Evaluation of fermentation dynamics of soluble crude protein from three protein sources in continuous culture fermenters

¹ ICREA (Institució Catalana de Recerca i Estudis Avançats), 08010 Barcelona, Spain; Grup de Recerca en Nutrició, Maneig, i Benestar Animal, Unitat de Remugants, IRTA (Institut de Recerca i Tecnologia Agroalimentàries), 08193 Bellaterra, Spain
² Department of Animal Science, University of Minnesota, St. Paul 55108

^* To whom correspondence should be addressed. E-mail: alex.bach{at}irta.es.

	Abstract

Eight dual-flow continuous culture fermenters (1.03 ± 0.05 L) were used to assess differences in microbial degradation of the soluble protein fraction of canola meal (CMSCP), soybean meal (SBMSCP), and fish meal (FMSCP) using a complete randomized design with two 9-d experimental periods and a solution of tryptone as a control treatment (CTRL). All fermenters received the same basal diet (58% ground corn, 40% canary grass hay, 0.4% vitamin-mineral premix, 1% CaCO₃, 0.6% salt on a DM basis) in 8 equal portions daily. During sampling on the last 3-d of each period, 90-mL doses containing soluble CP were infused into fermenters 30 min after the beginning of the first and last feedings of the day. The total amount of soluble CP supplied by the infusions of FMSCP, CMSCP, and SBMSCP was 3.2 g/d, representing 24% of daily dietary CP intake. Infusion of FMSCP resulted in the greatest (P < 0.05) ammonia-N concentration (4.6 ± 0.40 mg/dL) compared with the other treatments (0.5 ± 0.40 mg/dL). Microbial N flow (g/d) from fermenters was also greatest (P < 0.05) with FMSCP (1.42 ± 0.062) compared with the other soluble CP fractions (1.08 ± 0.062). The efficiency of microbial protein synthesis tended to be lowest with the CTRL diet, and the efficiency of N utilization was lowest with FMSCP treatment. These results indicate that N was limiting microbial growth in the CTRL diet and there was more rumen-available N with the FMSCP diet compared with the other dietary treatments. The degradation extent of the soluble CP fraction from fish meal, soybean meal, and canola meal was determined to be 99, 30, and 37% of soluble CP, respectively. These results indicate that the soluble CP fraction is not 100% degraded in all feeds, and that assuming a high degradation extent of the soluble CP fraction from soybean meal and canola meal may result in an underestimation of the supply of undegradable protein from these protein sources.

Key Words: in vitro, protein degradation, soluble protein