A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

Abstract

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A shortterm divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following

Between-breed variations in resistance/resilience to gastrointestinal nematodes among indigenous goat breeds in Uganda

“…The decreasing efficacy of anthelminthics coupled with the desire for less chemical use in production systems has stimulated search for alternatives for sustainable control of parasites. Genetic resistance against GINs is well described within and between sheep breeds and to a lesser extent in some goat breeds (Bishop and Stear 2003 ; Fakae et al 2004 ; Gruner et al 2004 ; Mandonnet et al 2001 ). The use of relatively resistant animals improves growth, and there is less contamination of pastures, thus minimizing the need for anthelmintics and the development of anthelmintic resistance (Matika et al 2003 ).…”

La résistance génétique des ovins aux strongles gastro-intestinaux

“…Cependant l'intensité de l'infestation naturelle est très dépendante des conditions climatiques : en période sèche, elle peut être nulle ou en tout cas insuffisante pour provoquer une réponse significative de l'animal. Par ailleurs, les corrélations génétiques entre excrétions d'oeufs mesurées en infestations naturelles et en infestations expérimentales sont très élevées (proches de 0,9), signifiant que le même potentiel génétique est à l'oeuvre dans les deux types d'infestation (Gruner et al 2004b). La possibilité de faire plusieurs infestations suivies d'une ou de plusieurs mesures, ainsi que la connaissance des paramètres d'héritabilité et de répétabilité, permettent de définir des programmes optimaux d'infestations.…”

Gastrointestinal nematode infection in sheep – a review of the alternatives to anthelmintics in parasite control

“…FEC has been shown to have a good to high correlation (r=0.61-0.91) (Stear et al, 1995;Gasbarre and Miller, 2000) with nematode burdens and has remained the principal trait that can reliably estimate resistance (Nieuwoudt et al, 2002;Gruner et al, 2004b). It is assumed that egg numbers and subsequent worm numbers closely reflect the level of parasitic challenge to the host (Stear et al, 1995;Gasbarre and Miller, 2000).…”