Impact of gastrointestinal parasitism on dry matter intake and live weight gain of lambs: A meta-analysis to estimate the metabolic cost of gastrointestinal nematodes

•Effect of gastrointestinal nematodes on feed intake and growth of sheep was studied.•Metabolic cost of gastrointestinal nematodes was estimated by meta-analysis.•The worm burden had a detrimental effect on feed intake and growing sheep.•Metabolic cost was 0.30 mg CP/kgLW0.75 and 0.056 kJ ME/kgLW0.75 per adult parasite. This study aimed to estimate the effect of gastrointestinal nematodes (GIN) on the productive performance assessed by the live-weight change (LWC) of lambs, and the metabolic cost associated with parasitism by means of a meta-analysis. Data used in the meta-analyses were obtained from twenty papers selected using the following criteria: (a) lambs with (I) and without (NI) GIN; (b) lambs fed ad libitum; (c) LWC data; (d) feed consumption data; and (e) chemical composition of diets. The effect of diet composition (crude protein [CP] and metabolizable energy [ME]) on dry matter intake (DMI), and the effect of composition and nutrient intake (DMI and CP intake [CPI]) and ME intake (MEI) on LWC was evaluated using respective regression analyses. The metabolic cost of worm burden was determined as the difference in CP and ME requirements between NI and I lambs for each adult parasite. The CP and ME cost were evaluated for lambs at two different levels: maintenance level 0 g LWC and 100 g LWC. The worm burden had an impact on the DMI and LWC of lambs (P