In other words, this measures the average cost in feed for each kilo by which the animal's weight increased. You also find "per kilo gain".

See this table (abbreviated here; sorry, it doesn't reproduce well):
Granja A Granja B
Peso inicial 5,0 5,7
Peso final 17,4 14,2
Consumo (Kg.) 17,3 11,4
Coste lechón 1016 763
Coste kilo repuesto 81,9 89,8

http://www.3tres3.com/buscador/imprimir.php?sec=caso&id=132

A couple of calculations show that "coste kilo repuesto" means what I have said. On Farm A the net weight gain (peso final - peso inicial) was 12.4 kilos. The feed cost per animal was 1016 (ptas). 1016 / 12.4 = 81.9, so this is the cost per kilo gained. The figures for Farm B are 8.5 kilos gained, total feed cost per animal 763, cost per kilo gained: 763 / 8.5 = 89.76: again, as the table says under "coste kilo repuesto".

As I'm sure you're aware, kilo vivo is "per kilo live weight", also known as "on the hoof" if it's that sort of animal. There are entries on this in the KudoZ archive.