Seasonal patterns of gastrointestinal nematode infection in goats on two Lithuanian farms
© Stadaliene et al.; licensee BioMed Central. 2015
Received: 21 July 2014
Accepted: 4 March 2015
Published: 19 March 2015
This study investigated seasonal changes in naturally acquired gastrointestinal nematode (GIN) infections on two Lithuanian goat farms with different parasite control practices.
On both farms, nematode faecal egg counts (FEC) and larval cultures were obtained from 15 adult and 10 young goats at bi-weekly intervals from April 2012 to April 2013. Goats on farm A were dewormed with ivermectin (0.3 mg/kg body weight) in October/November 2012, whereas the animals on farm B were left untreated. Thirteen young goats were slaughtered in August/November 2012 and April 2013 and worm burdens in the gastrointestinal tract were enumerated. In goats from both farms, Teladorsagia, Trichostrongylus, Oesophagostomum, Chabertia and Haemonchus were the dominant GIN genera. Herbage contamination with infective third-stage larvae (L3) peaked in July/August and resulted in high FEC in September/October. Parasitological examination at slaughter showed that Teladorsagia spp. and Haemonchus contortus survived the winter, both in the abomasal mucosa as adults and as early fourth-stage larvae (EL4). Deworming on farm A significantly reduced FEC, especially of H. contortus, at the start of the grazing period compared with the untreated farm B (P < 0.05).
Goats were heavily infected with several GIN throughout the year. Strategic anthelmintic treatment during housing significantly reduced nematode egg output, in particular by H. contortus, at the start of the grazing season.
The risk of gastrointestinal nematode (GIN) infections in small ruminants is determined by factors such as climate, level of nutrition, stocking density and management. During the past two years, the goat population in Lithuania has increased by 28%, to 9,300 animals in 2014 . This has led to increased stocking rates on pasture, with associated productivity losses from GIN infections .
The effects of GIN are predicted to become more severe due to global warming [3,4]. One such example of the possible influence of ongoing climate change is the increased infection levels of Haemonchus contortus observed in Scandinavia [5,6]. However, as long as anthelmintics are effective, strategic treatments reduce parasite pasture contamination and lower the exposure to GIN associated with increased milk yields in goats . Deworming during housing is the most commonly used control practice against GIN in Norway  and it has been shown that it significantly reduces faecal egg counts (FEC) in the next grazing season . Reduced FEC at the start of the grazing period prevents pasture contamination, especially by H. contortus since its free-living stages are sensitive to sub-zero temperatures [3,10]. H. contortus mainly survives the winter inside the host, as arrested forms in the abomasal mucosa . Previous studies on GIN in Lithuanian sheep and cattle have shown high levels of larval inhibition [12,13]. In contrast, information from Lithuanian goats has hitherto been lacking.
This study investigated seasonal fluctuations in GIN on two goat farms in central Lithuania, of which farm A was treated with anthelmintics and farm B was left untreated. Both farms had White Shorthaired Goats. The study took place between April 2012 and April 2013 and the grazing period was from late April until late October. During housing, the animals were fed hay/haylage, vegetables (sugar-beet, carrots) and grain. The kidding period on both farms started in late January and lasted until late February. Kids were weaned after approximately 3 months. On farm A, the kids grazed separately from the adult goats until October in a paddock with 500 kg/ha (adults 320 kg/ha), whereas on farm B they grazed in the same paddock (235 kg/ha).
Mean monthly temperature was similar and peaked (19.6°C) in July. Compared with the long-term average (1961–1990), the temperature on both farms was on an average 1–3°C higher during grazing. Winter temperature varied on average between −1.0°C and −6.7°C. The highest level of rainfall was observed in June/July (89.7 − 138.6 mm).
Anthelmintics had not been used on either farm for 4 months prior to the start of the trial. On farm A, the young goats received injectable ivermectin (Ivomec® 1%, 0.3 mg per kg body weight) in early October, while the adults were dewormed in late November. On farm B, all goats were left untreated throughout the study.
The work was performed in compliance with Lithuanian animal welfare regulations (No. B1-866, 2012; No. XI-2271, 2012) and was approved by the Lithuanian Committee of Veterinary Medicine and Zootechnics Sciences (Protocol No.07/2010).
Animals in each flock were selected by stratified random sampling by sex (female) and body weight, and categorised as young goats (<1 year; n = 10) or adults (>1 year; n = 15). Faeces samples were collected directly from the rectum at bi-weekly intervals. FEC were performed using a modified McMaster technique with minimum detection level of 20 nematode eggs per gram (EPG) faeces . Furthermore, 1 g samples of faeces from each animal in the same grazing group were pooled and faecal cultures were prepared to obtain infective third-stage larvae (L3) . Identification to genus or species level was based on morphological keys . In addition, triplicate (≈400 g) samples of herbage were collected between May and November 2013 from each of the paddocks used by the goats on both farms, for determination of number of L3 . Furthermore, six young females from farm A and seven from farm B were sent to the local slaughter-house for slaughtering between 25 August and 25 April 2013 and the viscera of the goats were collected for parasitological investigation. The abomasa and small- and large intestines were opened for enumeration and identification of GIN, while the abomasal mucosa was digested and examined for inhibited stages according to Grønvold . Nematodes were collected and identified to species or genus . Statistical comparisons of FEC between farms were performed using Repeated Measures Analysis of Variance (ANOVA) analysis in BMI SPSS Statistics 21 version. Prevalence of nematode infections in the gastrointestinal (GI) tract and standard 95% confidence intervals (CI) were also calculated. Worm burdens on the two farms were compared using one-way ANOVA, with P < 0.05 as statistically significant.
Teladorsagia dominated both in the samples from pasture (42 − 100%) and in faecal cultures (42%) on both farms, confirming results from other European countries [6,20-22]. In addition, L3 of Trichostrongylus (26%), Oesophagostomum (13%), Chabertia (11%) and H. contortus (8%) were identified in the faecal cultures. Interestingly, H. contortus was only observed during the grazing period (May-October) on farm A (3 − 35% of the total nematode population) and farm B (8 − 31%). In addition, H. contortus was detected in faecal cultures of young goats from late June and increased between August and October. This was particularly the case on farm A, where H. contortus comprised 16 − 21% of the total nematode population. Similarly, pasture contamination with H. contortus larvae was first detected in mid-May, but was highest between August and October (9 − 50%). This is in agreement with Swedish findings on GIN in sheep .
Mean number of worms and proportion (% of total) of Haemonchus contortus and Teladorsagia sp. development stages in abomasum of young goats at slaughter
Mean number of worms and proportion (% of total) of Trichostrongylus and Oesophagostomum/Chabertia development stages in the small and large intestines of young goats at slaughter
In conclusion, the Lithuanian goats studied here were infected with a mixture of GIN, in particular Teladorsagia spp. but also several other genera, including the more pathogenic H. contortus. FEC fluctuated in relation to the level of herbage contamination, which varied according to season on both farms. Strategic anthelmintic treatment of adult goats in November significantly reduced FEC, especially of H. contortus.
The authors thank the owners of farms A and B for their participation in the study, veterinary students of the Veterinary Academy, Lithuanian University of Health Sciences, for their help in collection of samples and Dr. Mary McAfee for language editing.
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