I would prune out all the main branches that are below a 45 degree angle on those trees.
Some mango varieties have stronger trunks and branches at a given diameter than others. As a general rule I agree with Rob about not letting young trees fruit heavily if at all, especially for beginners. Unless you want fruit dragging on the ground and losing most of those or are 80 years old, you need to make sure the tree can set and hold the fruit at an appropriate height WITHOUT compromising the future structure of the tree. If you are really zone pushing and need to cover the tree completely during Winter, early fruiting with fruit dragging near the ground may be desirable.
If the tree holding fruit will get completely blown over or be in danger of snapping in wind, it is not strong enough yet. If the trunk and branches feel solid, I will let it hold some fruit.
My Edgar had branches bent so much by fruit that I had to prune to replace/retrain some main scaffold branches. This variety had what I would call normal mango branching habit, mostly upward with some spread. After letting it fruit too heavily in early years, one main scaffold branch was about 5 degrees downwards and fruit were touching the ground. That exact branch was at about 15 degrees UPWARD slope before fruiting that year. The year before, the slope was about 30. If I had let it hold a couple fruit instead of 20 on that scaffold branch, it may have been OK.
That is how I came up with my 45 degree rule. It is good to limit ultimate tree height with easy management, early fruiting, and eye appeal of the tree. My rule of thumb is that if the weight of a fruit or fruits on a young tree's branch will bend the MAIN branch below about a 45 degree angle, don't let it fruit. As long as smaller side branches on the main scaffold won't bend the main branch too much,the smaller fruiting branches can be allowed to fruit even if hanging down and be cut off after fruiting. It is not an absolute but an approximation. Maybe let it set one or a couple on its first fruiting IF the branches will support the weight without being bent below 45 degrees. The next couple years let it fruit heavier but don't let the weight of fruit bend branches much below about 45 degrees. The main branches will bend more down with fruit loads in future years, it you start with 45 the first few years you might end up with 40 or less in a few years. 30-35 degrees from horizontal will keep the tree smaller in height but more spreading than 45.
I should have let it fruit less heavily in its first years and thinned out most of what set. Pickering also had to have a few of the lowest branches removed but it seemed to have stronger branches so it was less severe. Some varieties have weak and spindly branches and those should be allowed several years to develop stronger branches to hold a fruit load.
Early fruiting will de- vigorate a tree,and this can be a very good thing. Richard Campbell had a few videos in which he said he let trees fruit early so they produce more fruit and less canopy. If done correctly, you get a dwarfing effect from main scaffold branches in competition. That means the main trunk splits into several but none of them really win out to grow tall. The fruit will weigh them down and keep the main branches from getting too tall.
My Little Gem tree seemed to naturally have a good balance. It was well anchored ,has strong branches and letting it produce as much fruit as it could hold at an early age let the main scaffold branches bend down to good angles with very little pruning needed.
Topic: I let 3gal mango trees bear fruit and then this happened (Read 988 times)