Influence of targeted selective anthelmintic treatment on the productive performance of wool and hair lambs naturally infected with gastrointestinal nematodes in Brazil.

Targeted selective treatment (TST) is an alternative method to reduce the use of anthelmintics and delay the development of resistant nematode populations. However, there is limited information on the actual effects of this type of treatment on livestock productivity. The objective of this study was to evaluate the production performance of Santa Ines (hair) and Ile de France (wool) lambs naturally infected with gastrointestinal nematodes (GIN) under TST based on packed cell volume (PCV) versus suppressive anthelmintic treatments. Thirty-eight lambs were divided into two treatment groups: Suppressive treatment, animals were drenched with monepantel every two weeks and TST, animals were treated with the same anthelmintic when they presented PCV ≤ 20%. Feces, blood, and weight were measured weekly to determine eggs per gram of feces, PCV, total plasma protein, and weight gain. After animals were slaughtered, carcasses were weighed to determine carcass yield. In the TST group, substantial productive losses of approximately 21.3% in the wool and 25.9% in the hair lambs were observed in body weight compared to their counterparts. Significant differences in hematological variables occurred over the experimental period, especially in the wool lambs under TST. Favorable environmental conditions enabled infective larvae to survive and thrive on pasture. Haemonchus contortus and intestinal nematodes were the most common parasites found in the Ile de France lambs and the Santa Ines lambs, respectively. Although TST prevented mortality, it did not prevent production losses. Both breeds showed a significant drop in production due to GIN parasitism.

Early-onset immune response to Haemonchus contortus infection in resistant Santa Ines suckling lambs compared with susceptible Ile de France.

Santa Ines, an indigenous Brazilian hair sheep, in comparison with European sheep breeds (e.g., Ile de France), show greater resistance against gastrointestinal nematode (GIN) infections, mainly to Haemonchus contortus. Here we bring novel findings that address some gaps regarding the resistance traits involved in the development of the immunity of young lambs in the first few weeks of life to H. contortus infection. This study aimed to compare parasitological, humoral, and local effector cell-mediated responses, also the histopathological differences in the abomasal mucosa of Santa Ines (SI) and Ile de France (IF) suckling lambs serially infected with H. contortus. Parasitological variables, local and circulating humoral immunity, and local cellular response were evaluated in naïve Santa Ines (n = 14) and Ile de France (n = 12) lambs, randomized into four groups: infected SI (n = 8), non-infected control SI (n = 6), infected IF (n = 8) and non-infected control IF (n = 4). Lambs from infected groups were first infected at 14 days old, and multiple infections were conducted every second day, until the age of 66 days old (52 days post first infection). In comparison with infected Ile de France, infected Santa Ines lambs had lower mean eggs per gram of faeces, lower total H. contortus worm burden, lower females' length, greater abomasal lymph node weight, greater mucosal thickness in the fundus, and also higher counts of eosinophils in the fundus, and mast cells and globule leukocytes in both fundic and pyloric mucosa of the abomasum. Intrabreed differences were observed into the infected Santa Ines group, with three of the eight lambs classified as highly resistant for displaying H. contortus burden ranging only from 1 to 42 worms. Overall, Santa Ines suckling lambs showed great resistance against H. contortus infection in comparison with Ile de France lambs, being able to mount a robust innate immune response at an early age, and before weaning.

Haematological variables of Santa Ines and Ile de France suckling lambs: Influence of Haemonchus contortus infection / Variáveis hematológicas de cordeiros lactentes Santa Inês e Ile de France: influência da infecção por Haemonchus contortus

Haemonchus contortus is the major gastrointestinal parasite of sheep raised in tropical and subtropical areas worldwide. This trial aimed to evaluate the influence of H. contortus infection on the bone marrow response of Santa Ines (SI) and Ile de France (IF) suckling lambs experimentally infected with H. contortus. Fourteen SI lambs and 12 IF lambs were randomized in four groups: infected SI (n=8), non-infected SI (n=6), infected IF (n=8) and non-infected IF (n=4). Lambs of infected groups were submitted to 27 infections, conducted every two days, from 14 to 68 days of age, and each lamb received a total of 5400 H. contortus infective larvae (L3). Ten blood samples were obtained during the experimental period to be used for erythrocyte and leukocyte counts, packed cell volume and total plasma protein estimation. Additionally, it was carried out a differential leukocyte count. Lambs from control groups did not shed eggs in faeces all over the experiment, while infected Santa Ines and Ile de France lambs presented means of 2963 EPG (Eggs Per Gram of faeces) and 8175 EPG in the last sampling (P<0.05), respectively. Infected Santa Ines lambs had an increase in eosinophil release, however differences (P<0.05) on circulation number in comparison with infected Ile de France lambs were identified only in the last sampling (54 days post first infection). The mild H. cortortus infection did not produce significant changes in the blood variables of the Ile de France and Santa Ines suckling lambs.(AU)

Haemonchus contortus é o principal parasita gastrintestinal de ovinos criados em áreas tropicais e subtropicais. Este estudo objetivou avaliar a influência da infecção por H. contortus na resposta medular de cordeiros lactentes das raças Santa Inês (SI) e Ile de France (IF) infectados experimentalmente com H. contortus. Quatorze cordeiros SI e 12 cordeiros IF, foram distribuídos em quatro grupos: SI infectado (n=8), SI não infectado (n=6), IF infectado (n=8) e IF não infectado (n=4). Cordeiros dos grupos infectados foram submetidos a 27 infecções, realizadas a cada dois dias, do 14º até 68º dia de vida, com um total de 5400 larvas infectantes (L3) de H. contortus por animal. Foram realizadas 10 coletas de sangue ao longo do período experimental para determinação do volume globular, proteínas plasmáticas totais, contagem de eritrócitos e leucócitos, além do diferencial de leucócitos. Cordeiros controles não infectados não eliminaram ovos nas fezes durante todo o experimento, enquanto que os cordeiros Santa Ines e Ile de France infectados apresentaram em média 2963 ovos por grama de fezes (OPG) e 8175 OPG na última coleta (P<0,05), respectivamente. Cordeiros Santa Inês infectados tiveram um aumento na produção de eosinófilos, mas diferenças (P<0.05) no número de eosinófilos sanguíneos em comparação a cordeiros Ile de France infectados foram detectadas somente na última coleta (54 dias após a primeira infecção). A infecção leve por H. cortortus não induziu alterações significativas nas variáveis sanguíneas de cordeiros lactentes Ile de France e Santa Inês.(AU)

Repeated vaccination against Haemonchus contortus provides continuous protection to young grazing sheep.

Haemonchus contortus is the most important gastrointestinal nematode in the tropics and subtropics causing huge economic losses to the small ruminant industry. Vaccination is potentially a sustainable approach to control this parasite and the performance of Barbervax® a vaccine containing integral membrane glycoproteins from H. contortus intestinal cells, was evaluated in naturally infected grazing sheep during their development from sucking lambs to adults. The sheep were randomly assigned to two groups: Vaccine and Control. The Vaccine group were vaccinated 23 times over the course of this two-year trial at intervals of 3-6 weeks. They responded with anti-vaccine specific antibodies, had 80 % lower Haemonchus egg counts and were less anaemic compared with the controls. Packed cell volumes (PCV) were always greater than 25 % in the vaccinated sheep but averaged between 23 % and 24 % in the controls. Total plasma protein values were higher in the vaccinated group from the third vaccination until the end of the trial. Throughout the trial, 88 % of the control sheep were drenched (average of 3.1 drenches per treated animal) but only 57 % of vaccinates, needed a salvage anthelmintic treatment (average of 1.9 drenches per treated animal), however, between group no differences in body weight were observed. In summary, these results indicate that a continuous course of Barbervax® can provide lambs with substantial year-round protection against H. contortus until they reached adulthood.

Long spelling periods are required for pasture to become free of contamination by infective larvae of Haemonchus contortus in a humid subtropical climate of São Paulo state, Brazil.

The objective of this trial was to evaluate the period of spelling necessary for a pasture to become free of contamination by infective larvae of gastrointestinal nematodes (GIN) of sheep, in different seasons of the year, as well as to determine when the greatest pasture contamination occurs and how long it lasts. An area was divided into four paddocks, one for each season (spring, summer, autumn, and winter). In order to contaminate the paddocks with free living stages of GIN, eight ewes, naturally infected, grazed on each paddock for 14 consecutive days, starting on the following dates: autumn, on April 4, 2017; winter, on July 4, 2017; spring, on September 26, 2017; summer, on January 2, 2019. At the beginning and end of the grazing period, faecal samples were taken directly from the rectums of the ewes to count eggs per gram of faeces (EPG) and for faecal cultures. Every 14 days pasture samples were collected to assess the number of infective larvae (L3) per kilogram of dry matter. At the end of the 14 day ewe grazing period, 21 stakes were placed where there were faeces on the paddock. Subsequently, every 14 days, the faeces located at three of the stakes were collected and the L3 were recovered. After the exit of the ewes, monthly, two tracer lambs, free of helminth infection, were allocated into the paddock for 14 days. At the end of this period they were housed in covered stalls for 28 days. Faeces from the lambs were collected for individual EPG counting and faecal culture at 21 and 28 days after grazing. Infective larvae recuperation was observed from faeces and pasture in all seasons. In the autumn, spring, and summer, high EPG counts were observed in the first tracer lambs (8521, 4800, and 8064 EPG, respectively), while in winter, high infection (14132 EPG) of the animals was observed only from the second pair of tracer lambs. For a pasture to become "clean", 322 days, 350 days, 294 days, and 182 days following contamination were necessary, respectively, in the autumn, winter, spring, and summer. In autumn, spring, and summer, massive contamination of the pasture with L3 occurred soon after an area had been grazed by infected sheep, while in winter this took a little longer. The contamination persisted, approximately, from a minimum of six months post contamination in summer to up to almost one year post contamination in winter.

Differences in immune responses to Haemonchus contortus infection in the susceptible Ile de France and the resistant Santa Ines sheep under different anthelmintic treatments regimens.

Understanding the immunological basis of resistance to gastrointestinal nematode infections in livestock is important in order to develop novel methods of parasite control such as vaccination or genetic selection for parasite resistance. The present study aimed to investigate differences in immune response between parasite resistant Santa Ines and susceptible Ile de France sheep breeds to natural Haemonchus contortus infection. Parasitological parameters, humoral immunity, local and circulating cellular immune responses were evaluated in 19 Santa Ines and 19 Ile de France lambs undergoing different anthelmintic treatments regimens: suppressive treatments (SUP) or targeted selective treatments (TST) over a 5-month grazing period. Santa Ines lambs had significantly lower Haemonchus faecal egg count and worm burden compared to Ile de France regardless of treatment regime. In addition, circulating blood eosinophils count and parasite-specific IgG levels were significantly higher and more rapidly induced in Santa Ines lambs. Abomasal immune responses were generally greater in the resistant breed, which had significantly higher levels of parasite-specific IgA in mucus, and elevated number of globule leukocytes and CD3+ T cells within the abomasal mucosal. Furthermore, numbers of POU2F3+ epithelial cells, a tuft-cell specific transcription factor, were also elevated in the Santa Ines breed, suggesting that this breed is better able to initiate T-helper type 2 immune responses within the abomasum. In conclusion, the differential immunological responses detailed here are relevant to understanding resistance to gastrointestinal nematodes in other host breeds, as well as to resistance breeding as a sustainable control approach for parasitic infections.