Molecular adjuvant effects of a conformationally biased agonist of human C5a anaphylatoxin

A conformationally biased decapeptide agonist of human C5a anaphylatoxin (YSFKPMPLaR) was used as a molecular adjuvant in stimulating Ab responses against peptide epitopes derived from human MUC1 glycoprotein and the human mu and kappa opioid receptors. C57BL6 mice were immunized with the MUC1 epitope (YKQGGFLGL); the C5a agonist (YSFKPMPLaR); YSFKPMPLaR and YKQGGFLGL together, but unconjugated; a C5a-active, MUC1 epitope construct (YKQGGFLGLYSFKPMPLaR); and a C5a-inactive, reversed moiety construct (YSFKPMPLaRYKQGGFLGL). High Ab titers specific for the MUC1 epitope were observed only in mice immunized with the C5a-active epitope construct. Similar results were obtained in BALB/c mice immunized with the C5a-active, MUC1 epitope construct. Abs from the sera of the C57BL6 mice were predominately of the IgG2a, IgG2b, and IgM isotypes and were reactive against human recombinant MUC1 and MUC1 expressed by the Panc-1 M1F.15 pancreatic cell line. When compared with the corresponding KLH-epitope conjugates in C57BL6 mice, the epitope-C5a agonist constructs produced titers of specific IgG Abs of isotypes distinct from those generated by the keyhole limpet hemocyanin-epitope conjugates. Rabbits immunized with a mu opioid receptor epitope-C5a agonist construct (GDLSDPCGNRTNLGGRDSLYSFKPMPLaR) or a kappa opioid receptor epitope-C5a agonist construct (FPGWAEPDSNGSEDAQLYSFKPMPLaR) generated high titer, epitope-specific Ab responses. Ab titers generated in response to the opioid epitope-C5a agonist constructs were comparable to those generated by the opioid KLH-epitope conjugates. The results of this study are discussed in terms of possible mechanisms by which the conformationally biased C5a agonist serves as a molecular adjuvant.

Molecular adjuvant effects of a conformationally biased agonist of human C5a anaphylatoxin

A conformationally biased decapeptide agonist of human C5a anaphylatoxin (YSFKPMPLaR) was used as a molecular adjuvant in stimulating Ab responses against peptide epitopes derived from human MUC1 glycoprotein and the human mu and kappa opioid receptors. C57BL6 mice were immunized with the MUC1 epitope (YKQGGFLGL); the C5a agonist (YSFKPMPLaR); YSFKPMPLaR and YKQGGFLGL together, but unconjugated; a C5a-active, MUC1 epitope construct (YKQGGFLGLYSFKPMPLaR); and a C5a-inactive, reversed moiety construct (YSFKPMPLaRYKQGGFLGL). High Ab titers specific for the MUC1 epitope were observed only in mice immunized with the C5a-active epitope construct. Similar results were obtained in BALB/c mice immunized with the C5a-active, MUC1 epitope construct. Abs from the sera of the C57BL6 mice were predominately of the IgG2a, IgG2b, and IgM isotypes and were reactive against human recombinant MUC1 and MUC1 expressed by the Panc-1 M1F.15 pancreatic cell line. When compared with the corresponding KLH-epitope conjugates in C57BL6 mice, the epitope-C5a agonist constructs produced titers of specific IgG Abs of isotypes distinct from those generated by the keyhole limpet hemocyanin-epitope conjugates. Rabbits immunized with a mu opioid receptor epitope-C5a agonist construct (GDLSDPCGNRTNLGGRDSLYSFKPMPLaR) or a kappa opioid receptor epitope-C5a agonist construct (FPGWAEPDSNGSEDAQLYSFKPMPLaR) generated high titer, epitope-specific Ab responses. Ab titers generated in response to the opioid epitope-C5a agonist constructs were comparable to those generated by the opioid KLH-epitope conjugates. The results of this study are discussed in terms of possible mechanisms by which the conformationally biased C5a agonist serves as a molecular adjuvant.

Dual diagnosis patients in the modified therapeutic community: does a criminal history hinder adjustment to treatment?

The efficacy of the drug-free therapeutic community (TC) in treating patients with chemical dependence and in rehabilitating persons with criminal histories has been extensively studied and is well established since the late 1960's. More recently, this format has been modified in order to treat individuals suffering from both addictive disorders and chronic, severe mental illness. In an indigent inner-city population, this latter group includes many patients who also have significant histories of criminal behavior. To date, there have been no systematic attempts to assess the impact of a history of criminality on the course of treatment of these patients, as they might be thought less adaptable to the milieu of a TC. In the current study, data from a sample of homeless male MICA patients were analyzed to determine if those patients with a history of criminal convictions were as likely as non-criminal patients to adjust effectively to the social milieu of a modified drug-free therapeutic community. Of 183 sequential admissions studied, 76 had never been convicted of a crime, 46 had 1 conviction, and 61 had 2 or more. No differences were observed between the groups with respect to length of stay, social adjustment on admission, and change in social adjustment during the first two months of treatment. These findings suggest that a history of criminal conduct does not compromise a dually diagnosed patient's likelihood of engaging in the social contract necessary for successful treatment in a TC.

Disseminated lymphangiosarcoma in a dog

This case is unusual due to its extended clinical course. Clinical, histopathological, and immunohistochemical findings are presented.

Alkaline phosphatase bone isoenzyme and osteocalcin in the serum of hyperthyroid cats

The effect of hyperthyroidism on serum markers for increased bone metabolism and turnover was evaluated in 36 cats with elevated serum levels of thyroxine and alkaline phosphatase. Serum was analyzed for total and ionized calcium and phosphorous. Alkaline phosphatase isoenzymes were separated by agarose gel electrophoresis and osteocalcin was measured by radioimmunoassay. Values for hyperthyroid cats were compared with those for healthy cats. Alkaline phosphatase bone isoenzyme was markedly increased in all 36 hyperthyroid cats. Osteocalcin was increased in 44% of the cats. There was no correlation among the magnitude of increase in alkaline phosphatase bone isoenzyme, osteocalcin, and serum thyroxine concentrations. Increased serum phosphorus was found in 35% of the cats. Total calcium was within the reference range in all cats, while 50% of the cats had reduced levels of serum ionized calcium. We conclude that hyperthyroid cats do have altered bone metabolism, although it is usually clinically insignificant.

Use of technetium Tc 99m sestamibi for detection of a parathyroid adenoma in a dog with primary hyperparathyroidism

Double-phase parathyroid gland scintigraphy, using technetium Tc 99m sestamibi, correctly identified the existence and location of a parathyroid adenoma in a dog with primary hyperparathyroidism. The parathyroid adenoma was removed surgically 2 days after scintigraphy. An area of focal radionuclide uptake persisted in the region corresponding to the left external parathyroid gland in the delayed-phase image. Delayed-phase images from 3 healthy dogs and a dog with hypercalcemia of malignancy caused by lymphoma did not reveal an area of persistent radiotracer uptake. Double-phase parathyroid gland scintigraphy, using 99mTc-sestamibi, is a simple, rapid, noninvasive test, which can be used for detection and localization of parathyroid adenomas in hypercalcemic dogs. It also can help to differentiate these dogs from dogs with hypercalcemia of malignancy.

Comparison of maxillectomy patients with immediate versus delayed obturator prosthesis placement

OBJECTIVE

To compare maxillectomy patients with immediate versus delayed placement of an obturator prosthesis in terms of patient outcomes.

DESIGN

Retrospective review.

OUTCOME MEASURES

The outcomes of 23 maxillectomy patients seen between 1975 and 1993 at St. Joseph's Health Centre in London, Ontario, were analyzed.

METHODS

For 17 patients, a prosthesis was placed immediately as part of the operative procedure, and for 6 patients, an occlusive dressing only was placed.

RESULTS

In all parameters studied (length of stay, i.v. requirements, swallowing, clear fluid diet and ambulation), the prosthesis group progressed more quickly and had a more rapid return to normal function.

CONCLUSION

This study demonstrates the benefits of immediate prostheses for maxillectomy patients and justifies their continued use.

Homologous serum increases fibronectin expression and cell adhesion in airway smooth muscle cells

This study describes altered patterns of growth and upregulation of fibronectin expression of cultured canine airway smooth muscle cells grown in homologous serum, which provides a model of the vascular leakage occurring in asthma, compared to fetal bovine serum (FBS). Cells were incubated in increasing concentrations of serum (2.5-40%) for 72 hours. Both homologous serum and FBS caused cellular proliferation which reached a maximum increase at 2.5-5% serum concentration. Differences in the cellular responses to the two types of sera were noted at higher concentrations of sera. At a concentration of 40% FBS, airway smooth muscle cells increased in number by 307 +/- 16% (n = 5) compared to serum-free control cells, whereas in canine serum the increase in growth was significantly smaller, 239 +/- 25% (n = 7) (P < 0.05). Airway fibrocytes similarity treated increased in number by 256 +/- 43% (n = 3) in 40% FBS, but exhibited a reduction in cell number to 80 +/- 10% (n = 3) of controls in 40% homologous serum (P < 0.05). Smooth muscle cells demonstrated a dose-dependent increase in fibronectin expression when grown in homologous serum but not in FBS, suggesting phenotypic change occurred in these cells when exposed to homologous serum. These data suggest that the leakage of plasma in the asthmatic airway may trigger phenotypic change in both airway smooth muscle cells and airway fibrocytes leading to cellular proliferation and expression of extracellular matrix molecules. These in vitro changes are consistent with the histological findings in clinical asthma.

Conformationally biased analogs of human C5a mediate changes in vascular permeability

A panel of conformationally constrained, decapeptide agonists corresponding to the C-terminal "effector" region of human C5a (C5a65-74 or ISHKDMQLGR) was evaluated for the ability to increase vascular permeability. One constrained analog, acyl-YSFKPMPLaR, expressed between 2 and 10% of full C5a activity in increasing vascular permeability, as measured by the extravasation of Evans blue dye in guinea pig skin. This analog was at least 10-fold more potent than its unconstrained sister analog C5a65-74465, F67++ (YSFKDMQLGR), which was used as an internal standard in these assays. Neither acyl-YSFKPMPLaR nor YSFKDMQLGR changed the transvascular equillibrium of an electrolyte, 86Rb, at the peptide injection site. However, both peptides effected a significant increase in the extravasation of two macromolecules, 125I-labeled bovine serum albumin and 131I-labeled monoclonal antibody BL-3. The extravasation of Evans blue dye mediated by 0.03 to 0.1 nmol of acyl-YSFKPMPLaR was nearly abolished by 1 to 10 nmol of the antihistamine diphenhydramine. For YSFKDMQLGR, however, the sensitivity toward diphenhydramine was observed only at low concentrations of the peptide (1 nmol). When incubated in human and mouse sera, acyl-YSFKPMPLaR was shown to be stable toward the actions of serum carboxypeptidases. However, the unconstrained analog YSFKDMQLGR was rapidly converted to the des-Arg form under the same conditions. Taken together, these results support a growing body of evidence that unique topochemical features expressed in conformationally constrained agonist analogs of C5a contribute favorably to their ability to modulate vascular permeability and to their stability in serum.

Excitatory movements in a dog following propofol anesthesia

A two-year-old, neutered male Labrador retriever was anesthetized with intravenous propofol for bronchoscopy to remove a bronchial foreign body. The dog previously had been diagnosed with idiopathic epilepsy. During anesthetic recovery, the dog exhibited excitatory movements characterized by forelimb extensor rigidity, opisthotonos, generalized tremors, paddling, horizontal nystagmus, and facial twitching. Intravenous administration of pentobarbital temporarily stopped the motor activity. The excitatory movements persisted for 20 hours. The dog went on to recover completely, although he remained an epileptic, having one brief, generalized grand mal seizure every three-to-four months.

Results and complications of arteriovenous access dialysis grafts in the lower extremity: a five year review

Virtually no objective data exist regarding the natural history of arteriovenous (AV) dialysis access grafts placed in the lower extremity for routine hemodialysis. From March 1988 until October 1993, 45 consecutive lower extremity AV dialysis access grafts were placed in 39 patients (16 males; 23 females; mean age 58 years) at a large teaching community hospital. All 39 patients had long-standing end stage renal disease and had required chronic hemodialysis from 7 to 237 months mean, 72 months) prior to leg graft placement. Polytetrafluorethylene (n=39) or bovine (n=6) loop lower extremity dialysis grafts were placed after multiple upper extremity dialysis graft failures (mean, 2.7 previous grafts with 9.6 thrombectomies and/or access revisions per patient). There were no operative deaths; however, in follow-up (1-132 months; mean 20 months; median 18 months), 33 percent of the patients had died from systemic complications of their renal disease, and only 20 (44%) leg grafts are currently patent [correction of patient] . Graft complications, excluding graft thromboses, occurred in 20 grafts including graft infection (n=8; 18%), severe ipsilateral leg ischemia (n=7; 16%), graft aneurysmal degeneration requiring revision (n=3; 7%), fistula-induced congestive heart failure (n=2; 4%), and major lower extremity amputation (n=3; 7%). Primary patency by life-table analysis was 47 percent at 24 months. Fifteen (33%) grafts thrombosed at least once, and all but one were salvaged with thrombectomy. The need for lower extremity AV dialysis access appears to be a significant marker for late mortality in this group of chronically ill patients. They are associated with multiple complications and should probably be placed only if significant patient morbidity can be accepted and justified.

Outcomes in the management of vascular prosthetic graft infections confined to the groin: a reappraisal

The management of vascular prosthetic graft infections confined to the groin continues to be controversial. To critically evaluate this problem, we reviewed the records of our vascular registry from December 1992 through February 1995 and found 17 incidences of groin sepsis involving a vascular prosthesis in 10 patients. These included a proximal prosthetic femoropopliteal bypass (n = 6), an aortobifemoral graft limb (n = 5), an ileofemoral bypass (n = 3), a prosthetic femoral patch (n = 2), and an aortofemoral/femorofemoral bypass (n = 1). The mean age of these patients was 65 years. Six patients were diabetic, four were on systemic steroids, and two were diabetic and on steroids. All infections were Szilagyi grade III including three in which the patients presented with local hemorrhage. Treatment consisted of irrigation, radical debridement with or without in situ graft replacement, and local rotational muscle flap coverage in nine cases, graft excision with extra-anatomic (obturator ileofemoral bypass) graft replacement in six cases, and excision alone in two cases. Of the 17 infections treated operatively and followed from 1 week to 18 months (median 5 months), eight (47%) showed no evidence of recurrence, six (35%) recurred, two (12%) caused early death, and one resulted in a thrombosed graft requiring extra-anatomic reconstruction. Of the nine infected grafted treated locally with muscle flaps, six showed recurrent infection from 3 weeks to 15 months and one thrombosed for a total local treatment failure rate of 78%. Only two grafts are free of infection at 4 and 5 months, respectively. Of the six incidences of infection treated with obturator bypass, four (66%) are free of infection and two resulted in patient death; both infections treated with excision alone were eradicated but resulted in a major lower extremity amputation. These data question the growing acceptance of debridement and local muscle flap coverage for the treatment of all prosthetic vascular graft infections confined to the groin, especially in patients who are diabetic or on systemic steroids.

Focal myasthenia gravis as a paraneoplastic syndrome of canine thymoma: improvement following thymectomy

A 10-year-old, neutered male cocker spaniel-cross experienced regurgitation, dry retching, and weight loss. A large, mediastinal mass and dilatation of the esophagus were seen on thoracic radiographs. Cytological, histopathological, immunohistochemical, and serological findings were consistent with a lymphoepithelial thymoma and focal, esophageal myasthenia gravis. Surgical removal of the mass resulted in rapid resolution of the megaesophagus and a decrease in serum acetylcholine-receptor antibody concentration. The dog was clinically normal until the thymoma recurred six months postoperatively. Clinical signs, diagnostic evaluation, management, and treatment of a dog with thymoma and megaesophagus are described.

Feline leukemia virus detection by ELISA and PCR in peripheral blood from 68 cats with high, moderate, or low suspicion of having FeLV-related disease

Clinicopathologic criteria were used to group 68 cats according to high, moderate, or low suspicion of having feline leukemia virus (FeLV)-related disease. Peripheral blood samples were tested for FeLV antigen by enzyme-linked immunosorbent assay (ELISA) and for FeLV DNA by polymerase chain reaction (PCR). There was no significant difference between ELISA and PCR results in the 68 cats. In the high-suspicion group, 46%(11/24) of cytopenic cats were test positive (ELISA and PCR) and 87% (13/15) with hemopoietic neoplasms were test-positive. Also within the high suspicion group, test-positive cats were 2.5 times more likely to die within the 1 year follow-up period than were test-negative (ELISA and PCR) cats. Among cats in the moderate-suspicion group, 15% (2/13) were test-positive, and none (0/16) of the cats in the low suspicion group was test positive. The relative risk of a positive test (ELISA and PCR) in the high suspicion group was 3.7 times that for the moderate-suspicion group and 22.8 times that for the low suspicion group. There was no significant difference in the relative risk of a positive test result between the moderate and low suspicion groups. The results indicate that FeLV detection by PCR can be adapted for diagnostic purposes using peripheral blood samples, however, results do not differ significantly from FeLV ELISA results. Also, a proportion of cats with a high suspicion of having FeLV-related cytopenia and hemopoietic tumors are negative for both circulating FeLV antigen and DNA. These cats may not have FeLV-related disease, or FeLV may exist in a disease-producing but nonreplicating form ultimately detectable by PCR in tissues other than peripheral blood.

Structural organization of the human folypoly-gamma-glutamate synthetase gene: evidence for a single genomic locus

The cytotoxicity, and probably the selectivity, of folate antimetabolites depend upon the expression of the enzyme folylpoly-gamma-glutamate synthetase in tumor cells. Evidence for the existence of multiple forms of this enzyme and the need to define the control mechanisms determinant of expression levels in normal and neoplastic cells has focused attention on the gene(s) encoding these forms. The organization of the genomic locus for the human folylpoly-gamma-glutamate synthetase (FPGS) gene has been determined. The complete 2256 nucleotides of cDNA for the 5'-untranslated region, mitochondrial leader sequence, coding region, and 3'-untranslated region were distributed on 15 exons stretching over 11.2 kb of genomic DNA. All of the restriction fragments found in diploid human genomic DNA could be accounted for by fragments contained on the isolated genomic clones. Likewise, Southern analysis of the transfected human genomic DNA that complemented the FPGS- phenotype of a hamster cell line indicated that the same gene had been integrated in all of three independently derived transfectants. We conclude that the genomic locus that we now report appears to be the only gene encoding FPGS-related sequences in the human complement.

The effect of C5a and U46619 on the isolated, perfused human placental lobule: development of a method for the online estimation of tissue fluid accumulation

A method for the automatic and simultaneous determination of perfusion pressure and fluid accumulation in the isolated, perfused human placental lobule is described. We demonstrated that the inflammatory mediator, C5a, a C5a agonist analogue peptide, and the thromboxane mimetic U46619 caused increased fetal perfusion pressure and increased tissue weight when administered via the fetal arterial circulation. Occlusion of the fetal venous effluent tubing caused significantly greater increases in tissue weight than the pharmacological agents. Detectable increases in tissue weight occurred within 47 +/- 3 sec (n = 21) following pressure increases caused by the pharmacological agents. In each case, the increase in tissue weight was accompanied by an increased permeability of the materno-fetal barrier, shown by the transfer of Evans blue albumin from the fetal circulation to the maternal compartment.

Blood volume restitution and growth in fetal lambs after acute hemorrhage

The effects of 15-50% fetal hemorrhage (at approximately 1%/min) were studied in 13 pregnant ewes at 130-135 days of gestation for up to 5 days posthemorrhage. The upper limit of acute blood loss appears to be approximately 45%, and the rate of restoration of blood volume decreases with the severity of hemorrhage, particularly with hemorrhage > 30-40%. The restoration of fetal blood volume was due primarily to the restoration of plasma volume; in the animals subject to 40-45% blood loss (n = 9), red cell mass was still only 69.1 +/- 3.9% of the prehemorrhage value at day 5 posthemorrhage. There appear to be two phases in the restoration of plasma: 1) plasma volume was restored by 2 h posthemorrhage and 2) the restoration of plasma protein mass occurred primarily from 2 to 24 h. There was a significant correlation between blood volume and plasma protein mass. However, the regression line for the posthemorrhage days was shifted significantly upward in relation to that for the hemorrhage day because of a significant rise of plasma protein concentration. This may be important for the maintenance of blood volume after hemorrhage. Finally, fetal growth rate was determined by comparing fetal weight estimated in utero (from blood volume) with birth weight in 12 nonhemorrhaged control fetuses and in the 9 fetuses subject to 40-45% hemorrhage. The average rate of growth per day was 1.57 +/- 0.34% and -1.82 +/- 1.02%, respectively. The latter value is not significantly different from zero, suggesting that the acute blood loss impaired fetal growth.

Oxygen consumption, acid-base status, and behavior during and after acute, severe hemorrhage in fetal lambs

The metabolic and behavioral effects of 40-45% hemorrhage (at approximately 1%/min) were studied in nine fetal lambs in utero (130-135 days of gestation) until 2 days posthemorrhage. Umbilical blood flow (Qum) fell from 192 +/- 14 to 100 +/- 9 ml.min-1.kg-1 at the end of blood loss, and on the day of hemorrhage it was linearly related to blood volume. However, on the posthemorrhage days, Qum was restored even though blood volume was still reduced. Fetal O2 delivery (DO2) fell with the decrease in Qum and later due to anemia (decrease in hematocrit from 33.4 +/- 1.2 to 23.6 +/- 1.2%), from 946 +/- 81 to 494 +/- 47 mumol.min-1.kg-1, but the decrease was lessened because of a rise in umbilical venous PO2 (31.7 +/- 2.6 to 45.9 +/- 2.8 mmHg). Fetal O2 consumption was reduced during and for 2 h after hemorrhage (262 +/- 17 to 190 +/- 16 mumol.min-1.kg-1), and this was associated with modest lactic acidemia (1.25 +/- 0.11 to 2.91 +/- 0.43 mM). There was also a temporary reduction in fetal breathing activity, low voltage electrocortical state, and rapid eye movements, but this was not associated with hypoxemia. It is concluded that reductions in fetal DO2 achieved via fetal blood loss are better tolerated than during hypoxemia and that the associated depression in fetal biophysical activities involves mechanisms other than systemic hypoxia.

Decapeptide agonists of human C5a: the relationship between conformation and neutrophil response

A series of decapeptide analogues corresponding to the C-terminal region of the human C5a anaphylatoxin (C5a65-74) was synthesized with residue substitutions to restrict conformational flexibility in the C-terminal region (residues 71-74). These analogues behaved as full agonists of natural C5a in their ability to induce shape change (polarization) and the release of enzyme (beta-glucuronidase) from human neutrophils (PMNs). There was a significant pharmacological correlation between the polarization and enzyme-release assays, suggesting similarities in PMN responsiveness toward these constrained peptides. Good correlations were also observed between these two PMN responses and spasmogenic activity (smooth muscle contraction of human fetal artery). A structure-function analysis for PMN polarization and enzyme release led to the identification of the following preferred backbone conformations: a twisted, helix-like conformation for residues 65-69, an extended conformation for residues 70-71, and a beta-turn of type V for residues (71)72-74. The existence of a C-terminal, type V beta-turn is supported by the NOE (nuclear Overhauser effect) results of two peptides from this series. These conformational features are reminiscent of those that were shown to correlate with the expression of spasmogenic and platelet aggregatory activities in an earlier investigation (Sanderson, S.D.; et al. J. Med. Chem. 1994, 37, 3171). These results suggest that PMNs and the cells responsible for smooth muscle contraction possess C5a receptors that respond to similar topochemical features presented by the agonist peptide ligand.

Craniomandibular osteopathy in a Shetland sheepdog

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Airway smooth muscle proliferation in asthma: the potential of vascular leakage to contribute to pathogenesis

Proliferation of the non-vascular smooth muscle in the walls of the bronchi and bronchioles is a prominent histopathological feature of asthma and is thought to contribute to airway hyperreactivity and narrowing. Increased vascular permeability with plasma leakage is also a feature of asthma pathology and causes submucosal oedema. We hypothesize that, in asthmatics, the accumulation of enriched plasma in the environment surrounding airway smooth muscle promotes respiratory smooth muscle mitogenesis and hyperplasia. This situation represents the in vivo correlate of the increase in airway smooth muscle cell growth seen in vitro with increasing concentrations of serum in the culture medium. Thus, we hypothesize that vascular leakage in the airways in asthma is a primary pathogenic event leading to airway smooth muscle hyperplasia and hypertrophy, and consequently airway narrowing, promoting the characteristic bronchial hyperreactivity associated with narrowing of the airway lumen.

Effects of treatment with topical ivermectin three and eight weeks after turnout on nematode control and the performance of second-season beef suckler cattle

Two groups of yearling suckled beef calves born between January and May of the preceding year and another two groups of lighter and slightly younger calves born between the previous March and July were grazed during their second year on four separate paddocks known to be contaminated with infective larvae of gastrointestinal nematodes. One of the heavier and one of the lighter groups were treated with a topical formulation of ivermectin three weeks and eight weeks after turnout. The treatment of the heavier group had only relatively minor parasitological effects and no effect on weight gains, whereas the treatment of the lighter cattle resulted in increased weight gains due to effective nematode control. The paper highlights that small differences in previous performances, age and exposure to parasites can have a substantial impact on the benefits accrued from anthelmintic treatment.