Effect of forage conservation method on ruminal lipid metabolism and microbial ecology in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio

Abstract

The effect of forage conservation method on ruminal lipid metabolism and microbial ecology was examined in 2 complementary experiments in cows. Treatments comprised fresh chopped grass, barn-dried hay, or untreated (UTS) or formic acid-treated silage (FAS) prepared from the same grass sward. Preparation of conserved forages coincided with the collection of samples from cows offered fresh grass. In the first experiment, 5 multiparous Finnish Ayrshire cows (229 d in milk) were used to compare the effects of feeding diets based on grass followed by hay during 2 consecutive 14-d periods separated by a 5-d transition during which extensively wilted grass was fed. In the second experiment, 5 multiparous Finnish Ayrshire cows (53 d in milk) were assigned to 1 of 2 blocks and allocated treatments according to a replicated 3×3 Latin square design with 14-d periods to compare the effects of hay, UTS, and FAS. Cows received 7 or 9 kg/d of the same concentrate in experiments 1 and 2, respectively. Conservation of grass by drying, but not ensiling, decreased forage fatty acid content primarily due to losses of 18:2n-6 and 18:3n-3. Compared with grass, feeding hay had no effect on dry matter intake (DMI), rumen pH, or fermentation characteristics, other than increasing ammonia content, but lowered whole-tract organic matter and fiber digestibility (experiment 1). Relative to hay, silage increased DMI, rumen volatile fatty acid (VFA) concentrations, and molar proportions of butyrate, and decreased molar acetate proportions (experiment 2). Compared with UTS, FAS increased DMI, had no effect on rumen ammonia or VFA concentrations, but tended to lower rumen pH and the molar ratio of lipogenic to glucogenic VFA. Conservation method had no substantial effect on ruminal or whole-tract digestibility coefficients. Compared with fresh grass and silages, hay decreased lipolysis and biohydrogenation (BH) of dietary unsaturates in the rumen, resulting in similar flows of 18:2n-6 and 18:3n-3, but lower amounts of trans-11 18:1 and Δ11,13 18:2 at the omasum. The extent of silage fermentation had minimal influence on ruminal lipid metabolism. Treatments were not associated with changes in the relative abundance of specific bacteria known to be capable of BH or rumen protozoal numbers. In conclusion, conservation method altered forage lipids, the extent of lipolysis and BH in the rumen, and the flow of fatty acids at the omasum, in the absence of substantial changes in ruminal Butyrivibrio populations.

Tifton 85 bermudagrass (Cynodon sp.) silage as a replacement for Tifton 85 hay to feed lactating cows

“…These data corroborate those of Halmemies-Beauchet-Filleau et al (2013b), who also observed no effect on milk composition when evaluating hay or timothy grass (Phleum pratense) silage and meadow fescue (Festuca pratensis). Studies comparing the use of hay and silage have demonstrated higher concentrations of ruminal acetate when hay is used (Shingfield et al, 2002;Halmemies-Beauchet-Filleau et al, 2013a), which could provide an increase in milk fat content, although this did not occur in the present study.…”

Grazing increases the concentration of CLA in dairy cow milk

“…These data suggest that increased milk CLA during grazing observed in this experiment was not a result of more production in the rumen. The observation is consistent with the analysis of Mohammed et al (2009) and Halmemies-Beauchet-Filleau et al (2013a and2013b) for the effect of grazing on milk CLA compared with feeding chopped grass or hay.…”

“…First, greater formation of t11-18:1 in the rumen could lead to more c9, t11-18:2 synthesized in the mammary gland through increased substrate availability (Halmemies-Beauchet-Filleau et al, 2013a and2013b). This mechanism may also offer some explanations for increased production of CLA in milk associated with 18:3n-3, whose classical biohydrogenation pathway does not involve formation of c9, t11-18:2, as discussed above.…”

Milk fatty acid composition, rumen microbial population, and animal performances in response to diets rich in linoleic acid supplemented with chestnut or quebracho tannins in dairy ewes

“…Nevertheless, some in vivo studies on rumen bacterial diversity in cows and ewes suggest that B. fibrisolvens and B. proteoclasticus do not play a dominant role in rumen lipid metabolism and that other as-yet-uncultured bacteria phylogenetically classified as Prevotella, Lachnospinaceae incertae sedis, and unclassified Bacteroidales, Clostridiales, and Ruminococcaceae might be more relevant (Boeckaert et al, 2008;Belenguer et al, 2010;Huws et al, 2011;Castro-Carrera et al, 2014). The literature also provides evidence that alterations in rumen outflow of 18-carbon BH intermediates and 18:0 induced by diets based on different types of forages or supplemented with fish oil are not accompanied by significant changes in B. proteoclasticus group (Kim et al, 2008;Huws et al, 2010;Halmemies-Beauchet-Filleau et al, 2013). Because diet composition plays a fundamental role in the selection of rumen microorganisms, further studies are needed to better clarify the effect of tannins on specific bacterial strains involved in BH processes.…”