Abstract
Disease caused by gastrointestinal nematodes (GIN) is one of the main constraints for sheep production worldwide. Although adult categories are more resistant to GIN, a temporary loss of acquired immunity is presented around parturition, which results in the so-called “periparturient rise” (PPR) in fecal excretion of GIN eggs. The objective of the present work was to study the dynamic of the PPR and to model the faecal worm egg count (FEC) curve during the periparturient period in Uruguayan Merino sheep. Faecal samples were collected from lambing ewes during 2009 and 2010 parturitions. FEC and infective larvae cultures of each sampling were recorded. A total of 2121 records from 748 ewes, the progeny of 107 sires, were used in the statistical analysis. FEC data were normalized using two logarithmic transformations: Log FEC= Loge (FEC+100) and Log FEC_st (Log FEC with the variance standardized within contemporary group). Three functions were compared to shape the PPR curve. Haemonchus spp. was the most prevalent parasite. Log FEC_st was the selected response variable of the model, for its better adjustment to a normal distribution and a more homogeneous residual variance. The fixed regression model with Legendre polynomials was the selected one, based on the selection model criteria (Akaike & Schwarz Bayesian Information Criteria). The highest egg output was observed between two and four weeks post-lambing. In conclusion, the PPR observed in Uruguayan Merino lambing ewes had the maximum egg output matched with the milk production peak.
Highlights
Gastrointestinal nematodes (GIN) are one of the main constraints for sheep production in Uruguay and worldwide (Castells et al, 1995; Perry & Randolph, 1999)
The periparturient rise (PPR) was firstly documented by Taylor (1935) and it can be defined as a temporary but marked increase in nematode eggs output by lambing ewes; that begins in the last weeks of gestation and reaches the maximum peak in the first weeks post-parturition
Because it is important to know the dynamic of the PPR for the flock management and parasite control, the aim of the present study was to model the phenotypic curve of faecal worm egg count (FEC) during the periparturient period in Uruguayan Merino sheep
Summary
Gastrointestinal nematodes (GIN) are one of the main constraints for sheep production in Uruguay and worldwide (Castells et al, 1995; Perry & Randolph, 1999). The PPR was firstly documented by Taylor (1935) and it can be defined as a temporary but marked increase in nematode eggs output by lambing ewes; that begins in the last weeks of gestation and reaches the maximum peak in the first weeks post-parturition It is an important event because it represents a pasture larval contamination source for newborn lambs (Bishop & Stear, 2001; Romero & Boero, 2001). The PPR was firstly described in Uruguay by Nari et al (1977a) in the Ideal breed, where Haemonchus spp. represented 82% of the total of the parasite genera presented They worked with only 71 animals which were divided in three groups: lambing ewes that were dewormed before parturition, lambing ewes without a pre-partum anthelmintic treatment and non-treated barren ewes (control group). These authors observed that the maximum egg output took place between six and eight weeks post-lambing, but they did not model the shape of the PPR curve
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