Persistent efficacy of doramectin pour-on against artificially induced infections of nematodes in cattle.

Two studies were conducted to determine the persistent efficacy of doramectin pour-on against an artificial, trickle challenge of mixed nematodes in calves. In each study, 42, 4-8 months old calves were randomly assigned into four groups of 10 animals each (T1-T4), plus two larval-viability monitor animals. All animals were treated with fenbendazole (10 mg kg(-1)) 14 days prior to the start of the study to clear any existing infection. Doramectin pour-on at 500 microg kg(-1) was used on each animal in Groups T2, T3, and T4 with intervals of 1 week (Day 0, 7, and 14, respectively). Calves in Group T1 were treated with saline solution on Day 0 and at the same volumetric rate (1 ml 10 kg(-1)) as the doramectin treated animals. All treatments were applied in a single passage along the midline of the back, from the withers to the tailhead. Subsequently, trickle inoculations with infective larvae were administered to all calves for 22 consecutive days (Days 14-35). Doramectin pour-on provided > or = 91.9% efficacy against challenge with Dictyocaulus viviparus, Haemonchus spp., and Ostertagia ostertagi for up to 35 days post-treatment and against challenge with Cooperia oncophora, Cooperia punctata, and Oesophagostomum radiatum for up to 28 days post-treatment.     

Pubertal development in the male pig: effects of treatment with a long-acting gonadotropin-releasing hormone agonist on plasma luteinizing hormone, follicle stimulating hormone and testosterone.

The effects of a long-acting gonadotropin-releasing hormone (GnRH) agonist, [D-Trp6]-GnRH (GnRH-A) on developmental profiles of plasma luteinizing hormone (LH), follicle stimulation hormone (FSH) and testosterone (T), and pituitary responsiveness to exogenous GnRH were studied in male Dutch Landrace x Large White crossbred pigs from 1 to 30 wk of age. Group 1 control animals (control; n = 12) were injected subcutaneously in the neck with vehicle at 1 and 16 wk of age. Group 2 animals (early treatment; n = 10) were injected with 600 micrograms [D-Trp6]-GnRH at 1 wk and with vehicle at 16 wk. Group 3 animals (late treatment; n = 8) were injected with vehicle and 3 mg GnRH-A at 1 and 16 wk, respectively. Group 4 animals (early plus late treatment; n = 9) were injected at both 1 and 16 wk with GnRH-A. Blood was collected by brachiocephalic puncture at weekly or biweekly intervals, and through brachiocephalic cannulae, to determine longitudinal profiles of LH, FSH and T, and plasma gonadotropin responses to intravenous injection of GnRH (0.1 microgram/kg), respectively. In control animals, LH and FSH declined over the first 5 wk of postnatal life and peaked again at 10-14 wk. Levels of both hormones were basal from 18 to 30 wk. Plasma T was high in the first week, declined progressively over the next few weeks and remained low until 24 wk when a transient increment was noted. The LH and FSH responses to acute GnRH stimulation were similar at 7 and 14 wk and declined significantly at 23 wk of age.(ABSTRACT TRUNCATED AT 250 WORDS)