Hi – You sound very dedicated to doing what is best for your animals and keeping them healthy. Kudos to you! Below is info taken directly from the PregGuard label (much more info not included here) that pertains to your question. I’ve bolded especially-relevant portions:

“PregGuard GOLD FP 10 is for vaccination of healthy cows and heifers prior to breeding… PregGuard GOLD FP 10 may be administered to pregnant cattle provided they were vaccinated, according to label directions, with any Bovi-Shield GOLD® FP or PregGuard GOLD FP vaccine within the past 12 months. PregGuard GOLD FP 10 may also be administered to calves nursing pregnant cows provided their dams were vaccinated within the past 12 months as described above. To help ensure safety in pregnant cattle, heifers must receive at least 2 doses of any Bovi-Shield GOLD FP or PregGuard GOLD FP product with the second dose administered approximately 30 days prebreeding…

Primary Vaccination: Administer a single 2-mL dose to all breeding cows and heifers approximately 1 month prior to breeding or being added to the herd, followed 2-4 weeks later by a single dose of Vibrio/Leptoferm-5.

Revaccination: Annual revaccination with a single dose of PregGuard GOLD FP 10 is recommended…

Do not use in pregnant cows (abortions can result) unless they were vaccinated, according to label directions, with any Bovi-Shield GOLD FP or PregGuard GOLD FP vaccine within the past 12 months. Do not use in calves nursing pregnant cows unless their dams were vaccinated within the past 12 months as described above. Do not vaccinate calves under 3 months of age.

To help ensure safety in pregnant cattle, heifers must receive at least 2 doses of any Bovi-Shield GOLD FP or PregGuard GOLD FP product with the second dose administered approximately 30 days prebreeding.

Do not vaccinate within 21 days before slaughter…”

You could give the Guardian scours-prevention vaccine at the same time at the PregGuard vaccine, I suppose, but it would compromise the optimal timing for one of the vaccines. The Guardian vaccine recommendations are “inject healthy pregnant cattle…3 months prior to calving. Repeat in 3 to 6 weeks following initial vaccination. For subsequent calvings, revaccinate with a single dose 5 to 7 weeks before calving.” If you wait until this time to give the PregGuard vaccine, you have lost many months of pregnancy protection. If you give the Guardian vaccine earlier, pregnant cattle will not have maximum levels of scour pathogen antibodies in their colostrum.

I bet the abortions “caused” by PregGuard in pregnant cattle reported by one of the veterinarians you consulted were the result of improper use of the vaccine. It is a modified-live vaccine and its safe use instructions are complicated (see above). If that veterinarian can guarantee the vaccines were used in pregnant cattle according to the manufacturer’s instructions and abortions still resulted, I too would be reluctant to use it at all in pregnant cattle (I would also recommend those producers contact the manufacturer and see if they can receive compensation for their losses). This is where excellent record keeping regarding vaccination history (dates, product, manufacturer, lot number, administrator, animal ID, location given, etc.) would pay off.

I bet you find some management issues during your current spring vaccination animal handling that are important to address (thin animals, teeth problems, lameness, etc.). If you switch to fall vaccination entirely, you would miss this opportunity for close inspection of each animal. Consider this factor when deciding whether or not to switch to giving all vaccinations in the fall.

p.s. You didn’t mention respiratory vaccines (IBR, PI3, BVD, BRSV, +/- Pasturella and Mannheimia) or when you give them. If you vaccinate for Pasturella and Mannheimia, that respiratory vaccine should be given by itself because it contains two gram-negative bacteria; giving more than that at one time can be dangerous.

Best wishes,