P,0.0001) and docosahexaenoic acid (DHA, n-3; P,0.0001) were greatest in the FO group. Plasma
concentrations of arachidonic acid were higher on FO ( P,0.05) compared with CON and WSB. Plasma triglyceride concentrations
increased, while b-hydroxybutyrate (BHBA) decreased with time on all diets (P,0.05). There was a diet3time interaction
( P,0.01) for non-esterified fatty acid (NEFA) concentrations. Plasma cholesterol was higher on WSB and FO ( P,0.01) compared
with CON. Progesterone (P4) and oestradiol (E2) concentrations, as well as follicle growth rate and CL diameter were similar across
diets ( P.0.05). There was a diet3day interaction for PGFM ( P,0.01). When corrected for systemic E2 : P4 ratio, day 15
concentrations of PGFM were higher in the WSB group at 15 and 30min ( P,0.01) post oxytocin administration compared with
CON and FO, which were similar ( P.0.05). Concentrations of PGFM on day 16 were similar for WSB and FO and were greater
than CON at 15 ( P,0.01) and 45 min ( P,0.05) post oxytocin administration, and at 30 min for FO ( P,0.05). With the
exception of PGFM, dietary lipid source did not affect the reproductive variables measured
Keywords :
Fish Oil , Progesterone , prostaglandin metabolite , linoleic acid , cattle
