Effects of particle size of a total mixed ration on in vivo ruminal fermentation patterns and inocula characteristics used for in vitro gas production
- Publication Type
- Journal contribution
- Authors
- Tafaj, M., Q. Zebeli, B. Junck, H. Steingass and W. Drochner
- Year of publication
- 2005
- Published in
- Animal Feed Science and Technology
- Band/Volume
- Vol. 123-124/
- Page (from - to)
- 139-154
- Keywords
- dairy cow, gas production, particle size, rumen fermentation, TMR
The objective was to investigate effects of particle size (PL) of a total mixed ration (TMR) on in vivo ruminal fermentation patterns and characteristics of the inocula used for in vitro gas production. A 3x3 randomized block design was used with three ruminally cannulated Holstein cows (640 kg BW, 63 DIM, 36 kg milk/d) fed ad libitum with TMR diets consisting of 450 g/kg grass silage (GS) with three PL levels (25, 11 and 5.5 mm), 500 g/kg cereal-based concentrate mixture and 50 g/kg of long hay. Replicates of samples of solid digesta from the dorsal (SRF-T) and ventral (SRF-B) rumen and free fluid (FRL) samples were collected 1 h before and 2,8 and 12h after the morning feeding. Samples were analyzed for pH and short chain fatty acids (SCFA), thiamine and protozoa concentrations. The same digesta collected 1 h before the morning feeding was used as inoculum for in vitro incubation in a gas test, and the gas production (GP) profile of all TMR were determined. The SCFA concentration of SRF-T increased with reduction of PL of TMR (P < 0.05), but that of FLR decreased (P < 0.05). There was no effect of PL of TMR on SCFA concentration in SRF-B. Reducing the PL of TMR to 5.5 mm decreased ruminal pH and the acetate: propionate ratio 1 h prior to the morning feeding (P<0.05), while 11 mm did not affect ruminal pH. Ruminal protozoa numbers increased by reducing the PL to 11 mm. These effects of PL on the ruminal milieu are also reflected in the digestive characteristics of inocula used for in vitro incubation. The inocula of SRF-T collected from cows fed TMR of 11 and 5.5 mm PL increased in vitro GP of blank and Substrate (TMR) in comparison to the 25 mm PL treatment. GP positively correlated with concentrations of SCFA and thiamine, and negatively to pH of the ruminal digesta in vivo, 2 h after incubation and feeding (P<0.05) only (i.e. at the start of fermentation of feed). Studies are needed to explain effects of PL reduction on microbial activity in vivo and in vitro.