Effect of maturity stage at harvest and kernel processing of whole crop wheat silage on digestibility by dairy cows

The study aimed to explore whether digestibility by cows of whole crop wheat silage harvested at two different dough stages of maturity was impaired due to its content of whole kernels. Wheat was harvested at early (ED) and soft-to-hard (SHD) dough and preserved as roundbale silage. After five months of storage, half of silage from each maturity stage was processed using a roller mill. Early dough silages contained 334 g dry matter (DM)/kg and 110 g starch/kg DM whereas SHD silages contained 423 g DM/kg and 254 g starch/kg DM.Total tract apparent digestibility and milk production by dairy cows was studied in a 2 × 2 factorial arrangement of silages harvested at the two maturity stages, either unprocessed or processed before feeding. Eight dairy cows were assigned to two Latin squares with four 3-week periods. Diets consisted of wheat silages offered ad libitum as the sole forage supplemented with 7.5 kg concentrates.Cows consumed on average 14.1 kg DM of wheat silage, 0.6 kg DM more of SHD than of ED silage (P < 0.001), and 0.4 kg DM more of processed than of unprocessed silage (P < 0.001). Apparent organic matter digestibility of wheat silage, calculated by difference, was 0.62 and 0.60 (P = 0.02) for ED and SHD respectively, and the respective starch digestibility was 0.98 and 0.99 (P = 0.02). There was no main effect (P > 0.20) of processing on total tract digestibility for any nutrient, but a weak interaction (P = 0.08) suggesting that starch digestibility was slightly higher in unprocessed than in processed wheat silage from SHD with an opposite tendency for ED. Daily yields of protein and lactose were higher, and milk yield tended to be higher (P = 0.07), with processed than with unprocessed silage from ED, as expected due to higher forage intake, whereas no effect of processing was found in SHD silage, in spite of higher intake. Soft-to-hard dough diets contained a high load of starch plus sugar compared with fibre. This might have influenced the rate and extent of ruminal neutral detergent fibre digestion. It is concluded that starch in wheat kernels harvested at the soft-to-hard dough stage or earlier, at a DM concentration in wheat silage up to 430 g/kg, is completely digested in dairy cows without processing.