Well I have struggled for ages to get weight on my dog tried so many things.. pasta,mince, suet .... tried it all.... but a friend recommended K9 Herbal Solutions Gain Weight!
My boy gained 4 kgs in 4 weeks... he is now the ideal weight!!

http://www.k9herbalsolutions.com/#!__complementary/productsstackergalleryv20=1

you sprinkle it on their dinner and it is incredibly palatable as my boy was soo fussy about eating, but eats this....

How much do you have to give, the website doesn't say to help indicate how long a tub is going to last?