We use Triangle 10 on every female here... Opens, breds, heavy breds, boughts, heifers prior to breeding... They get brought in and preg checked and doesn't matter what stage they are in...
Most all my dairy farms I test, use Triangle 10.
I use Triangle 5 on the steer calves when they are weaned and run through the chute when we bring them home from pasture, as well as any bought calves. We often buy some bull calves and work them and vaccinate, then integrate with others of the same size to make groups to sell.
Also, all calves get blackleg when they come home from pasture again. A booster so to speak.... Because it seems to be more prevalent, we sometimes give the cows blackleg also when run through for preg check. Especially the late fall preg checks for spring calving cows... This helps to boost the immune bodies in the colostrum. We lost several one year to black leg... 350-400 lb calves at a pasture... so are extra vigilant. They get black leg when they go out to pastures, or get moved around at home for winter pasture/feeding... most are in the 4-8 week old range. The way I look at it, it is cheap insurance (cost) and they are in the chute to get tagged or worked before they go "away" from the barn.... I know the thoughts are they have protection from the dam and colostrum for about 8 weeks, and to give it to newborns is said to be a waste and works against the dam's colostrum immunity.... so we give it when they are moved... some are older, some are younger than the 8 weeks. Again, cheap insurance in my book.
Have never had any adverse reaction from Triangle 10 in any pregnant cows that we are aware of.