Effect of alfalfa hay digestibility and inclusion rate in lactating dairy cows diets on feed intake, digestibility, ruminal pH and productive performance

The objective of this study was to investigate the effects of two alfalfa hay differing in digestibility in high producing cows diet with two level of forage neutral detergent fiber (NDF) inclusion (HF and LF respectively), on feed intake, digestibility, ruminal pH and productive performance. Alfalfa hay NDF in vitro digestibility at 24 and 240 hours were 40.2% and 31.2%, and 53.6 and 45.7% for high (HD) and low digestibility (LD) respectively. The four experimental diets (HF-HD; LF-HD; HF-LD and LF-LD) contained, on a dry matter basis, 46.8, 36.8, 38.8 and 30.1% of alfalfa hay respectively, 8.6% straw and 34.4% corn (50% flake and 50% meal), while soyhulls and soybean meal were used to replace part of the hay in order to balance protein and energy among diets. Eight multiparous Holstein cows (average milk production 46.0±5.2 kg/d, 101±38 days in milk and 662 ± 42 kg average BW), were assigned to a 4 x 4 Latin square design, with 3 weeks adaptation and 1 week of collection. Dry matter intake, milk production and quality, and rumination time were measured daily. Ruminal pH was measure continuously at 10 min intervals. Fecal samples were collected at multiple time points and averaged daily. Diets and feces were analysed for aNDFom, ADF, ADL, undigestible NDF (uNDF) and potentially digestible NDF (pdNDF), in order to calculated total tract fiber digestibility. Starch and protein analysis were performed on each diet. All data were statistically analyzed with a factorial arrangement of treatments using the PROC MIXED model in SAS. Milk production was not different, while dry matter intake where higher in HD diets. Rumination time was significantly higher for HD diets when compared to LD diets, regardless of forage amount. Rumination time was constant per unit of dry matter and differed when related to uNDF, aNDFom or peNDF intake. No differences were found among treatments on average ruminal pH, but the amount of time with pH <5.8 was lower in HF-HD diets. Total tract NDF and pdNDF digestibility showed good results for all the experimental diets. Higher digestion was observed in the LD diets (88.3 vs 85.8 in HDs), in which a lower feed intake was also observed. This fact could suggest that the first limiting factor of ruminal fiber digestibility is the retention time. HF-HD diet (high level of highly digestible alfalfa hay) allowed the higher dry matter intake, rumination time and the best ruminal pH values.