Influence of pasture on goat milk fatty acids and Stearoyl-CoA desaturase expression in milk somatic cells

The effect of pasture fatty acid profile along the year on the Stearoyl-CoA desaturase (SCD) expression was evaluated over 5 months using 30 pluriparous goats, delivered in February. The animals had free access to pasture constituted by 60% Leguminosae and 40% Gramineae, and received 500 g/head/day of concentrate. From the second half of April, goats were milked twice a day for 5 months. Daily milk yield was recorded and, monthly, representative individual milk and pasture samples were analysed for chemical composition and fatty acid profile. The SCD expression was studied by extraction of mRNA from milk somatic cells and analysed by RT-PCR. Average milk yield, fat and protein were 1420 (g/d), 4.45 (%) and 3.62 (%), respectively. Milk yield decreased along the lactation (P < 0.01) while milk fat was higher in August. Milk total CLA showed the highest levels (P < 0.01) in June and August (mg/100 g fat: 0.98 and 1.21, respectively) as consequence of the highest levels of pasture C18:2 and C18:3 in June (% of total FA: 34.1 and 42.7, respectively) and August (% of total FA: 42.7 and 46.3, respectively). The grazing season as well as lactation stage affected the SCD mRNA abundance determined from milk somatic cells with values (arbitrary units) that progressively decreased from April (1.95) until June (1.40), increased in July (1.70) and decreased again in August (0.83).