TLDR Minoxidil didn't significantly increase hair growth in minipigs.
In 2018, a 27-day study was conducted on Sinclair minipigs to evaluate the impact of Minoxidil on hair growth. The minipigs were treated with 2 mL of 5% Minoxidil twice daily, but the results showed no significant difference in hair growth in either male or female minipigs. The longest hairs in the male minipig grew to an average of 1.3 cm, while the female minipig's hair grew to 1.0 cm. The study concluded that Minoxidil did not have a significant effect on hair growth in these minipigs during this period, suggesting that a longer dosing period or different environmental conditions might yield more significant results.
January 2014 in “DOAJ (DOAJ: Directory of Open Access Journals)” Minoxidil can effectively treat patchy hair loss by stimulating hair growth.
January 2008 in “Acta Anatomica Sinica” 
30 citations,
September 2004 in “Experimental Dermatology” Scalp hair follicle culture has limits for testing minoxidil's hair growth effects.
397 citations,
February 2004 in “British Journal of Dermatology” Minoxidil boosts hair growth by opening potassium channels and increasing cell activity.
January 2003 in “Journal of Clinical Dermatology” TNF-${\alpha}$ slows hair growth, and minoxidil doesn't help.
3 citations,
June 1997 in “Veterinary Dermatology” Minoxidil treatment can stimulate hair growth in hairless puppies if applied early.
January 1997 in “Fundamental & Clinical Pharmacology” 
78 citations,
March 1987 in “Journal of The American Academy of Dermatology” Minoxidil promotes hair growth but stops working when discontinued.
37 citations,
January 1987 in “Dermatology” Minoxidil stimulates hair growth by increasing hair thickness and prolonging growth phase.
