Intake of trichostrongylid larvae by goats and sheep grazing together

Nemabiome metabarcoding reveals differences between gastrointestinal nematode species infecting co-grazed sheep and goats

Our current understanding of differences in the epidemiology of gastrointestinal nematode (GIN) species in co-grazed sheep and goats is inadequate with reference to the development of sustainable control strategies. The next-generation metabarcoding sequencing method referred to as the 'nemabiome' allows some of these differences to be explored to describe the intensity of co-infecting GIN species. We applied this platform to study sheep and goats that were co-grazed on Guinea grass pasture in northeastern Brazil. Co-grazed goats and sheep were treated with a monepantel anthelmintic, then exposed to the same gastrointestinal nematode species. Overall, there were differences in the prevalence of GIN species identified in the sheep and goats; Trichostrongylus colubriformis and Teladorsagia circumcincta predominated in goat kids, while Haemonchus contortus predominated in adult does, ewes and lambs once burdens became re-established after anthelmintic treatment. Description of the pattern of re-infection following anthelmintic treatment was prevented by the unpredicted poor efficacy of 2.5 mg/kg and 5 mg/kg, respectively, of monepantel against O. columbianum and T. circumcincta in lambs, and T. circumcincta adult does. Differences in drug efficacy between host age and species groups may be important when considering sustainable GIN control strategies for co-grazed animals. The aggregated FECs of the adult does and goat kids representing re-established GIN burdens, were higher than those of the co-grazed adult ewes and lambs. This implies that there are inherent differences in GIN species adaptation to the two naïve small ruminant host species, and shows the need for better understanding of the factors giving rise to this situation associated with exposure to infective larvae and host responses. At the start of the study, the adult does were co-infected with several GIN species, with the highest intensity of T. circumcincta, contrasting with the situation in the adult ewes, in which H. contortus predominated. However, once burdens became re-established after treatment, H. contortus predominated in both adult does and ewes. This demonstrates the potential for host burdens of H. contortus to establish and predominate after anthelmintic treatment when burdens of co-infecting GIN species are low.

Signatures of selection for resistance to Haemonchus contortus in sheep and goats

Background

Gastrointestinal nematode infection (GNI) is the most important disease affecting the small ruminant industry in U.S. The environmental conditions in the southern United States are ideal for the survival of the most pathogenic gastrointestinal nematode, Haemonchus contortus. Host genetic variation for resistance to H. contortus allows selective breeding for increased resistance of animals. This selection process increases the prevalence of particular alleles in sheep and goats and creates unique genetic patterns in the genome of these species. The aim of this study was to identify loci with divergent allelic frequencies in a candidate gene panel of 100 genes using two different approaches (frequentist and Bayesian) to estimate Fst outliers in three different breeds of sheep and goats exposed to H. contortus.

Results

Our results for sheep populations showed SNPs under selection in C3AR1, CSF3, SOCS2, NOS2, STAT5B, TGFB2 and IL2RA genes using frequentist and Bayesian approaches. For goats, SNPs in CD1D, ITGA9, IL12A, IL13RA1, CD86 and TGFB2 genes were under selection. Common signatures of selection in both species were observed in NOS2, TGFB2 and TLR4 genes. Directional selection was present in all SNPs evaluated in the present study.

Conclusions

A total of 13 SNPs within 7 genes of our candidate gene panel related to H. contortus exposure were identified under selection in sheep populations. For goats, 11 SNPs within 7 genes were identified under selection. Results from this study support the hypothesis that resistance to H. contortus is likely to be controlled by many loci. Shared signatures of selection related to mechanisms of immune protection against H. contortus infection in sheep and goats could be useful targets in breeding programs aimed to produce resistant animals with low FEC.

Haemonchotolerance in West African Dwarf goats: contribution to sustainable, anthelmintics-free helminth control in traditionally managed Nigerian dwarf goats

West African Dwarf (WAD) goats are extremely important in the rural village economy of West Africa, but still little is known about their biology, ecology and capacity to cope with gastrointestinal nematode (GIN) infections. Here, we summarise the history of this breed and explain its economic importance in rural West Africa. We review recent work showing that Nigerian WAD goats are highly trypanotolerant and resist infections with Haemonchus contortus more effectively than other breeds of domestic goat (haemonchotolerance). We believe that haemonchotolerance is largely responsible for the generally low level GIN infections and absence of clinical haemonchosis in WADs under field conditions, and has contributed to the relatively successful and sustainable, anthelmintics-free, small-scale system of goat husbandry in Nigeria's humid zone, and is immunologically based and genetically controlled. If haemonchotolerance can be shown to be genetically controlled, it should be possible to exploit the underlying genes to improve GIN resistance among productive fibre and milk producing breeds of goats, most of which are highly susceptible to nematode infections. Genetic resistance to GIN and trypanosome infections would obviate the need for expensive chemotherapy, mostly unaffordable to small-holder farmers in Africa, and a significant cost of goat husbandry in more developed countries. Either introgression of resistance alleles into susceptible breeds by conventional breeding, or transgenesis could be used to develop novel parasite-resistant, but highly productive breeds, or to improve the resistance of existing breeds, benefitting the local West African rural economy as well as global caprine livestock agriculture.

The influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 4. Gastrointestinal parasitism

Gastrointestinal nematodes limit the growth, production and welfare of goats but there are few reliable sources of information for recommending management practices across flocks. The effects of animal species (Angora goat, Merino sheep, mixed-grazed goats and mixed-grazed sheep at the ratio of 1 : 1) and stocking rate (SR: 7.5, 10, 12.5 animals/ha) on gastrointestinal parasitism were determined in a replicated experiment on improved annual temperate pastures in southern Australia, from 1981 to 1984. Detailed monitoring of gastrointestinal nematodes was undertaken on animals before, during (five times per year) and at the conclusion of studies using faecal strongyle egg counts (WEC) and total worm counts. Sheep had a greater proportion of nematodes as Teladorsagia spp. and goats a greater incidence of Trichostrongylus spp. Both goats and sheep developed resistance to Nematodirus spp. during the experiment. WEC was similar in goats and sheep at the start of the experimental period but, thereafter, was consistently greater in goats than in sheep. While WEC was highly related to total worm count, the regressions for sheep and goats were different. Increasing the SR increased the WEC of goats and mixed-grazed goats but not of sheep. During the experiment, WEC declined at 7 and 10 animals/ha but increased at 12.5/ha. Mixed grazing with goats provided beneficial effects for sheep at all stocking rates, but the effects for goats were dependent on the stocking rate, being beneficial at 7.5 and 10/ha but harmful at 12.5/ha. The WEC of separately grazed goats were generally higher than the WEC of mixed grazed goats. The WEC of mixed sheep were lower than those of separately grazed sheep. During the experiment, the WEC of mixed grazed sheep declined faster than the WEC of separately grazed sheep but the WEC of separately grazed goats at 12.5/ha and of mixed grazed goats at 10 and 12.5/ha increased. Under the environmental and pastoral conditions examined, Angora wether goats should not be grazed at SR above those recommended for wether sheep. In the present study, the impact of gastrointestinal-nematode infections in goats was reduced at lower SR. Further, mixed grazing of Angora wether goats with wether sheep at or below the recommended SR resulted in reduced gastrointestinal parasitism for both sheep and goats, compared with monospecific grazing conditions. Goats did not represent a gastrointestinal-nematode hazard to sheep.

The unique resistance and resilience of the Nigerian West African Dwarf goat to gastrointestinal nematode infections

Background

West African Dwarf (WAD) goats serve an important role in the rural village economy of West Africa, especially among small-holder livestock owners. They have been shown to be trypanotolerant and to resist infections with Haemonchus contortus more effectively than any other known breed of goat.

Methods

In this paper we review what is known about the origins of this goat breed, explain its economic importance in rural West Africa and review the current status of our knowledge about its ability to resist parasitic infections.

Conclusions

We suggest that its unique capacity to show both trypanotolerance and resistance to gastrointestinal (GI) nematode infections is immunologically based and genetically endowed, and that knowledge of the underlying genes could be exploited to improve the capacity of more productive wool and milk producing, but GI nematode susceptible, breeds of goats to resist infection, without recourse to anthelmintics. Either conventional breeding allowing introgression of resistance alleles into susceptible breeds, or transgenesis could be exploited for this purpose. Appropriate legal protection of the resistance alleles of WAD goats might provide a much needed source of revenue for the countries in West Africa where the WAD goats exist and where currently living standards among rural populations are among the lowest in the world.

Goat-nematode interactions: think differently

Goats (caprine) and sheep (ovine) are infected with the same principal gastrointestinal nematode (GIN) species, which provoke similar pathological changes and economic consequences. However, until now, the majority of data on host-parasite interactions have been accumulated from ovine studies. This article aims to emphasize the need for specific caprine studies. It is hypothesized that, owing to divergent evolutionary processes, sheep and goats have developed two different strategies to regulate GIN infections, respectively, based on immune response versus feeding behavior. Generation of additional comparative data should result in a better understanding of the possible trade-offs between these two basic regulatory processes. Goat studies should also help to avoid past errors in the control of GIN species owing to the lack of relevant information.

Influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 3. Mohair and wool production and quality

The effects of animal species (AS; Angora goats, Merino sheep, mixed-grazed goats and sheep at the ratio of 1 : 1) and stocking rate (SR; 7.5, 10 and 12.5 animals/ha) on fibre production and quality were determined in a replicated experiment on improved annual temperate pastures in southern Australia from 1981 to 1984. Separately grazed sheep produced the most total clean fibre/ha at each SR. Mixed-grazed treatments produced amounts of clean fibre/ha similar to the arithmetic mean of sheep and goat treatments at 7.5/ha (21.9 versus 21.3 kg/ha), 10% more at 10/ha (28.3 versus 25.3 kg/ha, P < 0.05) and 7% more at 12.5/ha (31.6 versus 29.6 kg/ha, P < 0.10). Clean wool production/head was affected by AS and SR but not year. Clean mohair production was affected by SR and year but not AS. Variation in mean fibre diameter (MFD) accounted for 67 and 71%, respectively, of the variation in clean wool and clean mohair production/head. There was an AS × SR interaction for clean fibre production/t pasture. Growth rate of mohair was highest in autumn and least in summer. In each season, an increase in the SR reduced the clean mohair growth rate. Growth rate of wool was highest in spring and least in summer. Wool and mohair MFD were affected by an AS × SR interaction. Mohair MFD was also affected by year and season. At 10/ha, wool from mixed-grazed sheep had a greater MFD than wool from separately grazed sheep (20.2 versus 18.9 μm) and mixed-grazed goats grew mohair 1 μm coarser than separately grazed goats. At 12.5/ha mixed-grazed goats grew mohair 1.9 μm finer than separately grazed goats. Mohair MFD was predicted by a multiple regression that included average liveweight for the period of fleece growth, season of growth (summer 1 µm finer than winter) and year (range 1.27 µm). Mohair MFD increased 4.7 µm/10 kg increase in average fleece-free liveweight (P = 6.4 × 10–14). Fleece-free liveweight alone accounted for 76.4% of the variation in mohair MFD. There was an AS × SR interaction for the incidence of kemp and medullated fibres; under severe grazing pressure their incidence was suppressed. This experiment indicated that the principles associated with the effects of SR on wool production on annual temperate pastures apply to mohair production. Mixed grazing of Merino sheep and Angora goats produced complementary and competitive effects depending on the SR. Angora goats should not be grazed alone or mixed-grazed with sheep on annual temperate pastures at SR greater than that recommended for Merino sheep.

Influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 2. Liveweight, body condition score, carcass yield and mortality

The effects of animal species (AS; Angora goats, Merino sheep, mixed-grazed goats and sheep at the ratio of 1 : 1) and stocking rate (SR; 7.5, 10 and 12.5 animals/ha) on the liveweight, body condition score, carcass yield and mortality of goats and sheep were determined in a replicated experiment on improved annual temperate pastures in southern Australia from 1981 to 1984. The pattern of liveweight change was similar for both species with growth from pasture germination in autumn until maturation in late spring followed by weight loss. In winter, sheep grew faster than goats (65 versus 10 g/day, P < 0.05). In mixed-grazed treatments between November and December goats either grew when sheep were losing weight or goats lost less weight than sheep (P < 0.01). Both AS (P < 0.001) and SR (P < 0.001) affected liveweight of sheep and an AS × SR interaction (P < 0.05) affected liveweight of goats. Mixed-grazed sheep were heavier than separately grazed sheep at all SR with a mean difference at 10 and 12.5/ha of 4.6 kg. Mixed-grazed goats at 10/ha were heavier than separately grazed goats from the end of the second year of the experiment, but at 12.5/ha, separately grazed goats maintained an advantage over mixed-grazed goats, with a 9.4-kg mean difference in December (P < 0.05). Body condition scores of goats and sheep declined with increasing SR; they were highest in late spring and were highly correlated with liveweight (r2 > 0.8). Both AS and SR affected (P < 0.001) carcass weight and GR tissue depth as a direct result of differences in liveweight. Adjusting for differences in carcass weight negated AS effects on GR tissue depth. The carcass weights of sheep and goats increased by similar amounts for each 1-kg increase in liveweight. Mortality of sheep (3.1% p.a.) was unaffected by AS or SR. An AS × SR interaction indicated mortality of separately grazed goats at 12.5/ha and mixed-grazed goats at 10 and 12.5/ha were higher (P < 0.05) than all other goat (29 versus 9%) and sheep treatments, primarily because of increased susceptibility to cold stress. Disease prevalence differed between sheep and goats. Mixed grazing of Merino sheep and Angora goats produced complementary and competitive effects depending upon the SR. Goats used summer pasture better but winter pasture less well for liveweight gain than sheep. Angora goats should not be grazed alone or mixed grazed with sheep on annual temperate pastures at SR greater than that recommended for Merino sheep and the evidence indicates a lower SR will reduce risks associated with mortality.

Nutrition-parasite interactions in goats: is immunoregulation involved in the control of gastrointestinal nematodes?

Compared to sheep, goats seem to develop a low immune response against the parasitic nematodes of the gastrointestinal tract. Nevertheless, some variability in the host response has been observed either at the individual level or depending on internal (genetic) or external (physiological status, nutrition) factors suggesting the possibility to exploit and manipulate this response. There is good evidence from field studies to suggest that a better plane of nutrition might contribute to improve goat resilience. However, the effects on immunoregulation and host resistance remain less clear. Due to their peculiarities in feeding behaviour ('intermediate browser'), goats represent a valuable model to explore the relationships between the three possible strategies to control nematode infection through nutrition: (i) by increasing the immune response; (ii) by avoiding the infective larvae; and (iii) by selecting plants with direct anthelmintic properties (self medication).

Comparison of nematode infections of the gastrointestinal tract in Angora and dairy goats in a rangeland environment: relations with the feeding behaviour

A study was conducted in order to examine the possible influence of feeding behaviour on differences in the diversity and the intensity of nematode infections of the gastrointestinal tract between two breeds of goats placed in the same rangeland environment. Within the same flock bred on rangeland conditions, 10 Saanen dairy goats and 14 Angora goats were surveyed for 5 months (from May to September) and parasitological and behavioural parameters were measured. The level of nematode infection was estimated by monthly measurements of faecal egg counts whereas the feeding behaviour was assessed every fortnight. During the whole survey, nematode egg excretion was repeatedly higher in the Angora goats compared to the Saanen ones and significant differences were observed in May and September. This difference in egg excretion was related to major difference in feeding behaviour between the two breeds. In contrast with the Saanen does, Angora goats did not show any browsing and resting activities at any date of observation. Hence, Angora goats can be considered mainly as grazers whereas Saanen goats exhibit feeding activities close to browsers. The relative influence of feeding behaviour and host immune response on the susceptibility to gastrointestinal nematode infection in goats is discussed.

Natural evolution of gastrointestinal nematodes in goats (Capra hircus) in the semi-arid ecosystem of the Paraíba backwoods, northeastern Brazil

This study was conducted in Patos county, a semi-arid area with caatinga vegetation in Paraiba State, northeastern Brazil. Twenty-four male goats of mixed breeds were used. The animals were separated in age groups from 1-12 months, i. e., 1-2, 3-4, 5-6, 7-8, 9-10, 11-12 months, with four animals in each group. The animals were slaughtered and necropsied to recover and identify adult worms. The goats were exposed to nematode infection from the first month of life. The most prevalent nematodes in decreasing order were: Trichostrongylus colubriformis, Haemonchus contortus and Oesophagostomum columbianum. Age of the goats did not appear to be a factor in resistance to gastrointestinal nematode infection. Worm burdens of 11-12 month old animals were significantly (P<0.05) higher than in other age groups.

Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Consequences on milk production

The objective of the study was to examine the ability of dairy goats to develop a response to nematode parasites of the digestive tract after a previous contact with the worms. One hundred dairy goats were initially divided into 2 groups. One remained free of parasites (not previously infected: NPI). The second group was infected thrice at 50 days interval with a mixture of Haemonchus contortus and Trichostrongylus colubriformis (previously infected: PI). After this initial exposure to nematodes, the goats were drenched with fenbendazole to eliminate the worms and remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating dairy goats from each initial group were challenged with a mixture of H. contortus and T. colubriformis and parasitological, pathophysiological and milk production parameters were measured fortnightly to assess the effects of challenge infection and the response of the goats. No difference in parasite egg excretion was found between group NPI and PI after challenge infection. Similarly, no difference in worm counts was detected in 5 culled goats from each group killed one month post challenge. In contrast, differences between both groups were detected when considering the pathophysiological parameters (packed cell volume, inorganic phosphate and pepsinogen concentrations) with consequences of infection being more severe in the previously infected animals. Moreover, the milk production was also depressed in the PI group when compared to the NPI one. These results indicate that the response developed by adult dairy goats after the challenge infection was unable to limit the worm populations but could have pathophysiological repercussions and consequences on production.

Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Differences between high and low-producers

The objective of the study was to analyse the influence of the level of milk production in dairy goats on the ability to develop resistance to gastrointestinal nematode infection. Two groups of 50 goats were initially exposed (Group 'Previously Infected' PI) or not exposed (Group 'Not Previously Infected' NPI) to repeated infections with a mixture of Haemonchus contortus and Trichostrongylus colubriformis. After anthelmintic treatment, goats from both groups remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating goats in each group were challenged with Haemonchus contortus and Trichostrongylus colubriformis. Parasitological, pathophysiological and milk production parameters were then examined fortnightly for 3 months following challenge. Within the PI and NPI group, the response to challenge was compared between the 25% goats exhibiting the lowest level of milk production and the 25% with the highest level of production. In the low producers, previous contact with the parasites was associated with a decrease in egg excretion which was not apparent in the high producers. Previous exposure to parasites was also associated with more severe pathophysiological disturbances in the high producers. Lastly, the response to challenge also induced more severe depression in milk production after previous infection in the animals with the highest productive potential. These results confirmed that the level of milk production in dairy goats could influence the resistance and/or resilience to parasitism with more severe consequences detected in the high producers. In addition, the results suggest that such differences could in fact be mainly related to differences in the host response to parasites.

Efficacy of an albendazole slow-release capsule for the control of susceptible or resistant nematode parasites of dairy goats

The efficacy of albendazole slow release capsules-ASRC- (Proftril-Captec) on gastro-intestinal nematodes of dairy-goats was assessed both for benzimidazole (BZ) susceptible and resistant strains. For BZ susceptible strains, the efficacy of ASRC, assessed by controlled test, ranged from 92% for Trichostrongylus colubriformis to more than 99% for Haemonchus contortus on existing worm burdens. The administration of the ASRC prevented infection with the same strains for 85 to 91 days post treatment. In a dairy goat farm, where both in vitro and in vivo tests indicated a high level of BZ resistance, the efficacy of ASRC on present infections, assessed by Faecal Egg Count Reduction test, ranged from 20 to 60% according to the sampling date (13 to 88 days post treatment). On the same farm the ASRC given at turnout to non infected (primiparous) goats prevented egg shedding up to 72 days (30 for controls). In contrast the ASRC given to infected (multiparous) goats did not prevent egg shedding. The present results show that the ASRC is an efficient device for controlling BZ susceptible nematodes. The ASRC prevents infection with BZ resistant larvae whereas existing infections are not reduced.

The influence of stocking rate on gastrointestinal nematode infections of sheep over a 2-year grazing period

Six groups of four ewes with twin lambs grazed six paddocks during two consecutive seasons from May to September in a two-factorial study on stocking rate (9, 13 and 17 ewes ha-1) and infected (designated I-low, I-medium and I-high) versus clean pasture (C-low, C-medium and C-high). All animals were treated with anthelmintic at turn-out and the C-groups were further treated fortnightly. The two sets of paddocks received 0, 80 and 160 kg N fertilizer ha-1 annually with increasing stocking rate. Ewes were withdrawn at the end of July, and all lambs were slaughtered at the end of the grazing season for total worm counts. Nematode infections were subclinical during the first year. The second year, diarrhoea and soiled hindquarters were present from early August onwards in all I-groups with highest incidence at high stocking rate. The faecal egg counts of I-ewes were similar the first year but were substantially higher in I-medium and I-high compared with I-low in the second year. The lambs had differences in faecal egg counts related to stocking rate both years (P < 0.05) and group I-high had faecal egg counts ten-fold higher than I-medium and I-low at the end of the second year. A significant effect of the interaction of stocking rate times +/- infection was found in serum-pepsinogen levels in lambs (P < 0.05). Worm burdens (predominantly Trichostrongylus vitrinus, Ostertagia circumcincta and Nematodirus filicollis) were not related to stocking rate in lambs at the end of the first year whereas there was a significant effect of stocking rate on T. vitrinus burdens the second year. Pasture larval counts and results of tracer lambs indicated a positive relationship between stocking rate and pasture infectivity. It is concluded that the level of ovine nematode infections, especially Trichostrongylus spp., in weaned lambs increased with increasing stocking rate even though pasture production was enhanced by increased rates of fertilizer application.