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Biomedical subjects

D J Mellor

Publications and source records attributed to D J Mellor.

At least 19 recordsLinked to original sources
PubMed1992

Onset of insensibility at slaughter in calves: effects of electroplectic seizure and exsanguination on spontaneous electrocortical activity and indices of cerebral metabolism.

Cerebral venous and femoral arterial blood samples were collected from 21 young calves either during electrical stunning and recovery or electrical stunning and slaughter by carotid severance or slaughter without stunning. The blood samples were analysed for PO2, PCO2, pH, glucose and lactate. The results were compared with simultaneous recordings of spontaneous electrocortical (ECOG) activity. Calves subjected to head-only electrical stunning and slaughter became permanently insensible at the time of the stun. The six calves slaughtered without stunning lost sensibility within 10 seconds. One calf, in which a clot formed in the carotid arteries inhibiting bleeding, maintained some evidence of cortical activity beyond 52 seconds; this was high amplitude low frequency activity and analysis by Fast Fourier Transform showed sensibility was not regained. In the remaining calves the ECOG activity was lost on average within 49 +/- 3.5 (SEM) seconds after slaughter. The cerebral extraction of metabolites increased after carotid severance, indicating inadequacy of cerebral bloodflow after slaughter. No correlations were found between indices of cerebral metabolism and the time of loss of cortical function.

Abattoirs↗
PubMed1992

Growth and morphological changes in the small and the large intestine in piglets during the first three days after birth.

Growth and morphological changes in the small and the large intestine of piglets were examined during the first three days after birth. There was a 72% increase in small intestinal weight, virtually all of which occurred during the first day and was due primarily to a 115% increase in the weight of the mucosa. Associated with the tissue weight gain there was a 24% increase in small intestinal length, a 15% increase in small intestinal diameter, a 33-90% increase in villus height and a 14-51% increase in villus diameter, during the first day. The cellular population in the small intestinal mucosa, as indicated by its DNA content, increased progressively with age, and at three days had increased by 84-154%. The percentage increase in mucosal DNA content was highest in the duodenum, intermediate in the jejunum and lowest in the ileum. Histological features and tissue protein contents revealed a transient epithelial cellular swelling related to intracellular accumulation of protein on the first day. Protein accumulation was evident in the jejunum and ileum but not in the duodenum. The positions of the nuclei in the epithelial cells suggested that on the first day protein absorption was at a more advanced stage in the jejunum and the proximal ileum than in the distal ileum. Large intestinal weight increased by 33% during the first day and had doubled by the third day, and this weight gain was due to both mucosal and non-mucosal tissue growth. Villus-like structures were observed in the caecum and the proximal colon in piglets at birth and one day after birth but not in piglets three days after birth. It is speculated that such villus-like structures may have a functional significance during the transition to complete dependence on oral nutrition in newborns.

Aging↗
PubMed1992

Growth and morphological changes in the stomach of newborn pigs during the first three days after birth.

Growth and morphological changes in the stomach of newborn pigs were examined during the first 3 days after birth. The stomach grew disproportionately faster than the body as a whole during this period. The growth was due to hyperplasia and hypertrophy during the first day and mainly to hyperplasia thereafter as gastric DNA content increased progressively after birth, and the protein:DNA and RNA:DNA ratios increased only on the first day. Histological and morphometric analyses revealed that the growth was more pronounced in the gastric body region than in the cardiac and pyloric regions, and more pronounced in the mucosal layer than in other layers. The percentage of mucosal volume occupied by parietal cells (volume density) and the number of parietal cells per unit volume of gastric mucosa (numerical density) increased significantly 3 days after birth in the cardiac and body regions, but not in the pyloric region, of the stomach. The observed morphological changes coincide with the known pattern of functional maturation during the immediate postnatal period. It is suggested that a high level of circulating gastrin and oral ingestion of milk-derived growth factors in the newborn pig contribute to these changes.

Animals↗
PubMed1991

Effects of castration on behaviour and plasma cortisol concentrations in young lambs, kids and calves.

Behavioural and cortisol responses to the husbandry practice of castration with tight rubber rings were investigated in lambs and kids one day after birth and in hand reared calves aged one to seven days. There were three treatments: control handling and blood sampling, castration and, in lambs and kids only, intravenous adrenocorticotrophin injection (ACTH). The integrated cortisol responses (area under the cortisol curve) in lambs and kids were least in control, intermediate in castrated and greatest in ACTH animals. No cortisol responses were detected in control or castrated calves. The incidences of behaviour used to assess the intensity of distress apparently experienced in the different species corresponded generally with the magnitudes of the cortisol responses. Behavioural and cortisol responses together suggested that the distress caused by castration was greatest in lambs, intermediate in kids and least but not necessarily absent in hand reared calves.

Adrenocorticotropic Hormone↗
PubMed1991

Effects of local anesthesia and intravenous naloxone on the changes in behaviour and plasma concentrations of cortisol produced by castration and tail docking with tight rubber rings in young lambs.

The reliability of some behavioral and physiological indices used for the recognition and assessment of acute pain in lambs after castration and tail docking has been examined. Changes in the indices were measured after blocking neural activity with local anaesthetic (lignocaine) and after an opioid antagonist (naloxone) was administered. Six lambs, aged less than one week, were allocated randomly to each of six treatments. (i) control handling and blood sampling; (ii) castration plus tail docking with tight rubber rings; (iii) local anaesthesia; (iv) local anaesthesia followed by castration and tail docking; (v) intravenous naloxone only (0.2 mg kg-1); and (vi) intravenous naloxone followed by castration and tail docking. Local anaesthesia eliminated the behavioural and plasma cortisol changes which usually follow castration and tail docking. Naloxone had a limited effect on the increase in cortisol but altered the behaviour. The results support the view that such indices are useful for assessment of the response to acute pain and that, although endogenous opioids do reduce pain in young lambs after castration and tail docking, the effect is small.

Anesthesia, Local↗
PubMed1991

Kinetics of lactate and glucose metabolism in the pregnant ewe and conceptus.

Two monotocous and two ditocous ewes were infused at 124-130 days of gestation with a mixture of L-[U-14C]lactate and D-[6-3H]glucose via a maternal or umbilical catheter, separate days being used for each infusion. Plateaux-specific radioactivities of plasma lactate and glucose were used to derive a four-pool model describing the fluxes between the lactate and glucose pools of the infused conceptus and mother. The average turnover rate of lactate was 23.3 and 13.2 mg carbon min-1 in the conceptus and 32.0 and 44.0 mg carbon min-1 in the mother for monotocous and ditocous ewes, respectively. Glycolysis rates within both conceptus and mother in all sheep were high, accounting for about 80 and 60% of the respective rates of lactate turnover. The synthesis of glucose from lactate accounted for 13 and 31% of the glucose turnover in the mother in monotocous and ditocous ewes, respectively, but was insignificant in the conceptus. Glycolysis within the conceptus used only glucose which had entered and mixed with the conceptus glucose pool; there was no direct transfer of carbon from the maternal glucose pool to the conceptus lactate pool. This finding is an important validation for the use of tracer methods to determine glucose use within the whole conceptus rather than within fetal corporeal tissues alone.

Animals↗
PubMed1990

Teladorsagia circumcincta egg output at the onset of natural and induced lactation in ewes.

Nineteen ewes maintained under 'worm-free' conditions received anthelmintic and 1 week later were dosed on 5 days each week with 500 Teladorsagia circumcincta larvae for between 10 and 12.5 weeks. Faecal egg counts were determined twice weekly. There were three groups: pregnant (P) ewes (n = 6) which each reared twin lambs, hormone-treated (H) ewes (n = 7) which were not pregnant and were given exogenous hormones (dexamethasone, oestradiol-17 beta, progesterone) for 37 days to induce udder development and milk production, and untreated barren (B) ewes (n = 6). The plasma concentrations of oestradiol-17 beta, prolactin and progesterone were measured. Starting 10-15 days before birth in Group P, there was a biphasic periparturient rise in egg count and the onset of the first peak in egg count preceded the parturient peak in plasma prolactin concentration by several days. Most Group H (5/7) and all Group B ewes remained highly resistant to Teladorsagia infection throughout, despite an induced rise in prolactin concentrations in Group H ewes. It was concluded that factors other than prolactin initiate the periparturient rise but that prolactin is one factor which maintains the response once lactation commences.

Animals↗
PubMed1989

Effects of tail docking and castration on behaviour and plasma cortisol concentrations in young lambs.

Behavioural and cortisol responses of lambs to the usual husbandry practices of castration and, or, tail docking using tight rubber rings were investigated between birth and seven days old. There were four treatments: control handling and blood sampling (n = 52), tail-docking (T) (n = 57), castration plus tail-docking (CT) (n = 54) and intravenous adrenocorticotrophin injection (ACTH) (n = 52). After treatment there was a transient rise in plasma cortisol concentration, the magnitude and duration of which increased in the following order; control, T, CT and ACTH. Behavioural characteristics indicative of distress included restlessness (standing up and lying down frequently, rolling, kicking, stamping), lateral recumbency, immobility with neck extension and hyperventilation. Using changes in cortisol concentrations and behaviour the lamb responses were characterised as reflecting 'mild disturbance without distress' (control, ACTH), 'mild distress' (T) and 'marked distress' (CT). The mild distress lasted for about 30 minutes in T lambs and marked distress for about 60 minutes in CT lambs.

Adrenocorticotropic Hormone↗
PubMed1989

Changes in the cortisol responses of lambs to tail docking, castration and ACTH injection during the first seven days after birth.

Cortisol responses of Dorset and Scottish Blackface lambs were investigated at six ages between birth and seven days. There were four treatments: control handling and blood sampling (n = 52), tail docking (T) (n = 57), castration plus tail docking (CT) (n = 54), and intravenous adrenocorticotrophin (ACTH) injection (n = 60). Most lambs exhibited transient rises in plasma cortisol concentrations after treatment and the results in individuals were expressed as the area under the cortisol curve (integrated response). Postnatal changes in the integrated responses of control, T and CT lambs differed significantly between the two breeds; in Dorsets they increased markedly between four hours and one day and then decreased, whereas in Scottish Blackface lambs there were no significant changes. The cortisol responses of ACTH lambs decreased markedly between four hours and seven days in both breeds. The results shed light on postnatal changes in the activity of the hypothalamic-pituitary-adrenal axis and suggest for both breeds that the average increments in ACTH secretion caused by noxious stimuli increased markedly during the first one to three days after birth. Whether this reflected parallel increases in the levels of distress experienced by the lambs remains to be clarified.

Adrenocorticotropic Hormone↗
PubMed1987

Clinical, biochemical and pathological study of perinatal lambs in a commercial flock.

The birth and fate of 818 lambs born to 571 ewes on a low-ground farm in the Scottish Borders with a history of substantial perinatal mortality were monitored with a range of physiological, biochemical and pathological measurements. In lambs which survived, the rectal temperature, birthweight and plasma concentrations of fructose, insulin, thyroxine and the third component of complement at birth, and the weight at four months of age, decreased with litter size. One hundred and thirty-seven lambs were stillborn or died within four days and seven others died later. The mothers of 77 per cent of these lambs had low condition scores, but the lamb deaths did not correlate significantly with the condition scores. From data relating to birthweight, temperature, packed cell volume and plasma composition it was deduced that placental insufficiency was involved in 24 per cent of these deaths; acute hypoxaemia at birth accounted for 35 per cent, inadequate thermogenesis for 12 per cent and starvation for 13 per cent. The remaining 16 per cent of dead lambs could not be assigned to any of these categories. Using only clinicopathological criteria, 37 per cent of the lamb deaths were attributed to antenatal influences which included immaturity, developmental anomalies, and degenerative or inflammatory changes. Thirty-three per cent of the deaths were due to post natal factors which included, in declining order of frequency, starvation, enteritis, misadventure, pneumonia, navel infections and septicaemia. No conclusions could be drawn from the pathological examinations alone in the remaining 30 per cent, although almost half of these had low rectal temperatures after birth, death being attributed to hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Relationships between plasma hormone concentrations, udder development and the production of early mammary secretions in twin-bearing ewes on different planes of nutrition.

Ewes carrying twin fetuses were maintained during late pregnancy on a uniformly high plane (well fed), a uniformly low plane (underfed) or a low plane rising to a high plane (refed) of nutrition. The maternal plasma concentrations of hormones concerned with udder development, colostrum production and milk secretion were measured in samples obtained during the last 32 d before and the first 18 h after birth. Udder weights were derived from their linear dimensions, the yields of mammary secretions by hand milking during the first 18 h after birth and the transition from colostrum to milk was indicated by changes in the concentrations of lactose, lipid and immunoglobulin G. Underfeeding reduced prenatal udder development and colostrum accumulation and delayed the post-natal transition to milk secretion. Refeeding previously underfed ewes to a high plane during the last 5 d before birth had no effect on udder growth, but it did return the secretory functions of udder tissue to the levels observed in well-fed ewes. Nutritional effects on the plasma concentrations of insulin, placental lactogen, prolactin, cortisol and oestradiol-17 beta were small or absent. The relative changes in the plasma concentrations of growth hormone and insulin were such that the growth hormone: insulin ratio increased markedly during the last 11 d before birth in the underfed and refed ewes but not in the well-fed ewes. These differences in the growth hormone: insulin ratio were associated with greater increases in udder growth rate in the underfed and refed ewes than in the well-fed ewes. The plasma concentrations of progesterone decreased before birth in all ewes, but the decrease was delayed by underfeeding and refeeding rapidly overcame this effect. The slower progesterone withdrawal in the underfed ewes was associated with a delay in lactogenesis. It is concluded that the nutritionally induced changes in the growth hormone: insulin ratio and in the progesterone concentrations were the most likely endocrine determinants of the observed differences in the rates of mammogenesis and lactogenesis, respectively, but possible independent effects of substrate supply to the udder remain to be clarified.

Animals↗
PubMed1986

Making the most of colostrum at lambing.

Lambs require between 180 and 210 ml colostrum/kg bodyweight during the first 18 hours after birth in order to provide sufficient fuel for heat production. Colostrum intakes of this order would usually provide enough immunoglobulins for protection against infections. Ewes which are well fed during late pregnancy produce more colostrum than their lambs need, those with singletons having enough for a second lamb, but in most underfed ewes the lamb's requirements for colostrum exceed the ewe's production. Colostrum can be readily obtained and stored for subsequent use. The yields are increased markedly when hand milking is preceded by an oxytocin injection, the intravenous dose being 5 iu and the suggested intramuscular dose being 10 to 15 iu. There is little practical benefit in milking ewes more than three times during the first 18 hours after birth.

Animals↗
PubMed1986

A comparison of energy metabolism in the new-born infant, piglet and lamb.

Characteristics of energy metabolism in the new-born infant, piglet and lamb have been compared quantitatively in order to assess how the constraints imposed by the availabilities of energy substrates in body reserves and colostrum differ between species and affect the new-born's well being during the first day after birth. Three air temperature ranges, described as thermoneutral (32-38 degrees C), moderate (18-26 degrees C) and cold (0-10 degrees C) and representing the usual birth environments of infants, piglets and lambs, respectively, have been considered. The analysis revealed the following noteworthy points. Carbohydrate and lipid are the major energy substrates for heat production because protein catabolism is minimal during the first day after birth in all three species. The availability of carbohydrate determines how long the new-born can avoid hypoglycaemia, which threatens well being because it leads to hypothermia or compromised cerebral function, but lipid availability can affect the periods for which the carbohydrate can last. Thus, in unfed piglets and lambs the available reserves of liver and skeletal muscle glycogen (g/kg body weight) are similar in normal (n.) and growth retarded (g.r.) individuals, but glycogen exhaustion occurs earlier in g.r. new-borns because a reduced lipid availability in them increases their dependence on carbohydrate. In contrast, lipid energy is plentiful in g.r., preterm (p.) and n. infants, so that the faster depletion of glycogen in g.r./p. than in n. individuals is primarily due to a restricted prenatal glycogen deposition in the former. The usual colostrum intakes of n. infants are very low during the first day, but their body reserves can supply the required energy, the major source of carbohydrate being liver glycogen. However, g.r./p. infants require supplementary feeding, the choice of feed being determined by factors such as the intakes the infants can achieve, the carbohydrate content of the feed and the need to ensure a balanced supply of minerals, electrolytes and other substances. In their usual birth environments piglets and lambs, whether growth retarded or not, require colostrum to avoid hypothermia during the first day. The colostrum of both species is rich in lipid, which corrects any deficit in the new-born and thus extends the availability of glycogen, but at the usual colostrum intakes the amounts of lactose can provide sufficient carbohydrate energy for only about half a day. Piglets and lambs, even when fed fully, are therefore obliged to call on their body glycogen reserves in order to make up the difference.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Effects of maternal nutrition on udder development during late pregnancy and on colostrum production in Scottish Blackface ewes with twin lambs.

Effects on udder development and colostrum production of changing the level of ewe nutrition were investigated. Udder weights at term were derived from their linear dimensions and yields of colostrum were obtained by hand milking on three occasions between one and 18 hours after birth. The linear dimensions of the udder increased progressively in all animals between 100 days of gestation and term (about 145 days), but udder development was retarded significantly within three days of the onset of underfeeding at 105 days of gestation. Underfeeding reduced the total yield of colostrum during the first 18 hours after birth by decreasing the prenatal accumulation of colostrum and its subsequent rates of secretion. Improving the ewe's nutrition from one hour after birth tended to increase the secretion rates of colostrum between 10 and 18 hours. Refeeding previously underfed ewes to high levels from about five days before birth had no effect on udder growth but did increase the prenatal accumulation of colostrum and its subsequent rates of secretion to levels which, when corrected for differences in udder weight, were similar to those of ewes which were fed well throughout. Calculations revealed that by ignoring udder growth the Agricultural Research Council recommendations for the energy requirements of pregnant ewes underestimate the cost of tissue synthesis during the last four weeks of pregnancy by about 100 per cent.

Animal Nutritional Physiological Phenomena↗
PubMed1985

Effects of maternal nutrition on the availability of energy in the body reserves of fetuses at term and in colostrum from Scottish Blackface ewes with twin lambs.

Ewes carrying twin fetuses were maintained during late pregnancy on a uniformly high plane (n = 22), a uniformly low plane (LP) (n = 24) or a low plane increasing to a high plane (n = 14) of nutrition. Seven ewes at each nutritional level were killed at 142 days of gestation and the liver and muscle glycogen and body lipid concentrations of the fetuses were determined. The rest of the ewes lambed naturally at about 145 days and the colostrum yields were obtained by hand milking after oxytocin injections during the first 18 hours after birth. The lactose, lipid and protein concentrations of colostrum were determined. Undernutrition in the LP group did not apparently affect the body concentrations of available glycogen, reduced available body lipid by about 47 per cent and reduced the lactose, lipid and protein available in colostrum during the first 18 hours by about 50 per cent. Refeeding previously underfed ewes to a high plane during the last five to 10 days of pregnancy did not improve the available reserves of glycogen or lipid in the lambs but did increase the yields of colostral constituents by about 30 per cent. The relative contributions of body reserves and colostral constituents to the maintenance of high, medium and low metabolic rates in lambs from different groups was assessed. It was concluded that under normal field conditions refeeding undernourished ewes during the last weeks of pregnancy would improve only marginally the survival potential of the lambs and that most lambs would be compelled to draw on their body glycogen reserves in order to maintain heat production during the first 18 hours after birth, even when they consumed all the available colostrum.

Animal Nutritional Physiological Phenomena↗