Daily rhythms of 25 physiological variables in Bos taurus maintained under natural conditions

Chronophysiology of domestic animals

This review highlights recent findings on biological rhythms and discusses their implications for the management and production of domestic animals. Biological rhythms provide temporal coordination between organs and tissues in order to anticipate environmental changes, orchestrating biochemical, physiological and behavioural processes as the right process may occur at the right time. This allows animals to adapt their internal physiological functions, such as sleep-wake cycles, body temperature, hormone secretion, food intake and regulation of physical performance to environmental stimuli that constantly change. The study and evaluation of biological rhythms of various physiological parameters allows the assessment of the welfare status of animals. Alteration of biological rhythms represents an imbalance of the state of homeostasis that can be found in different management conditions.

The Effect of Short-Wavelength White LED Illumination throughout the Night on the Milk Fatty Acid Profile of High-Yielding Dairy Cows

Fatty acid levels in milk vary between day and night milking. Many dairy cows are still kept under white light-emitting diode (W-LED) illumination throughout the night, although it is known to disrupt endogenous circadian rhythms. We investigated the effects of whole-night W-LED illumination (125 lux) on milk yield and circadian composition, compared to a natural light−dark (LD) cycle of 10 h light. Mid−late lactation cows (n = 34) that were exposed to natural LD cycle showed circadian variation in milk fat composition, characterized by higher health-promoting monounsaturated fatty acid (MUFA; 24.2 ± 0.4 vs. 23.2 ± 0.4 g/100 g fat, p < 0.001) and lower saturated fatty acid levels (71.2 ± 0.4 vs. 72.5 ± 0.4, p < 0.001) at 13:30 h (day milk) than at 03:30 h (night milk). Compared to natural LD (n = 16), W-LED (n = 18) did not affect milk production or milk fat yields, yet abolished the milking time variation in milk fat composition towards a less healthy fatty acid profile. This lowered MUFA levels of day milk (23.8 ± 0.4 vs. 26.7 ± 0.4, p < 0.01). Therefore, W-LED has no commercial advantage over the tested natural LD cycle, and conversely, even shows circadian disruption. Accordingly, a natural LD cycle of 10 h light is preferable over W-LED from the perspective of cost savings, the cows’ well-being, and preserving the natural milk fat profile, as the nutritional value of the day milk is slightly higher.

The diurnal patterns of ruminal enzymatic activity and in vitro digestibility of starch, neutral detergent fiber, and protein

The objective of this study was to determine whether diurnal patterns in starch, neutral detergent fiber (NDF) and protein digestibilities and amylolytic, fibrolytic, and proteolytic activities exist in dairy cows. Rumen fluid was collected from 4 ruminally cannulated Holstein dairy cows before the morning feeding and subsequently every 4 h for a 24-h period. Two of the cows were restricted from feed for 8 h overnight, and the other 2 continued to receive their feed ad libitum, to isolate and quantify the effects of changes in feeding behavior at night. After 2 runs the cows were crossed over between night feeding treatments. Rumen fluid was analyzed for enzymatic activity and in vitro starch, NDF, and nitrogen digestibility. Circadian rhythm analyses of enzymatic activity and in vitro digestibility were conducted by fitting the linear form of a cosine function with a 24-h period. Patterns were observed in activity for amylase, lichenase, endoglucanase, and xylanase, with the highest activities observed at the time points subsequent to milking and feed delivery. Protease activity was unaffected by either feeding treatment or possible feeding behavior. When fitted to a cosine function, all the parameters tested followed a daily pattern that was sensitive to the overnight availability of feed, although the parameters responded differently to the feeding treatment. The patterns displayed by in vitro digestibility results of starch, NDF, and nitrogen, across the various fluid collection time points, were highly variable. The time at peak (acrophase) observed in the enzymatic analysis did not correspond to those observed in the in vitro analysis. These results suggest that different interpretations should be given to enzymatic activities and in vitro digestibility values, and the time of rumen fluid collection relative to feeding time should be considered and reported when rumen fluid is used for research or commercial purposes. Maximum digestibility appears in fact to be reached around 4 to 5 h after the main ration delivery for NDF and starch and around ration delivery for protein.

Circadian Gene PER2 Silencing Downregulates PPARG and SREBF1 and Suppresses Lipid Synthesis in Bovine Mammary Epithelial Cells

Simple Summary

The present study was constructed to determine the effects of the core circadian clock gene, Period 2 (PER2), on lipid synthesis in bovine mammary epithelial cells (BMECs). Data revealed that PER2-regulated genes were involved in fatty acid de novo synthesis, desaturation, TAG accumulation, and lipid droplet secretion in primary BMECs, partly by inhibiting PPARG and SREBF1. Our overall data suggests that PER2 in bovine mammary cells plays a role in regulating milk fat synthesis directly, or via the activation of the transcription regulators PPARG and SREBF1. This study provides molecular evidence underscoring a link between the circadian clock and lipid metabolism in bovines.

Abstract

PER2, a circadian clock gene, is associated with mammary gland development and lipid synthesis in rodents, partly via regulating peroxisome proliferator-activated receptor gamma (PPARG). Whether such a type of molecular link existed in bovines was unclear. We hypothesized that PER2 was associated with lipid metabolism and regulated cell cycles and apoptosis in bovine mammary epithelial cells (BMECs). To test this hypothesis, BMECs isolated from three mid-lactation (average 110 d postpartum) cows were used. The transient transfection of small interfering RNA (siRNA) was used to inhibit PER2 transcription in primary BMECs. The silencing of PER2 led to lower concentrations of cellular lipid droplets and triacylglycerol along with the downregulation of lipogenic-related genes such as ACACA, FASN, LPIN1, and SCD, suggesting an overall inhibition of lipogenesis and desaturation. The downregulation of PPARG and SREBF1 in response to PER2 silencing underscored the importance of circadian clock signaling and the transcriptional regulation of lipogenesis. Although the proliferation of BMECs was not influenced by PER2 silencing, the number of cells in the G2/GM phase was upregulated. PER2 silencing did not affect cell apoptosis. Overall, the data provided evidence that PER2 participated in the coordination of mammary lipid metabolism and was potentially a component of the control of lipid droplets and TAG synthesis in ruminant mammary cells. The present data suggested that such an effect could occur through direct effects on transcriptional regulators.

Clock genes determination in whole blood in goats housed under a long light cycle

An innate 24 h circadian clock drives various behavioral processes via expression of clock genes that regulate circadian rhythmicity and temporal signals. Elucidating the gene expression in goats may contribute to improving the knowledge of the regulation of circadian rhythms in this species. Five nonpregnant and nonlactating Maltese goats with no evidence of disease were kept in an indoor pen under the natural long photoperiod (05:05-20:56 h) and natural environmental temperature (23°C and 60% RH). They were fed an Alfalfa hay and concentrate mixture provided twice a day; water was available ad libitum. Blood samples were collected every 4 h over a 48 h period into PAX gene Blood RNA Tubes and stored at -80°C until processing. Clock genes (Clock; Cry1; Cry2; Per2; Per3) were determined using real-time quantitative polymerase chain reaction. During the experimental period, locomotor activity was monitored by an actigraphy-based data logger that records a digitally integrated measure of motor activity as a means to assess indices of discomfort during study and stability of the circadian rhythm. All of the tested genes showed daily rhythmicity in their expression in whole blood. Differences in their circadian parameters were observed. Mesor and amplitude were statistically different among the tested gene (Mesor: F_(4.30) = 205.30; p < .0001; amplitude: F_(4.30) = 104.80; p < .0001), with each gene showing its acrophase at a different time of day (F_(4.30) = 81.17; p < .0001), and differences were observed between the two days of monitoring (F_(1.30) = 10.25; p = .003). The application of two-way analysis of variance (ANOVA) on robustness of rhythm values did not show statistical differences among the tested genes (F_(4.30) = 1.83; p = .14) and between the two days of monitoring (F_(1.30) = 1.16; p = .28). Locomotor activity data recording were in accordance with the data reported in literature, indicating the absence of discomfort or alteration of circadian rhythms during the experimental period. Our results support the presence of a cyclic transcription of clock genes in whole blood of healthy goats housed under a long light natural photoperiod and natural environmental conditions.

Influence of Different Lactation Stages on Circadian Rhythmicity of Metabolic Biomarkers in Dairy Cows: A Pilot Study

Simple Summary

Circadian rhythms are present in most species and play an important role in their metabolism. Metabolic biomarkers, which are commonly used to assess the health status, are also affected by those rhythms. In this study, we investigate the influence of lactation and time on four metabolic biomarkers in dairy cows. Our findings provide new insights into the physiology of circadian rhythms in dairy cows, which enables novel metabolic monitoring approaches.

Abstract

Currently, subclinical metabolic imbalances at the individual cow and herd level are detected by measuring biomarkers in single blood samples. However, diurnal variations have not been fully described yet but need to be considered when sampling for a robust ad consistent analysis. The study describes the influence of lactation phases on circadian rhythms and diurnal variations for non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), total bilirubin (tBIL) and aspartate aminotransferase (AST) in dairy cows. In an observational pilot study, we used 16 clinically healthy Simmental dairy cows subdivided in four different lactation stages (dry-off, fresh, high and late lactating). Every cow was monitored for 24 h, with blood sampling and assessment of clinical parameters every 2 h. Time and lactation stage influence the concentration of the biomarkers NEFA, BHB and tBIL in serum. Further, circadian rhythmicity was found in high lactating cows for NEFA peaking at 5:39 am and BHB peaking at 4:20 pm. We suggest blood sampling for single-point measurements within three hours after the first feeding until two hours after the last feeding of the day. The results provide a new insight into the physiology of circadian rhythms in dairy cows and enable improved metabolic monitoring.

Methods to quantify heat stress in ruminants: Current status and future prospects

The physiology of hyperthermia or heat stress in mammals is complex. It is a totally systemic condition that in varying degrees involves all organs, tissues and body fluid compartments. The nature and magnitude of the response is influenced by animal specific characteristics (e.g. age, diet, body condition, gender, reproductive stage), environment and animal management. Given the multifaceted nature of heat stress, and the varied ruminant production systems based in varied geoclimatic zones, it has been difficult to find appropriate measures of heat stress for production ruminants. This has become an urgent challenge as production systems intensify globally in a warming climate. Bioclimatic indices such as the Temperature-Humidity Index (THI) have evolved to incorporate some measure of animal physiology. However, these indices do not have strong relationships with core temperature trajectories and altered respiratory dynamics of animals with excessive heat load. In recent decades, the careful physiology studies of the 1950-80s, have given way to numerous studies trialling a plethora of new technologies and computational approached to measure heat stress. Infrared thermography of body surface temperatures, automated measures of respiration rate and radiotelemetry of internal body temperatures are the most intensively researched. The common goal has been to find the 'holy grail' decision-making threshold or timepoint as to the animal's wellbeing. Are we making any progress?

Night-restricted feeding of dairy cows modifies daily rhythms of feed intake, milk synthesis and plasma metabolites compared with day-restricted feeding

The timing of feed intake can alter circadian rhythms of peripheral tissues. Milk synthesis displays a daily rhythm across several species, but the effect of feeding time on these rhythms is poorly characterised. The objective of this experiment was to determine if the time of feed intake modifies the daily patterns of milk synthesis, plasma metabolites and body temperature in dairy cows. Sixteen lactating Holstein dairy cows were randomly assigned to one of the two treatment sequences in a cross-over design with 17 d periods. Treatments included day-restricted feeding (DRF; feed available from 07.00 to 23.00 hours) and night-restricted feeding (NRF; feed available from 19.00 to 11.00 hours). Cows were milked every 6 h on the last 7 d of each period, and blood samples were collected to represent every 4 h over the day. Peak milk yield was shifted from morning in DRF to evening in NRF, while milk fat, protein and lactose concentration peaked in the evening in DRF and the morning in NRF. Plasma glucose, insulin, NEFA and urea nitrogen concentration fit daily rhythms in all treatments. Night feeding increased the amplitude of glucose, insulin and NEFA rhythms and shifted the daily rhythms by 8 to 12 h (P < 0·05). Night feeding also phase-delayed the rhythm of core body temperature and DRF increased its amplitude. Altering the time of feed availability shifts the daily rhythms of milk synthesis and plasma hormone and metabolite concentrations and body temperature, suggesting that these rhythms may be entrained by food intake.

Effects of winter housing system on hygiene, udder health, frostbite, and rumination of dairy cows

The objective of this study was to evaluate the effects of 2 winter (December to April) housing systems on dairy cow hygiene scores, frostbite, teat condition, clinical mastitis, and activity and rumination across 3 winter seasons (2013, 2014, and 2015). Certified-organic cows (n = 268) were randomly assigned to 2 treatments (2 replicates per system): (1) outdoor straw pack (outdoor) or (2) 3-sided compost-bedded pack barn (indoor). Cows calved during 2 seasons (spring or fall) at the University of Minnesota West Central Research and Outreach Center, Morris, Minnesota, organic dairy. Organic wheat straw was used as bedding for the 2 outdoor straw packs, and bedding was maintained by farm management to keep cows dry and absorb manure throughout the winter. The compost-bedded pack barn (2 pens in the barn) was bedded with organic-approved sawdust, and the bedding material was stirred twice per day with a small chisel plow. Hygiene scores were recorded biweekly as cows exited the milking parlor. Incidence of clinical mastitis was recorded in a binary manner as treated (1) or not treated (0) at least once during a lactation. Frostbite incidence was collected monthly. Activity and rumination times (daily and 2-h periods) were monitored electronically using a neck collar sensor (HR-LD Tags, SCR Dairy, Netanya, Israel). Indoor cows had greater udder hygiene scores (1.75 vs. 1.46) and greater abdomen hygiene scores (1.79 vs. 1.43) compared with outdoor cows. Additionally, the indoor cows had greater upper and lower leg hygiene scores compared with outdoor cows. Incidence of clinical mastitis was greater for indoor cows compared with outdoor cows (27.1% vs. 15.1%, respectively). Frostbite incidence was not different between indoor (30.1%) and outdoor (17.5%) cows. Daily rumination was 509 min/d for indoor cows and 530 min/d for the outdoor cows. In summary, lactating cows housed outdoors on straw-bedded packs had cleaner udders and improved udder health compared with cows housed in a compost-bedded pack barn.

Daily Rhythms of Blood Parameters in Broiler Chickens Reared under Tropical Climate Conditions

Several studies carried out on humans and other mammals show that the temporal organisation of haematological parameters in the blood exhibit daily rhythms; however, such studies have been rare in poultry reared under a natural photoperiod. The present study investigated the occurrence of daily rhythms in blood parameters of broiler chickens kept under tropical climatic conditions. Ten 6-7-week-old broiler chickens served as subjects of the study. They were kept in standard individual cages under natural light-dark cycle and given access to feed and water ad libitum. Two milliliters of blood was collected from each bird via intravenous cannulae inserted into the wing vein. The blood samples were collected every 4 h over a 24-h period, starting from 09:00 h on the first day and completed at 09:00 h on the second day. The blood samples were analysed for erythrocyte, total and differential leucocyte counts. A trigonometric statistical model according to the single cosinor procedure was used to describe the periodic parameters and their acrophases, and ANOVA was used to determine significant differences. The results demonstrated the existence of daily rhythms in packed cell volume, haemoglobin, white blood cell, red blood cell, heterophil, lymphocyte, eosinophil and monocyte counts, while total protein displayed no rhythm. The characteristics of the haematological parameters showed that the acrophases were restricted to the light phase of the light/dark cycle, precisely at 09:00 h, except for eosinophil and heterophil counts, which had acrophases at 21:00 h. The amplitudes of the blood parameters varied, with packed cell volume having the greatest amplitude of 4.2 ± 0.5, closely followed by lymphocyte (3.4 ± 0.5) and heterophil (2.3 ± 0.2) counts. In conclusion, the results of the study demonstrated the existence of daily rhythms with diurnal acrophases in blood parameters of broiler chickens kept under natural photoperiods and tropical conditions.

Effects of Cold-Dry (Harmattan) and Hot-Dry Seasons on Daily Rhythms of Rectal and Body Surface Temperatures in Sheep and Goats in a Natural Tropical Environment

Studies on daily rhythmicity in livestock under natural conditions are limited, and there is mounting evidence that rhythm patterns differ between chronobiological studies conducted in the laboratory and studies conducted under pronounced natural seasonality. Here, we investigated the influence of cold-dry (harmattan) and hot-dry seasons on daily rhythmicity of rectal (RT) and body surface temperatures (BST) in indigenous sheep and goats under natural light-dark cycles. The RT and BST of the animals, and the ambient temperature (AT) and relative humidity (RH) inside the pen, were measured every three hours for a period of two days, twice on separate days during the hot-dry and the harmattan seasons, respectively. The AT and RH had minimum values of 16°C and 15% recorded during the harmattan and maximum values of 32°C and 46% recorded during the hot-dry season, respectively. A trigonometric statistical model was applied to characterize the main rhythmic parameters according to the single cosinor procedure. The result showed that RT and BST exhibited different degrees of daily rhythmicity, and their oscillatory patterns differed with the seasons (larger amplitude during the harmattan season than during the hot-dry season). The goats displayed greater (p < 0.05) amplitude of BST than the sheep in all seasons. The acrophases were restricted to the light phase of the light-dark cycle. The mesor of RT in goats was not affected by the season, but mesors of BST in both species were significantly higher (p < 0.05) during the hot-dry than the harmattan season. The goats had a more robust RT rhythm (70%) as compared to the sheep (56%). Overall, the results demonstrated that seasonal changes influenced considerably the daily rhythmicity of RT and BST in sheep and goats under natural light-dark cycle. Awareness of these changes may be useful in the improvement of diagnosis, treatment and prevention of diseases, and welfare and productivity of sheep and goats under cold-dry and hot-dry conditions.

Recent advances on the circadian gene PER2 and metabolic rhythm of lactation of mammary gland

Due to regulation by circadian rhythm, the lactation of the mammary gland has rhythmicity. As one of prominent members of period protein family which regulates biological rhythms, PER2 plays an important role in developing the milk duct and maintaining the polarity and the morphology of the mammary epithelium; at the same time, it is also closely related with the metabolism of milk protein and milk fat. This paper summarized recent researches on PER2 gene and related researches on mammary gland development and metabolism to provide some information for the studies of the theory and technology on physiological functions of the mammary gland and milk quality control.

The effects of feeding time on milk production, total-tract digestibility, and daily rhythms of feeding behavior and plasma metabolites and hormones in dairy cows

The timing of feed intake entrains circadian rhythms regulated by internal clocks in many mammals. The objective of this study was to determine if the timing of feeding entrains daily rhythms in dairy cows. Nine Holstein cows were used in a replicated 3 × 3 Latin square design with 14-d periods. An automated system recorded the timing of feed intake over the last 7 d of each period. Treatments were feeding 1×/d at 0830 h (AM) or 2030 h (PM) and feeding 2×/d in equal amounts at 0830 and 2030 h. All treatments were fed at 110% of daily intake. Cows were milked 2×/d at 0500 and 1700 h. Milk yield and composition were not changed by treatment. Daily intake did not differ, but twice-daily feeding tended to decrease total-tract digestibility of organic matter and neutral detergent fiber (NDF). A treatment by time of day interaction was observed for feeding behavior. The amount of feed consumed in the first 2h after feeding was 70% greater for PM compared with AM feeding. A low rate of intake overnight (2400 to 0500 h; 2.2 ± 0.74% daily intake/h, mean ± SD) and a moderate rate of intake in the afternoon (1200 to 1700 h; 4.8 ± 1.1% daily intake/h) was noted for all treatments, although PM slightly reduced the rate during the afternoon period compared with AM. A treatment by time of day interaction was seen for fecal NDF and indigestible NDF (iNDF) concentration, blood urea nitrogen, plasma glucose and insulin concentrations, body temperature, and lying behavior. Specifically, insulin increased and glucose decreased more after evening feeding than after morning feeding. A cosine function within a 24-h period was used to characterize daily rhythms using a random regression. Rate of feed intake during spontaneous feeding, fecal NDF and iNDF concentration, plasma glucose, insulin, NEFA, body temperature, and lying behavior fit a cosine function within a 24-h period that was modified by treatment. In conclusion, feeding time can reset the daily rhythms of feeding and lying behavior, core body temperature, fecal NDF and iNDF concentration, and plasma blood urea nitrogen, glucose, and insulin concentration of dairy cows, but has no effect on daily DMI and milk production.

Effects of different feeding time and frequency on metabolic conditions and milk production in heat-stressed dairy cows

The aim of this paper was to evaluate the effects of three different feeding management (FM) schedules on physiological markers of heat stress (HS), metabolic conditions, milk yield and quality during the hot season in dairy cows. The study involved 27 mid-lactating cows, subdivided in three homogeneous groups differing in feeding time and frequency: total mixed ration (TMR) delivered once daily in the morning (M); twice daily, half in the morning and half in the evening (ME); once daily in the evening (E). During the trial, blood samples were collected in the morning (a.m.) and in the evening (p.m.), breathing rate (BR), rectal temperature (RT), and milk yield were recorded and individual milk samples were collected. Microclimate data indicated that cows were subjected to mild-moderate HS. During the hotter days, cows receiving M treatment showed higher values of RT (38.97 °C vs 38.68 °C and 38.62 °C, in ME and E) and BR (71.44 vs 66.52 and 65.26 breaths min⁻¹, in ME and E), a.m. plasma glucose was lower in M (3.69 vs 3.83 and 3.83 mmol L⁻¹, in ME and E) and a.m. plasma urea was lower in E (4.82 vs 5.48 and 5.35 mmol L⁻¹, in M and ME). Milk yield was unaffected by FM, as well as milk composition and cheese-making properties. Only milk protein content and yield were higher in M (3.42 vs 3.36 and 3.27 g 100 mL⁻¹; and 1.11 vs 1.08 and 1.02 kg day⁻¹, for ME and E). Our results on cow physiology indicate that M seems a less suitable FM to match cow welfare during the summer season.