Frisbee

It's a dominance display. I had 3 dogs from the same litter: the alpha male and female, and the 'runt' female. The alpha female would constantly mount her weaker sister. She grew out of the behaviour as they got older (but did adopt subtler bullying tactics such as a super soft growl or the "stand over").

It was hit and miss with my cancer riddled boy with food in the end. He was always mad about cheese so I made him scrambled eggs (or more of an omelette really) with cheese and grated carrot and peas (not sure he wanted peas and carrots but I wanted to get fibre into him) which he would eat. He also enjoyed raw chuck steak cut into cubes. When they feel really unwell though, sadly, the appetite goes. Not sure if this is helpful or not, but I would hand feed the food to him at least to start him off and let him take over if he developed his appetite.