We evaluated the effects of supplementing bacterial direct-fed microbial (DFM) on performance, apparent total-tract digestibility, rumen fermentation, and immune parameters of lactating dairy cows. One-hundred and 14 multiparous Holstein cows (41 ± 7 DIM) were used in a randomized complete block design with an experiment comprising 14-d covariate (pre-experimental sample and data collection) and 91-d of experimental period. Cows were blocked based on energy-corrected milk yield during the covariate period and the following treatments were randomly assigned within each block: 1) Control (CON): Corn silage-based total mixed ration (TMR) without DFM; 2) PRO-A: Basal diet top-dressed with a mixture of Lactobacillus animalis and Propionibacterium freudenreichii at 3 × 10⁹ cfu/day; and 3) PRO-B: Basal diet top-dressed with a mixture of L. animalis, P. freudenreichii, Bacillus subtilis and B. licheniformis at 11.8 × 10⁹ cfu/day. Milk yield, DMI, and BW were measured daily while milk samples for component analysis were taken on 2 consecutive days of each week of data collection. Feces, urine, rumen, and blood samples were taken during the covariate period, wk 4, 7, 10, and 13 for estimation of digestibility, N-partitioning, rumen fermentation, plasma nutrient status and immune parameters. Treatments had no effect on DMI and milk yield. Fat-corrected milk (3.5% FCM) and milk fat yield were improved with PRO-B, while milk fat percent and feed efficiency (ECM/DMI) tended to increase with PRO-B compared with PRO-A and CON. Crude fat digestibility was greater with PRO-B compared with CON. Feeding CON and PRO-A resulted in higher total VFA concentration relative to PRO-B. Percentage of neutrophils tended to be reduced with PRO-A compared with CON and PRO-B. The mean fluorescence intensity (MFI) of anti-CD44 antibody on granulocytes tended to be higher in PRO-B compared with CON. The MFI of anti-CD62L antibody on CD8+ T cells was lower in PRO-A than PRO-B, with PRO-A also showing a tendency to be lower than CON. This study indicates the potential of DFM to improve fat digestibility with consequential improvement in fat corrected milk yield, feed efficiency and milk fat yield by lactating dairy cows. The study findings also indicate that dietary supplementation with DFM may augment immune parameters or activation of immune cells, including granulocytes and T cells; however, the overall effects on immune parameters are inconclusive.

There has been an intense debate regarding the economic, social, and environmental sustainability of confinement versus grazing dairy systems. Our goal was to conduct a meta-analysis to compare dry matter intake, milk yield and composition, nutrient use efficiency (i.e., feed efficiency, milk N efficiency), and predicted enteric CH₄ emissions using studies that simultaneously evaluated confinement and grazing. We were able to include in the meta-analysis 8 peer-reviewed articles that met the following selection criteria: (1) publication between 1991 and 2021 in English language, (2) report either SEM or SD, (3) inclusion of at least 1 confinement [total mixed ration or fresh cut herbage fed indoors (i.e., zero-grazing)] and 1 grazing treatment in the same study, and (4) use of markers (internal or external) to estimate herbage dry matter intake. Two unpublished experiments were added to the data set resulting in a total of 10 studies for comparing confinement and grazing. The magnitude of the effect (i.e., effect size) was evaluated using weighted raw mean differences between grazing and confinement systems for a random effect model. Enteric CH₄ production was predicted as follows: CH₄ (g/d) = 33.2 (13.54) + 13.6 (0.33) × dry matter intake + 2.43 (0.245) × neutral detergent fiber. Dry matter intake (–9.5%), milk yield (–9.3%), milk fat yield (–5.8%), milk protein yield (–10%), and energy-corrected milk (–12%) all decreased in grazing versus confined dairy cows. In contrast, concentration of milk fat and feed efficiency (energy-corrected milk/dry matter intake) were not affected by management system. Whereas milk protein concentration increased, milk nitrogen (N) efficiency (milk N/N intake) tended to decrease in grazing compared with confinement. Predicted enteric CH₄ production was 6.1% lower in grazing than confined dairy cows. However, CH₄ yield (g/kg of dry matter intake) and CH₄ intensity (g/kg of energy-corrected milk) did not change between confinement and grazing. In conclusion, while production performance decreased in grazing dairy cows, nutrient use efficiency and predicted enteric CH₄ emissions were relatively similar in both management systems. Results of our meta-analysis should be interpreted with caution due to the small number of studies that met our inclusion criteria leading to a limited number of treatment mean comparisons.

We evaluated the effects of incremental amounts of ground flaxseed (GFX) on diversity and relative abundance of ruminal microbiota taxa, enteric methane (CH₄) emissions, and urinary excretion of purine derivatives in lactating dairy cows in a replicated 4 × 4 Latin square design. Twenty mid-lactation Jersey cows were used in the study. Of these 20 cows, 12 were used for ruminal sampling, 16 for enteric CH₄ measurements, and all for spot urine collection. Each period lasted 21 d with 14 d for diet adaptation and 7 d for data and sample collection. Diets were formulated by replacing corn meal and soybean meal with 0, 5, 10, and 15% of GFX in the diet dry matter. Ruminal fluid samples obtained via stomach tubing were used for DNA extraction. Enteric CH₄ production was measured using the sulfur hexafluoride tracer technique. Diets had no effect on ruminal microbiota diversity. Similarly, the relative abundance of ruminal archaea genera was not affected by diets. In contrast, GFX decreased or increased linearly the relative abundance of Firmicutes (P < 0.01) and Bacteroidetes (P < 0.01), respectively. The relative abundance of the ruminal bacteria Ruminococcus (P < 0.01) and Clostridium (P < 0.01) decreased linearly, and that of Prevotella (P < 0.01) and Pseudobutyrivibrio (P < 0.01) increased linearly with feeding GFX. A tendency for a linear reduction (P = 0.055) on enteric CH₄ production (from 304 to 256 g/d) was observed in cows fed increasing amounts of GFX. However, neither CH₄ yield nor CH₄ intensity was affected by treatments. Diets had no effect in the urinary excretion of uric acid, allantoin, and total purine derivatives. Overall, feeding GFX decreased linearly the relative abundance of ruminal bacterial genera involved in fiber degradation (i.e., Ruminococcus, Clostridium) and enteric CH₄ production, but no change was seen for CH₄ yield and CH₄ intensity or urinary excretion of total purine derivatives, suggesting no detrimental effect of GFX on microbial protein synthesis in the rumen.

This study aimed to evaluate the effects of annatto seeds, linseed oil and their combination on DMI, apparent total tract digestibility, antioxidant capacity and milk composition of dairy cows. Four lactating Holstein cows (120 ± 43 days in milk; 15.98 ± 2.02 kg of milk/day, mean ± SD) were allocated in a 4 × 4 Latin square with a 2 × 2 factorial arrangement (with or without annatto seeds at 15 g/kg of dry matter (DM); with or without linseed oil at 30 g/kg of DM) and provided four different diets: control (no annatto seeds or linseed oil); annatto seeds (15 g/kg of DM); linseed oil (30 g/kg of DM); and a combination of both annatto seeds and linseed oil. Annatto seeds reduced DM intake, and milk yield, protein and lactose, but increased content of fat, total solids and short chain fatty acid, with no effect on total antioxidant capacity of milk. Linseed oil supplementation decreased medium chain fatty acid proportion and n-6/n-3 ratio, conversely it increased long chain fatty acids and n-3 fatty acid content of milk, ether extract intake and total-tract digestibility. Thus, linseed oil supplementation in dairy cow diets improved the milk FA profile but decreased milk fat concentration, whereas annatto seeds did not influence antioxidant capacity and depressed feed intake and milk yield.

A meta-analysis and a meta-regression were conducted to compare DMI, production performance, feed efficiency (FE), and milk N efficiency (MNE; milk N yield/N intake) of Holstein and Jersey cows. Only experiments in which purebred Holsteins and Jerseys enrolled in the same study, under similar experimental conditions, were used to build the datasets (n = 30 peer-reviewed articles). The weighted raw mean difference (WMD) between breeds was computed for each comparison, and weights were assigned based on the inverse of the variance. A meta-regression was run to explore the effect of continuous (year of publication, DIM, and dietary concentrations of NDF, CP, and forage) and categorical (forage type: corn silage, alfalfa/grass-clover mix, and other forage sources ["others"]) covariates on the WMD of different variables. Jerseys had lower DMI (-4.15 kg/d), milk yield (-10.8 kg/d), yields of milk fat (-61.6 g/d) and milk true protein (-211 g/d), and ECM yield (-5.11 kg/d) than Holsteins. In contrast, concentrations of milk fat (+16.1 g/kg) and milk true protein (+6.98 g/kg), DMI (% of BW [+0.44%] and % of metabolic BW [MBW = BW^0.75; +0.64%], and ECM yield (% of BW [+0.64%] and % of MBW [+1.63%]) were greater in Jersey than Holstein cows. Whereas FE (milk yield/DMI) was lower (-0.26 kg/kg) in Jerseys than Holstein cows, breed did not affect FE (ECM yield/DMI) and MNE. Year of publication widened the WMD of milk fat and milk true protein concentrations and ECM yield (% of MBW), and it narrowed that of DMI (kg/d), milk true protein yield, and N intake, favoring Jerseys over Holsteins in recent publications. In addition, DIM narrowed the gap between breeds for the variables yields of milk, ECM yield (kg/d), milk fat, and milk N yield, and widened the gap for DMI (% BW and % of MBW) and ECM yield (% of BW and % of MBW), all in favor of Jerseys as lactation progressed. Dietary concentrations of NDF, CP, and forage collectively affected the WMD of BW, yields of milk and milk lactose, milk true protein and milk lactose contents, ECM yield (% of BW and % of MBW), FE (milk yield/DMI), and N intake, but did not consistently benefit Holsteins or Jerseys. Corn silage affected all WMD, except milk fat yield, ECM yield (% of BW and % of MBW), FE (ECM yield/DMI), and MNE. Relative to corn silage, alfalfa-grass/clover mix diets affected the WMD of DMI (kg/d and % of MBW), milk yield, milk fat and milk true protein yields, ECM yield (kg/d), N intake, and milk N yield, favoring Holsteins over Jerseys. Compared with corn silage, the forage type others affected the WMD of milk fat and milk true protein concentrations, DMI (% of BW), and ECM yield (% of BW and % of MBW), benefiting Jersey versus Holstein cows. In conclusion, the WMD of FE (ECM yield/DMI) and MNE were similar between breeds and the continuous (year of publication and DIM) and categorical (forage type) covariates largely influenced the WMD of several variables.

We evaluated the supplementation of different sources of the brown seaweed Ascophyllum nodosum (ASCO) meal on taste preference in dairy heifers during a sequential elimination experiment. Six organic certified Jersey heifers averaging (mean +/- standard deviation) 16 +/- 1.15 wk of age and 92 +/- 9.88 kg of body weight at the beginning of the study were used. Treatments consisted of a ground corn-based concentrate mash without seaweed supplementation (control), or this same concentrate mash supplemented with 57 g/d of ASCO meal obtained from Acadian Seaplants (Acadian Kelp), North American Kelp (SeaLife Kelp), or Thorvin Inc. (Thorvin for Animals). The experiment was conducted with 1 heifer enrolled at a time for 11 d each (n = 66 d total) with the feeding regimens distributed as follows: d 0-2 (adaptation phase), d 3-6 (feeding segment 1), d 7-9 (feeding segment 2), and d 10-11 (feeding segment 3). During feeding segment 1 (d 3-6), the control diet was the most consumed treatment resulting in a total dry matter intake of 22.6 kg followed by Acadian, Thorvin, and SeaLife with 17.7, 13.2, and 11.0 kg, respectively. However, Acadian was selected as the most preferred treatment during feeding segment 1 for a total of 11 d, with control, Thorvin, and SeaLife totaling 8, 3, and 2 d, respectively. In the final ranking of treatments, when all 3 feeding segments were included in the evaluation, Acadian was selected as the first choice by 4 heifers with a ranking of 1.67 points, on a scale ranging from 1 (most preferred) to 4 (least preferred), followed by control (2.50 points), Thorvin (2.67 points), and SeaLife (3.17 points). Overall, the treatments containing Acadian and SeaLife were the most and least preferred, respectively, indicating that heifers were able to distinguish different sources of the same seaweed species based on a taste preference sequential elimination experiment.