Utilización de ensilados de cultivos forrajeros invernales obtenidos con fertilización orgánica alternativos al raigrás italiano en la alimentación de vacas lecheras durante el período de transición

The present research work were planned to evaluate a crop silage including a legume (fava bean forage) and crucifer (rapeseed forage, HC) as an alternative to Italian ryegrass silage (RI) in the diet of Friesian cows during the transition period in grazing conditions, under the premise of using quality forages supplemented with a minimal contribution of concentrate in the diet, in order to cope the current situation in which the dairy sector is immersed, and the necessity to find new alternative crops environmental friendly. Two winter crops (HC and RI) were grown on two similar and adjoining plots, with 1.7 ha each one. The intercropping HC was managed with sustainable environmental conditions (organic fertilizer and low herbicide imputs) while the RI were managed under conventional management (use of synthetic fertilizer and herbicides). The RI was harvested for silage in two cuts, and the HC in an unique cut. Forage production of HC in a single cut was higher than the RI accumulated production of the two cuts, for dry matter (9,82 vs. 7,88 tDM per ha respectively; P greater than 0,05) and for crude protein (1,63 vs. 1,11 tCP per ha respectively; P greater than 0,05) and lower organic matter digestible content (8,51 vs. 11,71 tOMD per ha respectively; P less than 0,01) and energy production (89 vs. 93 GjME per ha respectively; P greater than 0,05). The growth of weeds associated with subsequent summer crops (maize in both plots) was significantly lower in the HC plot than in RI plot (0,28 vs. 1,42 tMS per ha, respectively, P less than 0,01), despite the application of a lower dose of herbicide in the HC plot, which demonstrates the herbicide activity of rapeseed. The potassium (K) evolution in soil reflects the effect of organic fertilization (rich in K) and K extraction from deep soil layers by rapeseed. The estimation of the ensilability index of both winter crops classified the RI as high ensilability while the HC as of half ensilability. With these silages, two Total Mixed Rations (TMR) were prepared and offered ad libitum to two groups of Friesian cows: HC group (TMR based on HC silage, 5 cows) and RI group (TMR silage based on RI; 4 cows), from 4 weeks before the expected calving date until 4 weeks after calving. The cows had access to pasture between 12 and 16 hours per day. The HC-group animals had lower TMR intake than RI-group animals (P less than 0,001). This low intake was offset by an increased grass intake on pasture during the four weeks before calving. However this compensation did not continue in the postpartum period, therefore the recovery of the total postpartum dry matter intake was affected and was numerically higher in RI group than in the HC group. The lower dry matter intake in the HC-group did not affect milk yield (28,14 vs. 28,49 kg milk per d, in HC and RI group respectively) or protein content (3,31 vs. 3,26 per cent, respectively) however, the fat content was higher in RI group than HC group (4,36 vs. 3,91 per cent, respectively, P less than 0,05). Nevertheless, the HC-group fat milk was richer in polyunsaturated fatty acids than the milk fat of RI group (3,48 vs. 2,03 gAGPI per 100gAG respectively, P less than 0,001), especially in the proportions of linoleic (1,86 vs. 1,36 g per 100gAG, respectively, P less than 0,01), CLA (0,74 vs. 0,31 g per 100gAG, respectively, P less than 0,001) and linolenic acids (0,86 vs. 0,35g per 100gAG, respectively, P less than 0,001). Replacement of Italian ryegrass by the intercropping of fava bean and rapeseed provides the advantage of increasing the production per hectare and reducing the use of chemical fertilizers and herbicides. The use of fava bean-rapeseed silage in grazing dairy cows feeding during the prepartum period can reduce the concentrate contribution in the ration and increase the pasture grass intake, thereby, it could reduce feed costs during this period. The use of the same ration based on the HC silage after calving, had not effect on milk production and improves greatly the fatty acids profile of the fat, compared with the RI group. However, there is a limitation on dry matter intake after calving, which could affect milk production at medium and long term and the recovery of the reproduction activity. Hence, it should be research its contribution together with other forages and per or silage additives that allow increase its digestibility and voluntary intake after delivery.