Effect of varying sources of protein in glucogenic dairy diets on in vitro rumen microbial nitrogen yield Behnaz Eyni, Mohsen Danesh Mesgaran, Alireza Vakili, RezaValisadeh Ferdowsi University, Mashhad, Iran E-mail: behnaz_eyni@yahoo.com Take home message In vitro microbial protein synthesized in the rumen is influenced by the source of protein of glucogenic diets to meet the requirement of the dairy cows. Introduction Dietary crude protein supplies amino acids (AA) for the dairy cows to sustain their need for maintenance and milk production. Amino acids that reach the small intestine of the ruminant are mainly originated from microbial cp (MCP) synthesized in the rumen, the dietary protein that escapes ruminal degradation, and the endogenous protein (Van Duinkerken et al., 2011). Among these sources, microbial protein is considerable because of the AA pattern related to animal production, intestinal digestibility, and AA utilization. Thus, it is important to maximize the MCP synthesis in the rumen. Therefore, the objective of this study was to measure the effects of lipogenic diets on microbial protein production. Material & methods The glucogenic diets including as ground barley+ soybean meal (BSB), ground barley + xylose protected soybean meal (BXPS), steam-flaked barley+ soybean meal (SFBSB), steam-flaked barley + xylose protected soybean meal (SFBXPS). An in vitro gas production technique was carried out to determine the rumen microbial yield as described by Grings et al (2005). The time of half-maximal gas production (t1/2) was calculated after the first 96 hours of the gas run. Then, a second incubation was performed with the diets and were stopped at the diet-specific half time of gas production and the microbial N production was determined following the equation and using the N-balance equation, given as follows: Microbial N Production at t1/2 = Diet N + ΔNH3 – N - NDFN at t1/2. The conversion of dietary N to microbial N (MN/DN) was determined from the value of microbial nitrogen divided by dietary nitrogen. The concentration of ammonia-N per dietary nitrogen (ammonia/DN) and ammonia- N+MN per dietary nitrogen (ammonia+MN/DN) were measured as the rate of conversion of N to ammonia-N and microbial-N in the rumen. Results & discussion In vitro ruminal ratios of microbial nitrogen yield (MN/DN), ammonia-N (A/DN) and ammonia-N+microbial nitrogen to dietary nitrogen concentration (A+MN/DN) are demonstrated in Table 1. Highest MN/DN and lowest A/DN ratios were observed in SFBSB (P< 0.05). It has been indicated that moister heat-processed starch and grain could result in a greater proportion of propionic acid being produced during the fermentation in the rumen and could help to produce a higher amount of microbial protein. The results were in agreement with the previous study regarding the decrease in the ammonia-N concentration in steamflaked grains (Fu-qiang et al., 2015). Diet containing steam flaked barely and XPS tend to obtain less A +MN/DN ratio than those of the other (p < 0.05). Table 1 In vitro ruminal ratios of microbial nitrogen yield (MN/DN), ammonia-N (A/DN) and ammonia-N+ microbial nitrogen to dietary nitrogen concentration (A+MN/DN). BSB SFBSB BXPS SFBXPS SEM MN/DN 0.4bc 0.59a 0.38c 0.43b 0.02 A/DN 0.45a 0.27c 0.43a 0.34b 0.02 A+MN/DN 0.85a 0.86a 0.81b 0.78c 0.01 Conclusion The conversion of dietary nitrogen to microbial nitrogen was higher in diets with steam-flaked grains than that of the ground grain diets. Microbial protein synthesis is supposed to be energy-dependent and the processing of the grain can help to supply the energy. Thus, A good synchronization of SF grains with protein sources is the result of the highest MN/DN value. References Fu-qiang Q, Fei W, Li-ping R, Zhen-ming Z, Qing-xiang M and Yu-hong, B. 2015. Journal of Integrative Agriculture 14, 949-955. Grings EE, Blummel M, and Sudekum, KH 2005. Animal Feed Science and Technology123-124, 527-545. Van duinkerken G, Block MC, Bannin AK, Cone JW, Dijkstra J, Van vuuren AM and Tamminga S. 2011. The Journal of Agricultural Science 49, 351–367.

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