Do different sheep breeds show equal responses to climate fluctuations?

Large herbivores can be directly affected by climate through effects on thermoregulation, but the strongest effects are expected to operate indirectly through plant quality and biomass. The extents to which different herbivores are affected by climate conditions in contrasting ways are poorly understood. We used an extensive dataset containing information on 38,587 lambs from the years 1992-2007. The lambs represented two breeds differing largely in digestive anatomy, diet composition and possibly other traits. The yearly average body mass values of the two breeds were strongly correlated, however, responses to climate variables nevertheless differed in strength. There were positive relationships between lamb autumn body mass and snow depth the previous winter, spring temperature and temperature and precipitation in August in both breeds. In the Norwegian white sheep (NWS) breed, there was a negative relationship between lamb autumn body mass and spring precipitation. The Spel breed exhibited similar (although weaker) relationships with climate variables. Our results show that the NWS breed might, on a short time scale, benefit most from climate warming. However, the Spel breed were less variable in body mass among years suggesting that this breed might be the better choice if the aim is to reduce uncertainty in meat production. We discuss the likely mechanisms behind the contrasting responses of the two different breeds relative to morphological, physiological and behavioural differences.