Changes during eating in oxygen consumption, cardiac function and body fluids of sheep

Timing of host feeding drives rhythms in parasite replication

Circadian rhythms enable organisms to synchronise the processes underpinning survival and reproduction to anticipate daily changes in the external environment. Recent work shows that daily (circadian) rhythms also enable parasites to maximise fitness in the context of ecological interactions with their hosts. Because parasite rhythms matter for their fitness, understanding how they are regulated could lead to innovative ways to reduce the severity and spread of diseases. Here, we examine how host circadian rhythms influence rhythms in the asexual replication of malaria parasites. Asexual replication is responsible for the severity of malaria and fuels transmission of the disease, yet, how parasite rhythms are driven remains a mystery. We perturbed feeding rhythms of hosts by 12 hours (i.e. diurnal feeding in nocturnal mice) to desynchronise the host's peripheral oscillators from the central, light-entrained oscillator in the brain and their rhythmic outputs. We demonstrate that the rhythms of rodent malaria parasites in day-fed hosts become inverted relative to the rhythms of parasites in night-fed hosts. Our results reveal that the host's peripheral rhythms (associated with the timing of feeding and metabolism), but not rhythms driven by the central, light-entrained circadian oscillator in the brain, determine the timing (phase) of parasite rhythms. Further investigation reveals that parasite rhythms correlate closely with blood glucose rhythms. In addition, we show that parasite rhythms resynchronise to the altered host feeding rhythms when food availability is shifted, which is not mediated through rhythms in the host immune system. Our observations suggest that parasites actively control their developmental rhythms. Finally, counter to expectation, the severity of disease symptoms expressed by hosts was not affected by desynchronisation of their central and peripheral rhythms. Our study at the intersection of disease ecology and chronobiology opens up a new arena for studying host-parasite-vector coevolution and has broad implications for applied bioscience.

Effect of lairage during 24 h of transport on the behavioural and physiological responses of sheep

The effects on the behavioural and physiological responses of sheep of providing rest, food and water (lairage) during 24 h of either road transport or stationary confinement (treatment) were investigated. Twenty-four hours of continuous treatment was compared with 12 h of treatment followed by either 12 h of lairage, 3 h of lairage or 3 h of food and water on the vehicle, followed by a second 12 h of treatment. A further group of sheep was kept as controls. The plasma cortisol concentration was increased at the start of the journey and after 24 h of continuous transport it was still greater than that in controls (P < 0·05). Apart from a mobilization of body energy reserves as indicated by raised plasma concentrations offree fatty acids after 12 h and β-hydroxybutyrate after 24 h there was no evidence that the welfare of the sheep during the journey was compromised after a particular time. During the lairage and immediately after the second 12-h transport period, the sheep appeared to be hungry. Although sheep transported for 24 h without lairage drank more post transport than controls, there was no biochemical evidence of dehydration during the journey. The sheep lay down during the journey and there was no apparent difference between lairage treatments in the proportion of scans spent lying down during either the second 12-h treatment period or during the first 12 h post treatment. There were fewer potentially traumatic events during the second 22 h of the 24-h journey than during the first 12 h of the journey and no apparent effect of lairage during the journey on the frequency of potentially traumatic events during the second 12-h period of transport.

There was evidence to suggest that a period of lairage during a 24-h journey can be beneficial in providing sheep with an opportunity to eat, drink and avoid the stressors associated with transport. However, providing hay and water on the vehicle during a 3-h stationary period as compared with unloading into a lairage cannot be recommended. Although sheep readily ate hay on the vehicle, they did not drink sufficient water. This resulted in dehydration and a greater plasma cortisol concentration during the remainder of the journey than in those that had been lairaged for 12 h and a greater water intake post transport than in those given either no lairage or 12 h of lairage.

Effect of space allowance during transport on the behavioural and physiological responses of lambs during and after transport

There is limited information on the behavioural and physiological responses of sheep to the components of road transport. Behavioural observations and physiological measurements of ‘stress’, injury and dehydration were made on weaned lambs (35 kg) before, during and after either stationary confinement or transport for 22 h at four space allowances (0·22, 0·27, 0·31 and 0·41 m2 per sheep). Two groups were not loaded (a control group with access to food and water, and a group with no food and no water for 12 h). During the confinement and transport period, the proportion of scans spent lying and the proportion of scans spent ruminating was significantly less than that before treatment (P < 0·01). After 3 h of transport, the proportion of scans spent lying was significantly less at the 0·22 m2 per sheep space allowance than at the other space allowances. The proportion of scans spent lying down was only significantly greater during confinement compared with transport at the 0·22 m2 per sheep space allowance and during the first 6 h at the 0·31 m2 per sheep space allowance. During transport, the heart rate and plasma cortisol concentration were greater than during stationary confinement (P < 0·05), indicating that some aspect of the journey was acting as a stressor. During transport the frequency of losses of balance and the frequency of slips was less at the 0·22 m2 per sheep space allowance than at the 0·27 and 0·41 m2 per sheep space allowances. However, there was no effect of space allowance on either plasma cortisol concentration or biochemical measures of injury. The median frequency of potentially traumatic events during transport was <5 per h and there was little evidence to suggest that increasing space allowance increased the risk of traumatic injury. During the first 12 h after treatment, the proportion of scans spent eating was greater and the proportion of scans spent lying were less than those spent before treatment (P < 0·001). Post-treatment, water intake and packed cell volume were greater in transported sheep than in control sheep (P < 0·05). However, there was no significant effect of 12 h without water on total plasma protein concentration and plasma vasopressin concentration (P > 0·05). Under the conditions of this study, sheep with a live weight of 35 kg can be transported for 12 h at space allowances of between 0·22 and 0·41 m2 per sheep without showing major physiological changes indicative of injury and dehydration. However, the sheep appeared to be hungry after 12 h without food and showed a cortisol and heart rate response to transport, indicating that some aspect of transport was acting as a stressor. A space allowance of 0·22 m2 per sheep cannot be recommended for 35 kg sheep as there is insufficient space for most of the sheep to lie down during transport. Whereas a space allowance of at least 0·27 m2 per sheep does allow most sheep sufficient space to lie down.

Specific dynamic action: a review of the postprandial metabolic response

For more than 200 years, the metabolic response that accompanies meal digestion has been characterized, theorized, and experimentally studied. Historically labeled "specific dynamic action" or "SDA", this physiological phenomenon represents the energy expended on all activities of the body incidental to the ingestion, digestion, absorption, and assimilation of a meal. Specific dynamic action or a component of postprandial metabolism has been quantified for more than 250 invertebrate and vertebrate species. Characteristic among all of these species is a rapid postprandial increase in metabolic rate that upon peaking returns more slowly to prefeeding levels. The average maximum increase in metabolic rate stemming from digestion ranges from a modest 25% for humans to 136% for fishes, and to an impressive 687% for snakes. The type, size, composition, and temperature of the meal, as well as body size, body composition, and several environmental factors (e.g., ambient temperature and gas concentration) can each significantly impact the magnitude and duration of the SDA response. Meals that are large, intact or possess a tough exoskeleton require more digestive effort and thus generate a larger SDA than small, fragmented, or soft-bodied meals. Differences in the individual effort of preabsorptive (e.g., swallowing, gastric breakdown, and intestinal transport) and postabsorptive (e.g., catabolism and synthesis) events underlie much of the variation in SDA. Specific dynamic action is an integral part of an organism's energy budget, exemplified by accounting for 19-43% of the daily energy expenditure of free-ranging snakes. There are innumerable opportunities for research in SDA including coverage of unexplored taxa, investigating the underlying sources, determinants, and the central control of postprandial metabolism, and examining the integration of SDA across other physiological systems.

Temporal responses in energy expenditure and respiratory quotient following feeding in the muskox: influence of season on energy costs of eating and standing and an endogenous heat increment

Seasonal energy metabolism was investigated in young (2- to 3-year-old) muskoxen (Ovibos moschatus) during the winters of 1994 (January–April) and 1996 (January) and summer of 1995 (July and August). Energy expenditure (EE) increased 35%–42% following a meal of chopped brome hay (Bromus inermis) and declined as a double-exponential process over 8 h. The mean energy cost of eating (321 and 361 J·g dry matter–1) was lower in winter than in summer, and declined with body mass (BM) (r2 = 0.58). The mean energy cost of standing was 21% (SE = 2.7%) higher than that of bedding. Prefeeding energy expenditure (EEp) was 26% higher in summer than in winter. An endo genous heat increment, measured as EEp – EE, at 7-8 h post feeding was lower (P < 0.001) in winter than in summer (39 and 58 kJ·kg BM–0.75·d–1, respectively). Mean cumulative EE (minus activity costs) for 8 h post feeding was 124 (SE = 4) and 148 (SE = 4) kJ·kg BM–0.75 (P < 0.001) in winter and summer, respectively. Respiratory quotients (RQs) >1 were recorded during feeding in winter and a mean RQ of 0.9 was recorded in summer. Seasonal EEp, postfeeding EE, and RQ are consistent with a low cost of maintenance metabolism in winter and an increased requirement for productivity in summer.

Changes in blood levels of zinc, copper, selenium, glutathione peroxidase, vitamin B12 and total and free thyroxine in sheep removed from pasture and held without food for 50 hours

Blood was collected from a group of ten sheep immediately after removal from pasture and thereafter at regular intervals for 50 hours whilst maintaining them without food but with adequate water. The samples were analysed for parameters normally examined as an aid to the diagnosis of zinc, copper, selenium, cobalt and iodine status. Serum vitamin B12 levels increased with time. Mean plasma zinc concentrations and mean serum concentrations of both T4 and fT4 followed significant parabolic trends. Maximum mean zinc levels (50 +/- 10% higher than initial values) were recorded after 30 hours. T4 and fT4 levels peaked at approximately 26 hours. Zinc levels at two hours were 20 +/- 5% lower than the initial values. Whole blood copper, selenium and glutathione peroxidase levels did not change significantly with time the largest differences were 11 +/- 6%, 5 +/- 4% and 10 +/- 8% respectively.

Effects of hay-feeding on acid/base balance, renal sodium excretion, aldosterone and vasopressin secretion in the goat

Effects of 30 min intense hay-feeding on acid/base and sodium homeostasis were studied in semi-starved goats during hyper- and euhydration. Parallel analyses of carotid and jugular blood samples revealed that feeding induced metabolic acidosis, which to some extent was subjected to respiratory compensation. The acidosis was accompanied by renal sodium retention and urinary acidification persisting for 2-3 h. The sodium retention was succeeded by an increase in renal Na excretion above the initial level. This natriuresis was most accentuated during hyperhydration. Blood samples taken for hormone assays during euhydration revealed a 15% increase in haematocrit and a significant rise in plasma aldosterone at termination of feeding. Inhibition of the water diuresis in hyperhydrated animals, and moderate increases in renal arginine vasopressin (AVP) excretion and plasma AVP were inconsistent effects of feeding. It is concluded, that simply jugular vein blood provides reliable information on the acid/base status of goats, but that the feeding schedule has to be considered in all experiments where small ruminants are used to investigate the integrated control of acid/base and sodium homeostasis.

Dynamic changes in acid base balance during heatstroke in dogs

The dynamic changes in acid base balance and respiratory metabolism during the development of heatstroke in dogs were studied. Three groups of five unanesthetized dogs each were exposed to different climatic conditions while at rest: A) 24 degrees C, 50% relative humidity (RH); B) 35 degrees C, 35% RH, and C) 45 degrees C , 25% RH. These conditions were maintained for 4 h or until the dogs collapsed. The heatstroke dogs were cooled in tap water bathes and were observed for another 4 h. Dogs of groups A and B did not show any notable changes in rectal temperature (Tre) and acid base balance. All dogs in group C developed heatstroke. Their peak mean Tre (44.1 degrees C) was reached after a mean of 111 min of exposure, with respiratory alkalosis followed by increasingly severe metabolic acidosis above Tre of 42 degrees C. At peak Tre mean arterial pH was 7.26. Acidosis increased (pHa = 7.17) following cooling, as panting subsided. At Tre above 42 degrees C blood lactate increased and bicarbonate decreased significantly, attaining mean values of 58 mg% and 8 mEq/l, respectively. Bicarbonate changes correlated linearly with lactate changes. During recovery lactate decreased and blood pH increased approximating normal by the end of the experiment. The results illustrate the body's ability to spontaneously correct arterial pH without therapeutic means.

Cardiovascular and endocrine responses to feeding in the young calf

A number of cardiovascular and endocrine responses which occur during and after feeding in the unweaned calf are described. 2. There was a substantial increase in both heart rate and mean aortic blood pressure during feeding in these animals. This occurred within the first few seconds and persisted throughout the period of ingestion. 3. The concentrations of glucose, insulin and gastrin in arterial plasma rose abruptly during, or immediately after, feeding and elevated values persisted for at least 2 hr. A transient increase in glucagon concentration was also observed. In contrast, feeding appeared to produce no immediate rise in enteroglucagon concentration. 4. The adrenal output of glucocorticoids rose transiently in response to feeding but that of catecholamines was unaffected. 5. Cardiovascular responses to feeding were also examined in other species. In unweaned kids the changes were essentially similar to those observed in the calf but were less pronounced. In lambs a persistent hypertension occurred which was associated with a brief initial tachycardia. In adult dogs ingestion of solid food also caused tachycardia but although the aortic blood pressure rose for a short period at the beginning of feeding, hypotension developed thereafter. 6. The possibility that both the cardiovascular and endocrine responses, which occur during or immediately after feeding, are mediated by the autonomic nervous system is discussed.

Plasma catecholamines in foetal and adult sheep

1. Foetal and maternal plasma catecholamine concentrations were measured during and after hypoxia (mean maternal Pa,02 44mmHg) in chronically catheterized sheep, 118-141 days pregnant. 2. In most foetuses the initial plasma catecholamines were smaller than 0.07 ng/ml. During hypoxia plasma adrenaline and noradrenaline always rose; there was a rise in arterial pressure and a fall in heart rate. 3. The initial catecholamine concentration in the ewes was smaller than 0.05-2.3 ng/ml. During hypoxia there was no consistent change; the maternal plasma concentrations were less than the foetal. 4. Infusion of adrenaline at 0.3 mug kg(-1) min(-1) to the ewe resulted in plasma catecholamine concentrations higher than those observed during hypoxia. There was a rise in heart rate but no consistent change in arterial pressure. 5. Infusion of adrenaline 0.4 mug kg(-1) min(-1) into the foetal jugular vein caused a rise in plasma concentration similar to that seen during hypoxia. There was a rise in heart rate but no significant change in arterial pressure. 6. The half-life of adrenaline and of noradrenaline in the maternal and foetal circulation was 0.25-1 min. There was no evidence of transfer of labelled catecholamine across the placenta.

Renin and angiotensin-like levels in foetal, new-born and adult sheep

1. Plasma renin (measured as rate of formation of angiotensin I ng/ml.hr(-1) in the presence of added substrate at pH 7.5 and 37 degrees C) was much lower in recently nephrectomized foetal, new-born and older lambs than in intact siblings or other similar lambs.2. Angiotensin II-like concentrations were measured using a superfusion technique in an extracorporeal circuit. Resting concentrations in acute experiments under anaesthesia were deduced by comparison of carotid blood of intact lambs with that from recently nephrectomized lambs.3. Angiotensin II-like activity (mean +/- S.E. of mean, 315 +/- 117 pg/ml.) was readily detectable in foetal blood at 123-138 days gestation. The highest concentrations (mean +/- S.E. of mean 839 +/- 96 pg/ml.) were found in lambs less than 8 hr old, delivered vaginally. The lowest concentrations of angiotensin II-like activity occurred in lambs delivered by Caesarean section (mean +/- S.E. of mean < 123 +/- 12 pg/ml.). Concentrations declined with post-natal age.4. Hypovolaemia as a result of haemorrhage evoked an increase in angiotensin II-like concentrations in foetus, new-born lambs and adult sheep. The greatest increase of angiotensin-like concentrations was seen in new-born lambs. This rise was associated with increase of plasma renin.5. The rise of arterial pressure during bilateral carotid occlusion in new-born lambs was accompanied by an increase of angiotensin II-like concentration.6. It is concluded that the renin-angiotensin system is functional and can be stimulated during intra-uterine life. The increase of angiotensin II-like concentration following parturition is probably transient and associated with the trauma of delivery. This contrasts with observations made in the rabbit which suggest that full functional maturity of the renin angiotensin system is delayed until the second week of life.

The formation of synapses in reinnervated and cross-reinnervated striated muscle during development

1. A study has been made of the formation of synapses in reinnervated and cross-reinnervated developing striated muscles which normally receive either a focal or distributed innervation, using histological, ultrastructural and electrophysiological techniques.2. The focally innervated mammalian tibialis anterior muscle, denervated soon after birth, was reinnervated at both the original end-plates as well as on the new muscle added during the period of denervation; but not on the muscle present at the time of denervation. Nearly all the synapses which had formed, other than at the original end-plates, disappeared by 6 weeks post-natal.3. The avian anterior latissimus dorsi muscle (ALD), which receives a distributed innervation, was denervated during the first week post-hatched, and became reinnervated both at the original synaptic sites as well as on the new muscle added during the period of denervation; all these synapses were spaced approximately 200 mum apart along the length of individual muscle cells.4. The myofibres of the ALD muscle cross-reinnervated at hatching with the superior brachialis nerve, which contains fast motor axons that normally form a focal innervation, were each focally innervated by a single ;en plaque' terminal; these synapses had the same electrical properties as normal synapses formed by fast motor axons.5. Many of the myofibres of the avian posterior latissimus dorsi (PLD), which normally receive a focal innervation, received a distributed innervation from ;en grappe' terminals when cross-reinnervated with the ALD nerve at hatching.6. It is suggested that during development the nerve type determines the pattern of synapses over an effector; this is achieved by the nerve, after forming the initial synaptic contact, making the rest of the muscle cell membrane refractory to further synapse formation for some distance, this distance being determined by the nerve type.

The composition of maternal plasma and foetal urine after feeding and drinking in chronically catheterized ewes during the last two months of pregnancy

1. The fluid sacs and bladders of sixteen foetuses in fourteen ewes were catheterized between 81 and 92 days gestational age and the rumens of four ewes were also catheterized.2. Between 95 and 145 days gestational age in forty-six 24 hr experiments hourly samples of maternal plasma and foetal urine were obtained and in fifteen experiments foetal fluid samples were also taken at 4- to 6-hr intervals.3. The osmolality, pH, and concentrations of sodium, potassium, chloride, glucose, fructose and urea were measured on all samples.4. During experiment there was no significant variation in the composition of amniotic or allantoic fluid. Marked changes in osmolality occurred in maternal plasma and foetal urine when ewes drank after feeding, but not in ewes that received water intrarumenally via catheter while feeding or in fasting ewes. Post-prandial changes in maternal plasma osmolality may have altered transplacental water fluxes and as a result foetal plasma volume and osmolality.5. The results suggest that the foetus alters renal water retention by varying antidiuretic hormone (ADH) secretion in response to changes in blood volume and at later gestational ages plasma osmolality as well.6. Post-prandial changes in the [Na(+)]/[K(+)] ratio of foetal urine suggested that foetal adrenocorticotrophin (ACTH) secretion is influenced by variations in foetal blood volume and glucose concentrations.7. The post-prandial changes in foetal urine composition observed here support previous suggestions (Mellor & Slater, 1972) about the role of foetal urine in foetal fluid formation which were based on gestational changes in the composition of foetal fluids and urine sampled once daily during the post-absorptive state.

Portal blood flow and heat production in the digestive tract of sheep

1. A method is described for measurement of portal blood flow in the sheep by the principle of continuous thermal dilution produced by injection of cool saline into the portal circulation at 1 mg/s for 30 s.

2. In most animals phlebitis developed only around the catheter in the right ruminal vein. This affected their appetite and condition after surgery. When all catheters were introduced into the anterior mesenteric veins there was no phlebitis and appetite postoperatively was normal.

3. Portal blood flow in six out of nine sheep was 33–34 mg/kg body-weight per min in the morning before feeding. After a meal of dried grass it increased during the period about 2–6 h later.

4. Total heat production and oxygen consumption of the digestive tract were estimated from portal blood flow and arteriovenous differences in temperature and oxygen concentration. When the heat production of the digestive tract was increased by 1·77 kJ/min by the inclusion of a heating element in the rumen, estimated total heat production increased, on average, by 1·73 kJ/min.

5. During the period 2–6 h after a meal of dried grass, portal venous temperature rose, on average, by 0·7°, visceral O2 consumption did not alter significantly, but total heat production rose by 1·19 kJ/min.

6. These initial results suggest that the heat of fermentation can be determined in vivo. In these experiments it was about 10 kJ per 100 kJ digestible energy consumed.