Spatio-temporal factors influencing the occurrence of Syngamus trachea within release pens in the South West of England

Syngamus trachea is a pathogenic tracheal nematode that causes syngamiasis in wild and game birds, especially when birds are managed at high densities. Despite its pathogenic nature, very little is known about its epidemiology and relationship with ambient temperature and humidity. The spatial and temporal modelling of disease was undertaken on two pheasant estates within the South West of England from April 2014 to August 2014. Significant differences between the mean numbers of eggs per gram of soil were identified between pens at both site 1 and site 2 but did not differ significantly between sites. Egg abundance was significantly associated with soil moisture content, with greater egg survival between years in pens with higher average volumetric soil moisture content. Previous years stocking density and pen age were also associated with greater egg survival between years with more eggs being recovered in pens with greater stocking densities, and pens that had been sited longer. The greatest model to explain the variation in the numbers of eggs per gram of soil per pen was a combination of soil moisture content, stocking density and pen age. Larval recovery differed significantly between sites. Larval abundance was significantly and positively associated with temperature and relative humidity at site 1. Similarly, temperature and humidity were also positively and significantly associated with larval abundance at site 2. Rainfall did not influence larval recovery at either site 1 or site 2. The model with the greatest ability to explain larval abundance at both sites, was a combination of temperature, humidity and rainfall. Infection status (positive faecal egg counts) was significantly and positively associated with larval abundance at both sites, but rainfall was only positively associated at site 1. Temperature and humidity were positively associated with infection status at site 2, but not at site 1. The present study highlights the influence of climatic variables on both egg survival and larval abundance, and could therefore be used to develop more targeted treatment strategies around periods of higher disease risk. The frequent use of release pens is a clear factor in the epidemiology of syngamiasis, and it is recommended that pens be rested and/or rotated in order to reduce infection pressure in subsequent flocks.

The effect of an indirect anthelmintic treatment on parasites and breeding success of free-living pheasantsPhasianus colchicus

In Great Britain free-living common pheasantsPhasianus colchicusare often managed at high densities owing to their popularity as a quarry species. They are prone to infection by a range of parasite species includingHeterakis gallinarum,Capillariaspp. andSyngamus trachea. In 1995 the efficacy of an indirect anthelmintic technique for controlling parasitic worm burdens of pheasants was determined in a pilot study on a shooting estate in the south of England. Between 2000 and 2003 a large-scale field experiment was conducted on nine estates in eastern England to determine the effect of the technique on parasite burden and pheasant breeding success. In the absence of anthelmintic treatment worm burdens increased rapidly through March and April, whereas birds given anthelmintic-treated grain had lower worm burdens during the same period. The breeding success of pheasants was significantly higher on plots provided with anthelmintic treatment, although no long-term increases in population densities were observed. The burdens of the most common parasiteH. gallinarumwere significantly lower in pheasants from treatment plots six weeks after the anthelmintic treatment had ceased, but spring treatment did not influence parasite burden in the following winter.

Comparing growth and condition in post release juvenile common pheasants on different diets

ABSTRACT We studied juvenile common pheasants Phasianus colchicus in 10 large open-topped release pens in woodlands on a shooting estate in southern England in 1998. In six pens the pheasants were fed a pelleted high-protein feed from 6 to 16 wk of age; in the four other pens they were fed the diet from 6 to 10 wk and then wheat grain only from 10 to 16 wk. Natural plant and animal food was also available to the birds in and around the release pens. When a sample of previously tagged, numbered, and weighed birds was caught from each pen and reweighed at 16 wk of age, we noted that birds from pens that remained on the high-protein feed had gained more weight than those from pens in which the diet was switched to grain only (P < 0.05). Of approximately 500 tagged birds collected during shooting days between 5 and 15 wk later, differences in body mass gain between groups were still significant (P < 0.05). A subsample, 50 males and 50 females aged 22 to 24 wk, of tagged birds that were shot were kept for postmortem examination. From this smaller sample, the differences in body mass were not significant (P > 0.05). Breast muscle mass and tarsal length did not differ between treatments. However cloacal fat was higher in the birds fed a high-protein diet (P < 0.05), suggesting that the results relating to body mass were due to differences in fat accumulation. Most pheasants examined postmortem contained the gut nematode Heterakis gallinarum with an average burden of 118 +/- 14 worms per bird. Although the abundance of these worms was not related to diet, it was negatively correlated with body mass, breast muscle mass, and cloacal fat (P < 0.05).

The effect of an experimental infection of the nematode Heterakis gallinarum on hand-reared grey partridges Perdix perdix

We compared 26 hand-reared grey partridges given an experimental infection of the caecal nematode Heterakis gallinarum with 26 uninfected ones. Under laboratory conditions after 91 days, there were no measurable clinical effects of the infection. We found no effect of treatment on the amount of food eaten or on caecal dropping production. However, treated birds, in particular females, developed slightly lower body mass (around 2%) compared to the controls. At post-mortem examination, we found a positive relationship between breast muscle mass and the number of worms collected from the caeca of treated birds. Treated birds with no worms when examined had smaller breast muscle mass (4.6%) compared to the uninfected control birds. These results are largely different to those found in a similar study that documented significant negative impacts on most of these factors in 8 infected birds compared to 6 controls. Its findings were used in a published model to support a hypothesis that H. gallinarum maintained in the environment by common pheasants, the primary host for this worm, could negatively affect wild grey partridge productivity and survival. In the same model our data would not support this hypothesis. Possible explanations for the different results from the 2 experiments are discussed. Together they suggest that only in certain, as yet unidentified circumstances, could experimental H. gallinarum infections have deleterious effects on hand-reared grey partridges.