Temporal fermentation and microbial community dynamics in rumens of sheep grazing a ryegrass-based pasture offered either in the morning or in the afternoon.

Eight ruminally-fistulated wethers were used to examine the temporal effects of afternoon (PM; 1600h) v. morning (AM; 0800 h) allocation of fresh spring herbage from a perennial ryegrass (Lolium perenne L.)-based pasture on fermentation and microbial community dynamics. Herbage chemical composition was minimally affected by time of allocation, but daily mean ammonia concentrations were greater for the PM group. The 24-h pattern of ruminal fermentation (i.e. time of sampling relative to time of allocation), however, varied considerably for all fermentation variables (P⩽0.001). Most notably amongst ruminal fermentation characteristics, ammonia concentrations showed a substantial temporal variation; concentrations of ammonia were 1.7-, 2.0- and 2.2-fold greater in rumens of PM wethers at 4, 6 and 8h after allocation, respectively, compared with AM wethers. The relative abundances of archaeal and ciliate protozoal taxa were similar across allocation groups. In contrast, the relative abundances of members of the rumen bacterial community, like Prevotella 1 (P=0.04), Bacteroidales RF16 group (P=0.005) and Fibrobacter spp. (P=0.008) were greater for the AM group, whereas the relative abundance of Kandleria spp. was greater (P=0.04) for the PM group. Of these taxa, only Prevotella 1 (P=0.04) and Kandleria (P<0.001) showed a significant interaction between time of allocation and time of sampling relative to feed allocation. Relative abundances of Prevotella 1 were greater at 2h (P=0.05), 4h (P=0.003) and 6h (P=0.01) after AM allocation of new herbage, whereas relative abundances of Kandleria were greater at 2h (P=0.003) and 4h (P<0.001) after PM allocation. The early post-allocation rise in ammonia concentrations in PM rumens occurred simultaneously with sharp increases in the relative abundance of Kandleria spp. and with a decline in the relative abundance of Prevotella. All measures of fermentation and most microbial community composition data showed highly dynamic changes in concentrations and genus abundances, respectively, with substantial temporal changes occurring within the first 8h of allocating a new strip of herbage. The dynamic changes in the relative abundances of certain bacterial groups, in synchrony with a substantial diurnal variation in ammonia concentrations, has potential effects on the efficiency by which N is utilised by the grazing ruminant.

Methane emissions changed nonlinearly with graded substitution of alfalfa silage with corn silage and corn grain in the diet of sheep and relation with rumen fermentation characteristics in vivo and in vitro.

Feeding grain and corn silage have been proposed as practices to reduce enteric methane (CH) emissions per unit of intake from ruminants, but the inclusion level required in the diet is normally not specified. The objectives of the current study were to determine the CH emission factor (g/kg DMI) of sheep fed alfalfa silage substituted with increasing levels of corn silage or corn grain at a fixed DMI level (2% of BW) and determine its relationship with rumen fermentation characteristics and microbial community composition and with in vitro fermentation characteristics of the same diets incubated using a standard laboratory method. Romney ewe hoggets (approximately 14 mo old; = 64) were randomly allocated to 8 dietary treatments, which included chaffed alfalfa silage alone or substituted with either 25, 50, 75 or 100% corn silage or 25, 50 or 65% rolled corn grain on a DM basis. After acclimatization to the diet, DMI and CH emissions were measured from individual sheep for 2 consecutive days in open-circuit respiration chambers and a rumen sample was collected at 3 h after feeding. The same diets were also incubated in an automated in vitro gas production system for 48 h using rumen liquid of fistulated nonlactating dairy cows grazing pasture. Increasing the substitution of alfalfa silage with corn silage or corn grain in the diet of sheep resulted in a quadratic response ( < 0.01) in CH emissions per unit of DMI (CH/DMI) with either supplement. For both supplements, CH/DMI increased in mixtures of up to 50% supplement inclusion and then decreased with greater supplement inclusion, especially with corn grain inclusion, but the level did not fall below that for 100% alfalfa silage. The ratio of acetate + butyrate to propionate + valerate and the propionate proportion alone in rumen liquid were the strongest single predictors for CH/DMI in the overall data set and explained 37.1 and 32.5%, respectively, of the variation in CH/DMI. Methanogens of (21.1% of total methanogens; = 0.247) and (10.7% of total methanogens; = -0.411) clades had weak to moderate correlations with in vivo CH/DMI. There was a weak quadratic relationship ( < 0.35) between in vivo CH/DMI and the in vitro parameters of gas and CH production and total VFA, whereas there was a moderate relationship ( = -0.50) between in vivo CH/estimated rumen degradable carbohydrates and in vitro CH/DM. In conclusion, CH/DMI changed in a nonlinear fashion with increasing supplement inclusion in the alfalfa forage diet when fed at 2% of BW to sheep; however, implications on predicting its influence on greenhouse gas emissions per unit of animal product, for whole farm emissions in life cycle analysis or total national emissions in the national inventories, should be determined.

Nitrogen metabolism and rumen microbial enumeration in lactating cows with divergent residual feed intake fed high-digestibility pasture.

Dairy cattle selected for negative residual feed intake (n-RFI; efficient) should maintain production while reducing dry matter intake over a lactation because of improvements in feed digestion and efficient use of nutrients. The objective of this study was to measure nitrogen (N) digestibility and rumen microbial community composition over a short period during early lactation in lactating Holstein-Friesian cows selected previously for divergent RFI. It was proposed that n-RFI cows would have greater apparent digestibility of N than the positive RFI (p-RFI; inefficient) animals, to compensate for the lower dry matter intake determined during selection for divergence. Sixteen 3-yr-old rumen-cannulated, lactating cows (56 ± 10d in milk) selected for n-RFI (n = 8) and p-RFI (n = 8) were housed in metabolism stalls and fed fresh vegetative ryegrass (Lolium perenne L.) pasture ad libitum as a sole diet during an 8-d digestibility study. Intake of nutrients and outputs of milk, feces, and urine were determined. Rumen parameters were determined by removing, weighing, and sampling digesta, and by cobalt-EDTA dilution. Intakes of N, dry matter, organic matter, or its components did not differ with RFI. Compared with p-RFI cows, n-RFI cows had a greater apparent N digestibility (77.2 vs. 75.5%), and a tendency toward greater dry matter and organic matter digestibilities. The n-RFI cows had a lower fecal N output (126 vs. 138 g/d) and a lower partition of feed N to fecal N (23.1 vs. 24.7%) compared with p-RFI animals. We found no differences between phenotypes in the partition of N to urinary N or milk crude protein but did observe a trend for n-RFI cows to partition less N to milk casein (16.8 vs. 17.9%). Rumen digesta mass was similar for both groups, despite differences in calculated fractional liquid outflow rates, and most bacterial, archaeal, protozoal, and fungal communities were similar for both phenotype groups. In conclusion, dry matter intake and rumen function were similar for both phenotypes when the animals were fed highly digestible fresh ryegrass, but apparent digestibility of dietary N was higher in the efficient (n-RFI) cows. Future research should measure digestion parameters in cows with divergent RFI when fed diets differing in chemical composition (e.g., divergent crude protein contents).