Resistance Of Lambs Research Articles

Sustainable worm control practices in South America

A high prevalence of nematodes, especially Haemonchus contortus and Trichostrongylus colubriformis, that exhibit multiple anthelmintics resistance has been reported in sheep in several South American countries. For this reason, the development of strategies that are less dependent on anthelmintic treatments is imperative for the prophylaxis of gastrointestinal nematode infections in small ruminants. Integrated grazing using cattle and sheep can be used for pasture decontamination with considerable reduction of H. contortus and T. colubriformis infective larvae after cattle grazing. Several breeds of sheep exhibit genetically related resistance against nematode infections, as is the case of “crioulo”, “native” or naturalised breeds of sheep. These breeds descend from livestock introduced by Portuguese and Spanish settlers and have been submitted to a long process of natural selection in various environmental conditions. In the South, the Crioula Lanada breed is more resistant to H. contortus than are Corriedale sheep. In tropical areas, where the minimum temperatures are usually higher than 20°C, hair sheep flourish, especially the Santa Ines breed, which also display a higher level of resistance to nematode infections compared with certain breeds of European origin. However, Santa Ines sheep have inferior carcass quality compared with other commercial breeds. Recent studies showed that the crossbreeding of Santa Ines ewes with sires of breeds with high potential for growth and meat production, results in crossbred animals with high productivity and a satisfactory degree of resistance against nematode infections. Several studies have indicated that improvement in nutrition has a beneficial effect on the development of resistance in lambs that were naturally or artificially infected with nematodes. Therefore, supplementary feeding and breeding strategies to improve resistance to nematodes are feasible options in the effort to reduce dependence on anthelmintic drugs to control worm infections in sheep.

The production cost of anthelmintic resistance in lambs

The economic impact of anthelmintic resistance was investigated in lambs by comparing productivity parameters in groups of animals treated either with a highly effective anthelmintic, or an anthelmintic to which three species of resistant worms were known to be present. Ten farmlets, each stocked with 30 lambs, were rotationally grazed for 5 months, with monthly treatments of either albendazole, to which resistance existed, or a new combination product containing derquantel and abamectin (DQL–ABA) to which there was no resistance. Stock on five farmlets were treated with each anthelmintic and productivity measures, including liveweights, body condition and faecal soiling were assessed throughout. In addition, fleece weights and information on carcass weight and quality was collected at the end of the trial.Anthelmintic efficacy was measured at the last two treatment dates by faecal egg count reduction test with larval cultures. Albendazole demonstrated efficacies of 48.4% and 40.9% for Trichostrongylus spp. and Teladorsagia circumcincta respectively. By contrast, the DQL–ABA treatments were >99% effective against all genera. The difference in live-weight gain was 9kg in favour of the DQL–ABA treatments. This translated into a 4.7kg increase in carcass weight with a 10.4% increase in carcass value. Significant differences in body condition scores, faecal breech soiling and fleece weights were also recorded, all in favour of the DQL–ABA treatments. The time required for 50% of the animals to reach a target live-weight of 38kg was significantly shorter (by 17 days) in those animals treated with DQL–ABA.The results show that the production cost of subclinical parasitism as a result of using an anthelmintic product which is less than fully effective due to resistance can greatly exceed the cost of routine testing of anthelmintic efficacy and the adoption of new anthelmintic classes. There is a strong case for many farmers to re-evaluate their position on some of these issues in order to optimise financial performance.

ATIVIDADE ANTI-HELMÍNITICA DO TRICLORFOM E CLOSANTEL EM CORDEIROS NATURALMENTE INFECTADOS POR HAEMONCHUS SP

This study aimed to evaluate the activity of anthelmintic trichlorfon (Neguvon ®) and closantel (Zuletel ®) in lambs naturally infected with Haemonchus sp. Twenty-seven lambs, crossbred Ile of France with Corridale, 90 days-old, were divided into 3 groups of nine animals: Group 1, animals were treated with trichlorfon (Neguvon ®) orally at a dose of 97 mg.kg-1 body weight, Group 2 were treated with closantel (Zuletel ®) at a dose of 10 mg .kg-1 body weight and Group 3 did not receive any kind of anthelmintic treatment. Through the test of reduction of OPG could be noted that the trichlorfon showed effectiveness of 97.9% and 55.2% closantel. It is noted the first closantel resistance in lambs in the central area of the state of Parana, Brazil. KEY WORDS: Closantel, Haemonchus sp, sheep, triclorfon

The effect of supplementary feeding in browsing Criollo kids and hair sheep naturally infected with gastrointestinal nematodes

SummaryThe objective was to highlight the role of supplementary feeding on resilience and resistance of browsing small ruminants against natural gastrointestinal nematode (GIN) infections. GIN infections have a negative impact on productivity of browsing Criollo kids especially during the wet season of Yucátan. Epidemiological studies have demonstrated the threat of GIN infectivity in the native vegetation available for browsing goats. Control of GIN in browsing ruminants is threatened by the emergence of anthelmintic resistant nematodes strains in the local flocks. Browsing trials with kids and lambs have shown that supplementary feeding (100–108g/day) improved resilience and resistance of Criollo kids against GIN. Supplements used successfully include sorghum:soybean meal (74:26 respectively), maize:soybean meal (74:26) and maize only (108g/day). The later result showed that animals might benefit from supplementation with rumen fermentable energy that could improve utilization of available browsing legumes by the goats. Wet season trials showed that, in spite of supplementation, infected animals have lower productivity compared to non-infected animals. However, the combined use of supplementation and copper oxide wire particles or tactic anthelmintic treatment, can improve growth rate of infected kids to maximum production levels. Short-term supplementation strategies have shown to be less effective than long-term strategies in achieving better resilience against GIN in kids. Lambs are more resistant but less resilient against GIN infections than kids. Improved resistance of lambs seemed to require more nutrients than in goats. In conclusion, supplementary feeding can play an important role in improving both resilience and resistance of growing small ruminants in the tropics but it can be further improved through the complementary use of other strategies leading to a more sustainable integrated parasite control strategy.

Inheritance of fecal egg count and packed cell volume and their relationship with production traits in sheep infected with Haemonchus contortus.

This study describes responses to artificial infection with Haemonchus contortus in ewes and lambs of 50% Dorset, 25% Rambouillet, and 25% Finn-sheep ancestry and provides estimates of genetic parameters for measures of parasite resistance. One hundred ninety-eight ewes out of 64 sires, and 386 lambs out of 25 sires were evaluated in autumn and spring of 2 yr. Ewes were dewormed shortly after weaning their lambs and lambs were dewormed at about 120 d of age. One week after deworming, ewes and lambs were dosed with approximately 10,000 infective larvae of H. contortus. After infection, BW, fecal egg counts (FEC), and packed cell volume (PCV) were measured weekly for 7 wk in lambs kept in drylot and fortnightly for 11 wk in ewes on pasture. Summary traits were defined as initial PCV, mean BW across all times, and means for PCV (MPCV) and log-transformed FEC (MLFEC) at wk 3 to 7 after infection for lambs and wk 3 to 11 after infection for ewes. Ewes and lambs did not lose weight overall in any year or season, but there was no consistent effect of year or lambing season on mean LFEC or mean PCV during infection in either ewes or lambs. Yearling ewes were less resistant to infection than older ewes, with lower PCV (P < 0.05) and higher LFEC (P < 0.05). During infection, PCV was positively correlated with BW and negatively correlated with LFEC in both ewes and lambs. In lambs, heritabilities were 0.39 (P < 0.01) for PCV, 0.10 (P < 0.05) for LFEC across all measurement times, and 0.19 (P < 0.01) for three measures of LFEC taken at the peak of infection. Heritability estimates for ewes were 0.15 (P < 0.05) for PCV and 0.31 (P < 0.01) for LFEC. Repeatabilities for LFEC and PCV across measurement times were moderate in ewes and lambs. Correlations between dam and lamb records for MLFEC were generally low, suggesting different mechanisms of resistance in lambs and nonlactating ewes. Ewes with higher genetic merit for growth as lambs were less resistant to infection as adults, but genetic merit for fertility and prolificacy were not related to parasite resistance. Lambs with higher genetic merit for body weight were more resistant to infection. Selection for resistance to H. contortus is therefore possible and should not adversely affect growth of lambs and fertility of ewes in this production environment.

Performance of hair sheep composite breeds: Resistance of lambs to Haemonchus contortus1

Performance of hair sheep composite breeds: Resistance of lambs to Haemonchus contortus1

P3422 Chronic endothelin-A receptor blockade lowers pulmonary vascular resistance of lambs with increased pulmonary blood flow

P3422 Chronic endothelin-A receptor blockade lowers pulmonary vascular resistance of lambs with increased pulmonary blood flow

Genetic control of the periparturient rise in faecal egg counts in Scottish Blackface ewes facing mixed, natural nematode infections

Infection by nematode parasites is an almost-inevitable consequence of sheep grazing improved pasture. Susceptible classes of sheep include growing lambs and ewes during the period of physiological stress caused by gestation and lactation. Nematode infections in lambs are well documented, less well documented is the decrease in resistance in ewes during the periparuturient period. The consequent elevation in faecal egg counts, the periparturient rise (PPR), leads to pasture infestation by worm eggs (Morris et al., 1998) - thus serving as a trigger for the subsequent epidemic in the lambs. Alternative control strategies to complement anthelmintics are continually being sought, with genetic selection of resistant animals a promising option (Woolaston, 1992). Unlike resistance in lambs, relatively little information exists on the genetic control of the PPR in ewes. The aim of this study is to quantify, and estimate the heritability of, the PPR in Blackface ewes grazing improved pasture and facing a natural mixed, nematode challenge.

How lambs control infection with Ostertagia circumcincta

Two of the most important questions for immunologists studying nematode infections are what effect does the host response have on the parasite and which components of the host response are responsible for these effects. The number of nematodes and the mean length of adult female Ostertagia circumcincta was measured in over 500 6–7 month old lambs of the Scottish Blackface breed. Quantitative genetic analyses indicated that there was substantial genetic variation among lambs in faecal egg counts and in worm length but the analyses provided no evidence for genetic variation in worm numbers. Separate analyses have shown a strong relationship between decreased worm length and decreased worm fecundity. Therefore, genetic resistance in lambs appears to be due to control of worm growth and not to control of worm numbers. The only immune response that is consistently associated with reduced worm length is the IgA response to fourth-stage larvae. The association is remarkably strong. After allowing for the influence of worm number on worm length (density-dependence) essentially all of the variation among deliberately infected lambs in worm length can be accounted for, in a statistical sense, by variation in the strength and specificity of the local IgA response. Therefore, the IgA mediated suppression of worm growth and fecundity appears to be the major mechanism of resistance to O. circumcincta in lambs.

The effect of age and dietary protein on immunity and resistance in lambs vaccinated with Trichostrongylus colubriformis

Development of immunity and resistance to Trichostrongylus colubriformis was measured in sheep, 8–26 or 33–51 weeks of age, that were offered two levels of dietary protein (11 and 20%). Resistance to challenge infection was ascertained by measuring worm burden, faecal egg count and eggs in utero in the nematode. Development of immunity was measured by an in vitro lymphocyte blastogenesis test to T and B cell mitogens and to somatic antigen from infective (L3) larvae. Young lambs offered the low protein diet showed a significantly lower resistance to parasites than older animals. The young animals on the high protein diet developed better resistance. Age and dietary protein influenced in vitro T lymphocyte responses to parasite antigen and mitogens, which were particularly well developed in vaccinated lambs on the high protein diet. Lymphocyte responsiveness to L3 larval antigen was negatively correlated with parasite status in vaccinated older lambs, and may be important in the development of acquired resistance to T. colubriformis.

An information system to manage hypothermia in newborn lambs

AbstractManagement information can be used as a substitute for other business resources. Sheep farmers may find such substitution provides a means to maintain incomes as the price of information falls relative to other scarce resources during the severe cost price squeeze they are currently experiencing.To illustrate how management information may be obtained and used, a multivariate regression technique is described. This is applied to data on the physiological responses of newborn lambs to cold exposure. It shows that an increase of one standard deviation in total body insulation provides a significantly greater direct response in cold resistance in lambs bred for high cold resistance (HCR) compared with lambs bred for low cold resistance (LCR). The countervailing correlated drop in peak metabolic response to cold exposure did not show a significant between-line difference. This information suggests that HCR lambs give a metabolically more efficient response to cold exposure than LCR lambs. Subsequent research has provided physiological evidence to corroborate these findings.The cold resistance of lambs has been shown to be related to lamb survival in the field. Information obtained about the response of individuals or groups of lambs to cold exposure by methods such as those described here may suggest more cost-effective steps that managers should take in order to exploit to the full the varying abilities to resist cold. This in turn should improve enterprise gross output by reducing lamb mortality. It should also reduce costs by ensuring that steps to control cold exposure or alleviate its symptoms are provided only when necessary.

Effect of high-frequency ventilation on gas exchange and pulmonary vascular resistance in lambs.

We studied the effects of conventional mechanical ventilation (CMV) (15 ml/kg tidal volume delivered at 18-25 breaths/min) and high-frequency oscillatory ventilation (HFOV) (less than or equal to 2 ml/kg delivered at 10 Hz) on pulmonary hemodynamics and gas exchange during ambient air breathing and hypoxic gas breathing in 10 4-day-old lambs. After instrumentation and randomization to either HFOV or CMV the animals breathed first ambient air and then hypoxic gas (inspired O2 fraction = 0.13) for 20 min. The mode of ventilation was then changed, and the normoxic and hypoxic gas challenges were repeated. The multiple inert gas elimination technique was utilized to assess gas exchange. There was a significant increase with HFOV in mean pulmonary arterial pressure (Ppa) (20.1 +/- 4.2 vs. 22 +/- 3.8 Torr, CMV vs. HFOV, P less than 0.05) during ambient air breathing. During hypoxic gas breathing Ppa was also greater with HFOV than with CMV (29.5 +/- 5.7 vs. 34 +/- 3.1 Torr, CMV vs. HFOV, P less than 0.05). HFOV reduced pulmonary blood flow (Qp) during ambient air breathing (0.33 +/- 0.11 vs. 0.28 +/- 0.09 l . kg-1 . min-1, CMV vs. HFOV, P less than 0.05) and during hypoxic gas breathing (0.38 +/- 0.11 vs. 0.29 +/- 0.09 l . kg-1 . min-1, P less than 0.05). There was no significant difference in calculated venous admixture for sulfur hexafluoride or in the index of low ventilation-perfusion lung regions with HFOV compared with CMV.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the optical refractometer for lamb serum immunoglobulin estimation

Resistance of lambs to neonatal diseases has been shown to be related to their serum immunoglobulin levels. These may be estimated in the laboratory by the zinc sulphate turbidity test (ZSTT). An experiment was designed to evaluate the optical refractometer, a relatively simple and inexpensive piece of equipment which measures the refractive index of a serum sample and thus provides an estimate of its total protein content. Refractometer readings of neonatal lamb sera were found to be closely correlated to their ZSTT readings (r = 0.89). The refractometer appears eminently suited to farm use avoiding elaborate and time consuming laboratory procedures. The limitations of the tests are discussed.

An Attempt to Demonstrate Passive Resistance in Lambs to Three Species of Gastro-intestinal Nematodes as a Result of Sucking the Ewe

An attempt was made to demonstrate passive resistance in young lambs to Haemonchus contortus, Ostertagia circumcincta and Tricho-strongylus colubriformis, as a result of sucking the ewe. Twin lambs were used, of which one was allowed to suck normally while the other was deprived of colostrum and reared artificially. In one experiment lambs were challenged from 4 weeks of age and in a second from 6 days old, with a mixture of larvae. In neither case was there any evidence of passive immunity as a result of receiving colostrum.

Re-Infestation Experiments with Ostertagia Circumcincta in Lambs

The resistance of lambs to Ostertagia circumcincta was studied using artificial infestations in lambs reared under worm-free conditions. Lambs inoculated initially with small repeated doses of O. circumcincta infective larvae showed evidence of resistance to the establishment of a challenge infestation given after an interval of 9 weeks. Lambs in which a similar initial infestation was terminated after 9 weeks by chemotherapy were as susceptible as controls to the establishment of a challenge. They nevertheless manifested resistance to the harmful effects of the challenge and exerted a significant depressant action on the fecundity of female worms developing from the challenge. Initial infestations consisting of large, spaced doses of larvae whether of O. circumcincta or Trichostrongylus axei failed to elicit any manifestation of resistance in lambs to challenge with O. circumcincta. La résistance des agneaux à l’ Ostertagia circumcincta a été étudiée sur des animaux élevés dans des conditions exemptes de vers et infestés artificiellement. Les agneaux, inoculés préalablement et à plusieurs reprises avec de petites doses de larves infectieuses d’ O . circumcincta , firent preuve d’une résistance à l’établissement d’une forte infestation inoculée à un intervalle de 9 semaines. Les agneaux dont une infestation initiale semblable avait été arrêtée par chimiothérapie après 9 semaines, se sont révélés aussi susceptibles à une forte infestation que les animaux de contrôle. Ils ont cependant manifesté une certaine résistance aux effets nocifs de la forte dose et exercé une action déprimante significative sur la fertilité des vers femelles qui s’étaient développées á partir de la réinfestation. Des infestations initiales consistant en grosses doses, soit d’ O. circumcincta , soit de Trichostrongylus axei , inoculées à intervalles, n’ont pas fait ressortir, chez les agneaux, de phénomènes de résistance aux fortes doses d’ O. circumcincta. Der Widerstand von Schafen gegen Ostertagia circumcincta wurde studiert, indem man Schafe, die unter wurmfreien Bedingungen aufgezogen worden waren, künstlich infiszierte. Schafe, denen anfänglich unter wiederholten Malen kleine Dosen von mit O . circumcincta infiszierten Larven eingeimpft worden waren, erwiesen sich als widerstandsfähig gegen die Anwendung einer künstlich hervorgerufenen Infiszierung, die nach 9 Wochen verabreicht wurde. Schafe, bei welchen eine durch Chemotherapie hervorgerufene ähnliche Anfangsinfiszierung nach 9 Wochen zu Ende geführt wurde, reagierten empfindlich auf die Kontrollen nach Anwendung der künstlich hervorgerufenen Infiszierung. Sie widerstanden nichtsdestoweniger den schädlichen Wirkungen der künstlichen Infiszierung, die eine bedeutende depressive Wirkung auf die Fruchtbarkeit von weiblichen Würmern ausübte, die sich unter der künstlichen Infiszierung entwickelt hatten. Anfangsinfiszierungen bestehend aus grossen, zeitlich angeordneten Dosen von O . circumcincta oder Trichostrongylus axei larvae verfehlten Widerstandsanzeichen in Schafen hervorzurufen, die mit O. circumcincta künstlich infisziert worden waren. La resistencia de los corderos a la Ostertagia circumcincta se estudió haciendo uso de infestaciones artificiales en corderos criados bajo condiciones libres de lombrices. Los corderos inoculados inicialmente con pequeñas dosis de larvas infectivas de O. circumcincta mostraron evidencia de resistencia al establecimiento de la infestación de desafío dada después de un intervalo de 9 semanas. Los corderos en los cuales una infestación inicial similar se terminó después de 9 semanas mediante quimioterapia fueron tan susceptibles comolos controles al establecimiento de un desafío. No obstante, manifestaron resistencia a los efectos perjudiciales del desafio y ejercieron una acción depresiva significante en la fecundidad de las lombrices hembras que se desarrollaron del desafío. Las infestaciones iniciales que consistieron en grandes dosis espaciadas de larvas ya de O. circumcincta , ya de Trichostrongylus axei fallaron al no dar ninguna manifestación de resistencia en los corderos al desafío con O . circumcincta.

The Influence of Age on Naturally Acquired Resistance to Haemonchus contortus in Lambs

SUMMARY The resistance of lambs to reinfection with Haemonchus contortus appears to be a variable phenomenon. Lambs which were 10—12 months old were infected with 9000 larvae given either as 2 equal doses or as a trickle infection over a period of 60 days. They recovered from this infection and later completely resisted challenge with 15,000 larvae; this challenge produced haemonchiasis in previously uninfected control lambs of the same age. Lambs which were 2—4 months old and which were similarly infected with a total of 3000 larvae, failed to resist challenge with 5000 larvae and were as severely affected as the previously uninfected control lambs. The age of lambs is thus a factor to be considered carefully in experimental and field studies on immunity to H. contortus.

Development in sheep of resistance to the ked Melophagus ovinus (L.). II. Effects of adrenocorticotrophic hormone and cortisone

In four lambs that had developed resistance to sheep keds, resistance broke down in two of them within 2 weeks of being injected daily for a month with long-acting adrenocorticotrophic hormone (ACTH) and, in one, 3 weeks after oral treatment twice daily with acetylsalicylic acid (ASA). The second lamb given ASA twice daily for 6 weeks, remained resistant. The first three treated lambs regained their resistance when the treatments were discontinued. Daily injections of cortisone for 4 and ACTH for 6 weeks were given to separate groups of five resistant lambs each. Hormone doses were adjusted on the basis of thrice weekly absolute eosinophil counts. Both treatments broke the resistance, which was regained when cortisone treatment ceased but after only four weeks of treatment with ACTH. The role of the pituitary-adrenal system in modifying ked resistance in lambs is discussed. It is concluded that the basic annual ked population cycle can be affected by physiological or environmental stress such as pregnancy or undernourishment.

The Effect of Bleeding versus Previous Infection on the Resistance of Lambs to Subsequent Infections of Haemonchus Contortus

The Effect of Bleeding versus Previous Infection on the Resistance of Lambs to Subsequent Infections of Haemonchus Contortus

The effect of hemopoietic dietary factors on the resistance of lambs to parasitism with the stomach worm, Haemonchus contortus.

The effect of hemopoietic dietary factors on the resistance of lambs to parasitism with the stomach worm, Haemonchus contortus.