Recently, an intra-ruminal controlled-release capsule delivering ivermectin was developed for use in sheep. There are two formulations: one for sheep weighing 20-40 kg/44-88 lbs. (lamb capsule), designed to deliver ivermectin at 0.8 mg/day for 100 days and the other for sheep weighing 40-80 kg/88-176 lbs. (adult sheep capsule), designed to deliver ivermectin 1.6 mg/day for 100 days. Field trials were conducted in Germany, Slovakia and UK to determine the efficacy and productivity responses attributable to treatment of lambs with the controlled-release capsules.
One hundred and seventy-two (172) Merino Landrace (60), Valaška (60) and Suffolk cross (52) lambs, aged 3-8 months (weighing 20 to 40 kg/44-88 lbs.) were used in the experiments. The trials were conducted in Germany (trial 1), Slovakia (trial 2) and UK (trial 3). In each trial, the lambs were grazed together on unimproved (Germany and Slovakia) or fully improved pasture (UK). In the German and Slovak trials, the lambs grazed belonged to flocks of about 1000 or 500 sheep, which were tended by day and yarded up by night. In UK, the lambs were run as one group grazing one paddock. The trials commenced in July and ended in October (Germany) or November 1996 (Slovakia and UK).
In each trial, the lambs were ranked within sex, based on pre-treatment body weights and randomly allocated to one of the two treatment groups. One group remained untreated to serve as control and the lambs of the other group were treated on day 0 with the ivermectin controlled-release capsule. When necessary, the control lambs were salvaged treated with fenbendazole.
Before the start of the trial and on days 28, 56, 84, 98 and 112 after treatment individual fecal samples were collected to determine nematode egg counts. Body weights were determined using calibrated scales. Fecal soiling in the breech area was also scored.
In all three trials, the lambs were found to be shedding strongyle eggs. Lambs in trials 1 and 2 had low or moderate nematode infections, while lambs in trial 3 had considerably heavier infection. The mean fecal egg counts were not significantly different before treatment, but after treatment the egg and larval counts in the ivermectin controlled-release capsule treated lambs were always lower as compared to untreated controls. The ivermectin controlled-release treated sheep gained, on an average, 24.5% (Germany), 12.6% (Slovakia) and 50.4% (UK) more weight than the controls over the 112 days of the trials. The different weight gains correspond directly to the level of nematode infection, but may also be related to the general growth capacity of the different breeds and to the age of the animals involved. The treatment of lambs with the ivermectin controlled-release capsule also reduced the mean scores of fecal soiling.
The three field trials demonstrated that treatment of lambs with the ivermectin controlled-released capsule effectively removed existing nematode endo-parasites and prevented the establishment of newly ingested larvae for a period of at least 112 days, significantly improved weight gains and resulted in significantly lower accumulation of feces in the breech area of lambs.
Source: Small Ruminant Reseach (1999).
At North Carolina State University, solutions of commercial fertilizers, bleach and limestone were used to examine their effect on the motility of infective Haemonchus contortus larvae (L3) in vitro. Infective larvae were cultured from feces of one Suffolk ram lamb infected with 5000 L3. They were pipetted into individual petri dishes with 500 l of a known concentration of either urea (U), ammonium nitrate (AN), liquid nitrogen fertilizer (LNF), a mixture of ammonium nitrate + urea (ANU), dolomitic limestone (DLM), limestone (LM) and sodium hypocholorite (SH).
Percent non-motile L3 increased as they were exposed to increasing concentrations of N sources and SH. DLM and LM were not effective. Another trial compared the highest concentrations of the four N sources. Percent non-motile L3 were U, 81.3; AN, 96.8; LNF, 93.3; ANU, 89.2; SH, 99.8.
Thus, this research shows that larvicidal properties of N sources and SH could decrease gastrointestinal parasite loads. However, field studies are needed to corroborate results.
Source: Small Ruminant Research (1999).
Studies were conducted at the University of Thessaly in Greece to determine the reaction and safety of moxidectin 1% injectable solution and .1% oral drench. Two hundred (200) lambs 4-29 days old, were segregated into eight groups. Lambs in group A were injected with a single dose of moxidectin 1% injectable solution, those in group C were injected with a quadruple dose; those in group E with a single dose of moxidectin 0.1% oral drench and those in group G with a decuple oral dose. Lambs in group B, D, F and H were the controls. The reactions of lambs were recorded 14 days after administration of the test product. The only adverse reaction observed was in one Group C lamb, but its symptoms regressed within 12 hours without medical intervention. Therefore, it was concluded that moxidectin is safe for administration to young lambs.
In another experiment, three hundred ewes were allocated to one of three groups. Ewes in group A were injected with 1 ml moxidectin 1% injectable solution, those in group B with 1 ml ivermectin 1% injectable solution and those in group C with 1 ml phosphate-buffer saline. Reactions of ewes were assessed during insertion of the needle, during injection of the product and after injection of the product. They were classified into one of four scores. In group B, 11 ewes reacted during insertion of the needle, 28 during injection and 35 after. Respective numbers in group A were 10, 4 and 1 and in group C 9, 1 and 1 ewes. The findings indicate that moxidectin 1% injectable solution does not cause significant pain to sheep.
Source: Small Ruminant Research (1999).
Recent studies on 3 to 7 month old lambs have shown that there is genetic variation in the ability to withstand the effects of roundworm challenge and thus maintain acceptable performance (high growth) when left undrenched for extended periods. This trait is generally referred to as resilience.
The heritability of resilience has proved to be low. Three years of data with 213 sire groups and two separate approaches to measuring resilience gave estimates of 0.10±0.03 and 0.14±0.03. Nevertheless, progeny testing should successfully identify genetically resilient rams for use.
A selection experiment for high vs. low resilience was initiated in 1994 at the Ruakura Agricultural Research Centre in Hamilton, New Zealand. Four progeny-tested rams with high resilience (RL +) and four with low resilience (RL-) were mated to outlier RL+ and RL- ewes. Progeny were grazed on infective pasture with minimal drench treatment.
Relative to RL- progeny, RL+ progeny had 2.0 kg (4.4 lbs.)greater weaning to autumn gains, 2.2 kg (4.84 lbs.) greater live weights in April and a significant advantage in yearling weight. There was a 0.24 kg (0.528 lbs.) increase in yearling fleece weight (+10%). Whereas, there was no significant difference in January or March FEC. The results show that selection for resilience is possible, and that provided care is taken to avoid sires with high FEC, improved resilience in lambs should lead to lower drenching requirements without jeopardizing production.
Resistance to nematode infection, measured in terms of fecal egg count (FEC), is also known to be inherited in sheep, and studies of selection for low FEC have successfully improved resistance. However, resilience and resistance appear to be genetically independent.
Source: Proceedings of the New Zealand Society of Animal Production (1996).
A multivalent vaccine against gastro-intestinal parasites of sheep is being developed as part of a Woolmark Company and University of Melbourne initiative.
There are two approaches to vaccine development: the hidden antigen approach, which generally uses antigens from the parasite that are not normally seen by the host's immune system during infection; and the natural antigen approach, which uses larval antigens against which part of the host's normal immune response is directed. Candidate vaccine antigens for three parasites (Barber's pole worm, small brown stomach worm and black scour worm) are being identified, purified, characterized and tested in sheep trials.
The project reaches a major milestone when the funding organizations will access progress and likelihood of success. The project is of high risk nature and as much as antigen identification is a problem, the major issue is probably the sheep's immune system that the worms have been very successful for millions of years to circumvent.
Source: The Woolmark Company.
The effect of protein supply on the periparturient parasite status of the mature ewe was investigated by researchers at Lincoln University in New Zealand.
Thirty two (32) twin- and thirty two (32) single-bearing ewes were individually penned indoors nine weeks before lambing. Four dietary groups balanced for pregnancy status were established for energy (E) and protein (P) levels. These were E1P1, E1P2, E2P1 and E2P2 (groups 1-4) and were based on a lucerne hay and barley diet. E1 and E2 were designed to promote 0 and +50 g/day gain in maternal body weight, respectively. P1 and P2 contained approximately 120 and 200 g CP/kg DM, respectively with the difference achieved through the inclusion of fish meal in P2 diets. From seven weeks prior to and during parturition, all ewes were trickle infected with 10,000 Teladorsagia circumcincta and 7,000 Trichostrongylus colubriformis larvae. Fecal egg counts were determined weekly from five weeks prior and until three weeks after the parturition when worm burdens were determined.
Fecal egg counts and worm burdens were 1,610 and 145 eggs per gram (epg) and 12,020 and 1,540 worms, respectively on high and low protein diets and 310 and 750 epg and 2,290 and 8,090 worms, respectively for single compared to twin-bearing ewes. There was no effect of energy level.
The results of this experimentation indicate that the periparturient breakdown in resistance to parasitic infection appears to be counteracted by protein supplementation. Supplementation of the ewe may provide an alternative parasite control strategy by reducing parasite contamination and may have greatest effect in prolific flocks.
Source: Proceedings of the New Zealand Society of Animal Production(1997).
Reprinted from Maryland Sheep News.