Phosphorus and the formation of vesicular-arbuscular mycorrhizas

Infection of ryegrass roots by vesicular-arbuscular mycorrhizal (v.a.m.) endophytes occurring in an unfertilized virgin soil of low P status was more sensitive to increasing P supply than that by endophytes occurring in an adjacent fertilized agricultural soil.P application to soil depressed mycorrhiza formation in subterranean clover by increasing plant P status and not by direct effects of soil P on v.a.m. endophytes. Localized placements of superphosphate by banding or topdressing did not affect the development of mycorrhizas of roots in the fertilized zones differently from those of roots not in fertilized zones.The amount of infection was not correlated with P concentrations within the plant at harvest. However, the extent of infection could be correlated with P concentrations of roots at early stages of penetration by the fungi. Additionally, the effects of P supply on frequency of penetration by hyphae and subsequent mycorrhiza development closely paralleled effects of P supply on soluble carbohydrate concentrations in roots.     

Taking a moment to measure networks—an approach to species conservation

Landscape Ecology - Network-theoretic tools contribute to understanding real-world system dynamics, such as species survival or spread. Network visualization helps illustrate structural...     

Eradication of footrot of lesser clinical severity (intermediate footrot)

OBJECTIVE: To determine if intermediate footrot (IFR) can be eradicated from a flock of sheep by inspection and culling of cases during a non-transmission period and if prior antibiotic treatment or vaccination increases the likelihood of eradication. PROCEDURE: A replicated field experiment that compared the three eradication strategies was followed by an observational study of the best of these applied in a commercial flock of 3000 sheep. RESULTS: In the replicated experiment, IFR was eradicated either by inspection and culling alone, or when combined with vaccination. Eradication failed when the sheep were treated with parenteral antibiotics before inspection and culling during the non-transmission period. In the whole-flock program, eradication by repeated inspection and culling of footrot cases during the non-transmission period was successful and the flock remained free of infection 3 years later. CONCLUSIONS: IFR can be eradicated by inspection and culling but latent infections, which may persist undetected for at least 34 weeks, require surveillance inspections to be repeated during the non-transmission phase of the program. The use of parenteral antibiotics as an aid to the eradication of IFR is contraindicated.     

An Avian Model for Comparative Studies of Insulin Teratogenicity

This study was designed to explore the effects of purified insulin during early stages of chick embryo development, and to search for variations between different molecular structures of the hormone. Chicken embryos were treated in ovo with a single dose of insulin (porcine or bovine), in only one stage of development between day 0 and day 9. Two susceptible periods were found. The earliest period (day 0 to day 3), characterized by abnormalities in the caudal vertebrae and a high mortality rate, was followed by a period with a different set of malformations, a syndrome classified as achondroplasia. The rate of achondro-plastic embryos was significantly higher with porcine rather than with bovine insulin. Paradoxically, insulin at physiological doses has stimulatory effects in growth and development but, in contrast, has inhibitory effects at higher doses. The precise signalling cascade of events in the target cells is still unclear. The possible interpretations of our results are discussed. The similarity between the insulin-induced abnormalities in the chicken embryos and the caudal regression syndrome, the most common malformation found in infants of diabetic women, suggests a common mechanism. This circumstance offers the chicken embryos as an excellent in vivo model for research on the mechanism of action of insulin during normal and abnormal development.     

A comparison of the efficacy of two ivermectin formulations against larval and adult Ascaris suum and Oesophagostomum dentatum in experimentally infected pigs

A study was conducted to evaluate and compare the efficacy of two injectable formulations of ivermectin (IVM-1 and IVM-2) at a dose rate of 0.3 mg/kg bodyweight versus placebo in the treatment and control of larval and adult stages of Ascaris suum and Oesophagostomum spp. in experimentally infected pigs. Seventy helminth free pigs were allocated on a liveweight basis to 7 groups each comprising 10 pigs (A-G). Group A served as an untreated control group. Groups B and C were used to investigate the efficacy of both formulations against adult stages of A. suum and Oesophagostomum spp., Groups D and E for efficacy against larval stages of A. suum and Groups F and G for efficacy against larval stages of Oesophagostomum spp. Pigs of groups A, B, C, D and E were infected on Day-0 with 1000 infective A. suum eggs each. Infective larvae of Oesophagostomum spp. (10,000/pig) were given on Day-0 to pigs of Groups F and G and on Day-21 to pigs of Groups A, B and C. Treatment was given to pigs of Group A (saline as placebo) on Day-7 and -28, IVM-1 to pigs of Group F on Day-7, pigs of Group D on Day-14 and pigs of Group B on Day-49. IVM-2 was given to pigs of Group G on Day-7, Group E on Day-28 and Group C on Day-49. Pigs of Groups F and G were sacrificed on Day-28, pigs of Groups A, D and E on Day-49 and pigs of Groups B and C on Day-56. Post mortem worm counts showed the following efficacies: (IVM-1) against larval A. suum 100%, against adult A. suum 94.4%, against larval Oesophagostomum spp. 52.0% and against adult Oesophagostomum spp. 83.0%. (IVM-2) against larval A. suum 100%, against adult A. suum 90.3%, against larval Oesophagostomum spp. 94.0% and against adult Oesophagostomum spp. 94.7%.