Influence of advancement of age on intensity of strongyle infection and performance in sheep selected for resistance/resilience to infection

Abstract

An analysis was made to observe the influence of advancement of age on intensity of strongyle infection (predominantly Haemonchus contortus) and performance in sheep (Malpura and Avikalin breed) selected for improving the genetic resistance / resilience to infection. All the data pertaining to faecal egg counts, body weights, greasy fleece yield and disposal rate were classified according to age as up to 1 yr, 1–2 yr, 2–3 yr, 3–4 yr, 4–5 yr and > 5 yr. The monthly intensity of strongyle infection showed similar influence of advancement in age of animal in both the resistant and susceptible lines of both the breeds. Intensity of strongyle infection was significantly higher in animals of S-line across all the age groups. Within line, animals up to 1 yr of age had significantly higher faecal egg counts, particularly during wormy season. Monthly intensity of infection showed marginal rise in R-line animals in older animals (>1 yr of age), and in animals >5 yr of age compared to those between 1–5 yr during wormy season. Within line, younger animals (up to 1 yr of age) had significantly higher average daily gain in body weight (21.45 g in S-line to 25.82 g in R-line of Malpura; 29.09 g in R-line to 29.45 g in S-line of Avikalin) compared to other age groups. In adult animals (> 1 yr of age) during summer (April to June), body weights were usually either maintained (in S-line) or reduced marginally (in R-line) without much appreciable difference. In monsoon season there was evident rise in magnitude of daily weight gain up to 2–3 yr of age in both the lines. There was nonsignificant variation in annual greasy fleece yield among both the divergent lines across all the age groups. The disposal profile revealed that maintenance of animals in resistant line without anthelmintic intervention had similar pattern of disposal as in animals of susceptible line maintained with anthelmintic intervention. The present study demonstrated that the animals selected for resistant line not only restricted the use of anthelmintics but also led to low contamination of pasture due to low mean FECs compared to their counterparts in susceptible line, which required one strategic drench every year and contributed more eggs on pasture in grazing area. Animals of resistant line served as valuable resource for refugia and maintenance of anthelmintic efficacy. The acquired resistance to strongyle infection in sheep was unaffected by advancement of age of animal.