Fig. 1. The effect of dietary polyunsaturated fatty acids (PUFAs) on plasma progesterone
concentrations. Progesterone was measured each day in cows maintained on three
different diets: (i) control (j), (ii) high linolenic acid (LNA, n-3) (d) or (iii) high linoleic
acid (LA, n-6) (m) PUFA. There were seven cows per group. Four oestrous cycles were
monitored that are designated as cycles 1–4. Oestrous periods are labelled E1–E4; E1
occurred after the removal of the progesterone releasing intravaginal device (PRID).
Cows were re-synchronized by a single injection of Cloprostenol (PG) during cycle 3
and were artificially inseminated (AI) at E4. The lines show the estimated means. The
pooled SEs (ng ml–1) were: control: 0.24; LNA (n-3): 0.14; and LA (n-6): 0.22. ANOVA
detected a highly significant effect of diet in both the early luteal (days 4–8, P < 0.004)
and the mid-luteal phase (days 9–15, P < 0.02). There was no diet 3 oestrous cycle
interaction.