Factores que afectan a la fermentación microbiana y al perfil y flujo de aminoácidos de las bacterias asociadas con las fracciones líquida y sólida en un sistema de cultivo continuo

Abstract

The objective of this Thesis was the study of the factors affecting the profile and flow of AA from bacterial origin from the rumen, using liquid (LAB) or solid (SAB) associated bacteria composition data in continuous culture (CC). Three trials were conducted. The objectives of the first trial were: 1)To set up of the CC. 2)To isolate and obtain sufficient samples of LAB and SAB for chemical analysis. 3)To study the effect of the inclusion of the additive Regepro"on rumen microbial fermentation. Eight fermenters were used in three periods of 8 days each (5 for adaptation, 3 for sampling). Treatments were diet type (CS=Corn silage; RS=Ryegrass silage based diets) and Regepro"dose (0; 0,15; 0.30, 0.45 g/100gDM). Data was analyzed as a randomized block with a 2x4 factorial arrangement of treatments. Temperature (39ºC), pH (6.4)., liquid (10%/h) and solid (5%/h) dilution rates, and intake (100gDM/d) were maintained constant. LAB and SAB were obtained the last day of sampling, and enough samples of both bacterial groups were obtained (>1g/fermenter/treatment). Results confirmed the differences in chemical composition between LAB and SAB. The inclusion of Regepro"at intermediate doses (0.15-0.30) reduced ammonia N concentration (-18%), with no other effects on rumen microbial fermentation. Trial 2 (2 periods of 10 days each: 7 for adaptation, 3 for sampling) consisted in the evaluation of the effect of fiber content (FC: HF=67:33 and LF=39:61 alfalfa hay:concentrate ratio) and forage particle saze (PS: LS=≥3mm SS=≤1mm) on rumen microbial fermentation, and microbial AA profile and flow. Data was analyzed as a randomized block with a 2x2 factorial arrangement of treatments. Experimental procedures were similar to trial 1, except for intake (95gDM/d). VFA production was lower and the proportion of acetate was higher for HF compared with LF. When SS was fed instead of LS, there was a reduction in the acetate proportion and in the acetate to propionate ratio. Bacterial N flow was higher, and dietary N flow lower in SS compared with LS when LAB were used for calculations. Efficiency of microbial protein synthesis (EMPS=gbacterialN/kgTOMD) was affected by PS when LAB were used for calculations, and by FC when SAB were used. The AA profile of LAB differed from SAB in 4 out of 16 AA. The FC and PS had small effects on microbial AA profile and flows. However, the bacterial AA flow was higher in 13 out of 16 AA when SAB instead of LAB were used for calculations. Trial 3 was designed to study the effects of pH (High=6.5; low=5.5) and solid dilution rate (Slow: SSDR=4%7h; or Fast: FSDR=10%/h). Experimental design and procedures were similar to trial 2, except for intake (80gDM/d) and main factors. True DM and OM digestibilities were lower at low pH only when SAB were used for calculations. Fiber digestion was lower at low pH and FSDR. VFA production and profile were affected more by pH than by SDR. The FSDR had a higher bacterial N flow, protein degradation and ESPM, and lower dietary N flow compared with SSDR. Dietary N flow and protein degradation were dependent on the bacterial population used for calculations. The SDR and pH affected microbial AA profile, but the number of AA that changed were dependent on the microbial population used. Because few changes were observed in the AA profile between LAB and SAB, the differences in the estimated microbial AA flow were attributed to the differences in the estimation of microbial protein synthesis.

Date of Award	20 Jun 2003
Original language	Undefined/Unknown
Supervisor	Sergio Calsamiglia Blancafort (Director)