Feed conversion efficiency in sheep genetically selected for resistance to gastrointestinal nematodes

Context It has been indicated that there might be an antagonism between selection for gastrointestinal nematode resistance and high productivity and feed conversion efficiency in ruminants. Aims This study aimed to determine whether genetic selection for resistance to gastrointestinal nematodes would alter the feed intake and feed efficiency of sheep with or without an infection of Haemonchus contortus. Methods Sixty-seven Corriedale lambs (357 ± 14 days old) derived from flocks genetically selected to be resistant (n= 29) or susceptible (n = 38) to gastrointestinal nematodes (GIN) were evaluated for individual dry-matter intake (DMI), feed conversion ratio (FCR) and residual feed intake (RFI). Considering bodyweight (BW), GIN line and sires, males were allotted to one of three outdoor pens and females to one of two, each pen being equipped with five automated feeding systems and two automatic weighing platforms to record individual feed intake and BW. Feed (lucerne haylage, crude protein 20.5%, metabolisable energy 9.2 MJ/kg DM) and water were offered ad libitum. The experiment was conducted in two periods. First, animals were maintained worm-free (14 days of acclimatisation and 44 days of records) and then, in Period 2 (42 days), animals were artificially infected with 6000 L3 of Haemonchus contortus. Worm egg counts were recorded on Days 9, 23, 27, 30, 42 post-infection. While DMI, FCR, average daily gain and BW were analysed using a generalised linear model including dams age, pen and GIN line as fixed effects, RFI was analysed including only GIN line. Key results In both periods, GIN line did not have a significant (P > 0.05) effect on DMI, FCR, RFI, average daily gain or BW. Worm egg count was different (P < 0.05) on Day 23 post-infection (Period 2), being higher in susceptible line. Conclusions The most important finding of this study is that breeding GIN-resistant animals would not have a negative effect on feed conversion efficiency when evaluated as FCR or RFI in 1-year old lambs fed ad libitum with a high-protein diet. Implications Breeding for resistance to internal nematodes does not affect feed efficiency or productivity.