An association of faecal egg counts and prolactin concentrations in sera of periparturient Angora goats

Physiological, Immunological and Genetic Factors in the Resistance and Susceptibility to Gastrointestinal Nematodes of Sheep in the Peripartum Period: A Review

Parasitic diseases of sheep involving gastrointestinal nematodes (GIN) are one of the main problems that affect fl ock productivity, especially during the peripartum period. Around lambing, the ewes are immunosuppressed and the nematode faecal egg count (FEC) increases at four weeks before lambing, reaching a peak between the fourth and sixth week postpartum and subsequently decreasing towards weaning. Prolactin has been credited with a suppressive effect on immune system, along with other hormones that intervene in metabolism, such as leptin, which has an important role in the activation of other hormones. Cortisol has also been included; this is stimulated by any stressful event and inhibits the proliferation of T-cells and alters the function of immunoglobulins. Another related hormone is pepsinogen, which is considered a marker of the integrity of the abomasum mucosa, as well as the albumin concentration that increases in the presence of a GIN infection. The humoral and cellular immune response, as well as inflammatory reactions, are the main mechanisms of action against GIN. Lymphocytes direct the effector mechanisms in a Th2 cell response, including interleukins (IL-4, IL-5, IL-9, IL-10) and transforming growth factor beta (TGF-β) together with immunoglobulins (IgA, IgG, IgM and IgE), which prevent the invasion of pathogens. Eosinophils with a cytotoxic effect are indicators of a parasitic infection, with importance in the immune protection of infected individuals. The genetic selection of resistant individuals measured by FEC is dependent on the heritability (h²), which is moderately inheritable and highly repeatable. Effects that influence the resistance or susceptibility of sheep to GIN infections in the peripartum period are determined by the interaction of various factors, such as genotype or breed, nutrition, age, type of birth, season and production system, etc., which are studied in this review.

Studies on the prevalence of fascioliasis among ruminant animals in northern Bauchi state, north-eastern Nigeria

A study of prevalence of ruminant fascioliasis was undertaken from May 2017 to April 2018. A set of 7640 stool and 7640 bile samples were collected from slaughtered cattles, sheeps and goats in seven local abattoirs located within the seven Local Government Areas making up northern Bauchi state. The Sample collection was demarcated into four sections of three months each corresponding into four local seasons. 1910 samples were collected from the beginning to the end of each of the four local seasons. Direct postmortem investigation to detect adult Fasciola spp. was employed. Stool samples were analyzed using formol-etha concentration technique. ANOVA (Analysis of variance) was conducted to examine the prevalence of fascioliasis in six communities of northern Bauchi state. The prevalence of infection was statistically different on different localities. The highest infection rates from the seven sampling sites was Jama'are (48.5%) followed by Zaki (46.9%) p = 0.05. Specie specific prevalence of fascioliasis between the host species was statistically different. Cattles were more infected than sheep and goat. Prevalence of fascioliasis on gender was statistically different, with bulls showing a higher prevalence rate and female sheep and goat recorded higher prevalence. Prevalence of fascioliasis based on estimated ages of animals sampled was statistically significant, animals above 5 years had higher prevalence of 64.5% followed by animals below the age of 1 with 41.3% (p = 0.05). Prevalence of fascioliasis among sampled ruminants based on seasonal variations was statistically significant. Higher prevalence percentages were observed during the early and late rainy season (47.2% and 58.4%) compared to early and late dry seasons (36.2% and 20.1%) p = 0.05. The study, therefore, recommends regular meat inspection alongside public awareness campaigns.

Progesterone inhibits the in vitro L3/L4 molting process in Haemonchus contortus

We evaluated the direct effects of progesterone on the morphology, maturation and behavior of Haemonchus contortus larvae in vitro. The presence and location of possible progesterone receptors in these larvae were also determined. The addition of 8ng/mL of progesterone to larval cultures over 10days reduced larval enlargement, while the addition of 160ng/mL of the hormone increased the enlargement. Up to 62% and 65% of the H. contortus larvae molted from third-stage larvae (L3) to fourth-stage larvae (L4) when cultured in RPMI-1640 media without hormone for 5 and 10days, respectively. The addition of different progesterone concentrations (1, 8, 16, 80 and 160ng/mL) to the larval cultures significantly inhibited the molting process within the same periods. The addition of 8ng/mL or higher progesterone concentrations to the cultures significantly increased larval motility (p<0.05) compared with unstimulated larvae. Flow cytometry showed the expression of progesterone receptors (P4-R) in 15% of the cells from newly isolated H. contortus larvae. When the larvae were cultured for 5days in the presence of the hormone, the percentage of P₄-R+ cells remained the same. In contrast, unstimulated larvae showed a significant reduction in the number of P₄-R+ cells. Using confocal microscopy, a greater concentration of P₄-Rs was immunolocated in the anterior portion of the alimentary tract of the larvae, suggesting that the cells in this region are targeted by the hormone. The results of the present study show that H. contortus larvae have possible P₄-Rs and respond to this hormone by inhibiting their molting process, thereby suggesting the participation of progesterone in the larval arrest phenomenon.

Epidemiology and effect of gastrointestinal nematodes on dairy goats in Argentina

The aim of this work was to study the epidemiology and harmful effects of gastrointestinal nematodes (GINs) on dairy goats maintained in an intensive system. Two groups of goats were studied: untreated group (UG) (subdivided into UGjun goats that kidded in June, and UGjul goats that kidded in July) and treated group (TG) (with no subgroups, treated with monepantel: 3.75 mg/kg, orally, monthly). Eggs per gram (epg) in faeces were counted, faecal culture was performed to differentiate nematode genera and milk production was measured. Differences between groups were compared using least squares means analysis of variance (milk production and milking period length) and Kruskal–Wallis test (faecal egg counts). Nematode infection was moderate, with Haemonchus and Trichostrongylus being the dominant genera; the faecal egg counts reached the level of 2000 only once throughout the study. Goats that kidded in June had higher egg count after parturition (UGjun = 1564 epg), with significant differences (p < 0.04) from those that still had not kidded (UGjul = 962 epg). Over the entire trial period, the mean total milk production of TG (399.5 L ± 34.0 L) was significantly higher (p < 0.05) than that of UG (281.6 L ± 37.5 L), representing an increase of 41.8% in total milk yield. The results of this study show a post-partum peak in egg count and a negative effect of GINs on milk yield, even with moderate infections.

Interactions Between Nutrition and Infections With Haemonchus contortus and Related Gastrointestinal Nematodes in Small Ruminants

Interactions between host nutrition and feeding behaviour are central to understanding the pathophysiological consequences of infections of the digestive tract with parasitic nematodes. The manipulation of host nutrition provides useful options to control gastrointestinal nematodes as a component of an integrated strategy. Focussed mainly on the Haemonchus contortus infection model in small ruminants, this chapter (1) illustrates the relationship between quantitative (macro- and micro-nutrients) and qualitative (plant secondary metabolites) aspects of host nutrition and nematode infection, and (2) shows how basic studies aimed at addressing some generic questions can help to provide solutions, despite the considerable diversity of epidemiological situations and breeding systems.

Método FAMACHA para detectar anemia clínica causada por Haemonchus contortus em cordeiros lactentes e ovelhas em lactação

Resumo: O controle das endoparasitoses gastrintestinais em pequenos ruminantes tem sido tradicionalmente realizado por meio do uso indiscriminado dos anti-helmínticos, porém essa prática tem resultado em grande pressão de seleção de parasitas resistentes. Métodos seletivos (ex: FAMACHA/FMC e contagem de ovos nas fezes/OPG) e que apresentem boa sensibilidade para identificar os animais que necessitam receber o tratamento químico são importantes alternativas aos métodos tradicionais. O objetivo desse trabalho foi determinar a sensibilidade e a especificidade do método FMC, usado para detectar anemia causada por Haemonchus contortus em ovinos da raça Suffolk, em duas categorias de alta suscetibilidade; cordeiros lactentes e ovelhas durante a fase de lactação. A conjuntiva ocular de 42 cordeiros lactentes e 35 ovelhas em lactação foi avaliada usando o método FMC, em intervalos de 14 dias, durante cinco meses. O hematócrito (Ht) foi utilizado como padrão-ouro para avaliação clínica de anemia dos animais. Para o cálculo de sensibilidade e especificidade, diferentes critérios foram utilizados: animais classificados como 4 e 5 ou 3, 4 e 5 e anêmicos pelo Ht (teste positivo); animais classificados como 1, 2 e 3 ou 1 e 2 e não anêmicos pelo Ht (teste negativo). Três valores de corte para Ht (≤22%, ≤19% ou ≤15%) foram utilizados para confirmar a anemia. Entre os gêneros observados nas coproculturas, H. contortus (61,5%) e Ostertagiasp (21,3%) foram os mais prevalentes. Em ambas as categorias, a inclusão do FMC 3 como teste positivo, elevou a sensibilidade mas reduziu a especificidade do método. Quando o FMC 3 foi considerado anêmico, o percentual de falsos negativos foi próximo a zero, no entanto, houve aumento no número de tratamentos aplicados em animais não anêmicos (falso positivo). Durante as avaliações, a maior parte dos cordeiros (73%) e das ovelhas (53%) permaneceu nas categorias de FMC 1 e 2. Apenas 5% dos cordeiros e 8% das ovelhas foram classificados com os dois maiores graus de anemia (FMC 4 e 5). Os resultados indicam que o FMC pode ser utilizado para identificar os cordeiros lactentes e ovelhas em fase de lactação com sinais clínicos de anemia decorrentes da infecção por H. contortus. Para ambas as categorias, foi necessário incluir o FMC 3 como positivo para aumentar a sensibilidade do método; reduzindo o risco de morte de animais anêmicos não diagnosticados (falsos negativos).

Dinâmica de eliminação de oocistos de Eimeria sp. durante a gestação e fase inicial da lactação em cabras nativas criadas extensivamente em região semiárida

<p>Objetivou-se com este estudo caracterizar a dinâmica de eliminação de oocistos de<italic>Eimeria</italic>sp<italic>.</italic> em cabras sem raça definida (SRD), criadas em sistema extensivo na região semiárida, durante a gestação e fase inicial da lactação. Vinte cabras adultas, criadas extensivamente na Caatinga, foram selecionadas e monitoradas durante oito meses. Os valores de Oopg (quantidade de oocistos por grama de fezes) foram acompanhados quinzenalmente do 1º mês de gestação ao 90º dia pós-parto. O Oopg variou durante a gestação, sendo as maiores e menores contagens de 3.300 ± 709 e 1.726 ± 215, respectivamente. Após elevação na primeira quinzena, o Oopg diminuiu gradualmente até o 105º dia e voltou a subir até o final da gestação. No período pós-parto, seguindo a tendência da fase final da gestação, houve aumento progressivo na eliminação de oocistos até o 90º dia de lactação. A quantidade média de oocistos liberados durante a fase inicial da lactação foi de 3.006 ± 102,3 Oopg comparado ao período gestacional de 2.312 ± 98,03 Oopg (P<0,05). A dinâmica de eliminação de oocistos de<italic>Eimeria</italic> sp. em cabras gestantes e lactantes, criadas extensivamente em região semiárida, foi caracterizada por três situações distintas: elevação brusca no início da gestação, seguida por redução gradual no período intermediário da gestação e aumento constante da eliminação de oocistos na fase final da gestação até inicial da lactação.</p>

Endoparasitismo gastrintestinal em cabras da raça Anglonubiana

A dificuldade de manutenção do rebanho em condições sanitárias adequada compromete a eficiência da criação de caprinos, principalmente em relação ao controle de endoparasitas. O objetivo com este trabalho foi avaliar a sensibilidade de matrizes da raça Anglonubiana a nematoides gastrintestinais, considerando as cabras estratificadas por estágio fisiológico (lactantes e não lactantes) dentro de três classes de idade. Utilizou-se as características: Ovos por grama de fezes (OPG), Grau de anemia (indicado pelo método Famacha©), Peso e Escore da condição corporal e porcentagem de coletas de fezes cujo valor do OPG foi igual a Zero, variável utilizada para demonstrar a resposta ao antihelmintico, disponibilizadas pelo banco de dados dessa raça na UFPI. Os dados são referentes ao período de janeiro de 2009 a dezembro de 2011. As cabras em lactação apresentaram maior valor médio de OPG, maior grau de anemia, menor escore corporal e menor quantidade de coleta de fezes com valor de OPG zero, que as cabras não lactantes, independentemente da classe de idade considerada. Assim, a lactação aumenta a sensibilidade a endoparasitismo em matrizes da raça Anglonubiana. A elevação do OPG tende a se mostrar associada ao maior grau de anemia determinado pelo método Famacha©, que levam a redução da condição corporal.

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).

Control of Haemonchus contortus in goats with a sustained-release multi-trace element/vitamin ruminal bolus containing copper

The objective of this study was to determine the effectiveness of a sustained-release multi-trace element/vitamin ruminal bolus (TEB) containing copper administered to mature does for control of gastrointestinal nematodes (GIN) during summer months and during late gestation. Haemonchus contortus was the predominant nematode during these trials. In Experiment 1, yearling Spanish does were untreated or administered TEB (n=11/group) on Day 0 (August 2005) prior to breeding. In Experiment 2, Spanish and Boer does were untreated or administered TEB 6 weeks before kidding. Fecal egg counts (FEC) and blood packed cell volume (PCV) were determined weekly between Days 0 and 42. In both experiments, FEC were reduced within 7 days in TEB-treated compared with untreated does. PCV was similar between treatment groups (Experiment 1) or tended to be lower in the TEB group (Experiment 2). GIN control did not persist more than 28 days. These studies suggest that TEB may be an effective means of GIN control in mature goats, but additional control measures may be necessary.

Impact on productivity of peri-parturient rise in fecal egg counts in Creole goats in the humid tropics

The control of gastrointestinal nematodes requires an understanding of their epidemiology so that particular parasite stages can be targeted. Dam infection during early lactation is one example of this in ruminant nematode infections. The existence of the peri-parturient relaxation in immunity and its impact on productivity were examined in a Creole goat flock from Guadeloupe, exposed to mixed natural infection (predominantly Haemonchus contortus and Trichostrongylus colubriformis). A total of 1,511 l were obtained from 909 does resulting from 463 dams and 150 sires. Fecal and blood samples were collected at kidding before anthelmintic drenching, 4 and 6 weeks after kidding. The traits analyzed were logarithm transformed fecal egg counts (FEC), packed cell volume (PCV), and logarithm transformed blood eosinophilia counts (EOS) for does at each sampling point and changes in these during the postpartum period. With the exception of the PCV values measured at kidding, lactating does had significantly higher FEC and lower PCV than control dry does at every sampling point. Geometric means of FEC in lactating does were 819 +/- 174, 677 +/- 146 and, 699 +/- 160 eggs per gram (EPG) at kidding, 4 and 6 weeks after kidding respectively. Geometric means of FEC in dry does were 187 +/- 57, 89 +/- 28, 133 +/- 43 at these time points, respectively. EOS differences were not consistent between groups and probably not specific enough for variations in Creole goats' peri-parturient rise to be discussed. As does aged, their egg output decreased and primiparous does always had greater egg output than multiparous ones. Overall, does' FEC at 4 weeks after kidding decreased by 1.3% each year. The higher the litter size, the higher the FEC at kidding and inverse applied for PCV measurements. Does that stopped lactating had significantly lower FEC and higher PCV values than lactating does with low milk yields. Higher infection rates during early lactation in Creole goats were recorded in does with lower maternal ability assessed by the average daily weight gain of kids between 10 and 30 days of age. Kids from dams with higher FEC (i.e. >600 EPG higher than corresponding does) had 17% lower average daily weight gain between 30 and 70 days postpartum and were approximately 1 kg lighter at weaning than kids from dams with lower FEC. Thus, it is clear that a peri-parturient rise in FEC exists in Creole goats. By controlling the intensity of this peri-parturient rise in FEC, herd health and productivity could be substantially improved.

Validation of the FAMACHA© eye color chart for detecting clinical anemia in sheep and goats on farms in the southern United States

Recent studies on sheep and goat farms in the southern United States indicate that multiple-anthelmintic resistance in Haemonchus contortus is becoming a severe problem. Though many factors are involved in the evolution of resistance, the proportion of the parasite population under drug selection is believed to be the single most important factor influencing how rapidly resistance develops. Therefore, where prevention of resistance is an important parallel goal of worm control, it is recommended to leave a portion of the animals untreated. Recently, a novel system called FAMACHA was developed in South Africa, which enables clinical identification of anemic sheep and goats. When H. contortus is the primary parasitic pathogen, this system can be applied on the farm level to reduce the number of treatments administered, thereby increasing the proportion of the worm population in refugia. Since most studies validating the FAMACHA method have been performed in South Africa, it is important that the method be tested in other regions before its use is broadly recommended. We performed a validation study of FAMACHA by testing the system in sheep (n = 847) and goats (n = 537) of various breeds and ages from 39 farms located in Arkansas, Georgia, Louisiana, Florida, and the US Virgin Islands. The color of the ocular conjunctiva of all animals were scored on a 1-5 scale using the FAMACHA card, and blood samples were collected from each animal for determination of packed cell volume (PCV). Fecal samples were also collected from a majority of the animals tested for performance of fecal egg counts (FEC). Correlations between PCV and eye scores, PCV and FEC, and FEC and eye scores were all highly significant for both sheep and goats (P < 0.001). Data for both FAMACHA scores and PCV were evaluated using two separate criteria for anemia: eye score values of 3, 4 and 5 or 4 and 5, and PCV values of < or =19 or < or =15 were considered anemic. Specificity was maximized when eye score values of 4 and 5 were considered anemic and PCV cut off for anemia was < or =19, but sensitivity was low. In contrast, sensitivity was 100% for both sheep and goats when eye score values of 3, 4 and 5 were considered anemic and PCV cut off was < or =15, but specificity was low. In both sheep and goats, predictive value of a negative was greater than 92% for all anemia and eye score categories, and was greater than 99% for both eye score categories when an anemia cutoff of < or =15 was used. Predictive value of a positive test was low under all criteria indicating that many non-anemic animals would be treated using this system. However, compared to conventional dosing practices where all animals are treated, a large proportion of animals would still be left untreated. These data indicate that the FAMACHA method is an extremely useful tool for identifying anemic sheep and goats in the southern US and US Virgin Islands. However, further studies are required to determine optimal strategies for incorporating FAMACHA-based selective treatment protocols into integrated nematode control programs.

Periparturient increase in faecal egg counts in a captive population of mohor gazelle (Gazella dama mhorr)

The objective of this study was to assess whether there was a periparturient rise in the faecal egg output of a population of North African gazelles (Gazella dama mhorr) kept in captivity in Almeria, southern Spain. In one experiment faeces were collected from 47 female gazelles on three days in winter, in November and December 1995 and January 1996; in a second experiment faecal samples were collected from nine pregnant gazelles at weekly intervals from July 1996 to June 1997. The mean trichostrongylid faecal egg counts were significantly higher (P < 0.05) in the periparturient gazelles than in the pregnant and non-pregnant animals only when the births took place in winter. Other factors, including the gazelle's age, its level of inbreeding, the number of previous births, and its trichostrongylid egg output at the beginning of the study did not affect whether it showed a periparturient rise. The parasites responsible for the rise were different in the two experiments.

Peri-parturient helminthosis in strains of small East African goats in Tanzania

The effect of physiological status (e.g. pregnancy and lactation) on the susceptibility to gastrointestinal nematodes was studied in the Dodoma and Kigoma strains of small East African goats in Morogoro. Forty-six pregnant does (19 Dodoma and 27 Kigoma strain) and 123 non-pregnant/dry (68 Dodoma and 55 Kigoma) from a controlled-breeding programme were used. Does were grazed on naturally contaminated pastures at Sokoine University of Agriculture for 8 months. Faecal samples and whole blood for determination of faecal egg counts (FEC), packed-cell volume (PCV) and blood eosinophils (EOS) from each animal were collected at monthly intervals from the mating period (through the gestation period) to 3 months after kidding. From kidding to 3 months after kidding, lactating does had significantly higher FEC than non-lactating/dry does. From 1 month after kidding to 3 months after kidding, lactating does had significantly lower PCV than dry does. Blood eosinophils were higher in non-lactating/dry does than lactating does but only significant at 3 months after kidding. There were no significant differences in FEC, PCV and EOS between lactating Dodoma and lactating Kigoma does. We concluded that there was no difference in peri-parturient helminthosis between Dodoma and Kigoma strains and that blood eosinophilia decreased during peri-parturient helminthosis in both strains.

Resistance of Galla and Small East African goats in the sub-humid tropics to gastrointestinal nematode infections and the peri-parturient rise in faecal egg counts

A study was carried out from 1994 to 1996 to compare the resistance to naturally acquired gastrointestinal (GI) nematode infections (predominantly Haemonchus contortus) of 88 Galla and 114 Small East African (SEA) goats (does) in the sub-humid coastal region of Kenya. Live weights (LWT), blood packed cell volume (PCV) and faecal egg counts (FEC) were recorded each year at mating, 3-4 months after mating, 1-2 weeks before kidding and 1-4 months after kidding. There was a significant increase in FEC and a decline in PCV in lactating does compared to non-lactating does over the peri-parturient period. This peri-parturient rise in FEC occurred in both breeds but was more marked and persistent in the Galla than in the SEA. The SEA does were more resistant to GI nematode infections than Galla does as shown by their significantly lower FEC and higher PCV at all sampling times over the reproductive cycle, but this breed difference was particularly marked over the lactation period.

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.

Strongyle infections in sheep and goats under the traditional husbandry system in peninsular Malaysia

Faecal egg counts were used to study patterns of trichostrongyle infections in sheep and goats according to season, age, pregnancy and lactation on traditional farms in west Malaysia. Haemonchus contortus and Trichostrongylus spp. were the most important strongyles in sheep and in goats, H. contortus, Trichostrongylus spp. and Oesophagostomum spp. were most prevalent. The faecal egg counts of sheep and goats were apparently not influenced by the small seasonal climatic variations. Strongyle infections were acquired at an earlier age in sheep than in goats. Mean faecal egg counts decreased from the age of 8 months onwards in sheep while in goats this occurred from 12-18 months onwards. A periparturient rise in strongyle egg counts was observed in both animal species. Haemonchus contortus was mainly responsible for this rise in faecal egg counts. The results are discussed with reference to control of gastrointestinal strongyle infections in sheep and goats.

Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment

A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostronglyus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments.

Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism

Bulls and rams are notorious among stockmen and stud breeders for their apparently greater susceptibility than cows, ewes, steers or wethers to diseases caused by excessive infection with parasitic nematodes. Extension advice given to farmers generally includes a recommendation to treat entire male animals as though they were weaners. In contrast, the scientific literature contains little documentation of this fact, although the phenomenon has been well-described in laboratory animals. Scientific interest in the susceptibility of lactating cows and especially ewes to nematode parasitism has been more extensive, but unproductive in terms of elucidating responsible mechanisms. Where ewes have acquired immunity to nematode infection, they tend to lose it around the time of parturition and during lactation, with important epidemiological and productivity consequences. In strains of sheep selected for resistance to nematode infection, principally through a more rapidly acquired immune response, resistant ewes still undergo a periparturient loss of immunity but retain their relative superiority over unselected or susceptible ewes. The mechanisms involve effects of hormones associated with lactation on the immune system, but an unequivocal role for prolactin or any other hormone has not yet been identified. Collaboration between immunologists, endocrinologists and parasitologists is required.