Numerous studies have looked at alfalfa as a possible preventative for Equine Gastric Ulcer Syndrome (EGUS) due to the high calcium properties believed to reduce the acidity of the stomach acid. However, Fedtke et al. (2015a) and Vordran et al. (2016, 2017) investigated the effects of alfalfa on gastric ulcer scores in weanlings and adult horses. They found that those fed alfalfa chaff over alfalfa pellets or hay had higher glandular ulcer scores, causing mechanical damage and scratching. Bäuerlein et al. (2020) compared alfalfa hay to grass hay carried out in a cross over design over 21 days with a 21 day washout period. They found that the alfalfa hay group increased BW by 0.6%, while the grass hay group decreased BW by 0.5%. The results of this study were that alfalfa hay does not cause the same mechanical irritation that alfalfa chaff appears to generate and has a positive effect on the squamous mucosa. The alfalfa group had a median squamous ulcer score of one before the study and 0 after, while the grass hay group had a median score of 0 before and after. The alfalfa group had a 0 median glandular score before and after, while the grass hay group had a median glandular ulcer score of 0 before and one after. This study has demonstrated that alfalfa hay could still be beneficial as a high-quality forage for horses, and it may be the particle size that causes the mechanical scratching seen in the studies using alfalfa chaff (Vondran et al.,2017; Vondran et al.,2016; Fedtke et al., 2015). It is therefore able to be concluded that while alfalfa chaff may lead to higher glandular ulcer scores, alfalfa hay could still be a beneficial high-quality forage for horses, potentially avoiding the mechanical scratching associated with smaller particle sizes observed in studies using alfalfa chaff. Particle size may play a role in the effects on gastric ulcers (Vondran et al., 2017; Vondran et al., 2016; Fedtke et al., 2015).

References:
BAEUERLEIN, V., SABBAN, C., VENNER, M., and VERVUERT, I., 2020. Effects of feeding alfalfa hay in comparison to meadow hay on the gastric mucosa in adult Warmblood horses. Pferdeheilkunde, 36 (1), 29-35.
FEDTKE, A., PFAFF, M., VOLQUARDSEN, J., VENNER, M., and VERVUERT, I., 2015. Effects of feeding different roughage-based diets on gastric mucosa after weaning in warmblood foals. Pferdedheilkunde, 31, 596-602.
VONDRAN, S., VENNER, M., COENEN, M., and VERVUERT, I., 2017. Effects of alfalfa chaff on the gastric mucosa in adult horses. Pferdeheilkunde, 33 (1), 66-71.
VONDRAN, S., VENNER, M., and VERVUERT, I., 2016. Effects of two alfalfa preparations with different particle sizes on the gastric mucosa in weanlings: alfalfa chaff versus alfalfa pellets. BMC Veterinary Research, 12,