New bucks can be easily traumatized by older does. Did she chase him? The bucks often mount the head first, probably gets his scent on her, and then change around on their own. After you put him in the right position, did he complete the breeding? Or did he feel like he was doing something wrong when you moved him, and quit trying? I've had both things happen. The doe would be anxious and try to breed the buck and chase the buck, and a young buck might simply cower and quit trying. I've also had older does that didn't want rebred, and the younger buck quit trying. I've repositioned bucks and then had them quit trying.
And lastly, check the vulva of the doe (the 'slit' under the anus when you turn the doe upside down.) Is it dark purplish red? If so, she may not be receptive, and the buck may know it. While rabbits are induced ovulators, the doe releases eggs when bred, they do have little mini cycles of receptivity. If the doe's vulva is dark red, give her a few days and try again. The same applies when the vulva is pale whitish pink and small. The buck may recognize she is not in a receptive mood. You want to see a nice pink, moist, somewhat enlarged vulva, it may be a gentle purplish/reddish/pink, but usually not super dark. This tells you the doe should be receptive to the buck, and the buck can usually smell the difference.
When you say 'fattened up', is the buck underweight? I had a buck that lost any interest in breeding the does. When I did my next condition check and found he had lost weight (hard to see under all that angora wool), I searched for the reason, and found that he wore a hole through his feed hopper by banging on it, and the feed was dribbling through and I didn't know it (we have chickens and ducks that clean up the spilled grain.) I changed the feed hopper to a bowl, gave him extra feed until he reached optimum weight again, and soon he was back to siring litters. So yes, condition can make a difference. However, too much fat can hamper any desire to breed.
Rabbit Size-O-Meter has a chart showing how to tell body condition.
The half-cup of pellets and grass may be sufficient depending on the quality and protein content of the pellets and the size of the rabbit. Looking at Purina's feeding chart at
https://www.purinamills.com/getmedi...Rabbit-Feed-Brochure-Update-2019.pdf?ext=.pdf, they're recommending as little as 2-3 oz. for a small breed, up to 12 oz. of pellets for a giant type breed. Do the body condition test to see if what you are feeding is working for you. If the rabbits are too thin, you may need to add more pellets, or find a pellet with more protein. 14% protein is sufficient for non-breeding stock for maintenance, but 16-18% is generally preferred for breeding stock.
Another potential issue is heat. After five days of temps over 85 degrees F, or three days over 90, bucks can be sterile for the next six weeks or so. Since you're in Ontario, that may not be a big issue this late in the season, but it can be a contributing issue in the summer.
