Evaluation of the comparative efficacy of selamectin against flea (Ctenocephalides felis felis) infestations on dogs and cats in simulated home environments.

The comparative efficacy of monthly administration of selamectin or lufenuron against Ctenocephalides felis felis on dogs and cats was evaluated over a 5-month period in flea-infested environments. Twenty-four dogs and 32 cats were randomly allocated to receiving a topical treatment with selamectin or an oral administration of tablets containing lufenuron/milbemycin oxime (for dogs) or lufenuron only (for cats). Each product was administered in accordance with the manufacturer's label recommendations. Eight dogs and four cats served as untreated sentinels. Treatments were administered on days 0, 30, 60, 90, and 120. Each animal received an application of 100 fleas on days -28 and -21, and then weekly applications of 20 fleas from days 91 through 147. Flea comb counts were performed on day -6, and every 2 weeks after day 0. From day 29 (dogs) or day 44 (cats) to day 150, geometric mean flea counts for selamectin were < or =0.4. Mean flea counts for animals assigned to treatment with selamectin were significantly lower (P=0.0001) than for animals assigned to treatment with lufenuron at all assessments after day 0.

Evaluation of efficacy of selamectin and fipronil against Ctenocephalides felis in cats.

OBJECTIVE: To evaluate efficacy of monthly administration of selamectin and fipronil against Ctenocephalides felis in cats. DESIGN: Randomized controlled trial. ANIMALS: 36 healthy cats. PROCEDURE: Cats known to be free of fleas were infested with 100 unfed adult fleas on days -28 and -21. On days 0, 30, 60, 90, and 120, sixteen cats (8 pairs/treatment group) were treated by topical administration of selamectin (6 mg/kg [2.7 mg/lb] of body weight) or fipronil (7.5 mg/kg [3.4 mg/lb]). Four control cats (2 pairs) were not treated. On day -6 and every 2 weeks after initial treatment, comb counts were performed to detect fleas. Flea counts were recorded, and fleas (< or =50) that had been removed were replaced onto the cat. On day 89, fleas were not replaced. On day 91 and every 7 days until the end of the study (day 150), cats were challenged with 20 adult fleas. Flea counts were compared between and within treatments. RESULTS: 14 days after treatment, geometric mean flea counts were reduced by 71.2% by fipronil treatment and 35.3% by selamectin treatment. Both treatments resulted in 97 to 98% reduction in flea counts on day 29 and 99.8 to 100% reduction from day 44 to the end of the study. CONCLUSIONS AND CLINICAL RELEVANCE: Selamectin is as effective as fipronil in treating infestation in cats housed for 3 months in a flea-infested environment under conditions known to support the flea life cycle and in protecting against subsequent weekly challenges with C felis for an additional 2 months.

Evaluation of efficacy of selamectin, fipronil, and imidacloprid against Ctenocephalides felis in dogs.

OBJECTIVE: To evaluate efficacy of monthly administration of selamectin, fipronil, and imidacloprid against Ctenocephalides felis in dogs. DESIGN: Randomized controlled trial. ANIMALS: 44 healthy dogs. PROCEDURE: Dogs known to be free of fleas were infested with 100 unfed adult fleas on days -28 and -21. On days 0, 30, 60, 90, and 120, dogs (12/group) were treated by topical administration of selamectin (6 mg/kg [2.7 mg/lb] of body weight), fipronil (7.5 mg/kg [3.4 mg/lb]), or imidacloprid (10 mg/kg [4.5 mg/lb]); 8 untreated dogs were used as controls. On day -6 and every 2 weeks after initial treatment, comb counts of viable adult fleas were made, and fleas (< or =50/dog) were replaced onto the dog from which they were removed. On day 89, fleas were not replaced. On day 91 and every 7 days until the end of the study, dogs were challenged with 20 adult fleas. RESULTS: 14 days after initial treatment, geometric mean flea counts were reduced by 97.5 to 99.1 % for all treatments, compared with pretreatment counts on day -6. Selamectin, fipronil, and imidacloprid reduced geometric mean flea counts by 99.7 to 100% from day 29 to the end of the study. CONCLUSIONS AND CLINICAL RELEVANCE: Selamectin is as effective as fipronil and imidacloprid in reducing C felis infestation in dogs housed for 3 months in a flea-infested environment under conditions known to support the flea life cycle, and in protecting against subsequent weekly challenges with C felis for an additional 2 months.

The effect of simulated rainfall on the efficacy of doramectin pour-on against nematode parasites of cattle.

Two studies were conducted with doramectin topically administered at 500 microg/kg body weight to assess retention of therapeutic efficacy against nematode infections of cattle before, and after, simulated rainfall. In the first study, 50 heifers, with patent nematode infections, were allocated to one of five treatment groups. An untreated control group and one doramectin-treated group were not exposed to simulated rainfall. Simulated rainfall was applied at a rate of 25.4 mm of water in 35 min to three of the five groups: one group immediately before treatment, the second group 90 min after treatment, and the third group 24 h after treatment. Fecal samples were collected for determining egg counts 14 days after treatment. Percentage efficacy ranged from 97.3% to 100% in all treated calves, regardless of exposure to simulated rainfall. The second study involved 40 mixed-sex cattle that were allocated to one of four treatment groups (one saline control and three doramectin-treated groups). All cattle were confirmed to be free of nematode infections prior to oral gavage with infective larvae of Dictyocaulus viviparus, Cooperia oncophora, and Ostertagia ostertagi. Twenty-six days after infection, three groups were treated with doramectin pour-on and exposed to 20 mm of simulated rainfall over 40 min: one group 60 min before treatment, the second 20 min after treatment, and the third 40 min after treatment. Approximately two weeks after treatment, all cattle were necropsied for worm counts. In all treated groups, the percentage efficacy against O. ostertagi and D. viviparus was >99% to 100%. Percentage efficacy against Cooperia ranged from 97% to 98%. Results indicated that doramectin pour-on remains efficacious against nematodes of cattle when administered immediately before or after rainfall.

Persistent efficacy of doramectin and ivermectin against experimental infestations of Sarcoptes scabiei var. suis in swine.

Two studies were performed to compare the persistent efficacy of doramectin and ivermectin in swine experimentally infested with Sarcoptes scabiei var. suis. In the Study 1, 84 pigs were treated with doramectin, ivermectin, or saline solution on Day 0. Pigs were then challenged with mites on Days 0, 7, 14, 21, 28, 35, or 42. Weekly evaluations were performed for 5 weeks following challenge with mites. Weekly evaluations included physical examination for clinical signs of sarcoptic mange and collection of skin scrapings for determination of mite counts. In the Study 2, 80 pigs were treated with doramectin, ivermectin, or saline solution on Day 0, and challenged with mites on Days 3, 6, 9, 12, 15, 18, 21, 24, or 27. Weekly evaluations were performed for 6 weeks after challenge exposure. All negative-control (saline-treated) animals in both studies developed evidence of mite infestation. In the Study 1, doramectin prevented mite infestations 7 days longer than ivermectin. Results from the Study 2 indicated that the persistent efficacy of doramectin was 18 days on the basis of mite recovery. This was twice as long as the persistent efficacy of ivermectin, which was 9 days on the basis of mite recovery.

A decrease in FSH receptors of granulosa cells during follicular maturation in the domestic hen.

The follicles of the ovary in the domestic hen are arranged in a hierarchy. Responsiveness of the adenylyl cyclase enzyme system of the granulosa cells to FSH decreases as follicles proceed towards ovulation. To test the hypothesis that this decline in FSH responsiveness could be the result of a decrease in FSH receptor numbers, an FSH receptor assay was characterized for chicken granulosa cells and used to measure receptor number and affinity of the largest (F1), third largest (F3) and fifth largest (F5) follicles removed 18 h before ovulation. The numbers of binding sites for F1, F3 and F5 follicles (n = 4) were 0.22 +/- 0.05, 0.5 +/- 0.14 and 1.22 +/- 0.27 pmol hormone bound/mg protein respectively, and were significantly (P less than 0.001) different among follicles. The apparent association constants for the F1, F3 and F5 follicles were not different and had a value of 23.4 +/- 4.9 litres/nmol (n = 12). Our results indicate that FSH receptor numbers decrease in granulosa cells without a change in affinity as follicles approach ovulation. The decrease in FSH receptor numbers is associated with the reported decline in FSH-stimulated steroidogenesis and adenylyl cyclase activity which occurs during follicular maturation.

Adenylate cyclase activity of the corpus luteum during the oestrous cycle of the pig.

Basal adenylate cyclase values for corpora lutea (CL) removed from cyclic gilts on Days 3, 8, 13 and 18 were 178 +/- 61, 450 +/- 46, 220 +/- 25 and 208 +/- 18 pmol cAMP formed/min/mg protein, respectively. Basal activity was significantly elevated on Day 8 (P less than 0.001). LH-stimulatable adenylate cyclase values for CL from Days 3, 8, 13 and 18 were 242 +/- 83, 598 +/- 84, 261 +/- 27 and 205 +/- 17 pmol cAMP formed/min/mg protein respectively. Serum progesterone concentrations of 12 gilts bled every 2 days through one complete oestrous cycle ranged from 1.1 to 26.9 ng/ml with highest values between Days 8 and 12. The decline in serum progesterone concentrations was coincident with the decrease in basal adenylate cyclase activity. There was no LH-stimulatable adenylate cyclase activity present in the CL at the specific times of the oestrous cycle examined. We conclude that progesterone secretion by the pig CL is apparently dependent on basal activity of adenylate cyclase.

Catecholamine content of the preovulatory follicles of the domestic hen.

The role of catecholamines in ovarian function of the domestic hen has not been examined extensively. The aim of this study was first to determine the location of catecholamines in the preovulatory follicle of the domestic hen. Second, norepinephrine (NE), epinephrine (EPI) and dopamine (DA) were measured in the isolated theca layer of the five largest preovulatory follicles at specific times during the ovulatory cycle and changes in catecholamine content were correlated with ovarian events. The five largest preovulatory follicles were removed from chickens at 24, 18, 12, 6 and 2 h before ovulation of the largest (F1) follicle. Theca and granulosa layers were isolated, frozen, weighed and prepared for measurements of catecholamines by the double isotope radio-enzymatic assay. Catecholamines were localized primarily in the theca layer with only small amounts present in the granulosa layer. Norepinephrine was present in the theca layer in concentrations 6- and 30-fold those of EPI and DA, respectively. The content of NE and EPI in the theca layer of the F1 follicle was significantly (p less than 0.01) higher at 6 h before ovulation than at other times for the F1 follicle. In contrast, NE and EPI content of the theca layer of second (F2) and third (F3) largest follicles did not change during the ovulatory cycle. The content of DA was elevated (p less than 0.05) at 12 h before ovulation in F1 and F2 follicles. There was a significant reduction in NE in the theca layer of the fifth largest (F5) follicle between 24 and 18 h before ovulation of the F1 follicle.(ABSTRACT TRUNCATED AT 250 WORDS)