About

Paul A. Bartell is an Associate Professor of Avian Biology at the Department of Animal Science at The Pennsylvania State University. His research focuses on the regulation of biological clocks in birds at the systems level, utilizing behavioral, molecular, and electrophysiological techniques to understand the neural and endocrine mechanisms by which daily clocks and yearly calendars control the temporal organization of behaviors and life history stages. His current projects include investigating how protein and gene expression changes enable diurnal birds to become nocturnally active during migration, despite limited sleep, and exploring the signals transmitted by biological clocks that influence reproductive development and viability. Dr. Bartell has implemented advanced molecular techniques such as in situ hybridization and real-time quantitative PCR to examine molecular circadian rhythms in central and peripheral oscillators. He has also used infrared videography to monitor nocturnal behaviors unobtrusively. His work has demonstrated that the control of nocturnal migratory restlessness in songbirds is directly under the circadian system's control and identified seasonal changes in neuronal structures within the avian brain related to migratory status. His contributions extend to understanding the influence of biological clocks on reproductive timing, aiming to elucidate the proximal mechanisms involved in reproductive development and maintenance.

Research topics

• Biology
• Animal science
• Internal medicine
• Medicine
• Ecology
• Endocrinology
• Chemistry
• Physics
• Zoology
• Immunology
• Biochemistry
• Food science

Selected publications

• Effects of timing of abomasal infusion of fatty acids on the daily rhythms of milk synthesis and plasma hormones and metabolites in dairy cows

  Journal of Dairy Science · 2025-05-16

  articleOpen access

  Dairy cows display daily rhythms of milk synthesis that appear to be driven by a circadian clock located in the mammary gland. These rhythms are altered by the time of feed availability. Fatty acids have been shown to entrain circadian rhythms in liver and adipose tissue in experimental models, but their role in the mammary gland has not been well investigated. Our objective was to determine the effects of the timing of fatty acid absorption on the daily rhythms of milk synthesis. Nine lactating Holstein cows were arranged in a 3 × 3 Latin square design. Treatments were abomasal infusions of 350 g/d of a free fatty acid stock enriched in cis-9 18:1 either continuously throughout the day for 22 h (CON) or for 8 h from 0900 to 1700 h (DAY) or from 2100 to 0500 h (NGT). Treatment periods were 12 d with a 5-d washout. Cows were milked every 6 h during the final 7 d of each period to determine the daily patterns of milk synthesis. A 24-h rhythm was fit to time course data using cosine analysis, and the amplitude and acrophase (time at peak) were determined. Daily milk and milk protein yields were decreased by DAY and NGT compared with CON, whereas milk fat yield was not changed. Milk yield fit a 24-h rhythm in CON and DAY but not in NGT. Furthermore, DAY delayed the peak of the daily rhythm of milk yield by 2 h compared with CON. Fat and protein concentrations exhibited daily rhythms in CON and NGT but not DAY. Fat yield only fit a 24-h rhythm in DAY. Both de novo and mixed-source fatty acid yields were reduced by DAY and NGT, suggesting that the faster infusion rates may have resulted in concentrations of fatty acids that exceeded a threshold sufficient to inhibit de novo fatty acid synthesis. Plasma glucose concentration failed to display a daily rhythm in any treatment, whereas nonesterified fatty acids showed a rhythm in CON and NGT, but this rhythm was abolished by DAY. Insulin fit a rhythm in NGT and tended to fit a rhythm with a lower amplitude in CON, but no rhythm was present in DAY. Blood urea nitrogen exhibited a daily rhythm under all treatments, and both the mean and amplitude were increased by DAY. Daily rhythms of milk synthesis were also modified by DAY, with a slight delay in the daily peak of milk yield and elimination of the rhythms of milk fat and protein concentrations. Infusion at night had little effect. Daytime infusion also modified the daily rhythms of plasma metabolites by reducing the amplitude of nonesterified fatty acid concentration and increased the amplitude of blood urea nitrogen.

  PublisherOA PDFDOI

• Effects of the timing of protein infusion on the daily rhythms of milk synthesis and plasma hormones and metabolites in dairy cows

  Journal of Dairy Science · 2023-06-01 · 6 citations

  articleOpen access

  Milk synthesis exhibits a daily rhythm that is modified by the timing of feed intake. However, it is unknown how specific nutrients entrain this daily rhythm. Amino acids have an important role in milk synthesis, and may have a role in entrainment of mammary circadian rhythms. The objective of this study was to determine the effects of intestinally absorbed protein on daily rhythms of milk and milk component synthesis and key plasma hormones and metabolites. Nine lactating Holstein cows were assigned to 1 of 3 treatment sequences in a 3 × 3 Latin square. Treatments included abomasal infusions of 500 g/d of sodium caseinate either continuously throughout the day (CON), for 8 h/d from 0900 to 1700 h (DAY), or for 8 h/d from 2100 to 0500 h (NGT). Cows were milked every 6 h during the final 8 d of each period. A 24-h rhythm was fit to data using cosine analysis and the amplitude and acrophase were determined. Night infusion of protein decreased the daily milk yield and milk protein yield by 8.2% and 9.2%, respectively. Milk fat yield was increased 5.5% by DAY and milk fat concentration was increased 8.8% by NGT. Milk yield exhibited a daily rhythm in all treatments, with NGT increasing the amplitude of the daily rhythm 33% compared with CON. Milk fat concentration fit a daily rhythm in CON and NGT, but not DAY, whereas milk protein concentration fit a daily rhythm in CON and DAY, but not NGT. Moreover, DAY abolished the daily rhythm of plasma glucose concentration, but induced rhythms of plasma insulin and nonesterified fatty acid concentrations. Results suggest that feeding increased protein levels during the early part of the day may increase milk fat yield and modify energy metabolism through increased daily variation in insulin-stimulated lipid release, but additional research focused on feeding multiple diets across the day is required.

  PublisherOA PDFDOI

• Effect of the timing of sodium acetate infusion on the daily rhythms of milk synthesis and plasma metabolites and hormones in Holstein cows

  Journal of Dairy Science · 2022 · 7 citations

  • Animal science
  • Chemistry
  • Internal medicine

  Dairy cows have a daily pattern of feed intake which influences ruminal fermentation and nutrient absorption. Milk synthesis also exhibits a daily rhythm and is altered by the timing of feed availability. Nutrients can regulate physiological rhythms, but it is unclear which specific nutrients affect the rhythms of milk synthesis in the cow. The objective of this study was to determine the effect of the timing of acetate infusion on the daily rhythms of feed intake, milk synthesis, milk fatty acids, plasma insulin and metabolites, and core body temperature. Ten lactating ruminally cannulated Holstein cows (127 ± 24.6 d in milk; mean ± standard deviation) were arranged in a 3 × 3 Latin square design. Treatments were ruminal infusions of 600 g/d of acetate either continuously throughout the day (CON) or over 8 h/d during the day (day treatment, DT; 0900 to 1700 h) or the night (night treatment, NT; 2100 to 0500 h). Experimental periods were 14 d with a 7-d washout between periods. Cows were milked every 6 h during the final 7 d of each experimental period to determine the daily pattern of milk synthesis. Blood samples were taken to represent every 4 h across the day and plasma glucose, insulin, β-hydroxybutyrate, urea nitrogen, and acetate concentration were measured. An intravaginal temperature logger was used to measure core body temperature. Data were analyzed with cosinor-based rhythmometry to test the fit of a cosine function with a period of 24 h and to determine the acrophase (time at peak) and amplitude (peak to mean) of each rhythm. Milk yield fit a daily rhythm for all treatments and DT and NT phase-delayed the rhythm and DT increased the robustness of the rhythm. Milk protein concentration fit a daily rhythm for all treatments and DT increased robustness, whereas NT phase-delayed the rhythm. Plasma acetate concentration also fit a daily rhythm in all treatments. Plasma acetate peaked at ∼1600 h in CON and DT and at 0053 h in NT, reflecting the timing of treatment infusions. There was a daily rhythm in plasma β-hydroxybutyrate that reflected the plasma acetate rhythm. Core body temperature fit a rhythm for all treatments, but the amplitude of the rhythm was smaller than previously observed. In conclusion, the timing of acetate infusion influences peripheral rhythms of milk synthesis and plasma metabolites.

  PublisherOA PDFDOI

• Ecoimmune reallocation in a native lizard in response to the presence of invasive, venomous fire ants in their shared environment

  Journal of Experimental Zoology Part A Ecological and Integrative Physiology · 2020 · 13 citations

  • Biology
  • Ecology
  • Zoology

  Exposure to stressors over prolonged periods can have fitness-relevant consequences, including suppression of immune function. We tested for effects of presence of an invasive species threat on a broad panel of immune functions of a coexisting lizard. Eastern fence lizards (Sceloporus undulatus) have been exposed to invasive fire ants (Solenopsis invicta) for over 80 years. Fire ants sting and envenomate lizards, causing physiological stress, but we do not have a comprehensive understanding of the broad immune consequences of lizard exposure to fire ant presence. We conducted a suite of immune measures on fence lizards caught from areas with long histories of fire ant invasion and lizards from areas not yet invaded by fire ants. The effect of fire ant presence on immunity varied depending on the immune component measured: within fire ant invaded areas, some portions of immunity were suppressed (lymphocytic cell-mediated immunity, complement), some were unaffected (phagocytic respiratory burst, natural antibodies), and some were enhanced (anti-fire ant immunoglobulin M, basophils) compared to within uninvaded areas. Rather than fire ants being broadly immunosuppressing, as generally assumed, the immune response appears to be tailored to this specific stressor: the immune measures that were enhanced are important to the lizards' ability to handle envenomation, whereas those that were unaffected or suppressed are less critical to surviving fire ant encounters. Several immune measures were suppressed in reproductive females when actively producing follicles, which may make them more susceptible to immunosuppressive costs of stressors such as interactions with fire ants.

  PublisherDOI

• Annual rhythms of milk synthesis in dairy herds in 4 regions of the United States and their relationships to environmental indicators

  Journal of Dairy Science · 2020 · 11 citations

  • Animal science
  • Biology
  • Food science

  The annual rhythms of milk and milk component yields are not well described and are important to dairy management. Recent analysis of federal milk marketing orders in the United States observed that the amplitude and time at peak (acrophase) of the rhythms of milk fat and protein concentration differ among regions, but the rhythms of milk and milk component yields are not well described. Our objective was to determine the annual rhythms of milk and milk component production from 4 US regions at the herd level and examine potential environmental factors entraining these rhythms. Monthly Dairy Herd Improvement Association records of all available herds in Pennsylvania (PA), Minnesota (MN), Texas (TX), and Florida (FL) from the years 2003 to 2016 were obtained from Dairy Records Managements Systems. Milk yield, fat and protein yield, and fat and protein concentration were fit to the linear form of the cosine function with a 12-mo period using a linear mixed effects model. Additionally, the fit of models containing either the cosine function or environmental temperature were compared using an F-test. Milk yield and fat and protein yields and concentrations fit a cosine function in all 4 states, indicating an annual rhythm. The amplitude (peak to mean) of the rhythm of milk yield varied by state and was lower in PA (1.2 kg) and MN (1.2 kg) compared with TX (3.1 kg) and FL (3.3 kg). Fat and protein yields similarly showed greater amplitudes in the southern versus northern states. The amplitudes of the rhythms of fat and protein concentration were opposite by region, with greater amplitudes occurring in MN and PA than in TX and FL. The acrophases of milk yield and milk fat and protein yields and concentrations also varied by state, but all peaked between October and March. An annual rhythm fit the data better than changes in environmental temperature for all responses in all states, except for fat and protein concentrations in FL, which exhibited lower amplitude seasonal rhythms. The yearly pattern of milk yield closely followed the fixed yearly pattern of the day to day changes in day length, whereas the rhythms of milk fat and protein concentrations followed the yearly pattern of absolute day length. Results suggest that the region of the United States in which a herd is located affects their annual rhythms of production, with a greater yearly variation in milk, fat, and protein yields occurring in the southern United States. The consistency of annual rhythms across years and herds allowed development of regression equations to adjust expectations across the year to account for the annual rhythm.

  PublisherOA PDFDOI

• Corrigendum to “Annual rhythms of milk synthesis in dairy herds in 4 regions of the United States and their relationships to environmental indicators” (J. Dairy Sci. 103:3696–3707)

  Journal of Dairy Science · 2020-05-13

  erratumOpen access

  In the supplemental tables for this paper (https://doi.org/10.3168/jds.2019-17362), the adjustment factors were not standardized in the same way. Revised supplemental tables are now available online. The authors regret the errors. Annual rhythms of milk synthesis in dairy herds in 4 regions of the United States and their relationships to environmental indicatorsJournal of Dairy ScienceVol. 103Issue 4PreviewThe annual rhythms of milk and milk component yields are not well described and are important to dairy management. Recent analysis of federal milk marketing orders in the United States observed that the amplitude and time at peak (acrophase) of the rhythms of milk fat and protein concentration differ among regions, but the rhythms of milk and milk component yields are not well described. Our objective was to determine the annual rhythms of milk and milk component production from 4 US regions at the herd level and examine potential environmental factors entraining these rhythms. Full-Text PDF Open Archive

  PublisherOA PDFDOI

• Transcriptome Analyses of Heart and Liver Reveal Novel Pathways for Regulating Songbird Migration

  Scientific Reports · 2019-04-15 · 23 citations

  articleOpen accessSenior authorCorresponding

  Many birds undertake long biannual voyages during the night. During these times of the year birds drastically reduce their amount of sleep, yet curiously perform as well on tests of physical and cognitive performance than during non-migrating times of the year. This inherent physiological protection disappears when birds are forced to stay awake at other times of the year; thus these protective changes are only associated with the nocturnal migratory state. The goal of the current study was to identify the physiological mechanisms that confer protection against the consequences of sleep loss while simultaneously allowing for the increased physical performance required for migration. We performed RNA-seq analyses of heart and liver collected from birds at different times of day under different migratory states and analyzed these data using differential expression, pathway analysis and WGCNA. We identified changes in gene expression networks implicating multiple systems and pathways. These pathways regulate many aspects of metabolism, immune function, wound repair, and protection of multiple organ systems. Consequently, the circannual program controlling the appearance of the migratory phenotype involves the complex regulation of diverse gene networks associated with the physical demands of migration.

  PublisherOA PDFDOI

• 0281 Short Sleep Duration and Poor Sleep Efficiency Exacerbate Effects of Executive Functioning Problems on Facial Affect Recognition within Disadvantaged and Diverse Mothers

  SLEEP · 2019-04-01

  articleOpen accessSenior author

  Sleep problems (e.g., short duration, inefficient sleep) have been found to exacerbate effects of Executive Functioning (EF) problems on social functioning. However, this work has not utilized nuanced measures of social functioning (e.g., dynamic recognition of facial affect) and has not typically examined at-risk populations. This study examined disadvantaged and ethnically diverse mothers, many of whom had histories of perpetrating child neglect (a population at risk for EF problems and misappraisals during social interactions). Previous studies have begun to examine links between EF problems and misappraisals of social situations among this population, however, the role of EF problems in recognition of facial affect, and the moderating role of sleep problems have not been examined. This study predicted that maternal EF problems would be associated with greater inaccuracy for recognizing facial affect, and that this association would be stronger under conditions of poor sleep. Methods: Participants: 91 disadvantaged mothers of preschool-aged children, 29 with histories of perpetrating child neglect. Cognitive Measures: Wisconsin Card Sort (cognitive flexibility); Alternate Uses Test (divergent thinking); Trailmaking Test (EF/processing speed); WAIS-IV Coding (processing speed); WAIS-IV Digit Span (working memory) Actigraphy-Assessed Sleep Measures: Total sleep time; Sleep efficiency Recognition of Facial Affect: Dynamic Affect Recognition Evaluation (inaccuracy for evaluating facial affect) Factor analysis of EF measures supported a single factor representing global impairment of EF. Maternal EF problems were significantly positively associated with inaccurate recognition of facial affect (β = .25, p = .02). Moderation analyses indicated that sleep duration and sleep efficiency moderated the association between maternal EF problems and inaccurate recognition of facial affect such that the relationship between EF problems and inaccuracy was stronger at lower levels of sleep time and sleep efficiency. Short sleep duration and inefficient sleep exacerbated effects of EF problems on inaccurate recognition of facial affect. Findings suggest that in addition to direct benefits, improving sleep among disadvantaged mothers may mitigate the impact of underlying neurocognitive problems on social functioning. #R21HD082555

  PublisherOA PDFDOI

• The premammillary nucleus of the hypothalamus is not necessary for photoperiodic timekeeping in female turkeys (Meleagris gallopavo)

  PLoS ONE · 2018-02-20 · 7 citations

  articleOpen accessSenior authorCorresponding

  In birds, seasonal reproduction is regulated by day length, with long days in the spring activating the hypothalamic-pituitary-gonadal axis and reproductive behaviors. The photoreceptors mediating this process remain unknown, but recently, the premammillary nucleus (PMM) of the hypothalamus has been implicated as the site of photoperiodic signaling in turkeys. We performed electrolytic lesions of the PMM to elucidate its role in the photoactivation and maintenance of egg production in female turkeys. Our results show that ablation of the PMM does not alter the normal lay cycle. No differences were found between lesioned birds and sham controls in the latency to lay following photostimulation, nor in subsequent egg production over a period of 29 weeks. No differences in the incidence of gonadal regression were found, indicating that the PMM is not essential for the termination of breeding. We conclude that any role of the PMM in photoperiodic regulation, if it exists, is redundant with other components of the system.

  PublisherOA PDFDOI

• The effects of feeding rations that differ in fiber and fermentable starch within a day on milk production and the daily rhythm of feed intake and plasma hormones and metabolites in dairy cows

  Journal of Dairy Science · 2016-11-10 · 45 citations

  articleOpen access

  A daily pattern of feed intake, milk synthesis, and plasma metabolites and hormones occurs in dairy cows fed a total mixed ration once or twice a day. The objective of this study was to determine if feeding multiple rations within a day, complementing these rhythms, would improve milk production. Twelve Holstein cows were used in a replicated 3×3 Latin square design with 21-d periods. Cows were housed in tie stalls with feed tubs, and feed weight was recorded every 10 s for observation of feeding behavior. Rations were a low fiber and high fermentable starch ration [LFHS; 27.4% neutral detergent fiber (NDF) and 31.7% starch based on 55.7% corn silage and 14.1% steam-flaked corn], a high fiber and low fermentable starch ration (HFLS; 31.7% NDF and 22.3% starch based on 44% corn silage, 26.3% alfalfa haylage, and no steam-flaked corn), and a total mixed ration that was a 1:3 ratio of LFHS and HFLS (30.7% NDF, 24.5% starch). The control treatment (CON) cows were fed the total mixed ration at 0700h, the high/low treatment (HL) fed HFLS ration at 0700h and LFHS ration at 2200h, and the low/high (LH) treatment fed LFHS ration at 0700h and HFLS ration at 1100h (LFHS and HFLS rations fed at a 1:3 ratio). No effect was found of treatment on daily milk, but LH decreased milk fat concentration and yield compared with HL (0.2 percentage units and 0.24kg, respectively). Daily dry matter and NDF intake and total-tract digestibility did not differ between treatments. The HL treatment reduced intake at the morning-conditioned meal after feeding and reduced intake before the evening feeding. A treatment by time of day interaction was found for fecal NDF and indigestible NDF concentration, blood urea nitrogen (BUN), plasma insulin, and fatty acid concentration, and body temperature. The CON and LH treatments increased the daily amplitude of fecal NDF by 1.0 and 1.1 percentage units compared with HL. Plasma insulin was higher in HL than CON at 0100 and 0400h, but lower at 1300 and 1900h. Plasma fatty acids were higher for CON than HL at 0700h and HL was lower than LH at 0400 and 1900h. Plasma BUN was higher for HL than control at 0100h, but lower at 1000h. Body temperature in CON and HL treatments followed a similar diurnal pattern, whereas body temperature for LH was lower than that of HL treatment at 1300 and 2300h. No daily rhythm was found of fecal indigestible NDF concentration, plasma glucose, or fatty acids detected in the HL treatment, and the amplitude of plasma insulin and BUN was lower for HL compared with CON (70 and 60% decrease, respectively). In conclusion, feeding 2 rations that differ in fiber and fermentable starch modifies diurnal rhythms in dairy cows. Furthermore, feeding a high fiber and low fermentable starch ration during the high intake period of the day may stabilize nutrient absorption across the day.

  PublisherOA PDFDOI

Frequent coauthors

• Michael Menaker

  University of Virginia

  10 shared

• Manuel Miranda‐Anaya

  Universidad Nacional Autónoma de México

  8 shared

• K.J. Harvatine

  Cornell University

  8 shared

• Vincent M. Cassone

  University of Kentucky

  6 shared

• Maria Horvat‐Gordon

  Pennsylvania State University

  5 shared

• Ashli F. Moore

  Pennsylvania State University

  5 shared

• Yun Ying

  University of Pennsylvania

  5 shared

• Michael Smotherman

  Texas A&M University

  4 shared

Labs

• Paul A. Bartell LabPI

Education

• B.S., Departments of Biology and Psychology

  Hope College

  1993

• M.S., Department of Zoology

  University of New Hampshire

  1996

• Ph.D., Department of Biology

  University of Virginia

  2001