About

Kirby Krogstad is an Assistant Professor of Dairy Nutrition at The Ohio State University, based in the Department of Animal Sciences. His research focuses on dairy nutrition, contributing to the understanding of optimal feeding strategies and nutritional management to improve dairy cattle health and productivity. As part of his academic role, he engages in teaching, research, and extension activities aimed at advancing dairy science and supporting the dairy industry. He is actively involved in research that addresses key issues in dairy nutrition, with a particular emphasis on improving feed efficiency and animal performance. His work supports the department's mission to enhance the health, productivity, and well-being of dairy animals through scientific research and education.

Research topics

• Food science
• Animal science
• Chemistry
• Agronomy
• Biology
• Biochemistry
• Botany
• Microbiology
• Endocrinology

Selected publications

• Abomasal infusion of docosahexaenoic acid to mid-lactation cows alters circulating leukocyte profiles and affects immune response to ex vivo bacterial stimulation

  Journal of Dairy Science · 2025-09-19 · 2 citations

  articleOpen access

  n-3 Fatty acids have anti-inflammatory effects across species, and within the n-3 fatty acid family, different fatty acids have unique effects on immune responses. The objective of this study was to assess circulating leukocyte phenotypes and their ex vivo immune response to challenge following abomasal infusions of the n-3 fatty acid docosahexaenoic acid (DHA; C22:6). Eight mid-lactation Holstein cows (97 ± 37 DIM) were randomly assigned to treatment sequence in a 4 × 4 Latin square design. Treatments were 0, 2, 4, and 6 g/d DHA (supplied via an enriched oil containing 65% DHA) infused into the abomasum for 11 d. Blood samples were collected on the final 2 d of each treatment period. Circulating leukocytes and phenotypes were first assessed in the absence of any challenge. Additionally, whole blood was stimulated with Escherichia coli or Staphylococcus aureus bioparticles in the presence of dihydrorhodamine 123 to assess bacterial uptake and oxidative burst of neutrophils by flow cytometry. A separate whole-blood sample was stimulated with heat-killed S. aureus and plasma was collected to quantify cytokine concentrations. Increasing DHA dose reduced circulating eosinophil concentrations in a linear manner and tended to affect lymphocyte concentrations in a quadratic manner. Cytotoxic T and helper T cell populations, along with the abundance of L-selectin on these populations, showed quadratic effects, with peak abundance in cows receiving 2 to 4 g/d DHA. The γδ T cells responded in a cubic manner, with peak concentrations in cows receiving the 4 g/d DHA dose, whereas L-selectin expression in γδ T cells linearly decreased with increasing DHA dose. Unstimulated blood samples were affected by DHA dose in a cubic manner for IL-1α and VEGF-A and a quadratic manner for TNF and IL-36RA, where highest concentrations were observed at 2 g/d DHA. During whole-blood stimulation with S. aureus, MCP-1 concentration increased linearly with increasing DHA dose and TNF responded in a cubic manner, with a nadir at the 6 g/d DHA dose. Following whole-blood stimulation, DHA dose linearly increased the proportion of neutrophils with uptake of E. coli bioparticles, whereas DHA dose did not affect the proportion of neutrophils with uptake of S. aureus. These results indicate that despite the anti-inflammatory effects of DHA, neutrophil response is not blunted following bacterial stimulation. Further studies are required to assess the effects of DHA on in vivo immune responses.

  PublisherDOI

• Investigating ruminal resident immune cells in dairy cattle before and after a subacute ruminal acidosis challenge

  Journal of Dairy Science · 2025-04-17 · 2 citations

  articleOpen access1st authorCorresponding

  <h2>ABSTRACT</h2> 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.

  PublisherOA PDFDOI

• Effect of dietary supplementation with Saccharomyces cerevisiae fermentation product on clinical outcomes in dairy cows during challenge with Streptococcus uberis

  Journal of Dairy Science · 2025-08-29 · 1 citations

  articleOpen access

  Streptococcus uberis is a common mastitis pathogen that lacks an effective vaccine in the United States and often requires antibiotic therapy. Supplementation of feed with Saccharomyces cerevisiae fermentation products (SCFP) has been associated with decreased SCC in dairy cows. The objective of this randomized clinical trial was to evaluate the effect of oral supplementation with SCFP on clinical and production outcomes in lactating dairy cows in response to intramammary challenge with Streptococcus uberis. Healthy cows (n = 42; parities 1-5; >120 DIM) were enrolled if their pretrial test day SCC was <200,000 cells/mL and they had no history of clinical mastitis in the preceding 60 d. Four cohorts of cows were blocked based on bovine leukemia virus infection status, parity group, milk yield, and DIM then randomly pre-assigned to receive a challenge in one quarter before being assigned to receive a treatment or control diet during a 45-d prechallenge phase, 5- to 7-d challenge phase, and 45-d postchallenge phase. Diets of cows assigned to treatment were top-dressed with 19 g/d SCFP for 45 d, and the control cows received 19 g/d of ground corn. During the prechallenge phase, quarter milk samples were collected weekly and used to determine SCC and IMI. Cows that did not develop IMI during the prechallenge phase (n = 37) were challenged with ∼2,000 cfu of S. uberis 0140J in one rear mammary gland; quarter milk samples were collected daily until antibiotic treatment (d 5 or 7) and data collection continued for another 45 d. Statistical analyses were performed using linear mixed models. Supplementation with SCFP did not affect DMI, milk production, or milk components during the prechallenge, challenge, or postchallenge phases. During the challenge week, there was no effect of SCFP on number of colonies of S. uberis or SCC in milk. The mean time (± SE) from intramammary challenge with S. uberis until onset of clinical mastitis was 3.88 ± 0.42 d and 4.84 ± 0.44 d for cows in the control group and SCFP treated groups, respectively. The mean days to bacteriological cure were 25.9 ± 3.5 (control cows) and 22.5 ± 3.1 (SCFP treated). As compared with values in control cows, supplementation with SCFP did not affect milk yield, DMI, or SCC of cows that received an intramammary challenge with S. uberis 0140J. Interestingly in a subset of animals that were infected with bovine leukemia virus, but not lymphocytic, before challenge supplementation with SCFP increased DMI 1.3 kg ± 0.6 and increased milk production by 2.3 ± 0.9 kg/d. This study was performed using a challenge model and a single pathogen type, future studies focusing on naturally occurring mastitis may be of value.

  PublisherDOI

• Comparison of sources of rumen-protected methionine for lactating Holstein and Jersey dairy cattle

  Applied Animal Science · 2025-11-22

  articleOpen access1st authorCorresponding
  PublisherDOI

• Meta-analysis to determine the effects of supplementation of niacin during the transition or lactation period on performance in dairy cows

  Journal of Dairy Science · 2025-03-06 · 3 citations

  reviewOpen access

  = 61.7%) heterogeneity observed. Similarly, RPN supplementation during the lactation period led to linear increases in DMI and yields of milk, ECM, fat and lactose, with respective increases of 0.60, 1.10, 0.70, 0.06, and 0.05 kg/d when cows were supplemented with 4.7 g/d niacin. Across 12 treatment comparisons from 8 experiments, RPN-supplemented cows produced 0.96 kg/d more milk than CON cows (WMD = 0.96; 95% CI = 0.62-1.31), with no heterogeneity observed. Overall, feeding 9.1 g/d of niacin from RUPN or 4.7 g/d of niacin from RPN during the lactation period improved milk production without improving feed efficiency in dairy cows.

  PublisherOA PDFDOI

• Initial characterization of ruminal T lymphocytes in lactating dairy cows

  JDS Communications · 2025-10-10

  articleOpen accessSenior author

  γδ T cells may regulate immune responses through interleukin-10 secretion and reduce cytotoxic and helper T cell proliferation, in vitro. γδ T cells are prominent in ruminant peripheral blood, but their presence in a recently defined ruminal immune cell population remains unclear. Our study aimed to determine the relative proportions of T cell types within rumen tissue (heterogeneous tissue consisting of lamina propria, stratified epithelium, and vasculature) of healthy dairy cows through spectral flow cytometry, and we hypothesized that the largest proportion of ruminal T cells would be γδ T cells. We used spectral flow cytometry to assess ruminal and peripheral blood T cell proportions. The panel included CD45 (leukocytes), CD3 (T lymphocytes), CD4 (helper T cells), and TCRN-24 (γδ T cells). Results were analyzed with a mixed linear model that included the effect of blood versus rumen tissue and the random effect of cow. Cows were clinically healthy throughout the experiment, as indicated by their DMI (26.0 ± 3.44 kg/d), milk yield (50.6 ± 12.99 kg/d; mean ± SD), and ruminal pH (6.06 ± 0.55). CD3+ cells constituted 83.9% ± 2.85% (mean ± SEM) of ruminal CD45+ cells compared with 3.3% ± 2.85% of CD45+ cells in blood. On a CD3+ basis, TCRN24+ were the most prominent subset of T lymphocytes in rumen tissue samples and were enriched compared with blood (78.7% ± 6.92% of CD3+ vs. 38.1 ± 6.92% of CD3+). The CD4+ were reduced as a proportion of T cells in the rumen compared with blood (1.4% ± 1.95% of CD3+ vs. 21.4 ± 1.95% of CD3+). We observed a TCRN24+CD4+ population isolated from the rumen which was lesser in blood (9.0% ± 2.72% of CD3+ vs. 1.5 ± 2.72% of CD3+). We confirmed our hypothesis that γδ T cells are the most prominent proportion of T cells within the rumen tissue in healthy lactating dairy cows. Furthermore, we observed a unique population that was both TCRN24+ and CD4+; investigations of this potential T cell subtype are needed to confirm their presence and determine their function. Understanding the role of T lymphocytes in rumen immunity may guide strategies that strengthen rumen health and digestion while reducing gut-derived inflammation.

  PublisherDOI

• Investigation of HCAR2 antagonists as a potential strategy to modulate bovine leukocytes

  Journal of Animal Science and Biotechnology/Journal of animal science and biotechnology · 2024-03-06 · 5 citations

  articleOpen access

  Abstract Background Dairy cows experiencing ketosis after calving suffer greater disease incidence and are at greater risk of leaving the herd. In vitro administration of beta-hydroxybutyric acid (BHBA; the primary blood ketone) has inhibitory effects on the function of bovine leukocytes. BHBA is a ligand of HCAR2 and the activation of these receptors promotes an anti-inflammatory response which may be related with immunosuppression observed in transition dairy cattle. The objective of this study was to identify and test antagonists for HCAR2 in bovine immune cells cultured with BHBA. Results We observed expression of HCAR2 at the protein level within lymphocytes, monocytes, and granulocytes. The proportion of cells expressing HCAR2 tended to be greater in mid-lactation compared to early lactation cows; the increase was a result of increased proportion of T and B cells expressing HCAR2. Stimulation of HCAR2 with niacin or BHBA promoted Ca 2+ mobilization in neutrophils and mononuclear cells. Mononuclear cells treated with BHBA had diminished intracellular Ca 2+ responses when HCAR2 was knocked down by siRNA silencing, indicating Ca 2+ mobilization was mediated by HCAR2 signaling. Two candidate antagonists for HCAR2, synthesized from niacin (NA-1 and NA-5), were tested; monocytes and neutrophils pre-treated with NA-1 and NA-5 had reduced Ca 2+ mobilization after incubation with BHBA. Furthermore, NA-5 but not NA-1 prevented BHBA-associated reductions in cyclic AMP. Conclusions We demonstrated that HCAR2 is present on bovine leukocytes and has greater expression later in lactation. We confirmed that BHBA and niacin derived HCAR2 antagonists alter bovine leukocyte activity. Our results demonstrate that both BHBA and niacin affect bovine leukocyte Ca 2+ mobilization in a HCAR2-dependent manner.

  PublisherOA PDFDOI

• Associations of body condition score, body condition score change, and hyperketonemia with mastitis, reproduction, and milk production

  Journal of Dairy Science · 2024-12-20 · 3 citations

  articleOpen access1st authorCorresponding

  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 (ΔBCS), 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) ΔBCS (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, ΔBCS, and HYK within parity with mastitis, pregnancy, and hazard of leaving the herd during lactation. We examined the association of BCS, ΔBCS, 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.

  PublisherDOI

• Effects of rumen-protected niacin on inflammatory response to repeated intramammary lipopolysaccharide challenges

  Journal of Dairy Science · 2024-06-13 · 8 citations

  articleOpen access1st authorCorresponding

  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 LPS challenges, whether RPN resulted in any carryover effects, and whether repeated LPS challenges result in signs of immune tolerance or innate immune training. Twenty healthy, late-lactation Holstein cows (232 ± 65 DIM; 39 ± 5.8 kg/d of milk) were enrolled in a randomized complete block experiment that 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 (RR) mammary gland with 100 µg of LPS suspended in 5 mL of PBS. 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 [SE] 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 during the first LPS challenge. Plasma haptoglobin tended to be less after the second challenge for cows previously supplemented RPN, and lipopolysaccharide binding protein was similar for each treatment group after the second challenge. The second LPS challenge resulted in decreased plasma haptoglobin compared with the first LPS challenge, suggestive of tolerance, but it also induced a greater peak SCS than the first 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.

  PublisherOA PDFDOI

• On-farm supplementation of rumen-protected niacin: A randomized clinical trial

  Journal of Dairy Science · 2024-12-16 · 1 citations

  articleOpen access1st authorCorresponding

  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.

  PublisherDOI

Frequent coauthors

• B.J. Bradford

  Michigan State University

  10 shared

• L.K. Mamedova

  Michigan State University

  3 shared

• R J Vlietstra

  2 shared

• Matthew P. Bernard

  Michigan State University

  2 shared

• J.F. Fehn

  Michigan State University

  2 shared

• J.R. Pursley

  Michigan State University

  2 shared

• Ester Grilli

  University of Bologna

  2 shared

• Zelmar Rodriguez

  Michigan State University

  1 shared