I do not have any aritcles to back up abortions due to stress, but from the observations of a cattle farmer for over a decade I can tell you this. Others can chime in on their experiences as well
1. Cattle that are stressed are less likely to breed in the first cycle or two...cost to the bottom line in a uniform calf crop
2. Stress in cattle can supress the immunity causing the risk of infections, foot rot, pnemonia, bring out BVD if it prevelant. What happens is the virus or bacteria increases in the body of the animal. They shed it out of every opening they have. When the bacteria or viruses reach a point where the body can not fight the diease, it becomes sick. When it is sick, the cost of treatment is incured, the reduction in milk production, set back on cycling on time, decrease in weight gain on the cow and the calf.
3. Actions such as these can cause physical injuries to the cows and the bulls as well as the human factor
4. Stress out the bull and it significantly reduces the production of semen and can set them back three weeks ( the time it takes to develope new semen) This would cause delays in breeding, more open cows at the end of the breeding season
5. If a bull is stressed out the temps can rise causing a decrease in semen production as well as damage the semen "in the tank" so to speak.
6. long shot but a stressed out cow will have a set back in milk production if they have a calf at foot.
When you look at herd management, the whole picture needs to be looked at in order to see what damage is done when stress is involved. Not just a snap shot of the moment. In my opinion, what happens to a cow in the course of a year might not see immediate problems, but check out the calf at foot when weaned or even next calf.
The idea of having a vet come out to do Breeding Soundness Evaluation reduces the stress on the cows, reduces the stress on the bulls both physically and (for lack of a human term) emotionally.
Lastly and this should be at the top of the list is human injuries or the chance of sever injuries when handling animals who are stressed. Can happen pretty quickly.
Sorry for the long winded approach