Seasonal infections and nutritional status

Gastrointestinal nematode infections in German sheep

The objective of the present study was to determine the prevalence and variation of natural gastrointestinal nematode (GIN) infections in lambs according to birth type, gender and breed based on individual faecal egg counts (FEC) from various regions in Germany. A total of 3,924 lambs (3 to 15 months old) with different genetic backgrounds (Merinoland, German Blackhead Mutton, Rhoen, Texel and Merino long-wool) were individually sampled during the grazing period between 2006 and 2008. Furthermore, pooled faecal samples from each of the farms were cultured in order to differentiate the third-stage larvae of the nematode spp. Sixty-three percent of the lambs were infected with GIN. The infections were mostly low to moderate and involved several nematode species. The Trichostrongylus spp. was the predominant species based on the percentage of larvae in faecal cultures. Only 11.4% of the lambs were free of Eimeria oocysts. Tapeworm eggs were encountered in 13.2% of all samples. The prevalence of GIN infections varied significantly (P < 0.001) among farms. A significantly higher FEC (P < 0.05) was observed in multiple-born lambs when compared with singletons. Moreover, male lambs were more susceptible to infection than females (P < 0.001). No significant differences (P > 0.05) were observed between breeds regarding FEC. Inter-individual variations were higher than inter-breed differences, which may indicate the possibility of selection within these breeds for parasites resistance as described in earlier studies.

Environmental effects on nutrient and energy metabolism in ruminants

Domesticated animals all over the world are subjected to a wide variety of environmental conditions and challenges. Any deviation from "normal" may result in adaptive behavior of which changes in feed intake or feed intake pattern is by far the most important. Adaptive behavior may further include influences on passage rate of feed residues through the digestive tract, resulting in changes in digestibility. Adaptive behavior may also result in changes in heat production, either to maintain body temperature constant, or as a result of an elevated body temperature. Important environmental challenges are infectious diseases. Mild (sub-clinical) infections usually result in reduced performance, without affecting feed intake or digestibility. Severe infections may disrupt the barriers between the internal metabolism and the respiratory and/or digestive tract, resulting in severe losses of energy and protein. This situation is notably apparent in severe infections with parasites of the gastrointestinal tract and may be associated with severe protein losses. Feeding high protein diets may partly alleviate the negative effects. Contamination of air, water and feed may occasionally cause problems in farm animals. Such contamination may include pathogenic microbes, toxic secondary fungal metabolites and heavy metals. Negative effects associated with such contamination often show an impaired reproductive efficiency, but their influence on the utilization of energy and nutrients is not well documented.

The incidence of sheep strike by Lucilia sericata on sheep farms in Britain: a simulation model

Using a combination of a temperature-dependent simulation of the population dynamics of Lucilia sericata and a logistic model of sheep susceptibility, based on patterns of faecal soiling, fleece length and fleece humidity, a deterministic simulation model has been constructed to predict the incidence of sheep strike by L. sericata on lambs and ewes in Britain. Strikes are assigned to individual sheep in the flock according to a negative binomial distribution. The model shows that the majority of the first strikes of the season occur equally on ewes and lambs, when ewe fleeces are long and before lamb susceptibility increases though faecal soiling. With each subsequent generation of gravid blowflies, however, a greater proportion of strikes occur on lambs, while the number of strikes observed on ewes remains relatively consistent throughout the season. The increase in strike of lambs is due to the seasonal increase in lamb faecal soiling, associated with rising helminth infections and lamb fleece growth. The model shows that at the beginning of the season the incidence of strike is limited by the low number of flies present: towards the end of seasons, however, the blowfly population had grown large enough for the number of strikes to be limited by the number of susceptible ewes and lambs. The model shows that the seasonal incidence of strike is highly sensitive to the interactions between temperature, rainfall and would length. Strike was most prevalent under warm, wet conditions. However, there is a critical period during spring, where the short fleeces of lambs and ewes, in the latter case due to shearing, results in the desiccation of egg batches. If this coincides with dry conditions, the high levels of mortality result in suppression of the fly population and a reduction in the subsequent incidence of strike.