Just back from the vets with Odin ....I suspected that he might have a blockage as he has been straining and hasn't pooped for a couple of days ...he's been very quiet (for Odin) although still eating and drinking well.   He looks a bit "tucked up" and carrying his tail as if he has limber tail too - so all in all, not Odin-like behaviour.

Vet has given him a pretty thorough examination, emptied anal glands (which were virtually empty in any case) said that he had very little in his intestines - so would appear that he is being sick when out in the garden - no blockage as such.  However, an anal examination indicates a pretty enlarged prostrate - which I wouldn't expect to see in a lab who isn't 5 until May next year :-(    He has a raised temperature, so he's been given a/bs and an injection (superlorein?) as an initial treatment - have to take him back Thursday if he hasn't pooped by then.

Any experiences of this????

I would imagine the injection was Tardak, an anti testosterone drug. 

This is what a friends dog was given as she didn't want him castrated.

Suprelorin is a hormone Implant to make a dog temporarily sterile.

Tardak will not make a dog reliably sterile though it will reduce libido and may impair sperm production.

Thanks Brainless - brain fog!    That's the one.    He's not been a "humper" since he was a puppy - if necessary I'll have him castrated.

From what I have read the Tardak injections may need to be repeated more frequently
http://www.darwinvets.com/dogs/older-male-dog
"
Treatment of Prostatic Problems

Apart from tumours, all prostatic disease will require some form of anti-testosterone therapy to treat it. There are two options - one is Tardak, an injection of a progesterone. This can work in some cases although it needs to be repeated every 2 - 12 weeks. Possible side-effects include increased thirst, increased appetite and hair loss at the injection site. As the injection needs to be repeated so frequently, it can work out quite expensive, so unless the dog is very old or suffers from a condition that surgery would not be a good idea, it is generally best to use the second option - castration. This is a simple procedure, requiring only a short anaesthetic, and the effect on the prostate after the operation is rapid with the gland shrinking to a normal size within 2 - 3 weeks....."

so castration may be a better option.  My friends boy didn't need them very often so stayed intact.

I'll happily have him castrated if it helps - thanks for the information, Barbara x

My boy had this 3 weeks ago - vet admitted him and did an ultrasound to confirm enlarged prostrate. Came home with antibiotics and was showing better toilet behaviour within 24 hours. Vet gave him the Tarak (or something like that) injection 5 days later when he vwent back for check up. Hope your boy feels better soon.