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Mối liên hệ giữa sinh khí mê-tan invitro và invivo được đo đồng thời với các nguồn tinh bột và mức độ tinh bột trong khâu phần bò sữa

Thứ tư, 28/10/2015 - 13:40

To investigate the relationship between in vitro and in vivo methane (CH4) production measured simultaneously using the same rumen-fistulated cows in both experiments, four dietary treatments based on concentrate that accounted for 400 g/kg of the mixed diet DM, were formulated to contain starch varying in rate of fermentation (slowly (S) vs. rapidly (R): native vs. gelatinized maize grain) and level of inclusion (low (L) vs. high (H): 270 vs. 530 g/kg of concentrate DM).

Sixteen rumen-fistulated lactating dairy cows were used in a complete randomized block design with these treatments replicated in four periods of 17 d each. In experiment 1, after 12 d of adaptation, the cows were housed in respiration chambers for 5 d to measure CH4 production. In experiment 2, in each period in vitro gas and CH4 production were measured (in duplicate per period) for mixed diet samples from the same diet as fed to the donor cows using rumen inocula adapted to the respective diets for an average of 16 d. In addition, samples of two concentrate ingredients, viz. grass silage and beet pulp, were incubated with four different inocula obtained from individual donor cows. Gas production (GP) was measured using automated GP system with CH4 measured at distinct time points. In vitro (24-h) CH4 production of mixed diet was lower with R than S (42.9 vs. 49.5 ml/g of incubated organic matter (OM); P=0.004), and higher with L than H (49.8 vs. 42.6 ml/g of incubated OM; P=0.002). A significant interaction effect between source and level of starch (P=0.015) was also found, indicating the CH4 production of the RH diet decreased in particular. In vivo, an increased rate of starch fermentation resulted in a lower CH4 per unit of estimated rumen-fermentable OM (eRFOM; 55.6 vs. 61.2 ml/g of eRFOM; P=0.007), and higher level of starch tended (P=0.089) to reduce CH4 per unit of eRFOM, but dietary starch level and source did not affect CH4 per unit of OM consumed. Across the diets tested, 24-h in vitro CH4 (ml/g of incubated OM) correlated well with in vivo CH4 expressed per unit of eRFOM (R2 = 0.54; P=0.040), but not when expressed per unit of OM ingested (R2 = 0.04; P=0.878). For grass silage (the same trend for beet pulp), inocula adapted to R- and H-based diets compared with S- and L-based diets resulted in a lower CH4 production (36.1 vs. 44.8 ml/g of incubated OM, R vs. S; and 37.4 vs. 43.4 ml/g of incubated OM, H vs. L; P<0.001). These results indicate that adaptation of rumen inoculum to different diets affects CH4 production of a substrate differently. In conclusion, in vitro CH4 measurement can be indicative of the trend of in vivo CH4 production from different combinations of sources and levels of starch when in vivo CH4 is expressed per unit eRFOM, but not when expressed per unit OM ingested. This study suggests that complexity associated with rumen fermentation conditions needs to be considered to fully predict in vivo CH4 production from in vitro measurements.

 

Abbreviations

ADFom, acid detergent fibre excluding residual ash; aNDFom, neutral detergent fibre assayed with a heat stable amylase and excluding residual ash; CH4, methane; CP, crude protein; DM, dry matter; GP, gas production; H, high level of starch; L, low level of starch; OM, organic matter; OMI, organic matter intake; eRFOM, estimated rumen-fermentable organic matter; R, rapidly fermentable starch; S, slowly fermentable starch

Keywords

In vitro; In vivo; Starch fermentability; Methane; Dairy cow

Animal Feed Science and Technology

Volume 202, April 2015, Pages 20–31


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