|BACH, A - UNIVERSITY OF MINNESOTA
|YOON, I - UNIVERSITY OF MINNESOTA
|STERN, M - UNIVERSITY OF MINNESOTA
|Jung, Hans Joachim
|CHESTER-JONES, H - UNIVERSITY OF MINNESOTA
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/1998
Publication Date: N/A
Interpretive Summary: In an effort to reduce the negative environmental impacts of dairy farming and improve both the economic and social welfare of farm families, there has been a move toward grazing based dairy systems. This approach reduces dependence on external chemical and fuel inputs to the farm and makes the entire enterprise more sustainable. However, dairy cows cannot reach their rmilk production potential by grazing alone and there are economic advantages to maximizing milk yield per cow. For these reasons information is needed about which high energy feedstuffs should be used to supplement dairy cows on pasture without adversely affecting animal health. Pasture plus three different energy feeds (corn grain, sugarbeet pulp, and soybean hulls) were compared to pasture alone for their impact on digestible energy yield and nitrogen utilization in an artificial rumen (the cow's stomach). All three energy feeds improved digestible energy yield for milk production, but soybean hulls were clearly superior for utilizing the nitrogen in pasture. The results indicate that farmers can increase both milk production and maintain good animal health. In addition, choice of the best energy feed can improve the environmental benefits of grazing systems by improving nitrogen utilization from pasture and further reducing pollutants such as nitrate run-off from dairy farms.
Technical Abstract: Eight single-flow continuous culture fermenters were used to study the effects of type of energy source on ruminal nitrogen utilization from high quality pasture. The four dietary treatments included: high quality 50:50 grass/legume pasture alone (P), pasture plus soybean hulls (PSH), pasture plus beet pulp (PBP), and pasture plus corn (PC). Energy supplemented diets (PC, PBP, and PSH) were isocaloric but differed in type and rate of carbohydrate fermentation. Energy supplements were 45% of the total ration dry matter and were fed twice daily at 12 h intervals in place of the P basal diet, which is characteristic of grain feeding at milking with animals in a grazing situation. Energy supplementation reduced pH, NH3-N flow, and NH3-N concentration, and increased bacterial N flow (as a % of N intake). Corn and soybean hull supplementation resulted in the highest microbial N flow (as a % of N intake). Corn had a tendency to reduce fiber rdigestion because of excessively low NH3-N concentrations. Beet pulp was similar to corn in decreasing NH3-N concentrations. Soybean hull supplementation resulted in a more synchronized fermentation, with greater volatile fatty acid production and fiber digestion. Supplementation of grazing dairy cows twice a day with soybean hulls or corn promotes maximal microbial N utilization. With pasture-based diets, improving bacterial N flow and bacterial utilization of N may be more important than maximizing efficiency of bacterial protein synthesis because better utilization of N by ruminal microorganisms results in higher bacterial N flow and higher fiber digestion.