Most farmers give it weekly or fortnightly at the standard dilution of 1:20 to 1:50, added to water troughs or feed. Frequency can be adjusted to suit your conditions:

Regular use: Weekly or fortnightly, as an ongoing part of the diet.
Higher-demand periods: During dry seasons, when feed quality is poor, or in late pregnancy and around calving, foaling and lambing, keep to a regular weekly or fortnightly routine.
Good feed conditions: When pasture and feed quality are good, some farmers reduce to monthly or a few times a year.

See Rates and Methods page for details