Biochemical differences in Merino sheep selected for resistance against gastro-intestinal nematodes and genetic and nutritional effects on faecal worm egg output

Abstract

The faecal egg count (FEC) and total egg output is reduced in parasite-resistant sheep and breeding sheep for resistance should reduce infective larval contamination of pastures. This research compares lambs and rams from the parasite-resistant flock, Rylington Merinos, with unselected controls at the same level of larval challenge and the same level of food supply in an animal-house environment. The sheep were penned individually. The parasite resistant sheep excreted 0·85-fold less eggs than the control animals after infection with Trichostrongylus colubriformis and Ostertagia circumcincta for 12 or 18 weeks. During the infection period the parasite resistant lambs had higher plasma immunoglobulin concentration and higher ratio of globulin to albumin than the control animals. In the mature rams these genotype differences diminished. They also had lighter mass of the small intestine with a higher proportion of mucosa, but heavier mass of the large intestine. Parasite infection caused a depletion of blood glutathione in the lambs given food at maintenance or 1·5 × maintenance, and the parasite-resistant sheep (both lambs and rams) also had lower glutathione concentration. Maintaining good body nutrient reserve before the infection reduced the egg output in the early stage of the infection. Food intake had little effect on worm egg production in young sheep given food at maintenance or above. It is suggested that an improvement of nutrition, sulphur-containing amino acids in particular, is required to recover the loss of productive performance caused by the infection.

Associations between nematode larval challenge and gastrointestinal tract size that affect carcass productivity in sheep

“…The increase in gastrointestinal tissue mass of sheep challenged with nematode larvae may be due to stimulation of the local immune response (including infiltration of mucosal mast cells and globule leukocytes and mucous production), and sheep selected for low worm egg count have heavier small and large intestines (relative to carcass weight) compared to unselected sheep after trickle infection with T. colubriformis and Tel. circumcincta (Liu et al, 2005). The genotype of the sheep may therefore be expected to influence the magnitude of effect of parasite challenge on carcass productivity (Greer, 2008;Liu et al, 2005) and so assessment of the effect of parasite challenge on carcass productivity of sheep selected for parasite resistance using low worm egg count also warrants further consideration.…”

“…circumcincta (Liu et al, 2005). The genotype of the sheep may therefore be expected to influence the magnitude of effect of parasite challenge on carcass productivity (Greer, 2008;Liu et al, 2005) and so assessment of the effect of parasite challenge on carcass productivity of sheep selected for parasite resistance using low worm egg count also warrants further consideration. If increased size of the gastrointestinal tract relative to live weight is shown to be a consistent finding in sheep challenged and infected with T. colubriformis and Tel.…”

Chemical composition of Mopane worm sampled at three sites in Botswana and subjected to different processing

“…There are reports (Mpuchane et al 2000) that mopane worm exported out of Botswana to South Africa is used as animal feed but there is no literature highlighting performance of livestock offered mopane worm. The correct profile of amino acids is vital for supporting the immunity system in parasitized animals (Hoskin et al 2002;Liu et al 2005), for growth, foetal growth, milk production and it is achieved by supplying high quality undegraded protein to the small intestine. Amino acid profile of mopane worm (Ohiokpehai et al 1996) has revealed that it is comparable to fish meal.…”

Fractional protein synthesis rate and polyamine concentrations in tissues of Merino sheep selected for gastrointestinal nematode resistance

“…The potential benefit from their substantially low worm burden and faecal worm egg output (6-7 folds lower in FEC compared with control sheep) may be compromised by maintaining their altered immunity. For example, when the lambs (10 months old) of this resistant genotype were infected with nematodes, they had higher concentration of plasma immunoglobulin, higher globulin/albumin ratio, a higher proportion of the mucosal mass in the jejunum, and lower blood concentration of glutathione at the same plane of nutrition as the control lambs (Liu et al, 2005b). These physio-pathological changes may contribute to costs of the resistance to nematodes.…”