Our objective was to compare abomasal infusions of linoleic (18:2n-6) and α-linolenic (18:3n-3) acids on the enrichment of n-6 and n-3 fatty acids (FA) into the plasma lipid fractions of lactating dairy cows and evaluate their potential carryover effects in plasma lipid fractions postinfusion. Six rumen-cannulated multiparous Holstein cows (252 ± 33 DIM) were fed the same diet and assigned to 1 of 2 treatments in a completely randomized design with repeated measures. Treatments were abomasal infusions (67 g/d total FA) of (1) n-6 FA blend (N6) to provide approximately 43 g/d 18:2n-6 and 8 g/d of 18:3n-3 or (2) n-3 FA blend (N3) providing 43 g/d 18:3n-3 and 8 g/d 18:2n-6. Treatments were dissolved in ethanol, and the daily dose for each treatment was divided into 4 equal infusions, occurring every 6 h. The treatment period lasted from d 1 to 20, and the carryover period lasted from d 21 to 40. Results are presented as FA contents within each of the 4 main plasma lipid fractions: cholesterol esters (CE), phospholipids (PL); triglycerides, and plasma nonesterified fatty acids. Concentrations of individual lipid fractions in plasma were not quantified. Plasma CE and PL had the highest content of PUFA during both the treatment and carryover periods. In plasma PL, N3 increased the contents of total n-3 FA (134%), 18:3n-3 (267%), and eicosapentaenoic acid (96.3%, 20:5n-3), and decreased total n-6 FA (8.14%) and 18:2n-6 (8.16%) from d 4 to 20 compared with N6. In plasma CE, N3 increased the contents of total n-3 FA (191%) from d 4 to 20, 18:3n-3 from d 2 to 20 (178%), and 20:5n-3 from d 6 to 20 (59.9%), while N3 decreased total n-6 FA from d 4 to 20 (11.2%) and 18:2n-6 from d 2 to 20 (10.5%) compared with N6. In addition, compared with N6, N3 decreased arachidonic acid (20:4n-6) at d 2 (45%) and from d 10 to 20 (14.7%) in PL and tended to decrease 20:4n-6 without interacting with time for CE. Phospholipids were the only lipid fraction with detectable levels of docosahexaenoic acid (22:3n-6) in all samples, but we did not observe differences between treatments. In plasma trigylcerides, N3 increased the contents of total n-3 FA (135%) and 18:3n-3 (146%) from d 4 to 20, increased 20:5n-3 from d 12 to 20 (89%), decreased or tended to decrease total n-6 FA content from d 6 and 8 (26.9%), and tended to decrease 18:2n-6 at d 8 compared with N6. A similar pattern was observed for plasma nonesterified FA. We observed positive carryover effects for both N3 and N6 at different degrees in all lipid fractions, with N3 promoting more consistent outcomes and increasing total n-3 FA throughout the carryover period (from d 22 to 40) in both PL (52.8%) and CE (68.6%) compared with N6. It is important to emphasize that the higher magnitude responses observed for n-3 FA are also influenced by the content of n-3 FA being much lower than those of n-6 FA in all lipid fractions. Although these data provide important and robust information, future research quantifying changes in concentrations of individual lipid fractions in plasma and the entry and exit rates of specific FA will further enhance our understanding. In conclusion, abomasally infusing N3 and N6 increased the contents of n-3 and n-6 FA, respectively, in all plasma lipid fractions. These responses were more evident in PL and CE. We also observed positive carryover effects in all lipid fractions, where N3 had more consistent outcomes than N6. Our results indicate that dairy cows have a robust mechanism to conserve essential FA, with a pronounced preference for n-3 FA.

Mitochondria are central to metabolism and are the primary energy producers for all biosynthesis, includ-ing lactation. The objectives of this study were to de-termine if high-and low-producing dairy cows exhibit differences in peripheral blood mononuclear cell mito-chondrial enzyme activities of citrate synthase, complex I, complex IV, and complex V during early lactation and, thus, to determine whether those differences were related to differences in lactation performance in the dairy cow. Fifty-six Holstein cows were assigned to 1 of 4 groups: (1) primiparous high, (2) primiparous low, (3) multiparous high, or (4) multiparous low. Primiparous and multiparous cows were analyzed separately. Then, cows were divided into high or low production groups for each production parameter [peak milk, average milk, energy-corrected milk (ECM), fat-corrected milk (FCM), milk lactose, milk fat, milk protein, total solids (TS), solids-not-fat, feed efficiency, and somatic cell count (SCC)]. For all data analysis, production param-eters are expressed as yields (kg/d) and SCC (103 cells/ mL). High and low production groups were defined by their respective mean production parameters for the 56 cows, with below average cows defined as low and above average cows defined as high. Whole blood samples were collected at one time point, approximately 70 d in milk at 0800 h, and processed for crude mitochondrial extracts from peripheral blood mononuclear cells to determine the activity rates of mitochondrial enzymes. Milk samples were collected 9 times (3 d, 3 times per d) during the week of blood collection and analyzed for major components (fat, protein, lactose, TS, and SCC). Multiparous cows had lower citrate synthase ac-tivity than primiparous cows across all production pa -rameters. High-producing cows had greater complex I activity for peak milk, milk yield, ECM, FCM, milk fat, TS, and feed efficiency, and greater complex V activity for ECM, FCM, milk lactose, milk fat, and TS across parities. These findings imply that the most influential respiratory chain enzymes on the level of milk produc-tion are those responsible for electron transport chain initialization and ATP production.

Summary: Mammals do not synthesize essential fatty acids (FA) vital for proper physiological functioning; thus, these FA must be provided in the diet. The essential FA linoleic (18:2n-6) and a-linolenic acids (18:3n-3) are partially converted to longer-chain FA: 18:2n-6 to arachidonic acid (20:4n-6), and 18:3n-3 to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). We compared abomasal infusions of 18:2n-6 (N6) and 18:3n-3 (N3) on the incorporation of essential FA into the milk fat of cows. Infusions lasted 20 days, with subsequent carryover evaluation until day 36. During the treatment period, n-3 FA transfer efficiency to milk for N3 was 47%, whereas n-6 FA transfer efficiency to milk for N6 was 39%. In addition, only n-3 FA had a positive carryover effect. However, the absolute quantity of n-3 FA in milk fat was still very low, especially considering 20:5n-3 and the lack of 22:6n-3.

Buffering of the rumen environment can alleviate some of the negative effects of acidosis, and the same may hold true in the hindgut. The objective of this study was to evaluate the potential for 2 dietary buffers at different dosages to mitigate excessive intestinal fermentation and systemic inflammation due to hindgut acidosis. Ten ruminally cannulated lactating cows were randomly assigned to a replicated 5 × 5 Latin square with a 7-d adaptation period, 14-d experimental periods, and 7-d washout periods between each experimental period. Daily treatments during experimental periods were abomasal infusion of water without feeding supplemental buffer (CON), abomasal infusion of corn starch without feeding supplemental buffer (IS), or abomasal infusion of starch with 150 g/d of buffer A (calcium carbonate, magnesium oxide, and crushed oyster shell blend; T1), 300 g/d of buffer A (T2), or 150 g/d of buffer B (magnesium oxide; T3). Daily abomasal starch infusions were 2 g/kg BW in period 1 and 4 g/kg BW in periods 2-5 and split into 2 bolus infusions, provided every 12 h during the 14-d experimental periods. Cows were fed a 30.9% starch TMR (on a DM basis) and 1 cow was removed from the study between periods 1 and 2. Although not intended, the high starch TMR seemed to induce SARA, as evidenced by mean rumen pH of 5.8 to 6.0. Compared with CON, abomasal corn starch addition decreased fecal pH (6.80 vs. 6.37) and apparent total-tract starch digestibility (95.6 vs. 86.1%). Starch infusion did not increase serum acute phase proteins, and effects on fecal LPS and total fecal VFA concentrations were modest, suggesting that infused starch was only partially digested. Buffer addition increased fecal pH as expected (mean of 6.76 for T1, T2 and T3, respectively), but also increased fecal acetate (64.0 mM for IS compared with a mean of 74.5 mM for T1, T2 and T3, respectively) and total VFA concentration (81.5 mM for IS compared with a mean of 100.1 mM for T1, T2, and T3, respectively), suggesting that they may have increased hindgut fermentation. Additionally, the T2 treatment may have had an inflammatory effect as evidenced by increased serum amyloid A compared with IS (71.5 vs. 22.0 µM, respectively). Despite increased fecal pH, the inclusion of different buffer formulations in a high starch diet seemed to increase hindgut fermentation as evidenced by increased VFA concentration. The buffers employed in this experiment did not alleviate the negative effects of abomasal starch infusions and, in the case of T2, may have presented a challenge.

This research reports ruminal and fecal microbiota composition of lactating dairy cows enrolled in a study aimed at investigating the effects of a fermentation extract derived from Bacillus licheniformis (BLFE), monensin (Rumensin^®; R), and their interactions on feed efficiency (FE, FE = milk yield/DMI). In a completely randomized design, 48 Holstein cows at 108 ± 35 days in milk were matched for parity and assigned to monensin (0 or 17.6 g/kg of DM) and BLFE (0 or 166 mg/kg of DM) in a 2 × 2 factorial arrangement. Treatments were fed daily for 63 d, including a 21 d adaptation period followed by a 42 d measurement period (P2). On d 38 and d 39 of P2, rumen-fluid (RF) and fecal samples were collected. DNA from RF and feces was sequenced using 16S rRNA gene-amplicon sequencing on an Illumina MiSeq platform. Fecal and RF volatile fatty acid (VFA) concentrations were analyzed, and propionate/acetate (P: A) was determined. The BLFE increased milk yield (3.3 kg/d) and FE (1.20 to 1.28), when fed alone rather than with monensin, while monensin increased energy-corrected milk yield (2.5 kg/d, p < 0.05), regardless of the BLFE in the diet. The BLFE tended to increase ruminal Firmicutes/Bacteroidetes (F: B) when fed alone, while alpha and beta diversities remained unmodified. The BLFE increased the abundances of Bifidobacterium (p = 0.02) and Erysipelotrichaceae_UCG-002 (p = 0.01) in RF, whereas monensin increased and decreased the abundances of Oscillospirales_ge (p = 0.02) and an unclassified Clostridia genus (p = 0.03), respectively. The monensin-suppressed Clostridia were negatively associated with ruminal P: A (r = −0.66; p < 0.01) and feed efficiency (r = −0.30; p = 0.04). The BLFE and monensin interactively affected several fecal genera (p < 0.05), but they had negligible or weak correlations with fecal P: A and FE. Overall, the results showed the ability of dietary supplementations of monensin and BLFE to increase milk production performance and FE by modulating ruminal rather than lower-gut microbiota composition, this is predominantly attributed to the ratio between the Firmicutes and Bacteroidetes abundances in lactating dairy cows.

The study objective was to investigate the impact of monensin and a fermentation extract derived from Bacillus licheniformis-derived fermentation extracts (BLFE) when fed alone or in combination on production performance and feed efficiency in lactating dairy cows. Sixty Holstein cows matched for DIM (108 ± 35; mean ± SD) and parity were assigned to 4 treatments formulated to provide 2 doses of monensin (0 and 17.6 mg/kg DM) and 2 doses of BLFE (0 and 166 mg/kg DM) in a 2 × 2 factorial arrangement. Monensin and BLFE doses were top-dressed on a TMR without added monensin. Cows were allowed to adapt to treatments for 21 d before measuring DMI, milk yield, milk composition, and BW responses to treatments over the next 42 d. Rumen fluid VFA, apparent total-tract digestibility (ATTD) of nutrients, and blood AA concentrations were determined in the last week. The effects of treatments were analyzed, accounting for baseline measurements, using mixed-effects models. Neither monensin nor BLFE modified DMI, which averaged 30.8 kg/d across treatments. At this DMI level, the actual monensin and BLFE doses consumed by cows were 14 and 145 mg/kg of DM, respectively. The BLFE fed alone increased milk yield:DMI (1.19 to 1.26) and NEL:DMI (1.60 to 1.83). It tended to increase milk yield and FCM and ECM yields, DMI and milk protein yields, and CP intake. Supplementing BLFE with monensin attenuated those responses. Monensin fed alone increased BW gain (0.44 kg/d) and tended to increase the component-corrected milk yield: DMI, but supplementing it with BLFE negated those effects. Regardless of the presence or absence of monensin in the diet, BLFE increased milk protein content (3.45% to 3.52%), while monensin enhanced milk fat yield (95 g/d) and component-corrected milk yields (4.7% to 5.1%). Milk fat improvements from monensin were significant in multiparous cows but negligible in primiparous cows. In contrast, the feed and protein efficiency enhancements of BLFE were more pronounced in primiparous than in multiparous cows. Supplementing BLFE did not modify ruminal or fecal VFA profiles when supplemented alone or with monensin. Monensin tended to decrease the molar percentage of butyrate in both rumen fluid and feces, while molar percentages of acetate, propionate, and their ratio remained unmodified. Supplementing BLFE or monensin alone did not affect ATTD of CP, but supplementing both together increased ATTD of CP compared with supplementing BLFE alone (59.2% to 62.1%). The BLFE supplementation alone increased blood EAA concentrations (18%), whereas adding monensin to the diet containing BLFE reversed that increase. The poor alignment between blood AA and ATTD in CP suggests potential effects of treatment on gut microbiota metabolism or postabsorptive AA clearance. Under current feeding conditions, data show that BLFE and monensin distinctly increased milk protein and fat, respectively, and each supplement improved feed efficiency when fed alone. The potential antagonism observed when fed together suggests the need for further research to investigate interactions between monensin and BLFE at varying doses under different feeding conditions.