Horrible subject I know but here goes :
I am boarding a boxer who has strange toilet behaviour . As long a he is being walked he strains and strains only producing small offerings that are very loose . towards the end of a walk we are talking straining and just little amounts of orangy water or jelly .As long as I stay out he will keep straining .Once in his kennel he does not continue .
His owner discribed this "usual" behaviour when booking him in .
His anus is very red.
Has anyone any idea why he does this? or any advise . I wonder if he should have a special diet , I am feeding him arden grange large breed as the owner said any dry food would be fine .(i find a lot of owners choose not to bring their own food ! )
Thanks
Sally 

Sounds like colitis to me, usually controllable through diet. Surprised his owner considers this normal. He's probably in some discomfort if he's straining constantly.

http://www.isabellevets.co.uk/health_advice/dog/info/colitisdog.htm
http://www.vetbase.co.uk/information/colitis-explained.php

Just to add, if you do a search on the forum it'll come up with a fair bit of info.

Thanks Zara
This is interesting reading . I am hoping to be able to gently advise the owner that this may not be normal . I am not sure what he is fed normally although they did say dry dood , if it is a substandard food maybe a stay here might see an improvement I only have arden grange food though .. So far he hasn't eaten any of my meals  in his 36 hours stay .