Eight hybrids of sorghum forage were tested in large plots of two farms in two consecutive years to evaluate their chemical characteristics, nutritive value and yield as a possible substitute for maize silage. Two or three cuts were made depending on climatic conditions. On forage samples taken at ensiling chemical analyses and 24 h gas production were performed, to predict the NEl content. In comparison with maize silage, the sorghum hybrids registered higher protein (13.7% on DM) and NDF (62.6% on DM) contents. Interestingly, the fibre fraction had a low lignin content (3.1% on DM). NEl content ranged from 4.53 to 5.28 MJ/kg DM, the latter for the hybrid with the lowest NDF content. Hybrid effect was significant for ash, NDF, ADF and NEl contents, whilst cut effect was significant for EE, CP, NDF and ADF. Yield was strongly influenced by fertilisation; when the latter was applied, it was in the range of 10-18 t DM, 1.7-2.8 t CP and 47-88 thousand MJ NEl per hectare, as a sum of the 23 cuts. Sorghum forage seems to be a possible alternative to the fibrous maize silage fraction in diets of lactating cows, and an excellent forage for the rations of dry cows and heifers.

Rumen dry matter and fibre digestibility of brown midrib (BMR) sorghum forage silage (SF) in comparison to corn silage (CS) was determined in situ using 3 fistulated dry cows. The effect of replacing CS with SF on milk production was studied in a change-over design with 58 lactating Italian Friesian cows fed two diets with similar composition. CS had a higher (P<0.001) rapidly degradable dry matter (DM) fraction than SF (33.1 vs. 23.7, respectively), whilst the slowly degradable fraction was not different (46.3 vs. 48.7). Overall, the extent of DM rumen degradability was higher for CS. Rumen digestion rate of neutral detergent fibre (aNDFom) tended to be higher (P=0.06) for SF than CS (3.08 vs. 2.49 %/h, respectively); however, effective rumen degradability of fibre was not different between silages. Neither milk yield (kg/d) and 4%-fat corrected milk nor milk protein and fat contents were affected by treatment. Cows fed CS diet had lower (P<0.05) milk urea content compared with their SF counterparts (19.9 vs. 21.5 mg/dL,) suggesting a better nitrogen utilization at the rumen level. In conclusion, feeding a BMR sorghum forage resulted in milk yield and quality similar to corn silage. However, to obtain comparable milk production as corn silage, the SF-based diet had to be supplemented with more starch from corn meal.

Two experiments were conducted on alfalfa to investigate the effects of the addition of commercial chestnut hydrolyzable tannin at ensiling on 1) silage fermentation quality in lab-scale silos and protein degradation in the rumen, and 2) silage fermentation quality and proteolysis in bale silages. Wilted alfalfa was prepared with 4 tannin levels (0, 2, 4, and 6% on a dry matter (DM) basis; T0, T1, T2, T3, respectively) and ensiled in lab-scale silos. Silages (33% DM) were analyzed for fermentation quality, protein rumen degradability in situ, and organic matter digestibility in vitro through gas production after 120 d of conservation. Wilted alfalfa containing 0 and 4% tannin (T-0 and T-2) was harvested at 40% DM (wilting level I) and 53% DM (wilting level II) for bale (600 mm diameter) silage. Silages were analyzed for fermentation quality after 78 d of conservation. All the silages were well fermented with no butyric acid. Lab-scale silages showed reductions in ammonia, nonprotein nitrogen (NPN) and DM losses in T2 and T3 treatments, while the fermentation acid profiles were unaffected. In experiment 1, the untreated silage (T-0) had the highest protein degradability after being incubated in the rumen. The addition of tannin reduced crude protein ruminal disappearance in a dose-dependent manner. However, the tannin reduced the organic matter digestibility by 5.1% for all of the tannin addition levels. The tannin positively affected the silage quality in the round bale silages, in particular reducing ammonia and NPN in the lowest wilting level. In both experiments, T2 treatment reduced proteolysis without any influence of DM on the binding reaction and reduced the NPN by 15% in comparison to the control.

Riassunto Stima del valore nutritivo dell’insilato di mais mediante tecniche in vitro e con la spettroscopia nel vicino infrarosso (NIRS). Scopo del lavoro è stato valutare la validità della tecnica NIRS per la previsione del valore nutritivo determinato in vitro del silomais e caratterizzare quelli prodotti in Lombardia e analizzati negli anni 2001-2004 dal laboratorio dell’ARAL. Su 100 campioni di silomais sono state fatte analisi chimiche e biologiche (gas test e digeribilità in vitro) i cui risultati sono stati utilizzati per la calibrazione dell’analizzatore NIR e la successiva stima di tali parametri su tutti i 2443 campioni di silomais a disposizione. La digeribilità (IVTD) media della SS è risultata pari al 77,7%, mentre quella dell’NDF è risultata solo del 49%. La calibrazione del NIRS per la produzione di gas (GP) ha fornito coefficienti di determinazione elevati (0,90 e 0,85 per la GP a 8 e 24 h), mentre l’R2 per la digeribilità dell’NDF è risultato insoddisfacente (0,25). La tecnica NIRS conferma la sua potenzialità per la previsione del valore nutritivo dell’insilato di mais.