B vitamins, including niacin (vitamin B3), are synthesized by rumen microbes, but supplementation may provide additional benefits for ruminant health and productivity. Supplementing rumen-protected niacin (RPN) during the transition period can reduce lipolysis after calving and, consequently, may improve health and fertility of dairy cattle later in lactation. Our objective was to determine if supplementing RPN during the first 21 DIM would improve the health of dairy cows on a commercial dairy farm. We hypothesized that RPN would reduce mastitis, improve fertility, and reduce risk of leaving the herd during lactation. Holstein cows were blocked by parity and projected calving date, with treatments randomly assigned to cows within each block. Cows received RPN (n = 481; 26 g/d) through a supplement dispenser in the automated milk systems (AMS) in addition to their robot pellet, or the robot pellet only (CON; n = 593). Treatments were applied for the first 21 DIM, and cows were followed for the rest of their lactation. Milk yield, milk components (wk 1-3 of lactation), pre- and postpartum BCS, health records, and reproductive records were collected. Blood was collected from a random subset of 99 cows at 3 DIM and 97 cows at 10 DIM to assess plasma concentrations of niacin, metabolic biomarkers, and biomarkers of inflammatory status. Culling, proportion of cows pregnant, and mastitis risk were analyzed using Cox proportional hazard models. Mastitis incidence was analyzed with a linear mixed model and conception risk was analyzed using a chi 2 test. Supplementing RPN increased plasma nicotinamide concentration by 1,740 nM +/- 410.0 nM (SE; 50% increase), but it did not affect plasma nicotinic acid concentrations. Supplementing RPN reduced plasma insulin concentrations at 3 and 10 DIM across all parities. Circulating BHB and free fatty acid concentrations were greater for cows receiving RPN; the effect was greatest in cows in third or greater parity. Plasma haptoglobin was not affected by treatment. Rumen-protected niacin increased milk yield for first- and second-parity cows by wk 9 and 13 of lactation, respectively, and increased milk yield in those groups was sustained for the rest of lactation, resulting in 658 +/- 259.4 kg and 675 +/- 308.9 kg more milk for RPN-supplemented first- and second-parity cows. The risk of leaving the herd, mastitis incidence, and probability of pregnancy were not affected by RPN. Inquiries into the effects of RPN supplementation and its timing on metabolism are necessary to understand optimal supplementation strategies for RPN in dairy cattle.

Body condition score and hyperketonemia (HYK) have been associated with diseases, fertility, and culling, but data are contradictory about their association with pregnancy loss. Our objective was to conduct a retrospective cohort study to investigate associations between BCS, BCS change (Delta BCS), blood BHB, and HYK with mastitis, pregnancy per artificial insemination (P/AI), pregnancy loss (PGL), milk yield, and risk of leaving the herd on a Michigan dairy farm that uses an automated milking system (AMS). We recorded BCS for cows prepartum (14 d before calving) and postpartum (14-21 DIM), and multiparous cows were evaluated for HYK between 3 and 7 DIM. Records were gathered from herd management software. Univariable associations of BCS (prepartum n = 826, postpartum n = 956) Delta BCS (n = 819), and BHB (n = 628) with mastitis, P/AI, PGL, and risk of leaving the herd were evaluated. Survival analyses investigated the association of BCS, Delta BCS, and HYK within parity with mastitis, pregnancy, and hazard of leaving the herd during lactation. We examined the association of BCS, Delta BCS, and HYK with whole lactation milk yield using repeated-measures mixed models. Thinner cows both pre- (BCS < 3.25) and postpartum (BCS < 2.75) had greater risk of leaving the herd (odds ratio [OR] = 1.48 and 2.16, respectively) compared with their moderate BCS herd mates. Cows who lost >= 0.375 units of BCS after calving had greater risk of PGL (OR = 4.99). Cows that lost >= 0.75 units of BCS had greater risk of being culled (OR = 1.80). Cows with HYK were at greater risk of mastitis (risk ratio = 1.34) and being culled (OR = 2.27). Cows with increasing BHB had greater risk of PGL and being culled such that a 1 mmol/L increase in BHB resulted in 2.32 and 1.67 greater risk, respectively. Hyperketonemic cows within third+ parity made 5.4 kg/d +/- 1.04 kg/d (difference +/- standard error of difference) less milk yield over their lactation compared with non-HYK third+ parity cows. Our data support previous findings that BHB and HYK had adverse associations with mastitis, fertility, leaving the herd, and milk yield. Our data also suggest that BCS loss after calving and BHB during wk 1 of lactation are risk factors associated with incidence of PGL.

Immune cells have been observed in many tissues of the mammal including the gut, liver, adipose, bone, and neural tissue. Our objective was to demonstrate whether immune cells are present within the stratified rumen epithelium of healthy lactating dairy cattle. We hypothesized that immune cells would be found in the rumen tissue and that the total amount of leukocytes present would increase during a ruminal acidosis challenge. We conducted a 2-phase experiment with 9 rumen-cannulated lactating Holstein cows. During phase 1, cows were fed a diet containing 31% NDF, 24% forage NDF, and 27% starch (CON) for 14 d. The starch sources were corn silage and dry ground corn. During phase 2, cows were fed a diet with 28% NDF, 16% forage NDF, and 32% starch (acid induction diet, AID) for 7 d. The AID starch sources were corn silage, dry ground corn, ground wheat, and ground barley. During both phases, rumen fluid, fecal, blood, and rumen tissue samples were collected. Feed intake and milk yield were recorded each day and milk samples were collected at each milking during the final 2 d of each period. Data were analyzed with mixed models that included the fixed effect of phase (CON or AID) and the random effect of cow. The AID treatment reduced rumen pH and increased area under the curve for rumen pH beneath 5.8 and 5.6. Feed intake, milk yield, and milk protein yield increased for AID. Phase did not affect ruminal immune cell phenotype proportions or total presence. Most immune cells observed were CD3+ (T cells) for both CON and AID. The ruminal immune cells were located within the lamina propria, stratum basale, and stratum spinosum of the rumen papillae. Our data demonstrate that T lymphocytes are prominent in rumen tissue. Understanding the role of ruminal leukocytes may yield new insights into ruminant gut health, function, development, and maintenance.

Nutritional strategies that improve an animal's resilience to various challenges may improve animal health and welfare. One such nutrient is niacin which has reduced inflammation in mice, humans, and swine; however, niacin's anti-inflammatory effects have not been investigated in cattle. Our objective was to determine whether rumen-protected niacin (RPN) alters lactating dairy cows' inflammatory response to intramammary lipopolysaccharide (LPS) challenges, whether RPN resulted in any carry-over effects, and whether repeated LPS challenges result in signs of immune tolerance or innate immune training. Twenty healthy, late-lactation Holstein cows (232 ± 65 d in milk; 39 ± 5.8 kg/d of milk) were enrolled in a randomized complete block experiment which lasted 70 d. Cows received 26 g/d of RPN or no top-dress (CON) for the first 42 d of the experiment. During the final milking of d 27 and 55, cows were challenged in their rear-right mammary gland (RR) with 100 µg of LPS suspended in 5 mL of phosphate buffered saline. Milk yield, milk conductivity, and feed intake were measured daily. Milk composition was measured on d 14, 23, 24, 30, 37, 45, and 52. Blood samples were collected at 0, 8, 12, 24, 48, 72, 96, and 120 h after each LPS challenge, whereas RR quarter milk samples were collected at 0, 8, 16, 24, 48, 72, 96, 120, 144, and 168 h after each LPS challenge. Body temperature was measured continuously during each challenge with an intravaginal thermometer. Linear mixed models with repeated measures were used to analyze the results. Before LPS challenge, RPN did not affect feed intake or milk production, but it reduced SCS (1.24 ± 0.41 vs. 0.05 ± 0.45). After challenge, RPN did not affect feed intake, milk production, milk composition, SCS, body temperature, plasma glucose, or plasma insulin concentrations. Our results suggest RPN reduced peak plasma haptoglobin and lipopolysaccharide binding protein (LBP) during the 1st LPS challenge. Plasma haptoglobin tended to be less after the 2nd challenge for cows previously supplemented RPN while LBP was similar for each treatment group after the 2nd challenge. The 2nd LPS challenge resulted in decreased plasma haptoglobin compared with the 1st LPS challenge, suggestive of tolerance but it also induced a greater peak SCS than the 1st LPS challenge. Our results suggest that repeated LPS challenges promote a systemic tolerance but heightened local response to LPS-induced mastitis. Feeding RPN reduced SCS before challenge and reduced plasma acute phase proteins after challenge suggesting that RPN may reduce systemic inflammation without altering the local inflammatory responses.

Corn silage is one of the most common ingredients fed to dairy cattle. Advancement of corn silage genetics has improved nutrient digestibility and dairy cow lactation performance in the past. A corn silage hybrid with enhanced endogenous α-amylase activity (Enogen, Syngenta Seeds LLC) may improve milk production efficiency and nutrient digestibility when fed to lactating dairy cows. Furthermore, evaluating how Enogen silage interacts with different dietary starch content is important because the ruminal environment is influenced by the amount of rumen fermentable organic matter consumed. To evaluate the effects of Enogen corn silage and dietary starch content, we conducted an 8-wk randomized complete block experiment (2-wk covariate period, 6-wk experimental period) with a 2 × 2 factorial treatment arrangement using 44 cows (n = 11/treatment; 28 multiparous, 16 primiparous; 151 ± 42 d in milk; 668 ± 63.6 kg of body weight). Treatment factors were Enogen corn silage (ENO) or control (CON) corn silage included at 40% of diet dry matter and 25% (LO) or 30% (HI) dietary starch. Corn silage used in CON treatment was a similar hybrid as in ENO but without enhanced α-amylase activity. The experimental period began 41 d after silage harvest. Feed intake and milk yield data were collected daily, plasma metabolites and fecal pH were measured weekly, and digestibility was measured during the first and final weeks of the experimental period. Data were analyzed using a linear mixed model approach with repeated measures for all variables except for body condition score change and body weight change. Corn silage, starch, week, and their interactions were included as fixed effects; baseline covariates and their interactions with corn silage and starch were also tested. Block and cow served as the random effects. Plasma glucose, insulin, haptoglobin, and serum amyloid A concentrations were unaffected by treatment. Fecal pH was greater for cows fed ENO versus CON. Dry matter, crude protein, neutral detergent fiber, and starch digestibility were all greater for ENO than CON during wk 1, but differences were less by wk 6. The HI treatments depressed neutral detergent fiber digestibility compared with LO. Dry matter intake (DMI) was not affected by corn silage but was affected by the interaction of starch and week; in wk 1, DMI was similar but by wk 6, cows fed HI had 1.8 ± 0.93 kg/d less DMI than LO cows. Milk, energy-corrected milk, and milk protein yields were 1.7 ± 0.94 kg/d, 1.3 ± 0.70 kg/d, and 65 ± 27 g/d greater for HI than LO, respectively. In conclusion, ENO increased digestibility but it did not affect milk yield, component yields, or DMI. Increasing dietary starch content improved milk production and feed efficiency without affecting markers of inflammation or metabolism.

In the high-producing dairy cow, providing an adequate supply of digestible energy is essential. One strategy to meet this need is to provide fermentable starch from cereal grains or silages like corn, barley, or wheat. Unfortunately, excess dietary starch increases the risk of rumen acidosis. Rumen acidosis challenge models using high-grain diets, particularly with wheat and barley, have demonstrated that a sudden change in starch concentration or digestibility leads to the breakdown of the rumen epithelial barrier. As a result, increases in circulating lipopolysaccharide (a marker of bacterial translocation) and acute phase proteins (APP) have been observed. Feeding increasing amounts of starch in chronic feeding studies does not appear to consistently modulate inflammation in early-lactation cows that already experience inflammation. In mid- and late-lactation cows, increasing starch above 30% may increase APP, but the response is inconsistent and has not been investigated using different grains or differently processed starch sources. Abomasal starch infusion experiments indicate that increasing the intestinal starch supply consistently reduces fecal pH but does not lead to an APP response or changes in gut integrity. Increasing intestinal starch supply increases fecal butyrate concentrations, and butyrate has had positive effects on gut health and integrity in other species and experimental models. More chronic feeding experiments are needed to investigate how starch concentrations, sources, processing methods, and interactions affect inflammation and gut integrity. There is a paucity of data investigating the role that carbohydrate concentrations and sources play on ruminant hindgut health, integrity, function, structure, or microbiome. Currently, data indicate that feeding diets with less than 30% starch to lactating dairy cows does not contribute to systemic inflammation.

The physical form of feeds can influence dairy cow chewing behavior, rumen characteristics, and ruminal passage rate. Changing particle size of feeds is usually done through grinding or chopping forages, but pelleting feed ingredients also changes particle size. Our objective was to determine if pelleted dried distillers grains and solubles (DDGS) affected the feeding value for lactating dairy cattle. Seven lactating Jersey cows that were each fitted with a ruminal cannula averaging (± standard deviation) 56 ± 10.3 d in milk and 462 ± 75.3 kg were used in a crossover design. The treatments contained 15% DDGS in either meal or pelleted form with 45% or 55% forage on a dry matter basis. The forages were alfalfa hay, corn silage, and wheat straw. The factorial treatment arrangement was meal DDGS and low forage (mDDGS-LF), pelleted DDGS and low forage (pDDGS-LF), meal DDGS and high forage (mDDGS-HF), and pelleted DDGS and high forage (pDDGS-HF). Dry matter intake and energy-corrected milk were both unaffected by treatment averaging 19.8 ± 2.10 kg/d and 33.9 ± 1.02 kg/d, respectively. Fat yield was unaffected averaging 1.7 ± 0.13 kg/d, but protein yield was affected by the interaction of forage and DDGS. Protein yield was similar for both low forage treatments but was increased by when pDDGS was fed in the high forage treatment (1.05 vs. 0.99 ± 0.035 kg/d). When forage concentration was increased, starch digestibility increased by 1.9 percentage units, crude protein digestibility tended to increase 1.1 percentage units, and residual organic matter digestibility decreased 3.4 percentage units. Pelleting DDGS increased digestibility of neutral detergent fiber (NDF) digestibility (49.2 vs. 47.5 ± 1.85%) and gross energy (68.2 vs. 67.1 ± 1.18%). Increasing forage increased ruminal pH (5.85 to 5.94 ± 0.052). Passage rate slowed from 2.84 to 2.65 ± 0.205 %/h when feeding HF compared with LF. Rumination time increased from 417 to 454 ± 49.4 min with increasing forage concentration but was unaffected by the form of DDGS or the interaction of forage and DDGS. Eating time increased with pDDGS (235 vs. 209 ± 19.8 min), which may be a result of increased feed sorting behavior. Pelleting DDGS increased preference for particles retained on the 8-mm sieve and decreased preference for particles on the 1.18-mm sieve and in the pan (<1.18 mm). Results confirm that increasing forage concentration increases ruminal pH, rumination time, and slows passage rate, but contrary to our hypothesis increasing forage concentration did not increase NDF digestibility. Results also suggest that pelleted DDGS do not appear to affect milk production, ruminal characteristics, or passage rate, but pelleted DDGS may increase sorting behavior of lactating Jersey cows and increase NDF and gross energy digestibility.

ABSTRACT Objective Our objectives were to identify optimal dietary inclusion for Sweet Bran (SB; Cargill Inc.), a branded, modified wet corn gluten feed product, and determine whether there are other important factors to consider when feeding SB to lactating dairy cattle. Materials and Methods Experiments where at least 2 SB concentrations were investigated (n = 12; 50 treatment means) were compiled into a database for meta-regression analysis. Experiments were screened to ensure they reported nutrient and ingredient composition of treatments and milk yield and milk component responses. The meta-regression was conducted using lmer and step functions of the lmerTest package within R (v 4.0.2). Results and Discussion Dietary SB interacted with NDF concentration such that greater SB inclusion was associated with increased DMI, but the magnitude of this effect declined with increasing dietary NDF concentration. Milk fat percentage and protein yield were affected by an interaction between dietary forage NDF (fNDF) and SB; increasing fNDF when feeding greater SB inclusions had positive effects on milk fat concentration but negative effects on milk protein yield. Milk fat and protein yield were optimized at 26 and 11% SB inclusion, respectively. Implications and Applications Sweet Bran supports increased DMI and milk fat yield when included at 20 to 40% of diet DM, but total diet NDF must be controlled. Results also suggest that moderate fNDF when feeding SB is important. Too little fNDF reduces milk fat percentage, whereas too much reduces protein yield. Finally, feeding greater SB concentrations reduced milk protein yield, suggesting the need to focus on AA balancing.

Objective: Our objective was to determine whether the use of 30-h in vitro NDF digestibility (NDFD30) of fibrous ingredients included in rations fed to lactating dairy cattle improves the accuracy of milk and CH4 production predictions from the Cornell Net Carbohydrate and Protein System (CNCPS, v. 6.5). Materials and Methods: Animal performance from 8 energy-balance studies were compiled into a database along with the treatments fed during those studies. Observed animal performance was compared with milk and CH4 predictions from CNCPS (v. 6.5) when using CNCPS feed library NDF rate of digestion (k(d)) values or when using NDF k(d) calculated from NDFD30. The in vitro analysis was conducted according to Goering and Van Soest (1970), and ash-free, alpha-amylase-treated NDF of the residue was determined according to methods outlined by Mertens (2002). Results and Discussion: Predictions of milk production were poorer with use of NDFD30, the concordance correlation coefficient decreased from 0.87 to 0.82 and mean bias increased -0.23 to 1.30 kg. Methane production predictions were unaffected with use of NDFD30. The concordance correlation coefficient increased from 0.33 to 0.38, but slope and mean bias were similar. These results indicate that including NDFD30 to estimate the k(d) of NDF may not improve ME allowable milk or CH4 production predictions when using the CNCPS ration model. Implications and Applications: Our results suggest that milk production predictions from CNCPS (v. 6.5) are reliable but CH4 predictions can be improved. Including NDFD30 did not provide additional value to ration formulation because it did not improve milk or CH4 production predictions. The next steps should evaluate including more time points, such as 30, 120, and 240 h in vitro, to determine whether altering the total pool of potentially digestible NDF and the rate of NDF digestion would improve predictions from CNCPS.

Objective: Our objective was to evaluate the effects of fat concentration on the rumen degradability and intestinal digestibility of dried corn distillers grains with solubles (DDGS) from different ethanol biorefineries that produce DDGS with varying fat concentrations. Materials and Methods: Three rumen-cannulated primiparous Holstein cows were used to evaluate the in situ ruminal DM, alpha amylase Heated NDF, and CP degradability of DDGS. The 6 DDGS samples were placed in nylon bags with a 50 +/- 10 mu m pore size and incubated in the cows for 0, 2, 4, 8, 16, 24, 48, 72, and 120 h. The 16-h rumen residues were used in determination of in vitro intestinal and total digestible protein. Results and Discussion: Fat concentration affected in situ rumen degradability and in vitro intestinal digestibility. High fat and low fat DDGS had 51.5 and 58.0% rumen degradable DM, respectively (P = 0.03). Intestinal digestible protein and total digestible protein were greater for low fat than high fat DDGS samples (67.6 vs. 54.6%; 85.8 vs. 77.1%, respectively). Implications and Applications: Low fat DDGS were more rumen degradable and more intestinally digestible, which will affect the feeding value of DDGS. When feeding DDGS, determining the digestibility and understanding the biorefinery's processing method will aide in understanding the nutritional value of DDGS.

The objective of this study was to evaluate the effects of heat stress on the fecal microbiome of lactating dairy cows. We hypothesized there would be an increase in the richness and diversity of the bacterial communities in the feces of heat stressed cows. Six Holstein cows were housed in tie stalls in an environmental chamber. Cows averaged 175 ± 7 d in milk, 1.5 ± 0.5 parities and 36.3 ± 3.7 kg/d of milk and were fed and milked twice-daily. Cows were allowed 5-d acclimation to the chambers (d −5 to 0; temperature humidity index (THI)~65) and were then subjected to constant heat stress for 16d (d0 to 16; THI~76), followed by a 9d recovery period (d 16 to 24; THI~66). Feed and water were available ad libitum. Fecal samples were collected per rectum on d −1, 0, 6, 13, 16, 20 and 24. Samples were immediately frozen at −20°C. Fecal DNA was extracted using PowerFecal kits (Qiagen), the V4 hypervariable region of the 16S rRNA gene was sequenced using the Illumina MiSeq platform, and operational taxonomic units (OTUs) were assigned to the SILVA database using BLAST based on a 97% nucleotide identity to evaluate richness and composition of fecal bacterial populations. Number of OTUs, and diversity assessed by the Shannon Index (Bonferroni t-test), increased approximately 20% and 5%, respectively, during heat stress compared with d −1 (P < 0.05, ANOVA). Diversity returned to d −1 levels by d 20 whereas the total number of OTUs was not fully restored until d 24. Principal component analysis (Bray-Curtis distances) revealed that community composition was similar during acclimation but diverged during heat stress and into the recovery period (P < 0.001, PERMANOVA). Results revealed individual OTUs displaying markedly different patterns of abundance across the experiment (P < 0.05). For example, compared with the acclimation period, Bacteroides species abundance increased 112% by d 16 of heat stress, then increased an additional 15% by d 24. We conclude that heat stress altered the fecal microbiome of lactating dairy cows affecting both diversity and abundance of individual OTUs. Altered fecal microbiome may impact gut health or environmental pathogen loads.