Release Bolus Research Articles

Effect of sustained release bolus oral administration on body condition change, blood parameters, and uterine health in primiparous cows under heat stress.

The transition period is very stressful for primiparous cows due to their first calving experience and will be more challenging if it occurs under heat stress conditions. Heat stress reduces the feed intake of dairy cows. Therefore, it reduces the consumption of minerals and vitamins. Oral administration of boluses through the provision of mineral-vitamin compounds can reduce metabolic abnormalities after calving. The present study aimed to evaluate effect of sustained-release bolus on body condition score (BCS) change, serum metabolites, uterine health, and reproductive status in primiparous cows. Heifers were selected at the beginning of the close-up period (n = 60, BCS = 3.35 ± 0.12). There were 2 experimental treatments at the time of calving: (1) heifers without bolus oral administration (H - Bo, n = 30); (2) heifers with bolus oral administration (H + Bo, n = 30). The results showed that although the rate of BCS loss was lower in the group receiving bolus, the effect of bolus was not significant. The effect of bolus on blood level of glucose, non-esterified fatty acids (NEFA), and beta-hydroxybutyrate (BHBA) was not significant; however, the highest concentration of albumin (P = 0.05) was observed in the H + Bo group on day 42 after calving. The concentration of aspartate transaminase (AST) tended to increase (P = 0.06) on day 14 after calving and entire the study. Total antioxidant capacity (TAC) was affected (P < 0.05) by bolus throughout the period of study, and the highest (P < 0.05) concentration of glutathione peroxidase (GPX) and superoxide dismutase (SOD) was observed in H + Bo group on day 42 after calving. The H + Bo group had the lowest (P < 0.05) vaginal discharge score (VDS). In general, oral administration of the sustained-release bolus in heifers significantly affected the antioxidant factors and uterine health, as well as had positive effects on liver function, body condition, and reproduction status.

Managing plasma P concentrations in beef heifers with a slow release vitamin D supplementation

Context In extensive northern grazing systems, supplementation of P is recommended to maximise cattle growth rates and reproduction. Improving the absorption of P for the animal by influencing metabolic pathways has the potential to improve both the productivity and profitability of extensive livestock enterprises. Aims This study evaluated the efficacy of rumen bolus containing 25-hydroxyvitamin D (25OHD), commercially available as Hy-D®, and/or monensin on blood P and Ca concentrations in young cattle. Methods A total of 84 heifers, initial liveweight (mean ± s.e.m.) 184 ± 2.0 kg, were allocated to four groups, dosed with one of four slow release bolus: (1) placebo (control), (2) monensin (120 mg/day), (3) Hy-D® (6 mg/day), or (4) monensin with Hy-D®, and managed on a common unimproved native pasture from August 2012 to February 2013. On four occasions postdosing, liveweight, hip height and body condition scores were recorded, and individual faecal and jugular blood samples were collected. Key results Supplementation with monensin had a significant effect (P &amp;lt; 0.05) on average daily gains for the first 25 days. Interactions between 25OHD and monensin and time × monensin were also significant (P &amp;lt; 0.05). After 188 days, heifers receiving monensin or 25OHD + monensin were 5 and 10 kg heavier respectively, compared with their counterparts in the control and 25OHD groups. Plasma P concentrations at 25 days were 6.6 mg/dL, then increased to between 8.5 and 9.0 mg/dL and maintained this level for up to 109 days with a bolus releasing 6.0 mg/day 25OHD. Conclusions The study demonstrated that sustained and elevated plasma concentrations of both 25OHD and P, compared with control animals, can be achieved. The slow release rumen bolus maintained an elevated plasma concentration of 25OHD, and indicated that a target plasma concentration for 25OHD for increasing P absorption in beef cattle is between 200 and 300 ng/mL. Implications Supplementation of a metabolite of vitamin D influences P metabolism in Brahman heifers under grazing conditions. Integration with standard supplementation practices would optimise growth rates and reproductive performance.

Effects of prepartum sustained-release trace elements ruminal bolus on performance, colustrum composition and blood metabolites in Najdi ewes.

The aim of this study was to determine the effect of the supplementation of slow release bolus of selenium (Se), copper (Cu), zinc (Zn), cobalt (Co), phosphorous (P), manganese (Mn), and iodine (I) at late gestation (60day prepartum) on performance of Najdi ewes and their newborn. Twenty Najdi ewes at late gestation were randomly selected from a herd raised under an intensive system and equally divided into two groups (control and treated). Blood samples were collected from ewes and newborns at parturition. Body weights of newborns were taken at birth, 30 and 60days. A significant (P<0.05) increase in Cu and Co in blood of dams treated with boluses with an increase (P<0.05) in blood P, Zn, Cu, Co, and Se of their newborn lambs were observed. Creatinine and triglyceride were significantly (P<0.05) low in treated newborn while urea was significantly (P<0.05) high in the same group. In dams, significantly (P<0.05) low concentration of triglyceride was observed. Body weight of lambs from treated group at 30days was significantly (P<0.05) higher when compared with the control. In conclusion, bolus of trace minerals at late gestation improved some mineral status of ewes and the newborns with higher body weight.

New oral anthelmintic intraruminal delivery device for cattle

Background:The purpose of this work was to develop a new oral drug delivery system intended for cattle and that enables delayed and pulsed release of an anthelmintic agent.Materials:This new tailored dosage form, also called reticulo-rumen device (RRD) has been evaluated on grazing calves by means of measurements of milliunits of tyrosine concentration, number of eggs per gram of feces, mean number of infective larvae on cattle pasture and increase in mean weight of cattle.Methods:The in vivo evaluation was carried out during two grazing seasons on different groups of dairy cattle. During the first grazing season, Group 1 was designated as an untreated control group. The remaining two were assigned to different treatments as follows: Group 2, early season suppression with a marketed intraruminal slow release bolus (Chronomintic®, Virbac) administered immediately prior to turn-out and Group 3, mid-season suppression with a new RRD administered immediately prior to turn out. When the cattle were turned out at the start of the second grazing season, they were not given any anthelmintic treatment and were divided into two different groups, corresponding to the previous groups that received an anthelmintic treatment during the first grazing season, on that pasture that they had occupied as separate groups in the previous year. Furthermore, during the second season, samples of feces, blood and herbage were collected every month.Results and Conclusion:During the first grazing season, the results indicated that the fecal egg counts and the number of infective larvae in herbage samples were slightly lower for the group receiving the new RRDs. Regular weighing of the cattle receiving the new RRDs revealed no significant difference with cattle receiving marketed RRDs. Conversely, during the second grazing season, the results for the mean weights of the cattle demonstrated that the weights of animals having been administered new RRDs during the first grazing season were significantly different (P < 0.05) from those in the second group treated with a Chronomintic® during the first grazing season. A difference in mean weight of 26 kg was observed between these two groups.

Enhancement of dentate gyrus neurogenesis, dendritic and synaptic plasticity and memory by a neurotrophic peptide

Pharmacological enhancement of hippocampal neurogenesis is a therapeutic approach for improvement of cognition in learning and memory disorders such as Alzheimer's disease. Here we report the development of an 11-mer peptide that we designed based on a biologically active region of the ciliary neurotrophic factor. This peptide, Peptide 6, induced proliferation and increased survival and maturation of neural progenitor cells into neurons in the dentate gyrus of normal adult C57BL6 mice. Furthermore, Peptide 6 increased the MAP2 and synaptophysin immunoreactivity in the dentate gyrus. Thirty-day treatment of the mice with a slow release bolus of the peptide implanted subcutaneously improved reference memory of the mice in Morris water maze. Peptide 6 has a plasma half life of over 6 h, is blood-brain barrier permeable, and acts by competitively inhibiting the leukemia inhibitory factor signaling. The fact that Peptide 6 is both neurogenic and neurotrophic and that this peptide is effective when given peripherally, demonstrates its potential for prevention and treatment of learning and memory disorders.

Mathematical models to assess strategies for the control of gastrointestinal roundworms in cattle: 2. Validation

A computer model of the population biology of Ostertagia ostertagi in young cattle and the effect of the parasite on animal growth has been constructed. It was validated against results from field trials where worm populations and rate of growth of cattle treated with anthelmintics were compared to similar groups of untreated animals. A close correlation between observed and predicted values for faecal egg and pasture larval counts was seen in the cattle which had been treated with an oxfendazole pulse release bolus at turnout. Timings and peak values were less accurately predicted in the untreated cattle. Although predictions for live weight gain during the grazing season indicated that the model may be overestimating the potential growth rate of cattle, it is considered that the model provides a suitable tool for comparing the effectiveness of different worming programmes under farm conditions. The computer simulation also allowed examination of the underlying influences and interactions between parasitological factors, such as numbers of immature and adult worms, and animal and pasture factors, such as sward height, grass consumption and feed conversion, in the parasite's influence on animal performance.

Effect of horn fly and internal parasite control on growth of beef heifers

The effects of horn fly and gastrointestinal nematode control on body weight gain of yearling Angus–Brangus cross heifers were evaluated in three separate studies during the years 1999, 2000 and 2002. In each year, the studies started in late May and lasted for 150, 148 and 123 days, respectively. In all three studies, the tag treatment (10% lambdacyhalothrin+13% piperonyl butoxide impregnated ear tags) provided excellent horn fly control. In the three studies, the average weekly horn fly counts for tagged heifers were 1, 3, and 0 flies per side while the average on untreated heifers was 52, 163 and 90 flies per side. In studies 1 and 2, there was no difference ( P>0.1) in weight gain between tagged and untreated heifers, but in study 3, tagged heifers gained 50% more weight ( P<0.001) than the untreated heifers. For gastrointestinal nematode control, ivermectin (IVM) was administered on Day 0 in studies 1 and 3 using a sustained release bolus and on Day 0 and subsequent 56-day intervals in study 2 using either the injectable or pour-on formulation. Heifers treated with IVM in studies 1 and 3 had significantly lower ( P<0.05) GI nematode fecal egg counts compared to control heifers. In study 2, IVM treated heifers also had significantly lower GI nematode fecal egg counts compared to control heifers, except for Day 90 when no differences in fecal egg counts were observed between IVM pour-on treated and control heifers. Weight gain of heifers that received IVM was significantly greater ( P<0.005) than untreated heifers in each of the three studies. IVM treated heifers gained 45, 61 and 184% more weight than the untreated heifers during the three studies. There was no interaction ( P>0.1) between the main treatment effects of fly control and gastrointestinal nematode control.

A single pasture limited treatment approach to estimate production loss from gastrointestinal nematodes in grazing stocker cattle

The objective of this study was to evaluate the use of a single pasture, limited treatment methodology to assess the impact of gastrointestinal nematodes on weight gain in grazing cattle. From a group of 450 British crossbred, yearling spayed heifers, 60 animals were randomly selected (prospective randomization) prior to placement on summer pasture. Each of these 60 animals was weighed, a fecal sample obtained for nematode egg count and a uniquely numbered ear tag applied. A randomly assigned group of 30 received treatment with one ivermectin sustained release bolus, while the remaining 30 served as non-treated controls. The treatment and control groups rejoined the remaining non-treated 390 animals, and were grazed as a single group for 165 days. At grazing conclusion, treatment and control cattle were individually weighed, and fecal samples obtained for nematode egg counts. Treatment was associated with a 0.064 kg per grazing day gain increase, or a 10 kg increase over the grazing season ( P=0.02). Nematode egg counts at grazing initiation were not different between treatment and control ( P=0.30), though egg counts in treated cattle at study end were lower than control ( P<0.0001). Results of this study support the use of a single pasture limited treatment approach for measuring the effect that internal nematodes have on weight gain in grazing cattle under commercial range conditions.

Syringe size and flow rate affect drug delivery from syringe pumps.

To evaluate the effect of syringe size and infusion rate on drug delivery after vertical displacement of syringe pumps. Four syringes (10 ml, 20 ml, 30 ml, 50 ml) were studied at three infusion speeds (2 ml x hr(-1), 1 ml x hr(-1) and 0.5 ml x hr(-1)). Fluid delivery was measured gravimetrically using an electronic balance. Aspiration volume (amount of fluid retracted into the syringe-infusion line assembly) and zero-drug delivery time (time between the lowering of the syringe pump and reattainment of the initial weight) were determined after lowering the syringe pump 130 cm or 50 cm. Then, infusion bolus was measured after elevating the pump to its initial position. Syringe compliance was calculated from the occlusion release bolus at an occlusion pressure of 300 mmHg. Zero-drug delivery time, aspiration volume and infusion bolus increased with syringe size (P < 0.0001). At 0.5 ml x hr(-1), a zero-drug delivery time of 29.7 +/- 0.6 min was recorded for the 50 ml syringe and 5.5 +/- 0.15 min for the 10 ml syringe. As infusion rates increased, zero-drug delivery times decreased following a 1/x ratio. Zero-drug delivery time highly correlated with calculated syringe compliance (Pearson's r = 0.97, P < 0.001), which was closely related to syringe plunger area (R2 = 0.93, P < 0.001). Vertical displacement of syringe pumps causes flow irregularities which correlate directly with syringe size and indirectly with infusion rate. Extreme vertical maneuvering of syringe pumps should be avoided. Infusion rates > or = 1 ml x hr(-1) and low-compliant, small syringes are recommended when highly concentrated drugs are administered.

Effects of anthelmintic treatment and feed supplementation on grazing Tuli weaner steers naturally infected with gastrointestinal nematodes.

A study was carried out to determine the epidemiology of gastrointestinal nematodes in indigenous Tuli cattle and the effect of dietary protein supplementation and anthelmintic treatment on productivity in young growing cattle. Forty steers with an average age of 18 months were divided into 4 groups; 1) fenbendazole (slow release bolus) and cottonseed meal (FCSM group), 2) fenbendazole (FBZ group), 3) cottonseed meal (CSM group) and 4) control (no cottonseed meal and no fenbendazole) (control group). Performance parameters measured included worm eggs per gram of faeces (EPG), packed cell volume (PCV), albumin and live-weight gain. Results showed that faecal worm egg counts were lower and PCV was higher in the FCSM and FBZ groups than in the CSM and control groups (P < 0.01). Weight gains were higher in the CSM and FCSM groups than in the FBZ and control groups (P < 0.05). The cost benefits of anthelmintic treatment and dietary supplementation were apparent in this study. The improved growth performance of the FCSM, FBZ and CSM groups reflected a financial gain over the controls on termination of the study. The dominant genera of gastrointestinal nematodes on faecal culture, pasture larval counts and necropsy were Cooperia and Haemonchus. The incidences of Trichostrongylus, Oesophagostomum and Bunostomum were low.

Effect of the anti bloat agent poloxalene on n-alkane concentration in cattle faeces

Current pressures to extensify agricultural systems are leading to more emphasis on incorporating legumes, such as white clover, into swards thus reducing the amount of fertiliser nitrogen used. Cattle fed clover rich diets often receive poloxalene (Bloat guard ®, Agrimin Limited) as a feed additive to prevent bloat. Poloxalene is a surfactant, reducing surface tension of bubbles caught in froth, and thus reducing foam formation in the reticulo-rumen. The n-alkane technique (Dove and Mayes 1991) to measure intake is widely used in grazing experiments. Alkanes are saturated hydrocarbons found in the waxy cuticle of plants, which are used as internal markers to estimate herbage intake and to determine dietary composition in grazing ruminants. Animals are typically dosed with a controlled release bolus (CaptecTM FERNZ, New Zealand) containing an even-chained synthetic alkane (C32). Mean daily dry matter intake is calculated using the assayed release rate of C32 and the concentrations of C32 and C33 in herbage and faeces (Dove and Mayes, 1991). Given that poloxalene is a surfactant, it could potentially interact with the n-alkanes and therefore invalidate the technique. The aim of this experiment was to investigate the effect of including poloxalene in the diet on the n-alkane concentration in faeces from dairy cattle.

Growth and economic performance of grazing steers as influenced by growth implant and anthelmintic strategy

460 yearling steer calves were grazed on 6 improved mountain pastures in western North Carolina for 128 days. The pastures were matched into 3 pairs based on acreage, topography and botanical composition. Within each pair of pastures, calves in 1 pasture received a sustained release bolus containing ivermectin (Ivomec SR Bolus), and calves in the other pasture were drenched with fenbendazole at 5 mg/kg (Safe-Guard Suspension 10%). In the fenbendazole treatment groups, a loose mineral and fenbendazole mix (Safe-Guard Free-Choice Mineral) was provided to the calves for 5 days beginning at day 28 and day 56 to provide 5 mg/kg/animal over the 5 day period. Within each pasture, calves received 1 of 4 commercial implant treatments: Ralgro (36 mg zeranol), Synovex-S (20 mg estradiol benzoate and 200 mg progesterone), Revalor-G (8 mg estradiol-17 beta and 40 mg trenbolone acetate) or no implant. Calves receiving the Ivomec SR Bolus had a significantly higher average daily gain than the Safe-Guard treated calves (0.96 vs. 0.88 kg/day) resulting in a 11.93 kg advantage. At the end of the trial, 8 of 29 randomly sampled calves on the Safe-Guard treatment were shedding parasite eggs. No calf receiving the ivermectin bolus was shedding clinically significant levels of parasite eggs. When value of gain, cost of product, labour and equipment costs were considered, it was determined that the cattle treated with the Ivomec SR Bolus returned $6.70/head more than the cattle treated with Safeguard. Implanted calves gained more than the non-implanted calves with average daily gains of 0.83, 0.95, 0.95 and 0.94 kg/day for the control, Ralgro, Synovex-S and Revalor-G cattle, respectively. An economic analysis, which included the value of gain, the product cost and the labour to administer the implants, showed an average of $15.31 greater return for the implanted calves compared with control calves. It is suggested that the Ivomec SR Bolus should be considered for calves grazing large mountain pastures for extended periods.

Effects of preventive anthelmintic treatment on acquired resistance to gastrointestinal nematodes in naturally infected cattle

The objective of this study was to investigate the influence of different types of chemoprophylaxis in first season grazing calves on their resistance against a natural reinfection with Ostertagia ostertagi and Cooperia oncophora in the second grazing season. Thirty helminth-naive crossbred calves were randomly divided in three groups of 10 animals. The animals of group B received an ivermectin sustained release bolus on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg −1 BW). Group C was the untreated control group (`immune' controls). Although exposure to gastrointestinal nematodes in the first grazing season was only limited, the chemoprophylactic treatments in groups B and D resulted in three distinctly different infection levels (group C>group D>group B). At the start of the second grazing season, six helminth-naive steers (group N, `susceptible' controls) were turned out together with the second season animals. After 3 weeks of grazing, the `susceptible' controls were slaughtered, together with four animals from each other group. Parasitological and immunological parameters indicated that resistance to reinfection with Ostertagia was reduced in the chemoprophylactic treated animals, and was negatively related to the degree of suppression of host-parasite contact in the first grazing season (group C>group D>group B>group N). None of the groups had developed a complete resistance against Cooperia yet. A negative relationship was observed between reduction of first grazing season exposure, and weight gains early in the second grazing season. The remaining animals stayed on pasture until the beginning of November. At the end of the second grazing season, levels of acquired resistance against Ostertagia infection were similar in all groups, and all animals had become immune against Cooperia. No effect of first year chemoprophylaxis on total weight gains could be demonstrated. Because of discrepancy between pasture larval counts and tracer worm counts, it was not possible to draw firm conclusions on the effect of chemoprophylaxis on pasture infestation levels in the second year.

The effect of different infection levels on acquired resistance to gastrointestinal nematodes in artificially infected cattle

The objective of this study was to evaluate the effect of different infection levels of Ostertagia ostertagi and Cooperia oncophora in a simulated `first grazing season' on the resistance of calves to an artificial challenge infection. The infection levels were determined by the infection schedules and the chemoprophylaxis used. Thirty six 7–11-month old Holstein–Friesian bull calves were randomly divided into four groups. The animals of group B received an ivermectin sustained release bolus (ISRB) on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg −1 BW). Group C was the untreated control group. The calves of group N were used as helminth-naive controls, while the animals of groups B, C and D were trickle infected for 24 weeks. The infection schedules were designed to simulate the expected infection pattern for each treatment group under set-stocked conditions in temperate climate areas. After the last infection, all animals were treated with oxfendazole. One week later, all animals received a challenge infection of 50,000 O. ostertagi L3 and 100,000 C. oncophora L3, spread over 10 consecutive days. During the primary infection period the faecal egg output and the serum pepsinogen and antibody levels reflected the different levels of host–parasite contact between the groups (group C>group D>group B>group N). After the challenge infection, faecal egg counts, total Ostertagia burden, size of the adult worms and abomasal globule leucocyte counts all indicated a positive relationship between the level of Ostertagia infection during the primary infection period and the level of acquired resistance. A reduction of host–parasite contact during the primary infection period, as a consequence of the infection schedule and the chemoprophylaxis used, resulted in a diminished level of resistance to the artificial challenge infection with O. ostertagi. Faecal cultures and small intestine worm counts indicated that all previously infected groups had acquired a high degree of resistance to the Cooperia challenge infection.

Field evaluation of a fenbendazole slow release bolus in the control of nematode infections in first-season cattle

The efficacy of a fenbendozole slow release bolus in controlling nematode infections of first-season cattle was evaluated in a field study in northern Germany.&#x0D; Full article published in Veterinary Record (1997) 140, 395-399

Field evaluation of a fenbendazole slow release bolus in the control of nematode infections in first-season cattle

The efficacy of a fenbendazole slow release bolus in controlling nematode infections of first-season cattle was evaluated in a field study in northern Germany. Two groups, each of 11 male...

Prophylaxis of bovine trichostrongylidosis and dictyocaulosis in the alpine region: comparison of an early and late administration of the oxfendazole pulse release bolus to first year grazing calves

The effect of the oxfendazole pulse release bolus (OPRB) administered at turnout, in May, or in mid-July on the development of infections with gastrointestinal nematodes and lungworms in first year grazing calves was investigated with three groups of nine animals, all grazing the same pastures in the Swiss midland region. In the calves of Group A (OPRB on 21 May) less than 20 eggs per gram of faeces (e.p.g.) and less than three Dictyocaulus larvae per 10 g (l.p.10 g) of faeces were shed for a period of 126 and 140 days respectively. Towards the end of the grazing period calves of this group excreted significantly higher levels of lungworm larvae ( P < 0.05) compared with the other groups. Prior to OPRB administration on 14 July, the calves of Group B developed subclinical infections with trichostrongyles and lungworms which were similar to the untreated control Group C. By 4 weeks after bolus-administration the excretion of trichostrongylid eggs and lungworm larvae declined to levels below 20 e.p.g. and six l.p.10 g respectively. Serum pepsinogen values of the calves of Groups A and B were significantly lower ( P < 0.05) compared with the control animals on days 84 and 98 after turnout and reflected mainly subclinical infections. With the exception of one Group A calf developing clinical parasitic gastroenteritis (p.g.e.) at the end of the season, clinical disease was not observed in the treated calves, while seven out of nine control animals grazing on the same pastures exhibited clinical p.g.e. with mean serum pepsinogen values exceeding 4400 mU tyrosine. Calves of Groups A and B gained significantly more weight ( P < 0.01) compared with Group C (+36 kg and +41 kg respectively); grazing systems of treated and untreated calves, which are often found in the alpine region, administration of the OPRB in May or July provided good results with respect to performance of the calves. However, late administration of the OPRB has the additional advantage of coverage of the period of higher infection risk with trichostrongyles and lungworms in the late season until stabling, and should therefore be recommended.

Development of immunity to lungworm in vaccinated calves treated with an ivermectin sustained release bolus or an oxfendazole pulse release bolus at turnout

The ivermectin sustained release bolus (IVSRB), when used at turnout as recommended, will provide season-long control of parasitic bronchitis, thus obviating the need for use of a lungworm vaccine. However, some concerns have been expressed that calves treated with an IVSRB will receive so little exposure to Dictyocaulus viviparus that it will compromise their immunity in subsequent grazing seasons, which would be of particular importance in dairy herds. Although there is evidence that IVSRB-treated calves can develop immunity to D. viviparus when exposed to pasture infection, it was considered worthwhile to evaluate the compatibility of the IVSRB and lungworm vaccination to allow veterinary surgeons the option of using these products concurrently when they have particular concerns about the long term immune status of replacement dairy heifers. Thirty-two dairy replacement heifers were vaccinated with two doses of lungworm vaccine and, at turnout, half the calves received an IVSRB and the remainder an oxfendazole pulse release bolus (OPRB). At the end of the grazing season four replicate bolus treated pairs and four parasite-naive calves were challenged with 1000 D. viviparus infective larvae. At slaughter there was a 95% and 93% reduction in D. viviparus burdens in the IVSRB and OPRB treated calves respectively, compared with the unvaccinated, untreated controls. These results indicate that where it is considered necessary to use lungworm vaccination in addition to an IVSRB or an OPRB, the compatibility of these products with lungworm vaccine will allow development of a protective level of immunity to D. viviparus.

Response of cattle treated with fenbendazole slow release bolus to challenge from nematodes the following season

Nematode infection of cattle treated in their first year at pasture with the fenbendazole slow release bolus (‘Bolus group’) was compared during the second year with that of untreated cattle. Ostertagia was the most prevalent parasite associated with Cooperia. Except for the Dictyocaulus spp. which caused clinical signs of bronchitis in the ‘Bolus’ group the infection during the second year resulted in a moderate response of the cattle whatever the group. Rises in both pepsinogen and gastrin levels were correlated with the number of Ostertagia L 3 on herbage. Damages in the abomasal mucosa were more frequent and severe in the ‘Bolus’ group where more inflammatory signs were observed in spite of a smalleer number of worms. Nevertheless, the differencesin total weight gains were not significant thanks to a compensatory effect during the second part of the grazing season in the ‘Bolus’ group. Hypotheses related to a minimum threshold of infection during the first year necessary to develop high enough protection during the second year are discussed. The pathological effects of gastrointestinal nematodes seem to vary more according to the inflammatory response than to the number of worms.

Biopharmaceutical aspects of the development of a sulfamethazine oral sustained release bolus for lambs

Pharmacokinetic parameters of sulfamethazine (SMZ) administered intravenously or orally either as an aqueous solution or as a lipid matrix formulation, were determined in young lambs. The value of the rate constant for elimination ( k e ) for the intravenous solution was 0.18 h −1 compared to 0.10 h −1 for the oral aqueous solution. The absolute bioavailability of the oral solution was about 75%. A lipid matrix containing SMZ and a high density excipient is able to be retained in the reticulo-rumen and to produce a sustained release of the drug for at least 100 h provided that the mechanical strength of the bolus is sufficient. The pharmacokinetic data obtained with the lipid matrix show a release profile with two pulses due to both diffusion and erosion mechanisms. Plasma levels are maintained above the MIC of SMZ during 100 h with an absolute bioavailability of 51.7%.