Delivery of Bioencapsulated Oxytetracycline to the Marine Shrimp Penaeus monodon

Abstract Post larvae of shrimp Penaeus monodon were fed Artemia sp. enriched with oxytetracycline (OTC). The amounts of this antibiotic in the Artemia sp., the shrimp, and the water of the experimental system were measured by radial diffusion bioassay. The results indicated that 11% of the OTC was taken up by the Artemia sp. After 8 d of being fed OTC-enriched Artemia sp., the shrimp were found to contain 3.12 μg OTC/shrimp, which is twelve times greater than the average minimum inhibitory concentration (MIC) cited in the literature for sensitive strains of Vibrio spp. The recommended therapeutic dose for treatment of bacterial infections is four times the MIC.     

The effectiveness of fallowing strategies in disease control in salmon aquaculture assessed with an SIS model

Salmon production is an important industry in Scotland, with an estimated retail value >￡1 billion. However, this salmon industry can be threatened by the invasion and spread of diseases. To reduce this risk, the industry is divided into management areas that are physically separated from each other. Pathogens can spread between farms by local processes such as water movement or by long-distance processes such as live fish movements. Here, network modelling was used to investigate the importance of transmission routes at these two scales. We used different disease transmission rates (β), where infected farms had the probability of 0.10, 0.25 or 0.50 per month to infect each contacted farm. Interacting farms were modelled in such a way that neighbours within a management area could infect each other, resulting in two contacts per farm per month. In addition, non-local transmission occurred at random. Salmon are input to marine sites where they are raised to harvest size, the site is then fallowed; in the model the effects of different fallowing strategies (synchronised, partial synchronised and unsynchronised fallowing at the management area level) on the emergence of diseases were investigated. Synchronised fallowing was highly effective at eradicating epidemics when transmission rate is low (β=0.10) even when long distance contacts were fairly common (up to 1.5farm(-1)month(-1)). However for higher transmission rates, long distance contacts have to be kept at much lower levels (0.15contactsmonth(-1) where β=0.25) when synchronised fallowing was applied. If fallowing was partially synchronised or unsynchronised then low rates of long-distance contact are required (0.75 or 0.15farm(-1)month(-1)) even if β=0.10. These results demonstrate the potential benefits of having epidemiologically isolated management areas and applying synchronised fallowing.     

Urea hydrolysis and lateral and vertical movement in the soil: effects of urease inhibitor and irrigation

A glasshouse-based study was conducted to investigate the effect of urease inhibitor N-(n-butyl) thiophosphoric triamide (‘Agrotain’) and irrigation on urea hydrolysis and its movement in a Typic Haplustept silt loam soil (in 72 repacked soil cores). Half (36) of these cores were adjusted to soil moisture contents of 80% field capacity (FC) and the remaining 36 cores to 50% FC. Granular urea with or without Agrotain was applied at a rate equivalent to 100 kg N ha⁻¹. There were three replicates to these two sets of soil cores. After 1 day of treatment application, soil cores of the 50% FC were adjusted to 80% FC by applying surface irrigation. Twelve pots were destructively sampled at each day after 1, 2, 3, 4, 7 and 10 days of treatment application to determine urea hydrolysis and its lateral and vertical movement in different soil layers. Agrotain-treated urea delayed urea hydrolysis during the first 7 days after its application. This delay in urea hydrolysis caused by Agrotain enabled added urea, which is uncharged, to move away from the surface soil layer to the sub-surface soil layer both vertically and laterally. In contrast, most urea hydrolysed to soil NH₄⁺ within 2 days of its application. Irrigation after 1 day resulted in further urea movement both laterally and vertically from the surface soil layer (0–10 mm) to the sub-soil layer (30–50 mm) in Agrotain-treated urea. These results suggest that Agrotain delayed urea hydrolysis and allowed more time for rainfall or irrigation to move added urea from the surface layer to sub-soil layers where it is likely to make good contact with plant roots. This distribution of urea in the rooting zone has the potential to enhance N use efficiency and minimize N losses associated with ammonia volatilization from surface-applied urea.     

Macroinvertebrate status in relation to critical loads for freshwaters: A case study from N.E. Scotland

The Critical Load concept provides a method for the assessment of an ecosystem's sensitivity to acidification. This paper examines how variations in critical loads for freshwaters are reflected by the diversity and abundance of macroinvertebrates. The results indicate that acidified sites, those with the lowest critical loads, have significantly fewer species than less sensitive sites. The data are discussed in terms of ordination analysis relating catchment attributes to critical loads and macroinvertebrate status. It is concluded that although critical loads provides a good predictor for biotic status it is not as sensitive as parameters such as pH or alkalinity.     

Effects of manipulating intrauterine growth on post natal adrenocortical development and other parameters of maturity in neonatal foals

REASONS FOR PERFORMING STUDY: Intrauterine growth retardation (IUGR) impairs post natal adaptive responses and is associated with increased adrenocortical activity in many species. OBJECTIVES: To determine whether a restricted or enhanced intrauterine environment affects neonatal adaptation and adrenocortical function in horses. METHODS: Embryos from large (577 kg) Thoroughbred (TB) mares were transferred to smaller (343 kg) pony (P) mares and vice versa, to create a restricted (TB-in-P, n = 11) or enhanced (P-in-TB, n = 8) intrauterine environment. Control groups (TB-in-TB, n = 8; P-in-P, n = 7) were also included. RESULTS: Thirty foals were born live at full term (range 314-348 days) and 4 (3 TB-in-P, 1 P-in-TB) were stillborn between 275 and 335 days. TB-in-P foals were significantly (P<0.05) lighter than TB-in-TB, but heavier than P-in-P foals. TB-in-P foals took longer to first stand and suck and some had fetlock hyperextension and low (<4 g/l) plasma immunoglobulin G concentrations. Other foal groups showed normal behavioural responses. Haematological parameters were normal in all 4 groups of foals. Plasma ACTH levels were high at birth and plasma cortisol concentrations increased after delivery and returned to baseline within 6 h post partum in all but the TB-in-P foals, which had elevated levels until 48 h post partum. Plasma cortisol concentrations increased in all groups following exogenous ACTH administered on Days 1 and 5 postpartum. CONCLUSIONS: The TB-in-P foals showed IUGR and impaired post natal adaptive responses with basal hypercortisolaemia. POTENTIAL RELEVANCE: Foals born following IUGR may require clinical assistance in the early post natal period, but appear mature with respect to adrenocortical function.