Hi, 

I'm not completely sure what your data looks like, but I assume it is something similar to lat. long. coordinates? If so, maybe you could take the differences from each measured time-point as an absolute value (lat and long separate of course)? If you then add all these together you should get a  measurement for activity during the time period. 

I may be totally out in the blue here, but I thought I'd think out loud for a sec and maybe it could help somewhat.  

Is this a single flock with GPS coordinates for the entire flock or does each animal have a GPS transponder? If each lamb has GPS data, one could look at total distance traveled by tracking the GPS path daily or maybe GPS data could be used to estimate grazing or nursing time if the lambs are nursing ewes. If there are multiple flocks, one could do much more.

Well it's a multiple-single flock, We managed to have 3 different breeds whitin one flock.Therefore one gps collars per breed (one random adult). So the flock managment is the same, the grassland composition is the same, every condition is the same...except for the breed. 

I think the challenge statistically is that you only have one observation per breed, so there is no effective way to measure variation within breed. You need this to detect differences in variation among breeds.

Yes, concerning flock movements I'll have one observation per breed.. But I will have also 15 lambs per breed (at least) so, I guess, 15 "replications". Maybe I can use the gps-tracks just for correlation/regression (like hours of grazing vs something).

By the way thank you all for the suggestions!

Matteo, In your case you can't use GPS coordinates as treatment. You need several ecosystems coordinates with same breed to evaluate its effect. Best wishes.