Effect of supplement type on ruminal fermentation of an orchardgrass-based pasture diet during continuous culture

Authors: Soder, Kathy; Gregorini, Pablo

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2010
Publication Date: 5/21/2010
Citation: Soder, K.J., Gregorini, P. 2010. Relationship between supplemental protein and ruminal fermentation of an orchardgrass-based herbage diet. Professional Animal Scientist. 26(3):290-297.

Interpretive Summary: High-quality pastures in the northeastern United States are high in crude protein. Despite this, many grazing dairy producers continue to feed high levels of supplemental protein. However, the effect of high supplemental protein on ruminal fermentation and digestion is not known. A study was designed to determine the effects of varying levels of protein supplementation in a pasture-based diet on ruminal fermentation using continuous-culture fermenters. Supplementation of a high-quality pasture diet with different levels of supplemental protein did not affect pasture digestion and nutrient supply to the lower digestive tract. Increasing supplemental protein of cattle grazing high quality pastures may reduce herbage intake due to reductions in daily grazing time and meal sizes, which appears to be due, in part, to nutritional imbalances such as an excess of ruminal ammonia. Selective behavior of grazing ruminants is affected by aversion, which is the decrease in preference for a food/nutrient recently consumed as a result of sensory or post-ingestive effects. Grazing ruminants may avoid nutrient imbalances and modify nutrient intake when given the opportunity to select from an adequate range of dietary ingredients. Principals learned through these laboratory methods must be tested in the animal to account for live animal consequences of diet selection and supplementation strategies.

Technical Abstract: A dual-flow continuous culture fermenter system was used to investigate the effect of supplemental crude protein (CP) level on digestion and ruminal fermentation of a vegetative orchardgrass (Dactylis glomerata L.) pasture-based diet. Treatments were: 10, 12, 14, and 16% supplemental CP fed at a rate of 30 g DM**d to an herbage diet (45 g DM**d). Fermenters were sampled for pH, ammonia, and VFA four times daily at each feeding (0700, 1030, 1430 and 2030 h). Effluent was analyzed for DM, CP, OM, purine concentration and bacterial production. The DM and OM digestibility, as well as their flows were calculated. The DM, OM and NDF digestibilities, and total VFA production were not affected by supplemental CP. Mean rumen pH was lower for the 10% CP diet. Acetate and isobutyrate concentrations were lower while propionate and valerate were higher for the 10% supplemental CP than for the other diets. Total N input (g**d) and ammonia (mg N**00 ml) increased with increasing supplemental CP. N flows for non- ammonia, bacterial N, dietary N and efficiency of bacterial protein synthesis were not affected by supplemental CP level. Continuous culture fermentation systems can be used as a tool to quickly evaluate ruminal/animal responses to hypothetical feeding scenarios. Within the ranges evaluated in the present study, supplementation of high-quality pasture diets with different levels of CP did not affect herbage digestion and nutrient supply to the lower digestive tract.