Effects of alfalfa germplasm and stage of maturity on digestive process and productive response of dairy cows fed alfalfa hay-based diets

The effects on the digestive process and the productive performances of dairy cows fed diets containing alfalfa hay from different germplasms and maturity were assessed in the present study. Three different lots of first-cut alfalfa hay were used in the study: the improved variety "Boreal", harvested at two consecutive maturity stages (early flowering and full flowering) and the ecotype "Vogherese", at full flowering. Cutting the plant at an earlier stage of maturity improved hay quality in comparison with the more mature forages (crude protein: 21.4 vs 16.5% DM; P<0.01; NDF: 42.2 vs 53.5% DM; P<0.01). The comparison between improved variety and ecotype carried out at the same maturity showed a higher lignin content for the latter (8.6 vs 8.2% DM; P<0.01). Three isocaloric, isonitrogenous and isofibrous diets for lactating cows were formulated using an equal amount of corn silage and the maximum inclusion of one of the tested hays as forage base. The better quality of the early cut hay made it possible to increase its inclusion in the diet up to 44% of total dietary DM, while the two more mature hays covered only 36% of total DM of the respective diets. According to a 3 x 3 Latin square design, the diets were fed to 3 Italian Brown cows (initial average days in milk 121 ± 24 and milk yield 20 kg ± 1.3) fitted with ruminal cannula in 3 consecutive periods of 28 d each. Alfalfa stage of maturity and germplasm did not affect dietary DM intake (average 16 kg/d). Degradability parameters of dietary DM, calculated by in situ nylon bags technique, showed similar kinetics of rumen disappearance for all diets. No differences were noticed in the ruminal rate of passage of the solid phase among diets, while the liquid phase showed a slower rate of passage for the early flowering hay diet. Consistent with the degradation process, the stage of maturity or the alfalfa germplasm did not affect the rumen fluid data or the in vivo digestibility coefficients of the diets. Milk yield did not show any change due to either alfalfa maturity or cultivar, while milk protein was lowered when cows received the early cut hay diet. This result was likely due to an excess of rumen degradable dietary protein which could have been limited by replacing part of the dietary protein sources (soybean meal) with others more resistant to the ruminal degradation.