About

Thomas R. Overton is a Professor of Dairy Nutrition and Management and serves as the Department Chair within the Animal Science Program at Cornell University. His primary research focus is on the nutritional management of transition dairy cows, a critical period from late pregnancy to early lactation that significantly impacts health and productivity. His work aims to enhance the understanding of physiology during this phase and develop nutritional and management strategies to improve animal well-being and farm profitability. Overton's research includes controlled studies at the Cornell Ruminant Center Dairy and observational studies in collaboration with commercial dairy farms in New York, with particular emphasis on managing hypocalcemia, optimizing protein supplementation, and identifying biomarkers of metabolic and immune health in transition cows. His efforts provide foundational knowledge that informs his extension programs, which target dairy farm owners, agriservice professionals, and dairy farm employees, delivering practical solutions and educational initiatives. As the Director of PRO-DAIRY, he leads statewide efforts to positively impact the dairy industry in New York, and he also contributes to teaching undergraduate and veterinary students in dairy cattle nutrition.

Research topics

• Internal medicine
• Medicine
• Animal science
• Biology
• Endocrinology
• Chemistry
• Food science
• Obstetrics
• Bioinformatics
• Veterinary medicine
• Biochemistry

Selected publications

• Supplementary materials for Calcium status of multiparous Holstein cows during early lactation and its association with the health and production of dairies in Antioquia, Colombia

  eCommons (Cornell University) · 2026-01-01

  datasetOpen access

  This file contains data supporting forage and concentrate results reported in Graef et. al Calcium status of multiparous Holstein cows during early lactation and its association with the health and production of dairies in Antioquia, Colombia. In Graef et. al, we found: Periparturient hypocalcemia in dairy cows is known to negatively affect health and milk production. The grazing-based dairy industry of Colombia is the fourth largest milk producer in Latin America and is rapidly growing. However, with renewed commitments to sustainable intensification, Colombia may be disproportionately affected by poor forage quality and periparturient diseases due to limited access to technology and infrastructure. The primary objective was to assess the incidence of subclinical hypocalcemia (SCH) across three commercial dairy farms in Antioquia, Colombia, and its association with milk production, disease, and culling. Multiparous Holstein cows (n = 136) were enrolled in a prospective cohort study design on 3 farms in Antioquia, Colombia, from July to December 2023. Serum concentrations of total calcium were analyzed prepartum, between 1 and 10 d before expected calving, and postpartum at 1, 2, 4, and 7 days in milk (DIM). Cows were assigned either as eucalcemic (EU) or SCH based on the mean total calcium serum concentration at 4 DIM in this study [EU > 2.40 mmol/L and SCH ≤ 2.40 mmol/L]. Milk production was recorded daily. The SAS MIXED procedure with repeated measures was used to analyze differences between EU and SCH cows and respective milk production. The incidence of SCH was 39%. Pre and postpartum blood total calcium were greater in EU than SCH (prepartum = 0.23 mmol/L, 95% CI 0.39 to 0.07 mmol/L; and postpartum = 0.37 mmol/L, 95% CI 0.45 to 0.29 mmol/L). Over time, EU cows had greater milk yields in the first 9 wk of lactation than SCH cows (1.43 kg/d; 95% CI 2.90 to 0.20 kg/d) without significant changes in risk to disease or culling (P ≥ 0.13). Overall, SCH is a prevalent challenge in grazing systems in Colombian dairy herds and may affect the production and may unduly impact disease, culling, and reproduction outcomes.

  PublisherDOI

• Calcium status of multiparous Holstein cows during early lactation and its association with the health and production of three grazing dairies in Antioquia, Colombia

  JDS Communications · 2026-05-01

  articleOpen access
  PublisherDOI

• Metabolic and inflammatory response to an early lactation intravenous lipopolysaccharide challenge in Holstein cows fed differing levels of metabolizable protein during the transition period

  Journal of Dairy Science · 2025-04-01 · 6 citations

  articleOpen access

  The nadir in transition cow nutrient balance coincides with a period of heightened inflammation. Decreased circulating AA might contribute to an altered immune phenotype that favors a proinflammatory response. Objectives were to (1) investigate the effect of increasing MP supply in the prepartum, postpartum, or both diets on the response to an intravenous (IV) LPS challenge, (2) compare the response of IV LPS to fasted unstimulated control cows, and (3) determine the duration of the effect of IV LPS or fasting on milk production. Multiparous cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (85 g of MP/kg of DM) or high (113 g of MP/kg of DM) level of MP. Postpartum diets were formulated to contain either a control (104 g of MP/kg of DM) or high (131 g of MP/kg of DM) level of MP. To control the potential confounding effects of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and postpartum diet resulted in 4 treatment groups: control-control, control-high, high-control, and high-high. Cows (n = 24; 23 ± 2 DIM) were selected to undergo an IV LPS challenge (0.0625 µg/kg of BW over 1 h; IVLPS) in 6 blocks. Each block included 1 cow from each treatment and 1 unchallenged control cow (n = 6; DIM = 22 ± 2; CON) alternating between treatments. All cows were allowed 1 h of ad libitum feed intake before IV LPS and fasted for 10 h following challenge. Separate repeated measure ANOVA models were used to compare the effects of dietary treatment and IV LPS. Dietary treatment did not affect the clinical, inflammatory, or hematologic response to IV LPS. Compared with baseline values, DMI and milk yield decreased on the day of challenge 14.0% and 17.7% in IVLPS and 13.8% and 4.0% in CON, respectively. Compared with CON, IVLPS decreased leukocyte counts at 1 and 4 h and increased tumor necrosis factor from 1 to 4 h, IL-10 from 1 to 6 h, and haptoglobin from 24 to 72 h. Intravenous LPS increased concentrations of glucose at 10 h and decreased those of BHB at 10 h, fatty acid at 6 and 10 h, and calcium from 3 to 10 h relative to challenge. Intravenous LPS decreased circulating EAA from 2 to 8 h and NEAA at 4 h relative to challenge. Fasting and IVLPS decreased milk yield on the day of challenge compared with cows from the source population but milk recovered by d 2 relative to challenge. In conclusion, MP supply did not modify the inflammatory response to IV LPS, but IV LPS altered the metabolic response compared with CON. Furthermore, fasted and IV LPS-challenged animals recovered milk production within 2 d postchallenge.

  PublisherDOI

• 319 Investigating the adhesion of Staphylococcus epidermidis to corneocytes in atopic dermatitis

  Journal of Investigative Dermatology · 2025-11-24

  articleOpen access
  PublisherOA PDFDOI

• Effect of prepartum dietary cation-anion difference strategy and level of dietary calcium on postpartum blood calcium status and milk production of multiparous Holstein cows

  Journal of Dairy Science · 2025-05-16 · 3 citations

  articleOpen accessSenior author

  Hypocalcemia in dairy cows can be mitigated by manipulating prepartum DCAD. What remains unclear is the degree to which DCAD diets should be implemented and the appropriate level of dietary Ca to be fed in conjunction with negative DCAD. This study examined 2 prepartum DCAD levels, 2 prepartum dietary Ca levels, and their interactions on postpartum Ca metabolism, DMI, and milk performance of Holstein cows. In a randomized block design, data from parous Holstein cows (n = 98) enrolled in the study from 32 d before expected calving through 63 DIM were used for analysis. At 26 d before expected calving, cows were assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement with main effects of DCAD (-2.61 mEq/100 g, partial acidification [PAS] vs. -10.26 mEq/100 g, full acidification [FAS]) and Ca (1.5% DM, high Ca [HCa] vs. 0.7% DM, low Ca [LCa]). Cows fed FAS and PAS diets targeted urine pH of 5.5 to 6.0 and 6.5 to 7.0, respectively. Cows fed FAS had lower urine pH and greater prepartum urinary ammonium excretion than cows fed PAS (FAS 5.64 vs. PAS 6.71 ± 0.10 pH). Urine was collected for mineral analysis once per week upon enrollment until parturition and at 1, 2, and 3 DIM. Blood samples were collected once per week from enrollment until 1 wk before calving then at 0.5, 1, 1.5, 2, and 3 DIM for analysis of Ca, Mg, and P. Dry matter intake and milk production were recorded daily, and BW data were collected weekly. Statistical analyses were conducted using SAS software (v. 9.4) using linear mixed models with covariates and repeated measures when appropriate. Differences in pre- and postpartum DMI were not detected between FAS- and PAS-fed cows. Prepartum DMI was not affected by dietary Ca level. Postpartum DMI and ECM were greater for cows fed HCa than LCa prepartum. Circulating postpartum total Ca was not different by prepartum Ca nor prepartum DCAD. Cows fed FAS excreted more urinary Ca than cows fed PAS prepartum and cows fed LCa excreted more urinary Ca than their HCa fed counterparts. In the conditions of this study, milk production and postpartum intake were not affected by magnitude of prepartum acidification. Feeding greater dietary Ca in the prepartum period improved postpartum DMI and ECM yield, independently of prepartum acidification level.

  PublisherDOI

• Effect of supplying a portion of trace mineral amino acid complexes on serum folate concentration from the dry period to early lactation

  JDS Communications · 2025-10-31

  articleOpen accessSenior author

  Folates are required in one-carbon metabolism and DNA methylation. During the transition period, these roles are particularly important for the final stages of fetal development and the onset of lactation. The objective of this retrospective study was to assess plasma folate concentration when a portion of dietary inorganic chloride trace minerals (ITM) and cobalt (Co) carbonate was replaced by AA complexes of trace minerals (AATM) and Co glucoheptonate during the transition period. Relationships between serum folate concentration and health biomarkers were also evaluated. With dietary trace mineral concentrations being the same between treatments, a total of 36 Holstein multiparous cows were randomly assigned based on their parity number and previous 305-d mature equivalent milk production to either (1) an ITM blend consisting of zinc (75 mg/kg DM), manganese (65 mg/kg), and copper (10 mg/kg) as hydroxychlorides, and cobalt (1 mg/kg) as carbonate (ITM) or (2) partial replacement of ITM with AATM of Zn (40 mg/kg), Mn (20 mg/kg), Cu (3.5 mg/kg), and Co glucoheptonate (1 mg/kg; AATM, Availa-Dairy, Zinpro Corp.) from 1 wk after dry-off through 8 wk of lactation. Milk yields were recorded at each milking. Blood samples were taken at wk -8 (before treatment administration), -1, 1, 2, and 8 relative to parturition for serum folate analysis. Serum folate concentration from wk -1 to 8 relative to parturition averaged 8.39 (SE: 0.44) ng/mL and was not affected by treatments. Regardless of treatments, serum folate concentration significantly decreased from wk -8 to -1, plateaued from wk -1 to 2 relative to parturition, and then significantly increased through wk 8 of lactation. Milk yield, DMI, serum alanine aminotransferase, and alkaline phosphatase concentrations were positively correlated with serum folate concentration, whereas serum BHB concentration tended to be negatively correlated with serum folate concentration. In conclusion, in the current study, the source of the trace mineral supplement fed during the dry period and early lactation did not have an impact on serum folate concentrations.

  PublisherOA PDFDOI

• Associations between periparturient calcium dynamics of multiparous Holstein cows and inflammation markers during the transition period

  Journal of Dairy Science · 2025-08-05 · 1 citations

  articleOpen accessSenior author

  Recent work has established that proper classification of cows based on their periparturient status has important implications for risks of health, production, and reproduction outcomes during the postpartum period. However, the dynamics of blood calcium (Ca) status and inflammation are far less understood. The objective of this study was to determine the relationship between subclinical hypocalcemia (SCH) dynamics and periparturient circulating serum amyloid-A (SAA), haptoglobin (Hp), tumor necrosis factor-α (TNFα), interferon-γ (IFNγ), and interleukin-10 (IL-10) concentrations, DMI, and milk production during the first 9 wk of lactation. Data collected from multiparous Holstein cows (n = 96) were retrospectively classified into 1 of 4 calcemia groups based on blood concentrations of total Ca (tCa) at 1 and 5 DIM: normocalcemic (NC; [tCa] >1.95 mmol/L at 1 DIM and >2.32 mmol/L at 5 DIM, n = 53); transient SCH (tSCH; [tCa] ≤1. 95 mmol/L at 1 DIM and >2.32 mmol/L at 5 DIM, n = 15); delayed SCH (dSCH; [tCa] >1. 95 mmol/L at 1 DIM and ≤2.32 mmol/L at 5 DIM, n = 15); and persistent SCH (pSCH; [tCa] ≤1. 95 mmol at 1 DIM and ≤2.32 mmol/L at 5 DIM, n = 13). The MIXED procedure of SAS (v. 9.4, SAS Institute Inc.) was used to analyze pre- (-28 and -1 d relative to calving) and postpartum (1, 3, 5, and 7 DIM) blood mineral concentrations, SAA, Hp, cytokines, milk production, and differences between Ca groups, using repeated measures for time. Prepartum blood concentrations of IL-10 tended to be greater in tSCH cows compared with NC, dSCH, and pSCH. Postpartum concentrations of Hp, SAA, and TNFα were different by Ca group. Concentrations of SAA and Hp were highest in the pSCH group at d 3, and TNFα was highest for cows categorized as dSCH, irrespective of time. Overall, our results suggest that cows experiencing different SCH dynamics display different patterns of inflammatory markers and that elevated concentrations of proinflammatory biomarkers accompany some categories of hypocalcemia during the early lactation period.

  PublisherOA PDFDOI

• Associations between prepartum urine pH and periparturient blood calcium concentrations in multiparous Holstein cows

  Frontiers in Veterinary Science · 2025-08-20 · 1 citations

  articleOpen access

  Introduction: Metabolic alkalosis induced by prepartum diet cations impairs Ca homeostasis in the periparturient cow. Adding anions to prepartum diets reduces blood pH improving periparturient Ca homeostasis. Urine pH generally reflects blood pH and is practical to measure on farm. The degree to which urine should be acidified to increase periparturient blood Ca concentration is not well defined. Materials and methods: Prepartum urine pH and periparturient blood Ca concentrations determined in 660 multiparous Holstein cows from 9 studies were analyzed. Least Square Means of the lowest blood Ca concentration (Ca nadir) observed in cows within 6 urine pH categories (≤ 5.75, 5.76 to 6.25, 6.26 to 6.75, 6.76 to 7.25, 7.26 to 7.75, and ≥ 7.76) were determined. Data were analyzed across all 660 cows and then by parity. Results: Across all cows, the Ca nadir was lowest and the incidence of cows with Ca nadir < 2.00 mM, indicative of subclinical hypocalcemia (SCH), was greatest when urine pH was ≥ 7.76. Mean Ca nadir increased in all cows with urine pH < 7.75. There was no significant difference in Ca nadir or % of cows with SCH when prepartum urine pH was < 7.75. This was also the case for 2nd and 3rd parity cows. However, in ≥ 4th parity cows, those with urine pH between 6.26 and 6.75 had significantly higher Ca nadir than cows with urine pH above 7.25 or below 5.75. Calcium nadir and blood Ca concentrations at 2 days in milk (DIM) were highly correlated (r = + 0.58), and blood Ca concentrations at 2 and 4 DIM were moderately correlated (r = + 0.43). Blood Ca concentration at 4 DIM was weakly associated with Ca nadir (r = + 0.30). Discussion: These analyses support acidification of cows to achieve prepartum urine pH below 7.75 to increase blood Ca nadir for 2nd and 3rd parity cows. For ≥ 4th parity cows, the highest blood Ca nadir was observed with urine pH below 7.25 and above 5.75. For ≥ 4th parity cows, urine pH below 5.75 was associated with significantly lower blood Ca nadir.

  PublisherOA PDFDOI

• Evaluation of circulating cytokine concentrations and ex vivo indicators of the inflammatory response in transition dairy cows fed pre- and postpartum diets differing in metabolizable protein supply

  Journal of Dairy Science · 2025-04-11 · 2 citations

  articleOpen access

  The nutrient deficit during the transition period might alter activity of the nutrient-sensing mechanistic target of rapamycin, thereby influencing immune phenotype and the inflammatory balance of transition cows. We investigated changes in circulating markers of inflammation during the transition period. Additionally, we assessed changes in ex vivo indicators of the whole blood leukocyte cytokine response to LPS stimulation and leukocyte phagocytosis and oxidative burst. The second objective was to determine whether increasing the MP supply in the prepartum, the postpartum, or both diets would affect the measured parameters. Multiparous Holstein cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (85 g MP/kg DM) or high (113 g MP/kg DM) level of estimated MP. Postpartum diets were formulated to contain either a control (104 g MP/kg DM) or high (131 g MP/kg DM) level of estimated MP. To control the potential confounding effect of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and a postpartum diet resulted in treatment groups: control-control (CC), control-high (CH), high-control (HC), and high-high (HH). Serum concentrations of tumor necrosis factor (TNF), IL-10, and IFN-γ were determined at -6, 3, 10, and 21 d relative to calving using a multiplex assay. Complete blood cell count, whole blood cytokine response to LPS stimulation, and PMN and peripheral blood mononuclear cell (PBMC) phagocytosis and oxidative burst were determined at -28, -10, 7, and 21 d relative to calving. Serum concentrations of TNF were below the lower limit of detection (≤12 pg/mL) in 282 (75.4%) samples. Serum concentrations of IL-10 and IFN-γ were greatest at -6 d relative to calving. Serum concentrations of IFN-γ did not differ by treatment, but IL-10 was greater in CH compared with HH and HC at 10 and 21 DIM, respectively. Compared with CC, white blood cell counts were 13.9% higher in HC, granulocyte counts were 17.6% and 14.7% higher in CH and HC, respectively, and monocyte counts were 27.4% higher at 7 DIM in HC. Lymphocyte counts were 12.7% and 13.9% higher in HC compared with CC and CH, respectively. Phagocytic ability and oxidative burst of PMN and PBMC did not differ by treatment. Whole blood LPS-induced IL-10 and TNF concentrations increased to a greater extent at 7 DIM and 7 and 21 DIM compared with -10 d relative to calving, respectively, and similarly in all treatments. In summary, whereas serum IL-10 and IFN-γ concentrations were greatest during late gestation, whole blood LPS-induced cytokines and phagocytosis increased to a greater extent during early lactation, suggesting a robust inflammatory response. However, increasing the MP supply during the transition period did not meaningfully influence indicators of the inflammatory response.

  PublisherOA PDFDOI

• Effect of metabolic disturbances on the plasma concentration and hepatic expression of the appetite-reducing hormone growth differentiation factor 15 (GDF15) in dairy cows

  Journal of Dairy Science · 2025-10-21

  articleOpen access

  Early-lactating dairy cows are vulnerable to metabolic dysfunctions and diseases and the consequent negative effects of these disturbances on appetite. The exaggerated response of early-lactating cows to metabolic disturbances is illustrated by their response to a hyperinsulinemic-euglycemic clamp (HEC) performed over a 48-h period. Initiation of HEC on d 7 of early lactation (EL) reduced feed intake by 33% but had no effect when performed in late pregnancy (LP, 31 d prepartum). We asked whether growth differentiation factor 15 (GDF15), a novel hormone inhibiting feed intake via activation of neuronal centers, could explain the effect of HEC on appetite in EL. This focus was prompted by increased GDF15 production in primates and rodents experiencing metabolic stressors. In plasma samples collected immediately before and after a 48-h period of HEC in EL and LP, HEC increased plasma GDF15 exclusively in EL, and this increase was positively associated with the reduction in feed intake. The major site of GDF15 production in EL was identified as liver on the basis of 7.7- to 87-fold higher expression than adipose tissue or muscle and increased hepatic GDF15 mRNA abundance during HEC. The HEC stimulated hepatic expression of the GDF15 transcriptional activators ATF4 and CHOP across physiological states and expression of the indicator of amino acid deficiency ASNS in EL but not LP. We next asked whether plasma GDF15 is also regulated by a subset of metabolic disturbances prevailing in EL cows (elevated plasma fatty acids, excessive liver triglyceride, and ketosis). The effect of increased plasma fatty acids was evaluated by i.v. infusion of a lipid emulsion (intralipid) in nonpregnant, nonlactating cows in the absence or presence of glucagon treatment. Intralipid caused a progressive rise in plasma GDF15; this stimulatory effect was increased in the presence of glucagon, resulting in a 2.4-fold increase over control after 13 h of infusion. Positive effects of intralipid were associated with increased hepatic expression of GDF15 and its transcriptional activators ATF4 and sXBP1; presence of glucagon increased GDF15 mRNA further but had no additional effect on ATF4 or sXBP1. Indices of GDF15 production were examined in healthy cows segregated on d 7 of lactation as having low (<5.2%) and high (>11.5%) liver triglyceride; neither plasma GDF15 nor hepatic GDF15 mRNA differed between the 2 groups. Finally, plasma GDF15 was measured in early-lactating dairy cows remaining healthy or diagnosed with clinical ketosis. Plasma GDF15 was 1.8-fold higher in ketotic than healthy cows. Overall, these data show upregulation of GDF15 production by a subset of metabolic factors and raise the possibility that GDF15 could contribute to the lower appetitive drive of early-lactating cows experiencing metabolic disturbances.

  PublisherDOI

Frequent coauthors

• Michael Van Amburgh

  291 shared

• Kevin C. Dhuyvetter

  Elanco (United States)

  290 shared

• Jan K. Shearer

  Iowa State University

  290 shared

• Roger Cady

  290 shared

• D.K. Beede

  290 shared

• Judith L. Capper

  Harper Adams University

  290 shared

• Alan Rotz

  Agricultural Research Service

  128 shared

• D.V. Nydam

  Cornell University

  86 shared

Labs

• Dairy Nutrition and Management LabPI

Awards & honors

• Nutrition Professionals Applied Dairy Research Award - Ameri…
• CALS Award for Outstanding Accomplishments in Extension/Outr…
• Foundation Scholar Award and Lectur - American Dairy Science…
• CALS Award for Outstanding Accomplishments in Extension/Outr…