Abomasal pH Research Articles

Effect of Feeding Frequency and Route of Administration on Abomasal Luminal pH in Dairy Calves Fed Milk Replacer

The aim of this study was to determine the effect of feeding frequency and route of administration on abomasal luminal pH in suckling calves. Six male dairy calves with cannulae in the abomasal body were administered the following six treatments in a randomized crossover design: 24h fasting, suckling of a high-quality milk replacer (all-milk protein; 12% of body weight [BW]/d) at 12-h (2x), 8-h (3x), 6-h (4x), and 3-h (8x) intervals, and ruminal intubation of milk replacer (12% of body weight/day) at a 12-h (2x) interval. Abomasal luminal pH was measured every second for 24h with miniature glass pH electrodes. Least squares mean 24-h fasting abomasal luminal pH was 1.73, whereas mean 24-h pH after suckling and intubation of milk replacer every 12h were higher at 3.44 and 3.17, respectively. Increasing the frequency of milk replacer suckling to 3x, 4x, and 8x increased mean 24-h abomasal luminal pH; however, there was no difference in mean 24-h pH between 3x (3.69), 4x (3.64), and 8x (3.67) suckling. The percentage of the 24-h recording period that abomasal luminal pH was>3.0 was 0, 49, 53, 61, 61, and 71% for fasting, 2x intubation of milk replacer, and 2x, 3x, 4x, and 8x suckling of milk replacer, respectively. Increasing the frequency of milk replacer suckling may be efficacious in the prophylaxis of abomasal ulceration in milk-fed calves.

Effects of Ostertagia ostertagi and omeprazole treatment on feed intake and gastrin-related responses in the calf

Infection with the bovine abomasal nematode, Ostertagia ostertagi, results in a loss of acid-secreting parietal cells and an increase in gastric pH. The effects of an experimental infection with Ostertagia and/or daily treatment with omeprazole (OMP) at 2 mg kg −1 bodyweight for four consecutive days (experiment days 24–27, inclusive) on voluntary feed intake, blood and tissue gastrin concentrations, abomasal G-cell numbers, gastric pH, and blood cholecystokinin (CCK) and pepsinogen concentrations were investigated in the calf. Ostertagia-infected calves demonstrated a significant drop in feed intake between days 24 and 27 post-infection (38%; P<0.001) and in G-cell numbers (42%; P<0.05) and significant increases in abomasal pH ( P<0.001), fundic mucosal weight (99%; P<0.01), and blood gastrin ( P<0.05) and pepsinogen ( P<0.0001). OMP treatment of worm-free animals resulted in a significant drop in intake between days 24 and 27 (30%; P<0.001) and in G-cell numbers (17%; P<0.05) and significant increases in abomasal pH ( P<0.01) and blood gastrin ( P<0.001). OMP treatment of Ostertagia-infected animals with an existing hypergastrinaemia had no effect on feed intake, abomasal pH, blood gastrin or pepsinogen or abomasal G-cell numbers. Blood CCK concentrations were also unaffected by either Ostertagia infection or OMP treatment. These data suggest that: (a) the depression in feed intake associated with OMP in worm-free calves was not due to a side effect of drug treatment; (b) inappetance in Ostertagia-infected animals is closely associated with the parasite-induced hypergastrinaemia; and (c) the elevation in abomasal pH was a major factor responsible for the elevated blood gastrin concentrations seen in parasitised and OMP-treated animals.

Effect of an orally administered antacid agent containing aluminum hydroxide and magnesium hydroxide on abomasal luminal pH in clinically normal milk-fed calves.

To determine the effects of a commercially available orally administered antacid agent containing aluminum hydroxide and magnesium hydroxide on abomasal luminal pH in clinically normal milk-fed calves. Randomized trial. 5 male dairy calves. Throughout the study, calves were fed milk replacer at 7:30 AM and 7:30 PM. Cannulae for pH electrodes were placed in the abomasal body and pyloric antrum. Treatments consisted of oral administration of a high (50 ml) or low (25 ml) dose of the antacid agent and oral administration of milk replacer alone (control). Antacid was given at 7:30 AM, 3:30 PM, and 11:30 PM, and luminal pH was monitored continuously for 24 hours, beginning 15 minutes before administration of the first dose of antacid. Administration of the first dose of antacid at the time of the morning feeding resulted in an increase in mean abomasal body luminal pH of < 1 pH unit, whereas administration of the second and third doses of the antacid caused transient (< 3 hours) increases in mean luminal pH of approximately 1.5 (low dose) and 2.5 (high dose) pH units. Results suggest that clinically normal milk-fed calves given a commercially available antacid agent, PO, will have a transient increase in abomasal luminal pH. Such agents may, therefore, have a role in the treatment of abomasal ulceration in calves; however, the long-term effects of orally administered antacid agents in milk-fed calves and the clinical efficacy of such agents in treating abomasal ulceration remain to be determined.

Effect of orally administered cimetidine and ranitidine on abomasal luminal pH in clinically normal milk-fed calves.

To characterize the change of pH in the abomasal lumen throughout a 24-hour period, to determine whether pH of the abomasal body differs from pH of the pyloric antrum, and to determine whether oral administration of cimetidine and ranitidine alters pH of the abomasal lumen in milk-fed calves. 5 male dairy calves (4 Holsteins-Friesian, 1 Ayrshire), 5 to 15 days old. Cannulas were surgically positioned in the abomasal body and pyloric antrum of each calf. Calves received the following treatments in a randomized crossover design: milk replacer (60 ml/kg of body weight, q 12 h [untreated control calves]), milk replacer and cimetidine (50 or 100 mg/kg, q 8 h), or milk replacer and ranitidine (10 or 50 mg/kg, q 8 h). The pH of the abomasal body and pyloric antrum was measured for 24 hours, using miniature glass pH electrodes. Suckling of milk replacer immediately increased abomasal luminal pH from 1.4 to 6.0, followed by a gradual decrease to preprandial values by 6 hours. Preprandial and postprandial pH values were not significantly different between the abomasal body and pyloric antrum, indicating lack of pH compartmentalization in the abomasum of milk-fed calves. Administration of cimetidine and ranitidine caused a significant dose-dependent increase in mean 24-hour abomasal luminal pH. Abomasal acid secretion in milk-fed calves is mediated in part by histamine type-2 receptors. Cimetidine and ranitidine may be efficacious in the treatment of abomasal ulcers in milk-fed calves.

Effect if an Orally Administered Antacid Agent Containing Mg(OH)₂ and Al(OH)₃ on Abomasal pH in Milk-fed Calves

Abomasal ulceration occurs commonly in milk-fed calves and adult cattle, and severe ulceration can result in abomasal perforation, peritonitis and death. An important therapeutic goal in treating gastric ulceration in monogastric animals is maintaining gastric pH &gt;3.5 by administering oral antacid agents, proton pump inhibitors, or histamine H2-receptor antagonists. Because the efficacy of oral antacid agents in increasing abomasal pH is unknown in cattle, the purpose of this study was to determine the effect of a widely available oral antacid agent (Extra-strength Maalox®) on abomasal pH in calves. This antacid contains 90 mg of Mg(OH)2 and 100 mg of Al(OH)3 per mL, and the antacid increases gastric pH through the following chemical reactions:Mg(OH)2 + 2H+ ⇒ Mg2+ + 2H2OAl(OH)3 + 3H+ ⇒ AI3+ + 3H2O&#x0D; Purportedly, Mg(OH)2 / Al(OH)3 antacid agents have clinical efficacy in the treatment of abomasal ulceration in adult cattle. There do not appear to be any data available to support or refute such a claim.

Reduced Ostertagia circumcincta burdens in milk-fed lambs

Aims: To compare the susceptibility to parasitism by Ostertagia circumcincta of lambs fed entirely with bovine milk or weaned on to solid feed at 3 weeks of age. In addition, the effect of a single daily feed of milk on worm burdens was assessed. Methods: Eight lambs were assigned to each of the 3 diets: milk (M), milk plus solid feed (cereal-based pellets and lucerne chaff) (MS), or solid feed only (S). Those to be fed solid feed were converted from complete milk feeding to the designated diet during their third week of life. From 3 weeks of age, all lambs were infected with 1000 O. circumcincta larvae twice weekly for 6 weeks; 4 lambs from each diet group were given normal sheathed L3 and another 4 were infected with exsheathed larvae. Faecal egg counts (FEC) and serum gastrin and pepsinogen concentrations were monitored from Day 17 after first infection, and worm burdens and abomasal pH and morphology were determined at necropsy. Results: Total worm burdens and FEC were significantly lower in the M than MS and S groups, whereas there was no significant difference between those receiving sheathed and exsheathed larvae. The milk-fed lambs had a smaller reticulo-rumen and omasum and a more acidic abomasal pH. Serum gastrin and pepsinogen were increased in all groups, irrespective of diet or type of larvae used for infection. Conclusions: The cause of the lower worm establishment in lambs fed only milk was probably not failure to exsheath in the immature gastro-intestinal tract, as there were similar worm burdens in lambs whether sheathed or exsheathed larvae were administered. The lower pH of the abomasal contents of the preruminant lambs may have been a factor, as the parasites have previously been shown to die more rapidly in vitro at low pH. Alternatively, the milk itself had adverse effects on the parasites, but was ineffective when combined with solid feed. There was no benefit from feeding a milk plus solid diet over a solid diet.

The utilization of a commercial rapeseed meal product (RaPass) as a protein supplement for lactating dairy cows

Rapeseed meal is a common protein supplement in ruminant diets that is characterized by high rumen protein degradability (Bertilssonet al., 1994; Vanhataloet al., 1995). Appropriate treatment can however reduce ruminal protein degradability and increase the efficiency of protein utilization. RaPass (UM Feeds Marketing, Burton on Trent, Staffs, UK) is a commercial rapeseed meal product that made using the Maillard reaction. This is the non-enzymatic browning reaction between proteins and reducing sugars that protects protein from rumen degradation. Release of the protein at abomasal pH allows the peptide chains to be digested at an efficiency similar to that of untreated rapeseed meal (Mosset al2000). Cows fed rapeseed meal that was treated to increase the rumen undegradable protein (RUP) content have been reported to perform better than those fed untreated rapeseed meal (Bertilssonet al., 1994). This study evaluated the potential of using RaPass as a protein supplement in dairy cow rations.

A sequential study of the pathology associated with the infection of sheep with adult and larval Ostertagia circumcincta

Disturbances in the physiology of the abomasa of sheep infected with either adult Ostertagia circumcincta given via abomasal cannulae, or larvae (L3) given intraruminally were matched by pathological changes in tissues collected by repeated mucosal biopsy. Within 2–3 days of the transplant of adult worms, abomasal pH had increased markedly in five out of six animals, and there also had been rapid increases in serum gastrin and pepsinogen concentrations in all animals. Reductions in parietal cell number were recorded as early as 1 day after the transplant of adults and were associated with the rapid accumulation of many neutrophils and eosinophils. Mucosal hyperplasia, with increased numbers of cells closer in appearance to mucous/mucous neck cells, was a relatively late development, being most pronounced in the latter part of the infection. In sheep given larvae, changes in secretory physiology were again matched by a concurrent fall in parietal cell number and by the accumulation of inflammatory cells. Changes became maximal when most worms could be expected to be present as adults, confirming the role of adults in the natural disease. Some abnormalities were detected in biopsies collected from animals maintained free of parasites and, although milder in degree, there were similarities to those observed in parasitised tissues, there being fewer parietal cells, a modest degree of mucous cell hyperplasia and inflammatory infiltrates of predominantly neutrophils. These changes were the likely result of trauma to the tissues in the immediate vicinity of the cannula, due either to the presence of the cannula itself or to the frequent collection of biopsy material from areas close to it.

Abomasal bloat, haemorrhage and ulcers in young Norwegian lambs

An abomasal syndrome affecting mainly three- to four-week-old lambs was studied by using a case-control design involving 88 cases and 85 controls. The principal clinical signs were tympany and colic....

The effect of the plasma glucose level on the abomasal function in dairy cows.

We have studied the effect of plasma glucose level on the abomasal outflow rate of fluid using a hyperinsulinemic glucose clamp technique in dairy cows. Four nonpregnant, nonlactating cows were subjected to one of the following treatments: hyperinsulinemic normoglycemic clamp; hyperinsulinemic hypoglycemic clamp; hyperinsulinemic hyperglycemic clamp; or, as a control, an intravenous infusion of .9% sodium chloride in a Latin square design. The cows were previously fitted with a permanent fistula in the abomasum and the outflow rate of abomasal fluid was determined using Co-EDTA as a marker assuming that the outflow followed first-order kinetics. The abomasal pH was also registered. Insulin was infused continuously through a jugular catheter at a rate of 4.8 mU. kg(-1)min(-1) for 2.5 h in the three clamp treatments. A glucose solution was infused through the catheter at a variable rate to achieve a circulating concentration, near the preinfusion glucose level (approximately 4.1 mmol/L), 2 mmol/L below the preinfusion level, and 2 mmol/L above the preinfusion level for the three hyperinsulinemic treatments, respectively. There was a significant effect of treatment on the rate of abomasal outflow (P < .001). The rate of abomasal outflow was highest for the control treatment (7.8%/min). The slowest outflow was observed in the hyperglycemic cows (3.40%/min). The hypoglycemic and normoglycemic cows showed intermediate rates (6.0%/min and 5.2%/min, respectively). The rate of outflow for the hyperglycemic cows was significantly lower than for all the other treatments (P < .01). Abomasal pH was affected by treatment (P < .05). The highest pH was observed in the hyperglycemic cows (pH 2.3). The values for the other three treatments ranged from pH 1.9 to 2.0. These results show that hyperglycemia reduced the rate of outflow and increased the pH of abomasal fluid in dairy cows. An elevated plasma glucose level thus can be considered as a potential risk factor in the pathogenesis of left-displaced abomasum.

Hypergastrinaemia, abomasal bacterial population densities and pH in sheep infected with Ostertagia circumcincta

Serum gastrin and pepsinogen concentrations, food intake, abomasal pH and abomasal aerotolerant and anaerobic bacterial populations were measured in sheep infected with Ostertagia circumcincta to search for links between hypergastrinaemia, food intake and changes in the abomasal environment. Abomasal pH and serum gastrin and pepsinogen concentrations were elevated in each of five sheep infected via abomasal cannulae with 150 000 exsheathed larval stage three, followed 11 days later by 100 000 sheathed larvae given intraruminally. Unparasitised abomasa contained aerotolerant bacterial population densities of between 10 3 and 10 6 cells ml −1 and these did not change significantly following parasitism. In contrast, anaerobic bacterial population densities increased markedly by about 10 4-fold following parasitism. Anaerobic numbers changed rapidly when abomasal pH increased from 2.5 to 3.5. At pH 4 and above, anaerobic bacterial numbers approached levels expected in rumen contents but parameters other than pH did not relate to bacterial numbers. Brief periods when serum gastrin was lower than expected, coinciding with raised abomasal pH, were not explicable by increased bacterial numbers. Food intake, which decreased for a variable period from around Day 5 p.i., correlated poorly with serum gastrin concentration, suggesting hypergastrinaemia is not the sole cause of anorexia in parasitised animals. The survival of substantial numbers of rumen bacteria in the abomasum at only slightly raised pH may significantly lower the bacterial protein available to the sheep.

Abomasal secretion in sheep receiving adult Ostertagia circumcincta that are prevented from contact with the mucosa

Aims. Both adult and larval Ostertagia circumcincta infections raise abomasal pH and serum gastrin and pepsinogen concentrations, either because of physical effects of the worms or from their chemical secretions. The study was designed to examine whether adult worms require contact with the gastric mucosa to effect changes in gastric secretion. Methods. Abomasal pH and serum gastrin and pepsinogen concentrations were measured in four groups of sheep: Group A (n = 4): abomasal contents containing about 18 000 adult O. circumcincta were obtained from donor sheep, concentrated and infused into 5 µm mesh porous bags attached to surgically implanted abomasal cannulae. A second worm transplantation was carried out 1 week later to assess worm survival after 16 hours. Group B (n = 4): about 9000 adult worms, recovered after migration out of abomasal contents set in agar, were placed in small 5 µm mesh bags which were inserted through indwelling abomasal cannulae and left for 3 days. Group C (n = 2): about 9000 adult worms from the population recovered from agar were infused through abomasal cannulae which allowed. free movement in the abomasum. Group D (n = 3) was left uninfected. Results. Worms transplanted directly into the abomasum (Group C) caused rapid and marked effects on abomasal secretion. Adult O. circumcincta died within 16 hours of transfer into the abomasum when they were restrained within porous bags. Nevertheless, in sheep receiving 18 000 worms, abomasal pH increased soon after new feed was presented on Days 1, 2 and 4 after worm transfer; serum gastrin was elevated in three sheep from 113 hours and serum pepsinogen increased in one animal. Sheep receiving 9000 worms showed similar trends but the results were equivocal. Conclusions. Adult O. circumcincta prevented from physical contact with the gastric mucosa by restraint in porous bags are able to raise abomasal pH. This study implicates parasite excretory-secretory products in mediating changes in gastric secretion caused by adult abomasal worms.

Infection of sheep with adult and larval Ostertagia circumcincta: abomasal morphology

The infection of parasite-naive sheep with approximately 15 000 adult Ostertagia circumcincta via abomasal cannulae resulted in marked changes in the structure and function of the abomasum. The functional changes, which have been characterised previously, included elevated abomasal pH and increased serum concentrations of pepsinogen and gastrin. Eight days after the transplant of adult worms, the abomasa of recipient animals were significantly heavier than those of controls ( P<0.001), the thickness of the fundic mucosa was greater ( P<0.01), there were fewer parietal cells ( P<0.01) and increases in the numbers of mitotic figures and mucus-producing cells. Mucous cell hyperplasia was also evident in the fundic mucosae of sheep receiving a trickle infection of infective, third-stage O. circumcincta larvae and was prominent within nodules associated with larval development. In non-nodular mucosa, there was hyperplasia of mucous cells and changes in the distribution of parietal cells. Decreases in the number of parietal cells at the gland base were offset by increases at a mid-gland level, probably due to chronic hypergastrinaemia, so that, overall, total parietal cell number was unaffected. Mucous cell hyperplasia and the diminution of parietal cell number are seen in a diverse range of disease states and may be mediated by host growth factors such as Transforming growth factor-alpha. Alternatively, the cellular and\\or the secretory changes in response to the presence of adult worms are mediated by chemicals that are cytotoxic\\inhibitory for parietal cells, and released by the parasites themselves.

Effects of adult and larval Haemonchus contortus on abomasal secretion

Abomasal pH and serum pepsinogen and gastrin were increased in parasite-naive sheep by infection with either larval or adult H. contortus. Four sheep received 10 000 larvae intraruminally and 9000 adult worms were given directly via an abomasal cannula to another 4 sheep. The latter animals were dosed orally with 0.4 mg kg −1 ivermectin 4 days after worm transfer and their recovery was monitored for a further 8 days. Whereas the presence of adult worms rapidly induced changes in the secretory activity of the abomasum, the early larval stages had minimal effects up to the 4th day post-infection. After either larval or adult infection, the initial hypergastrinaemia began at the same time as the increase in abomasal pH, but serum gastrin continued to increase after abomasal pH had reached a maximum and returned more slowly to normal values after drenching. The increase in serum pepsinogen did not precede those in the other parameters, unlike the earlier hyperpepsinogenaemia which occurs with Ostertagia infection. Three of the 8 infected sheep had no detectable serum pepsinogen increases during the parasitism while showing typical effects on abomasal pH and serum gastrin. The rapidity of the responses to the transfer of adult worms and to their removal by treatment with anthelmintic supports a role for worm excretory/secretory (ES) products which possible are not produced by the early larval stages. The similarity of responses to H. contortus and O. circumcincta infection suggests the involvement of the same or very similar ES products.

Modified plasma and abomasal disposition of albendazole in nematode-infected sheep

The influence of gastrointestinal nematode infection on the kinetics of albendazole (ABZ) and its metabolites, albendazole sulphoxide (ABZSO) and sulphone (ABZSO 2) in plasma and abomasal fluid was investigated in sheep. A micronised suspension of ABZ was administered intraruminally at 7.5 mg kg −1 to the following groups of sheep: (a) non-parasitised (control); (b) artificially infected with Haemonchus contortus; (c) naturally infected with Haemonchus contortus and other species of gastrointestinal nematodes. Plasma and abomasal fluid samples were obtained serially over 72 h post-treatment and they were analysed by HPLC for ABZ and its metabolites. The ABZ parent drug was not detected in plasma at any time post-treatment, however the metabolites ABZSO and ABZSO 2 were recovered in the bloodstream. The active metabolite ABZSO was recovered in plasma between 0.5 and 48 (uninfected), 60 ( H. contortus infected) or 72 h (naturally infected sheep) post-administration. The area under the plasma concentration vs time curve (AUC) values for ABZSO were higher in both artificially infected (64.0 μg h ml −1) and naturally infected (79.3 μg h ml −1) sheep as compared with non-infected animals (41.8 μ g h ml −1). Peak plasma concentrations for ABZSO and ABZSO 2 were higher in both artificially and naturally infected sheep than in non-parasitised animals. No changes in the half-lives and mean residence times for these metabolites were observed in infected sheep. ABZ and its metabolites were found in the abomasum between 0.5 and 48 (infected animals) or 72 h (uninfected) post-treatment. The availability (total AUCs) of ABZ and its metabolites in abomasal fluid were lower in H. contortus infected sheep than in the uninfected control animals. The increased abomasal pH induced by the presence of the H. contortus infection may reduce the plasma/abomasum pH gradient, which results in a decreased ionic-trapping of ABZ and its metabolites in the abomasum. Such a phenomenon correlates with: (a) the higher total AUC values obtained for ABZ metabolites in the bloodstream of the infected compared to the control sheep, (b) the lower concentration profiles of the ABZ parent drug and its metabolites found in the abomasal fluid of the infected animals.

Infection of Sheep with Adult and Larval Ostertagia circumcincta: Effects on Abomasal pH and Serum Gastrin and Pepsinogen

Lawton D. E. B., Reynolds G. W., Hodgkinson S. M., Pomroy W. E. & Simpson H. V. 1996. Infection of sheep with adult and larval Ostertagia circumcincta: effects on abomasal pH and serum gastrin and pepsinogen. International Journal for Parasitology 26: 1063–1074. Infection of sheep with adult or larval O. circumcincta increased serum pepsinogen and gastrin and abomasal pH. The upper limits of the normal range, calculated from over 1000 samples collected from parasite-naive sheep, were set at 2 standard deviations above the mean; these were for serum pepsinogen, 454 mU tyrosine 1−1; serum gastrin, 64 pM and abomasal pH, 3.26. Five infection regimes were used: sheep previously exposed to field parasitism were infected with 30,000 larvae intraruminally (Group A), while parasite-naive sheep were administered either 50,000 larvae intraruminally (Group B), 150,000 larvae intraruminally followed by a trickle infection of 10,000 larvae thrice weekly from days 21 to 45 (Group C), 150,000 exsheathed larvae via an abomasal cannula (Group D) or 15,000 adult worms via an abomasal cannula (Group E). Whereas the presence of adult worms rapidly increased serum pepsinogen (after 8 h) and abomasal pH and serum gastrin (after about 19 h), the early infective larval stages, regardless of the infection regime, had minimal effects until the abrupt rise in all parameters 5–6 days after infection, Abomasal pH returned to near normal levels when the infections became patent and was not re-elevated by a subsequent trickle infection, whereas serum gastrin and pepsinogen remained high. The initial hypergastrinaemia was coincident with the increased abomasal pH, but was preceded by the increase in serum pepsinogen. In several sheep, serum pepsinogen increased very little during the parasitism, although there were typical effects on abomasal pH and serum gastrin. Serum gastrin was depressed when the abomasal pH exceeded about 5.5. It is suggested that an inhibitor of gastrin release is generated by proliferating abomasal microbes under these conditions and that this is a limitation to the use of elevated serum gastrin in the diagnosis of parasitism in individual sheep.

Infection of sheep with adult and larval Ostertagia circumcincta: Effects on abomasal pH and serum gastrin and pepsinogen

Lawton D. E. B., Reynolds G. W., Hodgkinson S. M., Pomroy W. E. & Simpson H. V. 1996. Infection of sheep with adult and larval Ostertagia circumcincta: effects on abomasal pH and serum gastrin and pepsinogen. International Journal for Parasitology 26: 1063–1074. Infection of sheep with adult or larval O. circumcincta increased serum pepsinogen and gastrin and abomasal pH. The upper limits of the normal range, calculated from over 1000 samples collected from parasite-naive sheep, were set at 2 standard deviations above the mean; these were for serum pepsinogen, 454 mU tyrosine 1 −1; serum gastrin, 64 pM and abomasal pH, 3.26. Five infection regimes were used: sheep previously exposed to field parasitism were infected with 30,000 larvae intraruminally (Group A), while parasite-naive sheep were administered either 50,000 larvae intraruminally (Group B), 150,000 larvae intraruminally followed by a trickle infection of 10,000 larvae thrice weekly from days 21 to 45 (Group C), 150,000 exsheathed larvae via an abomasal cannula (Group D) or 15,000 adult worms via an abomasal cannula (Group E). Whereas the presence of adult worms rapidly increased serum pepsinogen (after 8 h) and abomasal pH and serum gastrin (after about 19 h), the early infective larval stages, regardless of the infection regime, had minimal effects until the abrupt rise in all parameters 5–6 days after infection, Abomasal pH returned to near normal levels when the infections became patent and was not re-elevated by a subsequent trickle infection, whereas serum gastrin and pepsinogen remained high. The initial hypergastrinaemia was coincident with the increased abomasal pH, but was preceded by the increase in serum pepsinogen. In several sheep, serum pepsinogen increased very little during the parasitism, although there were typical effects on abomasal pH and serum gastrin. Serum gastrin was depressed when the abomasal pH exceeded about 5.5. It is suggested that an inhibitor of gastrin release is generated by proliferating abomasal microbes under these conditions and that this is a limitation to the use of elevated serum gastrin in the diagnosis of parasitism in individual sheep.

Susceptibility of two crossbreeds of sheep to Haemonchus contortus

Studies were conducted on 20 crossbred lambs of 4–5 months old. Ten lambs were Nah × Corriedale cross (Hisardale) and the other 10 were Nah × Lohi cross (Munjal). Seven lambs each of both crossbreeds were infected with 10,000 infective larvae of Haemonchus contortus. Three lambs of each crossbreed served as uninfected controls. Clinicopathological xaminations were done before and after infection and all the lambs were necropsied 28 days post-infection. The body weight gain, haemoglobin and packed cell volume were significantly lower in Hisardale lambs and the peripheral eosinophil count was significantly higher in Munjal lambs. Significant hypoalbuminaemia and hypoglobulinaemia, a sharp increase in albumin: globulin ratio; significantly higher faecal egg counts; adult worm counts; abomasal pH, volume, congestion and oedema were observed in Hisardale lambs as compared to Munjal lambs. Clinical signs of haemonchosis were more severe in Hisardale lambs and two of them died. Munjal lambs therefore seem less susceptible than Hisardale lambs to H. contortus infection.

A difference in abomasal pH between Canadian wapiti affected with chronic illthrift and unaffected deer

The pH of abomasal fluid from five purebred Canadian wapiti which were diagnosed with chronic illthrift ("fading") was found to be elevated compared to ten clinically normal red and hybrid (wapiti x red) deer. The average abomasal pH of the affected elk was 6.3, compared to 2.5 for the unaffected red and hybrid deer.

Interactions of Ostertagia species with their bovine and ovine hosts

Ostertagia spp. affect their hosts in several complex interactions involving structural, biochemical, hormonal, nutritional and immunological mechanisms. Following infection with Ostertagia spp. the specialised secretory function and junctional integrity of gastric epithelial cells is lost. The pH of the abomasal contents is elevated and pepsinogen concentration in the plasma increases. There is a concurrent elevation in the concentration of blood gastrin. The effects may be a response to the physical interaction of parasite with epithelial cells, may be mediated through parasite excretory/secretory products, or by neural mechanisms. There may also be interactions between the responses since elevated abomasal pH stimulates secretion of gastrin. Hormonal changes may also have a role in the increased susceptibility of host to parasite during the periparturient period. Prolactin was considered the most likely hormone candidate although there is now a body of evidence to suggest that elevated prolactin concentrations are not solely responsible. Infection with Ostertagia spp. causes a marked inappetance, negative nitrogen balance and reduction in apparent gross energy digestion. The level of nutrition may also affect the response of the host to the parasites and establishment of O. circumcincta is lower in animals on a low plane of nutrition than those on a high plane. Immunity of Ostertagia spp. develops slowly and once established is manifest following challenge by an initial hypersensitivity response, followed by a cell mediated response and then an antibody response. Parasites may fail to establish or may be expelled from immune animals and if they do establish may be stunted with small vulval flaps and lower biotic potential and may become inhibited at the early fourth stage of development.