Mares used in PMU production ultimately produce a by-product foal each year. The foals spend limited time with their mother as the cycle of impregnation begins again roughly 4 months later.
Many foals are sent to feed lots to be fatten for slaughter to cater to the horse meat trade in Europe and Japan. At industry peak, estimates suggest this number may have been upwards of 40,000 to 50,000 foals a year from US and Canada and colts are more likely to be sent to slaughter than fillies as they cannot be used by farmers to reproduce.
Of the foals kept there are concerns, as with the mares, over the level of care they receive. As the foal is a by-product of production their value to ranchers is not significant.
(Horse Aid, 2004), (PETA, 2015)