ARS | Publication request: Effects of timing of corn silage supplementation on ruminal digestion, fermentation pattern and nutrient flow during continuous culture fermentation of a short and intensive orchardgrass herbage meal

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2010
Publication Date: July 15, 2010
Citation: Gregorini, P., Soder, K.J., Waghorn, G. 2010. Effects of timing of corn silage supplementation on digestion, fermentation pattern and nutrient flow during continuous culture fermentation of a short and intensive orchardgrass meal. Journal of Dairy Science. 93:3722-3729.

Interpretive Summary: Timing of supplementation in relation to grazing periods may impact pasture digestion and utilization in grazing dairy cows. It may be beneficial to strategically supplement grazing cows before or after a grazing meal, or during the non-grazing periods of the day, to improve intake and animal productivity. However, few studies have evaluated the benefits of the timing of supplementation on fermentation and nutrient utilization of pasture in the rumen. We evaluated the effects of supplementing a pasture-based diet with corn silage either in the morning or in the afternoon (either 9 or 1 hour before a simulated afternoon grazing meal) on ruminal fermentation using continuous culture fermenters. Under the same resource allocation (pasture plus supplement), a simple change in timing of feed allocation improved utilization of nutrients supplied by herbage, whilst potentially reducing the negative environmental impact of N losses. This information will be used for supplementing strategy that affects actual grazing patterns through ruminal fill and post-ingestive feedback of nutrients.

Technical Abstract: Using a dual-flow continuous culture fermenter system, this study evaluated the effect of timing of corn silage supplementation on ruminal digestion and nutrient flows of a short and intensive orchardgrass herbage meal. Fermenters were operated over four 10-d periods. Treatments included: 28 g DM of corn silage either 9 (9BH; 0700 h) or 1 h (1BH; 1500 h) before providing 42 g DM herbage, or no corn silage (control; CTL; 70 g DM herbage). Herbage was fed as follows: 66% of the total herbage meal at 1600 h, 22% at 1720 h, and the remaining 22% at 1840 h. Effluent was analyzed for OM, CP and NDF. Purine concentrations in effluent and bacterial isolates were used to estimate the partition of effluent N flow into bacterial and non-bacterial fractions, and to calculate true OM digestibility and flows. Fermenters were sampled for pH, VFA, and NH3-N at 0730, 1100, 1530, 1600, 1720, 1840 and 2000 h on day 10. Data were analysed as a 3 × 4 Youden-square design. True OM (78.5% mean) and CP (84.6% mean) digestibilities were not affected by treatment. Apparent NDF digestibility did not differ between 1BH and 9BH (81.6% mean), nor between 1BH and CTL (83.9% mean). Mean ruminal pH was lower for 9BH than for 1BH, 5.6 and 6.5 respectively. Molar proportions of acetate were not affected by treatment. Propionate concentration was greater for 9BH than for 1BH, 20.5 and 18.1 Mmol/ml. Diurnal patterns of pH, NH3-N, and acetate:propionate ratio were affected by treatment; as the day progressed 9BH had the lowest values. The NH3-N concentration and effluent flow were higher for 1BH (11.4 mg/100ml and 0.26 g/d, respectively) than for 9BH (8.8 mg/100ml and 0.20 g/d, respectively). Effluent NH3-N flow (expressed as a % of total N flow) was the lowest for 9BH. Bacterial efficiency was not affected by treatments, with a mean of 10.5 g N/kg OM truly digested. Under the same resource allocation (pasture plus supplement), a simple change in timing of corn silage feeding (9 rather than 1 h before an orchardgrass herbage meal) changes ruminal fermentation pattern. This change increases the glucogenic nutrient supply and reduces NH3-N in rumen and its flow to the intestine, potentially reducing the environmental impact of nitrogen losses.