If you find
Fertility and fecundity are significant drivers of profitability in many livestock enterprises
AND
Feed conditions are not always ideal in the lead-up to mating season
Then,
When animals are on a diet that is steadily improving, it is called a rising plane of nutrition.
This is what typically happens with a lot of species naturally as they come into the mating season.
Because of this, their fertility and fecundity can be higher.
As fertility and fecundity are significant drivers of profitability in many livestock enterprises, it makes sense to use a rising plane of nutrition to boost profitability.
The effect is very marked with many breeds of sheep and you can make use of it even if pasture conditions are poor — by supplementary feeding.
The trick is to have the ewes on a rising plane of nutrition before you introduce the rams.
I don’t believe it has a benefit with the rams — they need to be well fed and not overweight if you want them to get among the females and deliver lots of fertile sperm into the right places.