Gastrointestinal trichostrongylosis can predispose ewes to clinical mastitis after experimental mammary infection.

Objective was to study, in an experimental model, the possible role of gastrointestinal nematode infection in predisposing ewes to mastitis during the lactation period. Twenty-four ewes (A or B [n=12]), free from nematode and trematode helminths, were used. Group A animals received 5000 third-stage larvae of a trichostrongylid helminth cocktail and group B ewes were unparasitised controls. Animals in group A developed gastrointestinal trichostrongylosis confirmed by >500epg in faecal samples; mean epg of group B ewes were <20 (P<0.001). Ewes were challenged by deposition of Mannheimia haemolytica into the teat duct. In group A, 7 ewes developed clinical and 5 subclinical mastitis; no ewe in group B developed clinical mastitis, but only subclinical (12 ewes) (P=0.002). M. haemolytica was isolated from 132/132 and 121/132 udder samples from group A or B, respectively (P<0.015); increased leucocyte numbers were recorded in 66/66 and 61/66 samples, respectively (P=0.023). During post-mortem examination, mean number of helminths in gastrointestinal content was 2523 and 7.5 in group A or B, respectively (P<0.001); within group A, proportions of Teladorsagia and Haemonchus were significantly greater in ewes that developed clinical mastitis than in others which did not (0.709 and 0.162 versus 0.662 and 0.136, respectively; P<0.035). M. haemolytica was isolated from 36/36 and 19/36 udder tissue samples from group A or B, respectively (P<0.001). In ewes with subclinical mastitis (in group A or B), inducible-lymphoid-follicles were observed in the teat, which were not observed in ewes with clinical disease. Total pathology scores summed over all days were 127 and 73 for group A or B ewes, respectively (maximum possible 192; P<0.05). In general, there was positive correlation between intestinal helminth counts and pathology score (P<0.001) and between Teladorsagia counts and pathology score (P=0.002) in ewes that developed clinical mastitis. It is concluded that, in view of bacterial challenge, gastrointestinal trichostrongylosis and particularly Teladorsagia infection, might lead to clinical mastitis, through various pathogenetic pathways.

Interactions between parasitic infections and reproductive efficiency in sheep.

This review article summarises the many reports in the literature, confirming that, in sheep, parasitic infections can adversely affect reproductive efficiency; examples, which refer to all parts of the reproductive cycle of sheep, are as follows: trichostrongylosis in ewe-lambs (which can lead to delayed attainment of puberty), myiosis of the prepuce (which can cause impediment of mating), chorioptic mange or trypanosomosis in rams (which can lead to testicular degeneration or azoospermia, respectively), trypanosomosis or sarcoptic mange in pre-conceptual ewes (which can lead to poor conception rates or reduced number of ovulations, respectively), toxoplasmosis or neosporosis in pregnant ewes (which are causes of abortion), trichostrongylosis or trematode infections in lactating ewes (which can cause reduction of milk yield and can be a risk factor for mastitis, respectively), cryptosporidiosis in newborn lambs (which can be a cause of deaths), coccidiosis in growing pre-weaned lambs (which can cause suboptimal growth rate). In other cases, the reproductive status of the animal can influence the parasitic infection; examples are as follows: the increase in faecal parasitic output during the peri-parturient period (as a consequence of the peri-parturient relaxation of immunity), the heavier trichostrongylid infections of twin lambs compared to lambs from single parities (as a consequence of developmental origin issues in twin lambs). All the above examples support the idea of presence of interactions between parasitic infections and reproductive efficiency in sheep.

Anthelmintic resistance in sheep in Europe: a selected review.

Intensive use of anthelmintics to control gastrointestinal nematodes selects for anthelmintic resistance, which has become an important issue in many European countries. Presence of nematode strains resistant to benzimidazoles, imidazothiazoles and/or macrocyclic lactones has been repeatedly reported, particularly for the three most important genera, Haemonchus, Teladorsagia and Trichostrongylus. Additionally, multiple drug-resistant populations of these parasites have also been detected. Examples are given for the situation in European countries with differing climatic conditions and management systems of small ruminants. The widespread emergence of multi-resistant nematodes proves that the past intensive suppressive chemical control strategies may not be a successful approach any longer. Experience from the up to now development of anthelmintic resistance suggests that modern control schemes should not rely on sole use of anthelmintics, but employ other, more complex and sustainable recipes, combing chemical, environmental and immunological control.

Administration of a long-acting antiparasitic to pre-pubertal ewe-lambs in Greece results in earlier reproductive activity and improved reproductive performance.

We studied the reproductive effects of administration of a long-acting antiparasitic (moxidectin) given to pre-pubertal ewe-lambs in Greece at the beginning of the reproductive season. 45 animals, naturally infected with trichostrongylids, were allocated into treated (n=30, treatment on D0, 21 June) or control (n=15) group. Rams of confirmed fertility, were introduced from 15 August (D55) to 20 December (D182) into the ewe-lambs. Throughout the study (performed at latitude N 36°26', in a flock free from brucellosis, Chlamydophila infection and toxoplasmosis), epg counts were monitored and reproductive performance of ewes was assessed. Up to D112, arithmetic mean epg counts in treated animals were 0; thereafter and up to D350, they were 23-473. Respective figures for controls were 190-977 epg. Reproductive performance parameters for treated and control animals respectively, were as follows; median 'Interval to first mating after ram introduction': 36.5 d and 71.0 (P=0.04); median 'Age at first mating': 8.5m and 10.0m (P=0.045); 'Cycling rate': 20.0% and 6.7% (P=0.03); 'Mating rate': 86.7% and 66.7%; 'Return-to-oestrus rate': 26.7% and 26.7%; 'Abortion rate': 3.3% and 0%; 'Lambing rate': 83.3% and 66.7%; 'Total lambs born per ewe' and 'Liveborn lambs born per ewe': 1.5 and 1.1 (P=0.01); 'Stillbirth rate' 0% and 0% and 'Lamb bodyweight per ewe': 5.0 kg and 3.8 kg (P=0.005). Anthelmintic treatment of pre-pubertal ewes, in order to maximise reproductive performance may be employed as a management strategy according to targets set in individual flocks.

The use of targeted selective treatments against gastrointestinal nematodes in milking sheep and goats in Greece based on parasitological and performance criteria.

This study compared the use of targeted selective treatment (TST) with systematic whole-flock treatments in 38 dairy sheep and goat farms in Greece. Criteria for individual treatments were either parasitological (nematode faecal egg count) or performance-based (body condition score or milk yield). The possible effect of treatment on resistance to benzimidazole anthelmintics was assessed using the Egg Hatch Test. Mean faecal egg counts decreased during the 12-month experimental period in all groups, and were lowest in the TST group treated according to faecal egg count (P<0.05). The number of sheep and goats treated by TST was reduced compared with systematic treatments. Mean thiabendazole-egg death dose(50) (TBZ-ED(50)) values from all groups were similar at the beginning and end of the study (P>0.05), but significant variation in TBZ-ED(50) was noted over the study period in systematically treated goats (P=0.045). Third stage larvae belonging to the genera Teladorsagia, Trichostrongylus and Haemonchus were dominant throughout the experimental period in all flocks. It was concluded that the use of targeted selective treatment reduced the number of anthelmintic treatments to achieve a similar level of parasite control or animal production and may offer a viable option to combine animal production with effective parasite control in Greece.