However, in the late 1940s, studies examining the supplementation of B12 in chicks' diets found that B12 produced from the fermentation of Streptomyces aureofaciens, an antibiotic for use in human medicine, produced a better weight gain for chicks than B12 supplied from other sources, and a reduced amount of feed to bring the birds to market weight.[24] Further studies on other livestock species showed a similar improved growth and feed efficiency effect with the result that as the cost of antibiotics came down, they were increasingly included at low ('sub-therapeutic') levels in livestock feed as a means of increasing production of affordable animal protein to meet the needs of a rapidly-expanding post-war population.[3] This development coincided with an increase in the scale of individual farms and the level of confinement of the animals on them, and so routine preventative antibiotic treatments became the most cost-effective means of treating the anticipated disease that could sometimes arise as a result.[22] Veterinary medicine increasingly embraced the therapeutic, metaphylactic and strategic preventative use of antibiotics to treat disease.