The critical importance of planned small ruminant livestock health and production in addressing global challenges surrounding food production and poverty alleviation

ABSTRACT

Small ruminants are particularly well suited to meet United Nations Sustainable Development Goals surrounding food security, human wellbeing and poverty alleviation in different environmental and climatic settings. However the current efficiency of food production from small ruminants in both developed agricultural regions and in lower and middle income countries is woefully inadequate to meet predicted global needs over the forthcoming decades. Most global research to address this challenge is focussed on the genetics of animal growth, conformation and disease tolerance or resistance traits, albeit the practical consequences of such selection and strategies to use genetically improved animals in the field are uncertain. Any long-term benefits derived from small ruminant genetic selection will only be impactful if steps are first taken to keep animals alive, healthy and productive through iterative planned health management. Parasites are the foremost global infectious disease constraints to efficient small ruminant production. Their genetic adaptability to exploit opportunities afforded by effects of climatic or management changes on free-living stages, or exposure of parasitic stages to drugs, presents specific challenges to their sustainable control. Hence, parasite control provides a relevant means of engagement with livestock keepers and farmers on the topic of planned animal health management. The value of parasitology in this regard is enhanced by the availability of simple to use and accessible diagnostic tools.     

Use of a long acting injectable formulation of moxidectin to control the periparturient rise in faecal Teladorsagia circumcincta egg output of ewes

A field study was conducted in a sheep flock in the south east of Scotland with a history of ivermectin resistance in Teladorsagia circumcincta. The objective of the study was to compare the effects of single anthelmintic treatments in ewes before turn-out onto pasture that was contaminated with a moderate level of overwintered, ivermectin resistant, T. circumcincta infective larvae. The ewes were treated according to label directions with either a long acting injectable formulation of moxidectin (1mg/kg; affording up to 14weeks persistent action against macrocyclic lactone (ML)-susceptible T. circumcincta) or an oral formulation of moxidectin (0.2mg/kg; affording up to 5weeks persistent action against ML-susceptible T. circumcincta). The lambs were enrolled in the normal management of the farm, and received a total of three oral ivermectin treatments during the 16week study. The efficacy of both treatment strategies in controlling the periparturient rise in faecal nematode worm egg counts and subsequent pasture contamination was assessed from the faecal worm egg counts of the ewes and their lambs between lambing and weaning. Ewes that were treated with the oral formulation of moxidectin shed approximately 3.5 times more T. circumcincta eggs between lambing and weaning than ewes that were treated with the long acting formulation of moxidectin. This difference was reflected in the faecal worm egg counts of the lambs that were grazed alongside the different treatment groups of ewes. The results of the current study demonstrate persistent efficacy of the long acting formulation of moxidectin against an ivermectin resistant T. circumcincta population. The decreased pasture contamination after treatment could lead to improved lamb growth and a need for fewer anthelmintic treatments, thus potentially reducing one possible selection pressure for anthelmintic resistance. However, treatment with the long acting formulation of moxidectin would give rise to fewer susceptible nematodes being present in refugia, which could increase another possible selection pressure for anthelmintic resistance, depending on the subsequent grazing management of that pasture. The rationale for use of a persistent anthelmintic drug to control the periparturient rise in faecal ML-resistant T. circumcincta egg output of the ewes is discussed and potential differences in selection for macrocyclic lactone anthelmintic resistance using the different formulations of moxidectin are acknowledged.     

Characterisation of autophagy disruption in the ileum of pigs infected with Lawsonia intracellularis

Veterinary Research Communications - Lawsonia intracellularis is the aetiological agent of proliferative enteropathy, an enteric disease endemic in swine. Survival in its intracellular niche of the...     

Melatonin treatment prior to the normal breeding season increases fetal number in United Kingdom sheep flocks

Litter size determined ultrasonographically at 45–90 days after mating in eight groups of commercial sheep (n = 2609) treated with slow release melatonin implants immediately prior to the natural breeding season showed a 19% treatment effect averaged over the eight groups, from 148% to 167% (P < 0.01) compared with controls (n = 2499). Control groups had a litter size ranging from 124% to 194% thereby representing most commercial production systems in the UK sheep industry. This is the first large scale study of slow release melatonin implants in commercial UK flocks to demonstrate a significant positive effect on litter size when used before the natural breeding season. The data indicate that increased productivity and profitability could be achieved while maintaining desirable purebred characteristics.     

An investigation of the possible effects of subclinical iodine deficiency on ewe fertility and perinatal lamb mortality

A controlled supplementation trial was performed in an assumed iodine-deficient Romney ewe flock in the Manawatu. Significantly more twin litters were born to iodine-supplemented ewes than to control ewes. Furthermore, the perinatal mortality rate in lambs born to iodine-supplemented dams was significantly lower than in lambs born to control dams. Ewe age and the use of different lambing paddocks for iodine-supplemented and control ewes may have been confounding factors. In both iodine-supplemented and control ewes, serum T₃ and T₄ concentration values remained above the currently used “normal” range throughout the trial period.     

Diagnosis and treatment of retropharyngeal injuries in lambs associated with the administration of intraruminal boluses

The administration of intraruminal identification boluses to a group of 76 lambs resulted in 24 (32 per cent) showing signs of pharyngeal damage. In 16 of them the bolus was found to be in the retropharyngeal region by means of a hand-held microchip scanner, radiography and endoscopy. Purulent tracts were identified in the dorsal pharynx. In 13 of the 16 lambs the surgical removal of the bolus under general anaesthesia was followed by a normal clinical recovery, although the lambs did not grow as well as similar unaffected animals; three of the 24 lambs died. The administration of a larger bolus to 10 yearling rams did not result in any clinical signs of pharyngeal damage. The most important factors influencing the occurrence of this type of injury among this group of lambs were the size and age of the lambs, the positioning of the lambs during bolus administration, the relative size of the dosing gun and bolus, and the large number of animals in the group.     

Further characterisation of a triple resistant field isolate of Teladorsagia from a Scottish lowland sheep farm

Anthelmintic efficacies against juvenile developing populations of Teladorsagia species that were known to be resistant to anthelmintics from all three broad spectrum families were examined using a controlled efficacy test. Fenbendazole (FBZ), levamisole (LEV), ivermectin (IVM), combinations of these anthelmintics and moxidectin (MOX) were assessed in parasite na?ve lambs artificially infected with 8,000 third stage larvae (Tci5) and treated orally 8-day post-infection with the compounds at the manufacturers recommended dose rates, FBZ, 5 mg/kg body weight (BW); LEV, 7.5 mg/kg BW; IVM, 0.2 mg/kg BW; MOX (0.2 mg/kg BW). The lambs were slaughtered 14-day post-treatment. The arithmetic mean worm burden reductions resulting from oral treatments with FBZ; IVM; LEV; FBZ+IVM; FBZ+LEV; FBZ, LEV+IVM or MOX were 36%, 82%, 38%, 86%, 60%, 88% and 97%, respectively. The results illustrate that combination treatments showed improved efficacies against the juvenile population compared to individually administered treatments but that these improvements were not wholly effective. Moxidectin was the only treatment that was over 95% effective, though caution should be noted when advising the use of MOX prophylactically since 3% of the infection still survived this treatment. Treatments directed at juvenile stages of Tci5 were less effective, with the exception of IVM, compared to a similar trial using Tci5 where the same treatments were directed against a predominantly adult population. No interaction was detected comparing the timings of treatments and its effectiveness with the exception of IVM (two-way ANOVA, p < 0.05). These findings suggest that, on the whole, the selection processes for anthelmintic resistance (AR) may occur at an early stage of development within the parasites, having severe implications for the early detection of AR.