Animal health and greenhouse gas intensity: the paradox of periparturient parasitism.

Abstract

Here we provide the first known direct measurements of pathogen challenge impacts on greenhouse gas (GHG) production, yield and intensity. Twin-rearing ewes were ad libitum fed pelleted lucerne from day -32 to 36 (day 0 is parturition), and repeatedly infected with 10,000 Teladorsagia circumcincta infective larvae (n=16), or sham-dosed with water (n=16). A third group of 16 ewes were fed at 80% of uninfected ewes' feed intake during lactation. Methane emissions were measured in respiration chambers (day 30 to -36) whilst total tract apparent nutrient digestibility around day 28 informed calculated manure methane and nitrous oxide emissions estimates. Periparturient parasitism reduced feed intake (-9%) and litter weight gain (-7%) and doubled maternal body weight loss. Parasitism reduced daily enteric methane production by 10%, did not affect the methane yield per unit of dry matter intake but increased the yield per unit of digestible organic matter intake by 14%. Parasitism did not affect the daily calculated manure methane and nitrous oxide production, but increased the manure methane and nitrous oxide yields per unit of dry matter intake by 16% and 4%, respectively, and per unit of digestible organic matter intake by 46% and 31%, respectively. Accounting for increased lucerne input for delayed weaning and maternal body weight loss compensation, parasitism increased the calculated greenhouse gasGHG intensity per kg of lamb weight gain for enteric methane (+11%), manure methane (+32%) and nitrous oxide (+30%). Supplemented with the global warming potential (GWP) associated with production of pelleted lucerne, we demonstrated that parasitism increased calculated global warming potentialGWP per kg of lamb weight gain by 16%, which was similar to the measured impact of parasitism on the feed conversion ratio. Thus, arising from a pathogen-induced feed efficiency reduction and modified greenhouse gasGHG emissions, we demonstrated that ovine periparturient parasitism increases greenhouse gasGHG intensity. This implies that ewe worm control can not only improve production efficiency but also reduce the environmental footprint of sheep production systems.