Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2008
Publication Date: 7/7/2008
Citation: Colombini, S., Broderick, G.A. 2008. In vitro ruminal protein degradation and microbial protein formation of seed legumes [abstract]. Journal of Dairy Science. 91(suppl. 1):43.
Technical Abstract: Seed legumes such as peas, lupins, and faba beans are important feeds for dairy cows in Europe and other regions. Ruminal protein degradability was quantified using the inhibitor in vitro (IIV) system for samples of 5 seed legumes: 2 peas (cv. Alembo and Helena), 1 white lupin (Lupinus albus, cv. Multitalia), 1 blue lupin (cv. Quilinok), and 1 faba bean (Vicia faba minor, cv. Chiaro). Incubations were stopped by adding acid at 0, 2, 4, and 6 h; ruminal escape was computed assuming a passage rate of 0.06/h. Five standard proteins were included. Additional incubations were conducted without growth inhibitors in an attempt to correct for N incorporation by bacteria. These were conducted for 2, 4, and 6 h, with ruminal inoculum containing ammonium sulfate enriched with N-15. Net microbial growth (growth above blank) was estimated from total non-ammonia N (NAN) plus N-15 enrichment of total NAN and isolated bacterial NAN. Significant differences were observed among protein sources in IIV degradation traits. Typical estimates of degradation rate and rumen-undegraded protein (RUP) were obtained for the standard proteins. The two pea sources had slower degradation rates and greater RUP than the lupins and faba beans. The IIV system ranked the RUP contents of the 5 legumes differently from the Cornell model. Excessive variation prevented reliable estimates of degradability in uninhibited inoculum. However, there was a trend (P = 0.15) for an effect of seed legume on microbial NAN formation; greater content of starch and water-soluble carbohydrate may have supported greater formation of bacterial NAN for Alembo peas and Chiaro faba beans. Both microbial growth and protein escape should be considered when evaluating feeds rich in protein and fermentable energy.