Comparison of Worm Control Strategies in Grazing Sheep in Denmark

Control of nematode parasites with reduced reliance on the use of anthelmintics was studied in 16 ewes with suckling twin lambs on contaminated pasture in Denmark. Ewes and lambs were treated with albendazole at turn-out 3 May. Ewes were removed from the groups on 26 July, and lambs were slaughtered on 11 October. The animals were allocated to 4 groups of 8 lambs and their 4 ewes. Group TS was treated with albendazole at weeks 3, 6 and 8 after turnout and set-stocked; group TM was similarly treated but moved to clean pasture in conjunction with the last drenching; group US was untreated and set-stocked, and group UM was left untreated but moved to clean pasture week 8 after turn-out. Supplementary feed was offered in June and August due to scarcity of pasture. Strategic treatments of ewes and lambs weeks 3, 6 and 8 after turn-out, with or without a move to clean pasture, were highly effective in controlling nematode infections for most of the season. This was reflected in better weight gains and carcass characteristics in the treated compared to untreated lambs, resulting in an average increase in the value of the product by 36%. The effect of moving without treatment (UM) on faecal egg counts was limited but peak pasture infectivity was reduced to less than 10% compared to the set-stocked group and weight gains of lambs were significantly better despite poor feed availability in late season. The study showed that under set-stocked conditions repeated anthelmintic treatments of both ewes and lambs in early season may ensure sufficient nematode control whereas moving animals to clean pasture without dosing was less efficient. The latter may, however, still be a viable option in organic and other production systems where routine use of anthelmintics is banned, particularly if weaning and moving are combined or a second move is performed.     

Low pasture allowance until late gestation in ewes: behavioural and physiological changes in ewes and lambs from lambing to weaning

Low pasture allowance during gestation affects ewes’ BW at parturition, the bond with their lamb, lamb development, and thus also may affect their responses to weaning. The objectives were to determine if native pasture allowance from before conception until late pregnancy affects ewe–lamb behaviours at lambing, ewes’ milk yield, lambs’ BW, and the behavioural and physiological changes of ewes and lambs at weaning. From 23 days before conception until 122 days of pregnancy, 24 ewes grazed on two different native pasture allowances: high (10 to 12 kg of dry matter (DM)/100 kg of BW per day; HPA treatment; n=12) or low (5 to 8 kg of DM/100 kg of BW per day; LPA treatment; n=12). Thereafter, all ewes grazed on Festuca arundinacea and received rice bran and crude glycerine. Ewes’ body condition score (BCS) and BW were recorded during pregnancy and postpartum periods. Milk yield was determined on days 32, 41 and 54 after lambing. Lambs’ BW was recorded from birth until 72 days after lambing. Latency from parturition until the ewe licked her lamb, maternal behaviour score (a test that evaluates maternal attachment to the lamb) and latency for lamb to stand up and suckle were determined. The behaviour of the lambs and ewes was recorded before and after weaning (at 65 days). The ewes’ serum total protein, albumin and globulin concentrations were measured before and after weaning. The HPA ewes presented greater BW (P<0.005) and BCS (P<0.005) than the LPA ewes during pregnancy and postpartum (P<0.04), and had a greater milk yield than the LPA ewes (P<0.03). Treatments did not influence any behaviour at lambing, lambs’ BW, neither the ewes’ behavioural and physiological changes at weaning. HPA lambs paced and vocalized more than LPA lambs (P<0.0001). The variation of albumin concentration before and after weaning was greater in the HPA lambs than in the LPA lambs (P<0.0001). In conclusion, although ewes’ BW, BCS and milk production were affected by pasture allowance until late pregnancy, this did not affect the behaviours that lead to the establishment of the mother–young bond, nor the ewes’ behavioural responses at weaning. Lambs reared by ewes that grazed on low pasture allowance during pregnancy presented fewer behavioural changes and a lower decrease of albumin concentration after weaning. Lambs’ BW was not affected by the feeding received by their mothers.     

A pre-partum lift in ewe nutrition from a high-energy lick or maize or by grazing Lotus uliginosus pasture, increases colostrum production and lamb survival

This experiment tested the hypothesis that a lift in the nutrition of ewes, before lambing, to increase colostrum production would enhance lamb survival. In all, 261 mature Corriedale ewes, each with a single fetus from a synchronised mating, grazed native pasture to day 130 after mating; at which point they were weighed, condition scored and allocated to graze either native pasture or a pasture dominant with Lotus uliginosus. Five days later (14 days before the expected start of lambing) the ewes were allocated to one of four treatments and fed: (i) native pasture alone, (ii) native pasture plus a commercial high-energy lick, (iii) L. uliginosus pasture alone or (iv) L. uliginosus pasture plus whole maize. The weight, viscosity and concentration of components and immunoglobulin G in the colostrum that had accumulated at parturition, were measured for 10 ewes in each treatment. The lambs that survived to 20 days of age from the 221 ewes that were not milked, were recorded. The ewes supplemented with the lick or maize grain and those that grazed the L. uliginosus pasture alone accumulated two to three times more colostrum at birth than the ewes that grazed native pasture alone (396, 635 and 662 g v. 206 g; P < 0.01). The colostrum from the ewes that grazed only native pasture was more viscous (lower score) than that from the ewes supplemented with the lick or maize grain or the ewes that grazed the L. uliginosus pasture alone (scores of 4.1 v. 6.2, 6.5 and 6.4, P < 0.001) and, not surprisingly, the concentration of lactose in the colostrum of the ewes fed only native pasture was also much lower (1.1% v. 3.0%, 2.8% and 2.6%; P < 0.001)he survival of lambs from the ewes fed only native pasture was less than that of the lambs from ewes fed native pasture plus the commercial lick (81.8% v. 95.5%; P < 0.05) or the L. uliginosus pasture alone (92.4%, P < 0.05), and also tended to be lower than that for lambs born to ewes fed L. uliginosus pasture plus maize (91.8%, P = 0.08). The concentration of glucose in the blood of the lambs from the ewes that grazed only native pasture was lower than that of the other lambs (42.1 v. 60.2 ng/ml, P = 0.012). We conclude that the marked increase in colostrum production associated with the lift in ewe nutrition, just prior to lambing, enhanced lamb survival.     

Biological Control of Sheep Parasites using Duddingtonia flagrans: Trials on Commercial Farms in Sweden

   

Trials were conducted on 3 commercial sheep farms in Sweden to assess the effect of administering spores of the nematode trapping fungus, Duddingtonia flagrans, together with supplementary feed to lactating ewes for the first 6 weeks from turn-out on pastures in spring. Also control groups of ewes, receiving only feed supplement, were established on all 3 farms. Groups were monitored by intensive parasitological investigation. The ewes and their lambs were moved in late June to saved pastures for summer grazing, the lambs receiving an anthelmintic treatment at this time. After approximately 6 weeks on summer pasture the lambs were weaned, treated a second time with anthelmintic, and returned to their original lambing pastures for finishing. Decisions as to when lambs were to be marketed were entirely at the discretion of the farmer co-operators. No difference in lamb performance was found between the two treatments on all three farms. This was attributed to the high levels of nutrition initially of the ewes limiting their post-partum rise in nematode faecal egg counts in spring, which in turn resulted in low levels of nematode infection on pastures throughout the autumn period. Additionally, pastures were of good quality for the lambs during the finishing period, so they grew at optimal rates as far as the farmers were concerned.     

The Dynamics, Prevalence and Impact of Nematode Infections in Organically Raised Sheep in Sweden

A three-year survey (1997–99) was carried out on organically reared sheep flocks throughout Sweden. The aim was to determine the prevalence and intensity of nematode infections and to establish relationships between sheep management practices and parasite infections. Faecal samples from ewes and lambs were collected from 152 organic flocks around lambing-time and during the grazing-period for analysis. Results were compared with the different management practices that farmers use to prevent parasitism in their flocks. A high proportion of the flocks was infected with nematodes. The most prevalent species were Haemonchus contortus, Teladorsagia circumeincta, Trichostrongylus axei, T. colubriformis and Chabertia ovina and infections progressively increased during summer in lambs grazing on permanent pastures. Severity of parasitic infection in lambs was highly dependent on egg output from the ewes. H. contortus was found in 37% of the flocks, even at latitudes approximating the Polar Circle. Nematodirus battus was recorded for the first time in Sweden during the course of this study. Lambs turned out onto permanent pasture showed higher nematode faecal egg counts (epg) than lambs that had grazed on pastures, which had not carried sheep the previous year. This beneficial effect of lambs grazing non-infected pastures persisted if the ewes were treated with an anthelmintic before turn-out and if the lambs were kept on pastures of low infectivity after weaning. In lambs, the prevalence and the magnitude of their egg counts were higher during autumn in flocks where lambs were slaughtered after 8 months of age, compared with flocks where all lambs were slaughtered before this age. These results will be used in providing advice to farmers of ways to modify their flock management in order to minimise the use of anthelmintics, but at the same time efficiently produce prime lambs.     

Gastro-intestinal nematode parasite populations in ewes and lambs and the origin and time course of infective larval availability in pastures

Changes in the numbers of infective larvae available on pasture and the development of helminth infection in spring-born lambs were studied in an environment with a mild winter and where pastures are grazed throughout the year. Prior contamination of pastures in autumn and early winter was compared with egg deposition by lambing ewes as sources of infection. Larvae derived from eggs deposited by lambing ewes did not appear on pasture until 8 weeks after the beginning of lambing but were present in increasing numbers for the last 7 weeks before weaning at 11–15 weeks of age. Lambs exposed to prior contamination became infected earlier than those exposed only to ewe contamination, but lamb egg output made no contribution to larval numbers on pasture before weaning. Lamb growth rates to weaning did not differ between groups exposed either to prior contamination alone, to ewe egg output alone or to both, but all groups carried appreciable infections at weaning. After weaning, lambs remained on the same pastures, and those exposed to ewe contamination suffered severe trichostrongylosis 5 weeks after weaning. Lambs exposed only to over-wintered contamination also developed severe trichostrongylosis 9 weeks after weaning. The results are compared with those of similar recent studies in Britain and their implications for control of infection are discussed.     

Characterization of immune responses against gastrointestinal nematodes in weaned lambs grazing willow fodder blocks

A 131-day rotational grazing experiment was conducted in the summer autumn of 2007/2008 to compare effects of feeding condensed tannin (CT)-containing willow (Salix spp.) fodder blocks (i.e., silvopastoral system) or perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) control pasture upon the immune response to gastrointestinal nematode parasite infection in Romney weaned lambs. Groups of lambs (n = 40) were allocated to either willow fodder blocks or control pasture; half of each group (n = 20) were regularly-drenched with anthelmintic at approximately 21 day intervals, whilst the remaining 20 weaned lambs were not drenched unless pre-determined faecal nematode egg counts (FEC) were reached, when all weaned lambs in that group were drenched with anthelmintic (i.e., trigger-drenching). Metabolizable energy and CT concentrations were higher in willow fodder versus pasture herbages. Weaned lambs grazing willow fodder blocks had lower live weight gain (92 g/day) and carcass weight (14.4 kg) than those grazing control pasture (134 g; 15.3 kg), with no effect of anthelmintic drenching. Regular anthelmintic treatment maintained similar and low FEC up to day 82, which then increased, whilst trigger-drenched lambs grazing willow fodder blocks had higher FEC than lambs grazing control pasture on three out of eight occasions. As judged by faecal larval cultures, grazing willow fodder blocks reduced the relative proportions of abomasal-dwelling parasites (Haemonchus contortus and Teladorsagia spp.). Trigger-drenched willow fodder block-fed sheep had higher platelet, eosinophil, total white blood cell and lymphocyte counts, greater CD21⁺ and greater γδ (Gamma Delta) TCR⁺ (T cell receptor) lymphocyte subsets than control pasture-fed sheep, and higher plasma levels of Immunoglobulin A (IgA) specific for carbohydrate larval antigen (CarLa) on day 105 (P<0.001). None of these parameters were affected by grazing treatment in regularly-drenched lambs. Higher immunological measurements in trigger-drenched lambs grazing willow fodder blocks could be due to higher larval intake and/or to the effects of secondary compounds in willow fodder blocks priming the immune system. Further research is required to separate these effects.     

Effects of reproduction,genotype and anthelmintic treatment of ewes on Ostertagia spp. populations

Donald A. D., Morley F. H. W., Waller P. J., Axelsen A., Dobson R. J. and Donnelly J. R. 1982. Effects of reproduction, genotype and anthelmintic treatment of ewes on Ostertagia spp. populations. International Journal for Parasitology12: 403–411. Merino and Border Leicester × Merino (BL × M) ewes, nearly all of the same age and reared at the same site, were either unmated or mated to Border Leicester rams. Ewes of each genotype and reproductive status were untreated or were given a single pre-lambing drench with thiabendazole at 50 or 100 mg/kg a week before the start of lambing in spring on pastures at Canberra which had been contaminated during autumn and winter by adult sheep. The two genotypes grazed together within each combination of reproductive status and anthelmintic treatment which grazed separately. Thiabendazole was highly effective in removing both fourth stage larvae and adults of Ostertagia spp., the most abundant genus. Eight weeks after the pre-lambing drench lactating ewes carried larger Ostertagia spp. populations than did unmated ewes of both genotypes, but as a result of reinfection after treatment, differences between drenched and undrenched ewes were not significant. At this time lactating as well as unmated ewes harboured large populations of arrested early fourth stage larvae of Ostertagia spp. acquired during the last 8 weeks, showing that arrest of development is not prevented by lactation. There was strong evidence that some ingested larvae which became arrested in lactating ewes were rejected by unmated ewes. At all stages of the reproductive cycle studied, BL × M ewes were substantially more resistant to Ostertagia spp. infection than Merinos. No persistent benefits in parasite control or in animal production were detected from the pre-lambing drench.     

Control of nematode parasites by grazing management—II. Decontamination of sheep and cattle pastures by varying periods of grazing with the alternate host

Commencing in December 1970, paddocks of a uniform series of sheep pastures were grazed for 6, 12 or 24 weeks by either yearling steers is or yearling ewes. Cattle pastures were treated similarly. All ewes and steers were pre-dosed with anthelmintic.At the conclusion of alternate grazing the effectiveness of the grazing treatments was evaluated by grazing each paddock for 1 month with either ten worm-free lambs (sheep pastures) or three wormfree calves (cattle pastures). The test animals were then slaughtered for total worm counts. The grazing of sheep pastures with cattle for 6, 12 or 24 weeks from December onwards resulted in reductions in numbers of Haemonchus contortus and Trichostrongylus colubriformis in test lambs. In comparison with continuous grazing by sheep, Nematodirus spp was only reduced after 24 weeks grazing by cattle. Cattle pastures grazed by sheep for 6 weeks showed no reduction in numbers of Ostertagia ostertagi or Cooperia oncophora in test calves. However after 12 weeks with sheep, numbers of O. ostertagi though not C. oncophora were reduced and after 24 weeks of alternate grazing both these species were reduced.Calves following the 6 week sheep treatments acquired both Haemonchus contortus and Trichostrongylus colubriformis and the calves from the 12 week sheep treatment paddock also carried H. contortus. For sheep the only evidence of cross-transmission was the occurrence of small numbers of Cooperia oncophora in test lambs from the 24 week cattle grazing treatment.The results provide evidence that sequential stocking with cattle and sheep in conjunction with anthelmintic treatment is an effective management strategy for preparing parasitologically safer pastures, but further information is required to determine the optimum timing of sequential stocking in farming situations.     

Resistance of young lambs to Haemonchus contortus infection, and its loss following anthelmintic treatment

1988. Resistance of young lambs to Haemonchus contortus infection, and its loss following anthelmintic treatment. International Journal for Parasitology 18: 1107–1109. A comparison of worm burdens of grazing Merino lambs that were untreated, treated once and allowed to graze for 2 weeks, or given suppressive anthelmintic treatment until their final 2 weeks on pasture, showed that resistance to reinfection with Ostertagia circumcincta and Trichostrongylus colubriformis did not develop until the lambs were about 8 months old. By contrast, there was clear evidence that untreated lambs, but not lambs given one or more treatments, had acquired substantial resistance to infection with Haemonchus contortus by an age of 4 months.     

Effects on ewe reproduction of grazing willow fodder blocks during drought

A grazing experiment was conducted in the summer/autumn of 2003 to determine the effect of grazing on willow fodder blocks at 6000 stems/ha during mating, relative to control ewes grazed on drought pasture, upon ewe production and reproduction. The fodder blocks contained a mixture of herbage and small trees. Grazing occurred over 10 weeks, from 19 February including three cycles of mating, with four groups of 100 ewes, comprising short drought pasture typical of drought pasture, long drought pasture typical of the pasture growing in the willow fodder blocks, short drought pasture with restricted access to willow fodder blocks (restricted access) and full access to willow fodder blocks (fenced on the willow fodder blocks all the time; full access). After mating, the four groups were joined and managed as one group until weaning in late November 2003. Ewe live weight (LW) and body condition score (BCS) change and reproductive rate at foetal ultra-sound scanning, lambing, docking and weaning were measured. Ewe wool production and staple length were measured at weaning. Short drought pasture had a pre-grazing mass of 1639 kg dry matter (DM)/ha with a dead matter content of 60%; typical of drought conditions. Herbage in the willow fodder blocks was similar to both control drought pastures (short and long) in nutritive value, with an organic matter digestibility (OMD) of 0.50. Tree yields were low in the fodder blocks, but they had higher concentrations of all secondary compounds, including 30 g condensed tannin (CT)/kg DM and OMD was higher, at 0.72. CT concentration was higher in the fodder block herbage than in short and long control drought pasture (5.0 g/kg versus 2.5 g/kg DM). Substantial LW loss occurred in the short control group (101 g/day), and reproductive rate was low, as would occur in severe drought conditions. Full access to fodder blocks lowered LW loss to 40 g/day and increased reproductive rate by approximately 20% units, with more ewes giving birth to twin lambs. Restricted access ewes had a low reproductive rate, similar to the short control group. Reproductive rate in full access treatment was slightly higher than in the long control group, despite similar calculated DM intakes in both groups. Calculated crude protein and CT intakes were higher for full access ewes than for any other groups, due to contributions from both the herbage and the trees; this may have increased the flow of undegradable dietary protein (UDP) to the small intestine and so have contributed to the increased fecundity of this group. Full access to willow fodder blocks proved beneficial in increasing ewe reproductive rate. However, both pasture and trees need to be managed as a tree/pasture system in order to produce herbage of higher nutritive value and more efficiently utilise willow fodder blocks as a supplementary feed.     

Faecal soiling and gastrointestinal helminth infection in lambs

The accumulation of faeces in the wool of the breech area (tail, perineum and anus) of lambs, known as faecal soiling, has been shown to be one of the major factors predisposing sheep to blowfly strike. However, the causes of faecal soiling of lambs in the UK are not clearly understood. Hence, in this investigation, the relationships between faecal soiling, gastrointestinal parasitic nematode infection and resultant diarrhoea were examined in a longitudinal study of 200 lambs at two farms in south-west England. Faecal egg counts, pasture worm burdens, faecal soiling and growth rates were recorded for individually tagged lambs over the summer of 2003. Grass growth and nutritional composition (protein and fibre) and weather data were also recorded over this period. Analysis using linear mixed models showed that faecal soiling was associated with higher strongyle-type egg counts, longer periods since worming, lower live-weights, female gender, lower faecal consistency and pasture quality. The data indicate that dag scoring, especially in mid- to late summer, could be used as a rapid, non-invasive technique for selecting animals, particularly lambs, with high faecal egg counts for selective drenching to reduce the incidence of anthelmintic resistance. Selective drenching of lambs with high dag scores would also be expected to aid in the control of blowfly strike.     

Feeding pregnant ewes a high-salt diet or saltbush suppresses their offspring's postnatal renin activity

If ewes consumed a high-salt diet or saltbush during the last 3 months of pregnancy and for 3 weeks after birth, we expected the renin activity of their lamb to be suppressed at birth and at 3 weeks of age. We also expected an increase in the concentration of cations other than sodium in the ewe's milk and an increase in the plasma Na concentration of the lamb at birth. To test these hypotheses, Merino ewes were fed a high-salt diet (14% NaCl) in an animal house and compared to control ewes eating a control diet (2% NaCl). In addition, we compared ewes grazing saltbush (about 13% salt in diet) to ewes grazing pasture from day 60 of pregnancy to 3 weeks after birth. Lambs born to ewes consuming saltbush had 85% lower (P < 0.001) renin activity than offspring from ewes consuming pasture at 3 weeks of age. Similarly, lambs born to ewes consuming a high-salt diet had 20% lower renin activity at birth and 3 weeks (P = 0.07). Feeding ewes a high-salt diet or saltbush altered the mineral composition of the milk; the largest change was a 10% increase in K levels (P 0.05). Consuming a high-salt diet or saltbush lowered the plasma Na of ewes at 130 days of gestation (by 3-5 mmol/l; P < 0.001), but only lambs from ewes fed the high-salt diet had a lower plasma Na at birth (P < 0.05). Suppression of the renin activity of lambs could lead to permanent physiological changes in salt balance in later life.     

Grazing multispecies swards improves ewe and lamb performance

A two-year (2015 and 2016) grazing study was established to compare ewe and lamb performance when grazed on a perennial ryegrass only sward compared to more diverse sward types. In that study four sward types were investigated: a perennial ryegrass (Lolium perenne) only sward receiving 163 kg nitrogen per hectare per year (N/ha/yr) (PRG); a perennial ryegrass and white clover (Trifolium repens) sward receiving 90 kg N/ha/yr (PRGWC); a six species sward (two grasses (perennial ryegrass and timothy (Phleum pratense)), two legumes (white and red clover (Trifolium pratense)) and two herbs (ribwort plantain (Plantago lanceolata) and chicory (Cichorium intybus)) receiving 90 kg N/ha/yr (6S); and a nine species sward containing cocksfoot (Dactylis glomerata), greater birdsfoot trefoil (Lotus pedunculatus) and yarrow (Achillea millefolium) in addition to the six species listed above, receiving 90 kg N/ha/yr (9S). Each sward type was managed as a separate farmlet and stocked with 30 twin-rearing ewes at a stocking rate of 12.5 ewes/ha under rotational grazing management from turnout post-lambing until housing. Lamb live weight was recorded fortnightly and lambs were drafted for slaughter at 45 kg. Ewe live weight and body condition score (BCS) were recorded on five occasions annually. Lamb faecal egg count (FEC) was recorded fortnightly and lambs were treated with anthelmintics when mean lamb FEC per sward type was above 400 eggs per gram. Ewes grazing the 6S and 9S swards had heavier (P < 0.01) live weights and BCS throughout the study than the ewes grazing the PRG sward. Lambs grazing the 6S sward were heavier than lambs grazing all other sward types of 14 weeks old (P < 0.05). Lambs grazing the PRG sward required more days to reach slaughter weight than lambs grazing all other sward types (P < 0.001). Lambs grazing the 6S and 9S swards required fewer anthelmintic treatments than lambs grazing the PRG or PRGWC swards. In conclusion, grazing multispecies swards improved ewe and lamb performance and reduced the requirement for chemical anthelmintics.     

Selection for thiabendazole resistance in Ostertagia spp. by low efficiency anthelmintic treatment

Thiabendazole (TBZ) treatment of grazing weaners infected with a predominantly susceptible strain of Ostertagia reduced worm burdens by 90%. The surviving sub population had a level of resistance four times greater than the original population when compared to similarly infected, but untreated, weaners. TBZ treated and control weaners were relocated to worm-free pasture so that the contamination on the plots grazed by TBZ treated weaners was from the survivors of the drench. The anthelmintic treated groups were subsequently managed under a two summer drench programme while control groups remained so throughout the experiment. Monitoring both parasite population size and the degree of resistance over the following 2 years indicated that after three anthelmintic treatments, resistance developed to a level where TBZ was ineffective. When compared to control groups, a mean reduction in population size of around 80% was maintained in the TBZ treated groups for 1 year. This difference, however, disappeared by the second year. A similar study over 1 year with a moderately TBZ resistant strain of Ostertagia indicated that TBZ treatment produced no significant reduction in population size but more than doubled the level of resistance. The study indicated the critical need for highly efficient anthelmintic treatment, particularly in situations where, through ecology or management, post treatment contamination is likely to contribute substantially to future generations of worms.     

Parasitological and immunological responses of genetically resistant Merino sheep on pastures contaminated with parasitic nematodes.

One hundred and twenty lambs were grazed continuously from weaning until 9 months of age on 12 plots contaminated with larvae of three nematode species (Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta). The lambs were sired by either a genetically resistant ram or susceptible rams (determined by the response of previous progeny to artificial H. contortus infection). Half the resistant and half the susceptible lambs were given strategic anthelmintic treatment and the remainder remained untreated. Faecal egg counts and blood packed cell volume were measured frequently in all animals. One and 5 months after weaning, two lambs from each plot were slaughtered, and worm burdens and larval establishment rates of the three species of nematode were estimated. At the second slaughter, leukotriene levels and larval migration inhibitory (LMI) activity were measured in mucus collected from the small intestine. The dominant species in all faecal samples and the gastrointestinal tract was T. colubriformis. Lambs of the resistant genotype had lower faecal worm egg counts, lower worm burdens and higher levels of resistance to larval establishment. There were no differences in larval migration inhibition (LMI) activity, but resistant lambs had higher levels of the leukotriene LTC4/D4/E4. Further, the resistant genotype, identified on responsiveness to artificial infections with H. contortus, was more resistant to infections of three important species acquired naturally from contaminated pastures. All these genetic differences were maintained while the lambs were subject to strategic anthelmintic treatment.     

Evaluation of lamb performance and costs in motherless rearing of German Grey Heath sheep under field conditions using automatic feeding systems

Performance and costs were evaluated for 205 German Grey Heath lambs reared artificially under field conditions using three feeding and three weaning regimes. In phase 1 (pre-weaning), ad libitum feeding of milk replacer (MR) on an automatic lamb feeder was compared to restricted MR feeding on the modified calf feeder “Stand alone II^®” or with buckets. In phase 2 (after weaning at 12 kg body weight), abrupt weaning was compared to gradual weaning systems with reduction of the amount or the concentration of MR over 2 weeks. In phase 1, average daily gains (ADG) were highest in the Ad libitum group (0.262 ± 0.032 kg/d), followed by Bucket and Stand alone with 0.227 ± 0.036 kg/d and 0.209 ± 0.023 kg/d, respectively (P < 0.05). In contrast, feed conversion rate was best for group Stand alone (1.17:1), compared to 1.20:1 in group Bucket and 1.23:1 in group Ad libitum. In phase 2, abrupt weaning caused weight loss in lambs from the Ad libitum and Bucket groups, but not in group Stand alone. No post-weaning growth check was seen in lambs weaned gradually. In general, differences in body weight (BW) between groups were low, and on d 70, no significant difference was seen between feeding groups, whereas lambs weaned abruptly still had lower BW than lambs weaned by reducing the amount of MR (P < 0.05). Total lamb mortality was 3.9%, with no accumulation of infectious disease in any of the feeding or weaning groups. Economic analysis revealed that total costs in phase 1 were highest for group Stand alone (57–70 € per lamb), followed by the Bucket group (63 € per lamb). Although MR consumption was higher in the Ad libitum group, this method was the most cost-efficient (50–54 € per lamb), because purchase price of the feeder and labor costs were relatively low. In phase 2, gradual weaning systems added costs of 4.70–9.50 € per lamb. Our findings indicate that the most efficient way to rear 60–120 lambs artificially under field conditions is by using an automatic ad libitum lamb feeder followed by abrupt weaning.     

Using a lamb's early-life liveweight as a predictor of carcass quality

The commercial value of lamb carcasses is primarily determined by their weight and quality, with the latter commonly quantified according to muscle coverage and fat depth. The ability to predict these quality scores early in the season could be of substantial value to sheep producers, as this would enable tailored flock management strategies for different groups of animals. Existing methods of carcass quality prediction, however, require either expensive equipment or information immediately before slaughter, leaving them unsuitable as a decision support tool for small to medium-scale enterprises. Using seven-year high-resolution data from the North Wyke Farm Platform, a system-scale grazing trial in Devon, UK, this paper investigates the feasibility of using a lamb's early-life liveweight to predict the carcass quality realised when the animal reaches the target weight. The results of multinomial regression models showed that lambs which were heavier at weaning, at 13 weeks of age, were significantly more likely to have leaner and more muscular carcasses. An economic analysis confirmed that these animals produced significantly more valuable carcasses at slaughter, even after accounting for seasonal variation in lamb price that often favours early finishers. As the majority of heavier-weaned lambs leave the flock before lighter-weaned lambs, an increase in the average weaning weight could also lead to greater pasture availability for ewes in the latter stage of the current season, and thus an enhanced ewe condition and fertility for the next season. All information combined, therefore, a stronger focus on ewes' nutrition before and during lactation was identified as a key to increase system-wide profitability.     

Conditioning ewes and lambs to increase consumption of spotted knapweed

Spotted knapweed (Centaurea maculosa Lam.) is an invasive plant that alters species composition and grazing value of rangelands in the northwestern United States. The spread of invasive plants may be reduced by using livestock as a biological control. We determined if mature ewes and their lambs (n = 34 ewe/lamb pairs) consume more spotted knapweed when ewes and/or lambs are conditioned to fresh-cut spotted knapweed. Ewe/lamb pairs were randomly assigned to one of four conditioning treatments: ewes and lambs not conditioned to spotted knapweed (N), conditioned ewes with non-conditioned lambs (E), non-conditioned ewes with conditioned lambs (L), or conditioned ewes and lambs (both—B). Then, ewes and lambs were observed together for 5 days (Trial 1); 11 days later, lambs were observed for 4 days without their mothers (Trial 2). During conditioning, intake by conditioned and non-conditioned ewes and lambs varied over time (as-fed basis, treatment by day interaction; ewes P = 0.03; lambs P = 0.05). Overall, non-conditioned lambs (N, E) consumed more than conditioned lambs (L, B; P = 0.02). In Trial 1, N ewes consumed similar amounts of spotted knapweed and bromegrass (Bromus inermis Leyss.) as the E, L, and B ewes (P = 0.67). E ewes spent more time eating spotted knapweed than L ewes (P = 0.001), and E ewe/lamb pairs consumed more spotted knapweed than L ewe/lamb pairs (P = 0.02). In Trial 2, N lambs consumed less spotted knapweed than E, L, and B lambs (P = 0.06). L lambs consumed more than E lambs (P = 0.007). Conditioning ewes, lambs, or ewes and lambs did not increase time spent eating spotted knapweed when both grazed together in a drylot, but conditioned lambs, without their mothers present, consumed more spotted knapweed 11 days later than non-conditioned lambs. Conditioning lambs only in a group setting with their peers may have the greatest potential to enhance consumption of spotted knapweed, because of social facilitation and the predilection for young animals to try novel feeds.     

Resistance of Sabi and Dorper ewes to gastro-intestinal nematode infections in an African semi-arid environment

Sabi and Dorper ewes were evaluated for resistance to gastro-intestinal nematode parasites (predominantly Haemonchus contortus) at the Matopos Research Station in Zimbabwe. Live weights (LWT), blood packed red cell volume (PCV) and faecal egg counts (FEC) were recorded at mating, 1 month before lambing and 1–3-month post-lambing for five separate lambings between 1996 and 2000. Dorper ewes were heavier (P<0.01) than Sabi ewes at all sampling times. Sabi ewes were more resistant to internal parasites than Dorper ewes as shown by their significantly lower FEC and significantly higher PCV at all sampling times except at 2-month post-lambing for FEC and at weaning (3-month post-lambing) for PCV. At all sampling times except at weaning individual ewes were treated with an anthelmintic when their FEC was greater than 1500 eggs/g (epg) and/or their PCV was less than 20%. The proportion of Dorper ewes that was treated with anthelmintic was significantly higher than that of Sabi ewes at all sampling dates. This effect was particularly marked 1- and 2-month post-lambing. There was a post-parturient rise in FEC in the 2-month period after lambing for both breeds.