The effect of concentrate type and supplementary lactic acid or soya oil on milk production characteristics in dairy cows offered grass silages of contrasting fermentation type

Sixteen first lactation dairy cows were used in a 2 x 2 x 2 x 2 factorial design experiment. Two silages, an extensively fermented inoculant-treated silage or a restricted fermented, mixed aliphatic carboxylic acid-treated silage were offered with two concentrate types (starch- or fibre-based) and supplementary lactic acid (LA, 0.4 kg/ day) or soya oil (SO, 0.41 kg/day). Concentrates containing 180 g crude protein per kg were offered at 6 kg/day. Silage dry-matter intake tended to he higher (P = 0.07) with restricted fermented silage compared with the inoculant silage. Milk fat or protein concentrations were not significantly affected (P > 0.05) by silage fermentation type. LA inclusion had no significant effect (P > 0.05) on animal performance. SO inclusion significantly increased (P < 0.05) milk yield (+ 0.8 kg/day), decreased milk fat concentration and yield (40.2, 32.9 g/kg and 779, 667 g/day for - and + SO; respectively, P < 0.001) and decreased milk protein concentration (- 0.8 g/kg, P < 0.01). A significant concentrate X soya-oil interaction (P < 0.01) suggested a greater reduction in milk fat concentration with the SO, starch compared with the SO, fibre combination. Modified acid-detergent fibre (P < 0.01) and neutral-detergent fibre (P < 0.001) apparent digestibility coefficients were significantly lower with starch- compared with fibre-based concentrates. Results suggest that milk production responses to changes in concentrate composition were not influenced by the extent of restriction of the silage fermentation process.