The effect of gradual dietary pine bark meal supplementation on milk production of dairy cows fed a grass silage-based diet

In a search for novel sustainable feed resources for ruminant livestock, interest towards wood-based feed materials such as bark has risen. To evaluate the feed potential of ground bark, a dairy cow feeding experiment was conducted using 24 high yielding (average milk yield in the beginning of the experiment 38.0 +/- 4.53 kg/d) Nordic Red cows in a 3 x 3 Latin square design using 21-day periods. The cows were offered grass silage-based diets supplemented with 3 different concentrate feeds; a control concentrate containing no additional bark meal (C) or two different concentrate feeds containing low (LB, 87 g/kg of dry matter (DM)) or high (HB, 173 g/ kg DM) level of dried ground pine bark meal supplement. Experimental concentrates were fed at a level of 12.4 kg per day resulting in feeding of ca. 1 and 2 kg of bark meal per day at low and high levels, respectively. The good quality grass silage used as the basal feed elicited high total daily feed DM intake which was on average 25.6 kg. The palatability of all experimental concentrates was good. Dietary bark meal increased the intakes of silage DM and total DM, but decreased yields of milk, energy-corrected milk, milk fat and protein, and concentrations of milk constituents although numerical differences between treatments were small. Bark meal supplements decreased linearly metabolizable energy intake, but had no significant effect on the estimated intake of amino acids absorbed from the small intestine as the concentrate feeds were balanced by rapeseed meal. Dietary bark meal decreased linearly the feed efficiency. Milk from all treatments had good sensory properties. This study demonstrated that the energy value of bark meal was very low compared to the traditional feeds as demonstrated by the decreased production results. The economic output of bark meal inclusion depends on the savings in replacing traditional feeds with bark meal, and the losses as reduced milk sales. In long term, other aspects may be considered such as potential shortage and elevated prices of traditional feeds and need to use non-human edible feed components in animal production, but under current conditions, it cannot be recommended as a feed component for high producing dairy cows.