Influence of grazing management practices on gastrointestinal nematode burden and clinical parameters in sheep

Abstract

Montado is an agrosilvopastoral ecosystem, defined by the association of soil, pastures, trees and animals with the Mediterranean climate, characteristic of Alentejo. Grazing management practices vary among farmers, most adopting continuous grazing (CG) while others practice deferred grazing (DG). DG entails use of pasture plots, with grazing durations adjusted to available biomass and typically supports a higher stocking rate (SR) compared to CG. Small ruminant gastrointestinal nematode (GIN) infections threaten a cost-effective and sustainable livestock production, causing subclinical to clinical symptoms. It is generally recognised that increasing SR leads to an increase in parasitic burden. The primary objective of this study was to evaluate differences in parasitological and haematological parameters between yearling female sheep managed under CG and DG. Grazing strategy defined two groups: CG group (13 yearling ewes stocked at 1 animal unit equivalent (AUE)/ha), and DG group (37 yearling ewes stocked at a 3 (AUE)/ha). Fresh faecal samples were collected directly from the rectum, blood samples via jugular venipuncture. Haematocrit (HT) was determined with the manual microhaematocrit technique; serum total proteins (PT) were accessed using an analogic refractometer. Faecal samples were analysed using the McMaster technique, with a detection threshold of 50 eggs per gram (EPG). Following individual EPG counts, pooled samples were prepared and subjected to coproculture for morphological identification of parasitic larvae. Statistical analyses were performed using R software. Descriptive statistics of the haematological and parasitological variables (HT, PT, and EPG) was computed, including measures of central tendency and dispersion. Group comparisons were tested using the non-parametric Kruskal-Wallis test (p < 0.05). EPG in the CG (150.0 ± 111.8; 150 EPG) did not differ (p = 0.52) from EPG in the DG (591.9 ± 798.7; 150 EPG). For HT, difference was also not significant (p = 0.43), CG (28.5 ± 5.6; 31%), and DG (31.0 ± 2.6 ;31 %). Similarly, PT values did not differ between groups (p = 0.96). CG: (5.0 ± 0.2;5g/dL), DG: (5.0 ± 0.3; 5g/dL); relative abundances of GIN genera were similar across groups: Trichostrongylus spp. were most prevalent, followed by Teladorsagia spp.; Chabertia spp. and Oesophagostomum spp. exchanged ranks between groups, while Haemonchus spp. remained the least abundant. In conclusion, no significant differences were detected in GIN egg excretion, HT, or PT between continuous and deferred grazing systems. These results indicate that grazing management had little effect on the evaluated parameters. Larger and longer-term studies are needed to confirm these findings within the regional context.