Does zakat apply to capital or profit or both if invested in livestock, and upon whom is it obligatory? And does zakat apply to a loan that does not reach the nisab on its own but increases it when combined with my wealth?

Zakat on money involved in Mudarabah (partnership in profit) is obligatory upon the Mudarib (investor/financier). Zakat on the profit is contingent upon the principal, if it materializes before the Hawl (one lunar year) and is not spent. In this case, Zakat on the principal becomes due, in addition to the share of the profit; otherwise, it does not. The preponderant opinion is that Zakat on Mudarabah funds should be taken from the profit before its distribution. As for loaned money, it is owned by the lender, and Zakat is obligatory upon him.