Daniel Claro M.1

The extensive mating system used in Magallanes with a stocking rate of 1 ewe/ha and 4% rams was compared with an intensive system of 4 ewes/ha in the scrub country during 3 seasons (1971-73). Adult Corriedale ewes used and changed every season. Bush density was low and slope gentle.
In experiment 1 with a complete randomized desing comparison of extensive system in a 500 ha paddock with intensive system in a 50 ha paddock gave a 15.9% and 6.9% barren ewes respectively, this difference being significant (P < 0.01).
Experiment 2, a 2 x 2 factorial, compared 2% vs. 4% rams in both mating systems. Intensive mating was carried out in 16.6 ha paddocks with a stocking rate of 6 ewes/ha while extensive mating was on 100 ha paddocks and 1 ewes/ha. Intensive mating with 2% or 4% rams showed no significant difference in percentage harren ewes, being 6.2% and 8.6%, respectively. Extensive mating with 2% instead of 4% rams showed no significant difference in percentage barren ewes, being 16.3% and 15.4%. respectively.
Acritical mating population density might exist for sorne breeds of sheep below which rams would not work with maximum efficiency, this being the situation of extensive mating in Magallanes.

1Ing. Agr., M. Agr. Sci., Programa Producción Ovina, Estación Experimental La Platina, Instituto de Investigaciones Agropecuarias (INIA), Casilla 5427, Santiago, Chile.