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J C MacRae

Publications and source records attributed to J C MacRae.

At least 37 records · Page 2Linked to original sources
PubMed1993

Characterization of sheep hepatocytes in primary culture.

1. Primary cultures of isolated sheep hepatocytes were used to characterize metabolic functions of liver: gluconeogenesis, ureagenesis and protein synthesis. The rates of all three metabolic activities were linear over a 20 hr culture period. 2. Hepatocytes in the presence of glucagon increased the synthesis of urea by approx 30% (P < 0.05) and increased release of glucose into the medium by 60% (P < 0.05). 3. In the absence of insulin, significantly more (35%; P < 0.05) glucose was released in the medium than in the presence of insulin. 4. Results help evaluate the primary culture of sheep hepatocytes as an appropriate experimental model to study nutritional and hormonal regulation of liver in the ruminant species.

Animals↗
PubMed1993

Fate of the antinutritive proteins of soyabean in the ovine gut.

Defatted raw soyabean flour was administered intraruminally at a level of 10 g/kg body weight to a sheep fitted with ruminal, duodenal, and ileal cannulas. Soyabean lectin and trypsin inhibitor appeared in the duodenum within one hour, both reached the terminal ileum and disappeared within 24 hours. The passage of the lectin along the gut progressively lagged behind that of the inhibitor, which indicates that the lectin binds to the intestinal surface. The effect of the inhibitors was neutralized by a marked pancreatic hypersecretion. Contrary to earlier assumptions, the antinutritional proteins were not effectively degraded in the forestomachs.

Animal Feed↗
PubMed1993

Effects of growth hormone and an antiserum to rat growth hormone on serum IGF-I and muscle protein synthesis and accretion in the rat.

Rats were injected twice daily for up to 10 days with GH or with a polyclonal antiserum to rat GH, commencing at 21-22 days of age. Administration of bovine or human GH (1mg/day) improved whole body growth rates by 22% and 29% respectively. Plantaris muscle mass was also increased, by 7 and 14% respectively. Anti-GH injected twice daily resulted in a 7% decrease in body weight at 4 days and a 10% reduction by 10 days. Similar decreases were observed in the total protein content of plantaris and soleus muscles. The decrease in the fractional rate of protein synthesis was proportionately greater than the decline in protein content in plantaris muscle whereas in the soleus no change in the rate of protein synthesis was observed, suggesting that the effect on this muscle was due to an increase in the rate of protein degradation. Serum total IGF-I was unchanged by treatment with either GH or anti-GH while the amount of hepatic IGF-I mRNA was also unaffected by anti-GH injection. These data are consistent with a direct effect of GH or an effect mediated by an autocrine/paracrine mechanism of action on muscle but do not support a role for serum total IGF-I as an endocrine mediator of GH action.

Animals↗
PubMed1991

The measurement of insulin-like growth factor 1 in sheep plasma.

A method is described for the radioimmunoassay (RIA) of insulin-like growth factor 1 (IGF-1) in neutralised formic acid-ethanol extracts of sheep plasma. The ability of the acid-ethanol pretreatment to remove the IGF-1 binding proteins (BPs), which interfere in the assay has been examined. Comparative plasma IGF-1 concentrations determined by the method correlated closely (P less than 0.001) with corresponding values where BPs were removed by acid gel filtration. The method has been applied to studies in which sheep were given exogenous growth hormone and indicated that plasma IGF-1 levels respond rapidly to the onset and termination of treatment.

Animals↗
PubMed1991

Influence of protein nutrition on the response of growing lambs to exogenous bovine growth hormone.

Interactions between protein supply and the anabolic response to exogenous bovine (b) GH have been examined in two experiments using 28-35 kg lambs sustained entirely by intragastric infusion of volatile fatty acids (700 kJ/kg W 0.75 per day) into the rumen and the casein (600 mg (low protein; LP) or 1200 mg (high protein; HP)/kg W 0.75 per day) into the abomasum. Sheep received continuous i.v. infusions of bGH for 6 days in experiment 1 and for 18 days in experiment 2. Nitrogen balances were determined daily throughout both experiments and blood samples, from indwelling catheters, were assayed for GH, insulin-like growth factor-I (IGF-I), insulin and glucose. Infusion of bGH increased plasma GH concentration by five- to sixfold in all animals. There was an increase in N retention in both HP and LP animals over the first 2-3 days of GH administration. HP animals sustained higher N retentions (31%; P less than 0.05) throughout the GH administration but LP animals did not. In contrast, plasma IGF-I concentrations increased progressively over the first 72 to 96 h of GH administration in all sheep and thereafter remained significantly (P less than 0.05) elevated until termination of the GH infusion. In lambs which received both HP and LP infusion in experiment 1 the increase in IGF-I and LP infusions in experiment 1 the increase in IGF-I concentration by day 6 of GH administration was significantly (P less than 0.05) greater when they received the higher protein intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Nutritional Physiological Phenomena↗
PubMed1988

Effect of prolonged subclinical infection with Trichostrongylus colubriformis on the performance and nitrogen metabolism of growing lambs.

Ten 5-month-old lambs, reared free of parasites and prepared with abomasal and ileal cannulas, were paired and given rations of pelleted dried grass by means of continuous feeders. From 7 months of age one of each pair was dosed daily with 2500 Trichostrongylus colubriformis larvae for 34 weeks. An untreated animal served as a pair-fed control to each infected lamb. During 5 experimental periods (pre-infection, and Weeks 6-8, 12-14, 18-20 and 29-34 of dosing) measurements were made of the amounts of N leaving the small intestine, the digestibility of 35[S]-labelled microbial protein in the small intestine, and the amounts of plasma protein leaking into the digestive tract. The infection caused a growth check (P less than 0.05) from Week 6 to approximately Week 13 of dosing. This resulted from inappetence, but also from a disruption in the N digestion and metabolism of the lambs. There was a marked eosinophilia at this time. Measurements of ileal flow rates during Weeks 6 and 12 indicated that significantly more N flowed to the terminal ileum of infected lambs during this period (Week 6, 3.1 g N day-1 P less than 0.05; Week 12, 5.0 g N day-1 P less than 0.001). Plasma N leakage into the intestine during Weeks 8 and 14 was higher in infected lambs (1.2 g N day-1 P less than 0.01 and 0.9 g N day-1 P less than 0.05, respectively) but the digestibility of 35[S]-labelled microbial protein was depressed below that of the controls during the later part of this period, i.e. during Week 13. Continued larval challenge beyond this point caused a less severe nutritional penalty. Voluntary feed intake increased and the animals started to gain weight. The amount of extra N flowing to the terminal ileum of infected lambs was less at Week 18 of dosing (3.5 g N day-1 P less than 0.01) than it had been at Week 12. Similarly, extra plasma N leakage into the tract of infected lambs was less during Week 20 (0.26 g N day-1) than during Week 14. There was however, still a detectable reduction in the coefficient of digestibility of 35S microbial protein in infected lambs during Week 19. By Weeks 29-34 the only detectable difference between the infected and control lambs was in their eosinophil counts.

Animals↗
PubMed1988

The effect of daily challenge with Trichostrongylus colubriformis larvae on the nutrition and performance of immunologically-resistant sheep.

Immunological resistance to Trichostrongylus colubriformis was developed in sheep by challenging them with 2500 larvae per day for 34 weeks. They were then rested for 24 weeks before being re-challenged with the same dose rate of the same larvae for 10 weeks. Nutritional, haematological and parasitological parameters were measured during the first 8 weeks of re-challenge infection. There were no faecal worm eggs excreted during the re-challenge infection. There was a small but significant increase in plasma-N leakage from Days 4 to 9 of dosing but this then declined to initial levels. There was no other detectable nutritional disturbance associated with re-infection. Re-challenge caused a rapid development of eosinophilia which peaked during Week 6 before declining to levels of the control animals by Week 8. Sheep resistant to T. colubriformis appear to be able to re-activate their immunological mechanisms when re-challenged with the parasite with little associated nutritional penalty.

Animals↗
PubMed1988

Measurement in vitro of a larval migration inhibitory factor in gastrointestinal mucus of sheep made resistant to the roundworm Trichostrongylus colubriformis.

Lambs were challenged by dosing with 2500 T. colubriformis larvae per day for 34 weeks, rested for 4 weeks and then re-challenged with the infective larvae for a further 10 weeks. A technique for the measurement of inhibition of larval migration from agar gels was used to investigate the antiparasitic activity of mucus, obtained from the small intestine and abomasum of the lambs, at the end of the re-challenge period. Measurements were also made on ileal digesta samples collected at different times during the development of the initial resistance, the rest period and the re-challenge period, and on faeces collected during the re-challenge infection. The mucus from the small intestine and abomasum paralysed and inhibited larval migration from agar gels significantly more (P less than 0.01 and P less than 0.05, respectively) than corresponding mucus from parasite-free control animals. This inhibitory activity was also detected (P less than 0.01) in the ileal digesta of infected animals from Week 6 of primary dosing. The magnitude of the inhibition in the ileal digesta increased with time during the infection period and was again detected during re-infection (P less than 0.01). It was not detectable in resistant sheep towards the end of the rest period. Slight inhibitory activity was detected in faeces after 2 weeks of re-infection. These observations suggest that substances secreted into the lumen of the small intestine of infected animals are responsible for resistance against ingested larvae.

Abomasum↗
PubMed1988

The action of the beta-agonist clenbuterol on protein and energy metabolism in fattening wether lambs.

1. Five Greyface wethers (42-45 kg) fed on various fixed amounts of dried grass pellets (either approximately 1.3 times maintenance or 2 times maintenance) by means of belt-type continuous feeders were housed in open-circuit respiration chambers for periods of 45 d. Between days 15 and 35 they received daily oral doses of 1.5 mg of the beta-adrenergic agonist clenbuterol (adsorbed on to the feed). Continuous energy and nitrogen balance measurements each of 5 d duration were conducted throughout the chamber confinement. 2. On six occasions (twice during the 15 d pre-clenbuterol period, on days +4, +11 and +18 of clenbuterol administration and once during the post-treatment period) animals were infused with [1-14C]leucine to determine the rates of leucine oxidation and the amounts of leucine available for protein synthesis. 3. Clenbuterol administration caused a marked increase in N retention (2-3 g N/d; P less than 0.001) throughout the 20 d treatment period. It also increased (P less than 0.001) the energy expenditure of the animals (on average by 1.1 MJ/d over the first 5 d, compared with immediate pretreatment values, and 0.6 MJ/d over the 20 d period, compared with the mean of pre- and post-treatment control values). The effect of treatment was calculated to result, on average, in the daily retention of 19 (SE 1.5) g more protein and 30 (SE 5.5) g less fat. 4. During clenbuterol treatment leucine oxidation was reduced (P less than 0.01). However, values for the amounts of leucine available for protein synthesis were equivocal, with an increase (P less than 0.001) on day 11 of treatment, but no change on days 4 and 18. 5. Withdrawal of the clenbuterol resulted in rapid alterations of N and energy metabolism towards those expected of control animals of that weight.

Animals↗
PubMed1987

Measurement of the rate of substrate cycling between acetate and acetyl-CoA in sheep muscle in vivo. Effects of infusion of acetate.

1. The rate of substrate cycling between acetate and acetyl-CoA in sheep hindlimb muscle was measured from the decrease of [14C]acetate specific radioactivity across the tissue in vivo. 2. The rate of cycling was 0.005-0.015 mumol/min per g and, in two of the three sheep investigated, was approximately doubled as a result of infusing 2 mol acetate/day intravenously. 3. The results indicate that this cycle contributes only approx. 0.5% of the total heat produced by the animal and would probably make only a relatively small contribution to any heat increment of feeding associated with diets producing large amounts of acetate.

Acetates↗
PubMed1987

Side effects of clenbuterol as a repartitioning agent.

Clenbuterol, a synthetic beta-adrenergic agonist drug, can be used to increase the ratio of protein to fat in the carcase of meat animals. During the first one to three days of its administration to sheep or calves clenbuterol increased their heart rate, and in sheep it decreased blood pressure. Continued administration had no further effect on heart rate or blood pressure but in sheep dose levels above 1.5 mg/day depressed appetite for up to five days; at all dose levels clenbuterol brought about a long term increase in metabolic rate.

Animals↗
PubMed1987

Measurement of volatile fatty acid production rates in sheep given roughage.

Measurement of the irreversible loss rate (ILR) of acetate, propionate and butyrate by radioisotope dilution of the respective tracers in sheep offered chopped dried grass from continuous belt type feeders gave 'plateau samples', the specific radioactivity of which had unacceptably high variance (coefficient of variation [cv] of the five or six samples taken from any one animal over the last four hours of 10 hours infusion ranged from 16 to 57 per cent). In an experiment which attempted to identify the source of this variability the distribution of the liquid phase marker 51Cr EDTA into different areas of the rumen was examined during its administration either in liquid form or impregnated on paper. The paper provided better mixing but incurred considerable spillage problems which would be unacceptable where calculations of ILR were required. Radiographic observations were made to examine the mixing of radio-opaque liquid and solid phase markers in the rumen. A better mixing of both was achieved with intermittent than continuous feeding. When 1-14C- and 2-14C-labelled acetate were each infused into the rumen of four sheep given two levels of chopped dried grass by means of hourly feeders, samples of rumen liquor gave much lower variability of the mean plateau specific radioactivity values than was obtained in experiment 1 (cv less than 15 per cent in all but one sheep). The ILRs of acetate and the transfer quotients of carbon from acetate to butyrate obtained using 1-14C- and 2-14C-labelled acetate were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1986

Nitrogen transactions in the digestive tract of lambs exposed to the intestinal parasite, Trichostrongylus colubriformis.

1. Ten 5-month-old lambs (29 (SE 1.2) kg), reared parasite-free and prepared with rumen duodenal and ileal cannulas, were paired and given rations of Ruminant Diet AA6 (90 g/kg live weight0.75) by means of continuous feeders. From 6 months of age one of each pair was dosed daily with 2500 Trichostrongylus colubriformis larvae for 14 weeks. Untreated animals received the amount of ration consumed by their infected pair-mates the previous day. 2. During three periods, [1) the week before and the first 2 weeks of dosing with infected larvae, (2) during weeks 5-7 and (3) during weeks 11-13 of dosing) all lambs underwent a series of experiments to determine their nitrogen balance, the amounts of N leaving the small intestine, the amount of 51CrCl3-labelled plasma protein leaking into the small intestines, and the disappearance of 35S-labelled bacteria from the small intestine. 3. The infection caused varying degrees of feed refusal in all infected animals. As a result the values for N balance and for the flow of N at the ileum during the latter two periods were regressed against dry-matter intakes for each group in each period. 4. The infection caused a reduction (P less than 0.05) in N retention and increased (P less than 0.05) flow of N at the ileum. The increase in N flow at the ileum of infected lambs was greater (P less than 0.01) at weeks 11-13 of dosing (infected-control 3.6 g N/d (standard error of difference (SED) 0.57), P less than 0.01) than at weeks 5-7 of dosing (infected-control 1.5 g N/d (SED 0.57), P less than 0.05). 5. There were no between-treatment or between-period differences in the disappearance of 35S-labelled bacteria from the small intestines of infected or control lambs, but the infection did cause an increase in plasma N leakage during both periods. During weeks 5-7 and 11-13, plasma N leakage in infected lambs was 1.1 g N/d (P less than 0.01) and 1.7 g N/d (P = 0.056) respectively higher than that in the control lambs. 6. A proportion of the endogenous secretions which enter the small intestine is likely to be resorbed before the ileum.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Calcium and phosphorus absorption in lambs exposed to Trichostrongylus colubriformis.

Ten lambs (29 +/- 1.2 kg) reared parasite-free and prepared with rumen, duodenal and ileal cannulae were paired and one of each pair was given a daily oral dose of 2500 Trichostrongylus colubriformis larvae for 14 weeks. Untreated animals received the amount of ration consumed by their infected pair-mates the previous day. During weeks 6 and 12 of infection, all lambs underwent a 7 day calcium (Ca) and phosphorus (P) balance. During weeks 7 and 13, duodenal and ileal samples were collected to determine the amounts of Ca and P entering and leaving the small intestine. The infection caused varying degrees of feed refusal in all infected animals. As a result, the data on Ca and P in excreta and the amounts of Ca and P entering and leaving the small intestine were regressed against dry matter (DM) intake for each group at each period. There were no between-period differences in these relationships. Calcium absorption and retention were unaffected by the stress of infection. Infection affected several aspects of P metabolism. Blood P concentrations were markedly reduced. Absorption of P from the small intestine was greater (P less than 0.01) in control lambs (at 1 kg DM intake 6.6 g per day) than in infected animals (2.2 g P per day), but there was a greater (P less than 0.05) duodenal flow rate of P in control lambs which suggested much higher rates of salivary secretion of P than in infected animals. Phosphorus flow rates at the ileum were greater (P less than 0.01) in infected lambs, despite the lower duodenal flow rates, which indicated a major abnormality (P less than 0.01) in small intestine absorption of P in infected animals; this may have contributed to the growth check experienced by these lambs.

Animals↗
PubMed1985

The influence of a chronic subclinical infection of Trichostrongylus colubriformis on gastrointestinal motility and digesta flow in sheep.

The influence of a chronic subclinical infection of Trichostrongylus colubriformis, 2500 larvae/day for 12 weeks, on gastrointestinal motility and digesta flow was studied in 12 sheep supplied ad libitum with food and water. Motility was recorded by X-radiography and electromyography from chronically implanted electrodes; abomasal volume and outflow were estimated by dilution of CrEDTA; small intestinal transit time was estimated by passage of Phenol Red. The findings were compared with measurements made prior to infection at restricted food intake and reported separately. The first effects of infection were seen after 3-4 weeks. No animal developed diarrhoea, but food intake was progressively reduced. Small intestinal transit time, abomasal volume and half-time of marker dilution increased while abomasal outflow decreased during infection. These changes occurred both in absolute terms and when compared with values predicted from the observed level of food intake. As the animals became resistant to the parasites abomasal volume and digesta flow returned towards control values (weeks 10-12). The migrating myoelectric complex (MMC) was disrupted in only one sheep, and only transiently. In all sheep the frequency of the MMC was increased during infection and there was a progressive inhibition of abomasal, duodenal and jejunal motility. X-radiography showed there was prolonged pooling of digesta in the proximal small intestine which was cleared only at the phase of regular spiking activity. Two sheep given an anthelmintic drench recovered normal motility and clearance of digesta. It is concluded that subclinical infection of sheep with T. colubriformis alters the normal pattern of gastrointestinal motility in the absence of any diarrhoea, and causes inhibition of abomasal and proximal small intestinal motility and digesta flow. The increased frequency of MMCs helps to maintain digesta flow through the proximal small intestine.

Abomasum↗
PubMed1983

Threonine metabolism in sheep. I. Threonine catabolism and gluconeogenesis in mature Blackface wethers given poor quality hill herbage.

In three experiments, mature Blackface wethers were given freeze-stored Agrostis festuca herbage by continuous feeder. In Expt 1, on separate occasions [U-14C]threonine, [U-14C]glucose and NaH14CO3 were infused over 12 h periods to obtain estimates of irreversible loss rate (ILR) of threonine, glucose and carbon dioxide in the plasma and of the exchange of C between these metabolites. In Expts 2 and 3, during periods when glucose and threonine metabolism were examined, glucose loss across the kidneys (23-29 g/d) was induced by infusion of phloridzin. Results from the four sheep used in Expts 1 and 3 are presented as three-pool models. They indicate that threonine ILR (7.8 g/d; 3.1 g C/d) was approximately three times the estimated rate of absorption of exogenous threonine (1 g C/d). Glucose ILR was approximately 76 g/d (mean +/- SE; 30.3 +/- 0.57 g C/d). Only 0.3% of the glucose-C (0.09 g/d) was derived directly from threonine-C (i.e. 3% of the threonine-C ILR). Bicarbonate ILR was 170 +/- 7.3 g C/d, and glucose contributed 11.1 +/- 3.52 g C/d to this, accounting for 51 +/- 4.4% of glucose-C ILR. Threonine contributed 0.20 +/- 0.026 g C/d to the bicarbonate-C ILR, accounting for only 6.4 +/- 0.87% of the threonine-C ILR. When, in Expts 2 and 3, phloridzin was infused, glucose ILR was increased by 28 +/- 1.5% and bicarbonate ILR was increased by 13 +/- 2.4%. Threonine ILR (3.1 g C/d) was not increased, but the metabolic distribution of threonine-C was altered. The transfer of threonine-C into glucose and CO2 was increased by 39 and 69% respectively to 0.125 and 0.45 g C/d, accounting for 4 and 13% of the threonine ILR respectively. Both technical and metabolic considerations which affect interpretation of these results in terms of rates of catabolism of threonine and of quantitative estimates of gluconeogenesis from threonine are discussed.

Animal Feed↗