The distribution of four trace elements (Fe,Mn, Cu,Zn) in forage and the relation to scrapie in Iceland

Background

Previous studies indicated that the iron (Fe)/manganese (Mn) ratio in forage of sheep was significantly higher on scrapie-afflicted farms than on farms in other scrapie categories. This study was conducted to examine whether Fe and Mn in forage of sheep varied in general according to the scrapie status of different areas in the country. Copper (Cu) and zinc (Zn) were also included because of a possible relation to scrapie.

Methods

The country was subdivided into seven Areas (I-VII). Three Areas (I, IV, VII) were designated scrapie-free (never diagnosed or eradicated) and three as scrapie-endemic (II, III, VI); status of Area V was taken as unsettled. Of the harvest 2007 1552 samples were analysed from 344 farms all over the country, mostly grass silage from plastic bales (>90%) and from the first cut (70% or more). Results were expressed as mg kg^-1 dry matter.

Results

Fe varied enormously from less than 100 mg kg^-1 to 5000 mg kg^-1. Mn varied nearly thirtyfold (17-470 mg kg^-1). Fe concentration was significantly lower in Area I than in Areas II, V and VI. Mn concentration was significantly higher in Areas I, IV and VII than in Areas II, III, V and VI. The Fe/Mn ratio was significantly less in Area I than in the other areas (except Area IV). Mean Cu concentration was 6.6-8.3 mg kg^-1 and the mean Zn concentration was 24-29 mg kg^-1. They differed significantly in some areas.

Conclusions

1) Fe tended to be in lower amounts in sheep forage in scrapie-free than in endemic areas; 2) Mn was in higher amounts in forage in scrapie-free than endemic areas; 3) the Fe/Mn ratio was lower in scrapie-free than in endemic areas; 4) the Fe/Mn ratio may possibly be used as an indicator of scrapie status; 5) Cu and Zn in sheep forage were not related to scrapie; 6) further study on the role of Fe and Mn in the occurrence of scrapie in Iceland is needed.     

Concentration of Infectious Aquatic Rhabdoviruses from Freshwater and Seawater Using Ultrafiltration

Abstract

Infectious hematopoietic necrosis virus (IHNV), viral hemorrhagic septicemia virus, and spring viremia of carp virus were concentrated and detected from freshwater and seawater samples by using hollow-fiber ultrafiltration. Within 60 min, virus in a 50-L freshwater or saltwater sample was concentrated more than 70-fold, and virus retention efficiencies were consistently greater than 88%. Retention efficiency was highly dependent upon concentrations of column blocking and sample stabilization solutions. A large column with a surface area of 1.15 m² and a filtration capacity of 5–200 L exhibited optimal viral retention when blocked with 2% fetal bovine serum (FBS) and when the samples were supplemented with 0.1% FBS. Conversely, a small column with 100-fold less surface area and a filtering capacity of 0.5–2.0 L was optimized when blocked with 1% FBS and when the samples were supplemented with 0.1% FBS. The optimized ultrafiltration procedure was further validated with water from a tank that contained IHNV-exposed juvenile sockeye salmon Oncorhynchus nerka, resulting in an average virus retention efficiency of 91.6 ± 4.1% (mean ± SE). Virus quantification of concentrated samples demonstrated that IHNV shedding in sockeye salmon preceded mortality; shedding of the virus was observed to increase significantly as early as 7 d postchallenge and peaked at day 14, when virus levels reached 4.87 × 10³ plaque-forming units/mL. We conclude that ultrafiltration is a reliable and effective method for concentrating viable aquatic rhabdoviruses from large volumes of water and has application for the analysis of environmental water samples.

Received April 22, 2011; accepted August 4, 2011     

Calf mortality rate and causes of death under different herd management systems in peri-urban Bamako, Mali

Calf mortality rate and causes of death were studied in peri-urban livestock production systems in Bamako, Mali, for calves born and dying from November 2002 to March 2004. Causes of death for 93 deceased calves were diagnosed from clinical autopsies, reported history of death and parasitic information. Calves originated from traditional, modernized and station management systems. Overall mortality rate was 17% during the first year of life (N = 756 live-births). Mortality rate was significantly lower for traditionally (10%) compared to modernized (19%) or to station managed calves (25%). Total perinatal loss (abortions + stillbirths + perinatal mortality) was 5% (N = 784 gestations). The most important death categories were digestive tract disorders (28%), perinatal mortality (16%) and accidents (14%). Vector-borne and infectious diseases were of low importance. Digestive tract disorders and perinatal mortality were the most important categories of death in modernized management while accidents and starvation were the most important causes of death in traditional management. Digestive tract disorders were more common in modernized than in traditional management (p = 0.02), revealing a serious problem with hygiene in stationary enclosures. With better calf management in regard to hygiene, surveillance and control of milk off-take, overall calf survival may be increased and peri-urban livestock production made more profitable.     

A nitrogen mineralization model based on relationships for gross mineralization and immobilization

Net N mineralization from plant materials represents the difference between the two opposing processes of gross N mineralization and immobilization. This complicates the derivation of useful relationships between rates of net mineralization and litter quality indices. The purpose of the current paper is to present a model for net N mineralization from plant material that is based on relationships between (1) gross N mineralization and respiration and (2) gross N immobilization and respiration found in studies applying ¹⁵N dilution techniques. Together these relationships produce an overall relationship between net N mineralization and C mineralization that can be used to predict net N mineralization from respiration. The applicability of the model was tested by applying it to the mineralization dynamics of 75 plant materials with widely differing qualities. In a model validation on eight independent plant materials, the relations between net N mineralization and C mineralization resulted in good predictions of observed net N mineralization patterns from the C mineralization pattern, depending only on the C/N ratio of the plant material (R²=0.90). This suggests that the relationship between net N mineralization and respiration is largely unaffected by the chemical composition of the plant material other than the C/N ratio. This means that the chemical composition of the plant material may primarily influence N mineralization through its effect on C mineralization. Furthermore, the relationship between net N mineralization and C mineralization is useful for predictions of net N mineralization because C mineralization is generally much easier to predict than net N mineralization.