Does microbial nitrogen contamination affect the estimation of crude protein degradability of concentrate feeds?1

• Published in: Journal of animal science 2017-09, Vol.95 (9), p.4164-4171
• Main Authors: Menezes, A. C. B., Filho, S. C. Valadares, Rotta, P. P., Santos, S. A., Pacheco, M. V. C., Silva, B. C., Pucetti, P., Alhadas, H. M., Detmann, E., Caton, J. S.
• Format: Article
• Language: English
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2017.1699

Abstract The effects of microbial contamination (MC) on CP degradability of concentrate feeds are still controversial. Therefore, the aim of this study was to use 15N to estimate the impact of MC on estimations of CP fractions (the soluble fraction of CP [a], the insoluble but potentially degradable fraction of CP [b], and the rate of digestion of fraction b [kd]) of concentrate feeds. Twelve types of feed were evaluated: 6 energy concentrates—wheat bran (Triticum aestivum L.), rice meal (Oryza sativa L.), ground corn (Zea mays L.), ground sorghum (Sorghum vulgare Pers.), ground corn cob (Zea mays L.), and soybean hulls [Glycine max (L.) Merr.]—and 6 protein concentrates—cottonseed meal (Gossypium hirsutum L.), soybean meal [Glycine max (L.) Merr.], ground bean (Phaseolus vulgaris L.), peanut meal (Arachis hypogaea L.), sunflower meal (Helianthus annuus L.), and corn gluten meal (Zea mays L.). The feeds were divided into 4 groups and were incubated in the rumen of 4 crossbred bulls. The samples were incubated for 0, 2, 4, 8, 16, 24, 48, and 72 h. To estimate the MC of the incubated residues, the ruminal bacteria were labeled with 15N via continuous intraruminal infusion of 15(NH4)2SO4. There was no difference (P = 0.738) between corrected and uncorrected parameters a, b, and kd for all feeds that were evaluated. All of the feed tests followed an exponential model of degradation, and the model fitted well to the data, except for corn gluten meal, probably because the maximum incubation time that was used (72 h) was not long enough to allow for an accurate estimation of the degradation profile. Therefore, correction of ruminal protein degradation to MC is irrelevant with regards to the concentrates that were studied.