Interest in cow herd expansion has created added incentives to keep and breed replacement heifers. Some producers are attempting to rebuild their own herd that was downsized during drought. Others are attempting to meet the strong demand for bred heifers occurring at livestock markets in many parts of the country.
In an effort to insure more replacement heifers are bred to calve early in their first calving season, ranchers should consider using a supplement containing an ionophore in the growing diet of the heifers. "Ionophore" is the generalized name for the feed additives monensin (Rumensin®) and lasalocid (Bovatec®). Both have been approved for use with growing programs for replacement beef heifers.
Research conducted in Texas and Wyoming (Moseley, 1977; Moseley, 1982) indicated that growing heifers fed 200 mg monensin per head per day reached puberty at an earlier age than did similar heifers fed similar diets containing no monensin. This is important because it should translate to a higher percentage of heifers cycling at the normal time of the start of the breeding season.
Most stocker cattle research has indicated that the addition of 100-200 mg of an ionophore will increase average daily gain by .1 to .2 pound per day. Over a 150 day growing period of a replacement heifer, this means an additional 15-30 pounds in average weight improvement of the heifers by breeding time.
In those situations where the diet for the heifers may be prone to cause bloating, adding the ionophore monensin in the feed or in the mineral has been shown to be helpful. Both the incidence and the severity of bloat on wheat pasture has been reduced by including monensin in the free-choice mineral mix. (Paisley and Horn, 1998).
Also, ionophores have been effective in preventing coccidiosis in young growing cattle. After all they got started as poultry coccidiostats before they became available and approved for cattle many years ago. Most “natural” and “organic” beef programs will not allow the use of ionophores, therefore you may wish to check with the potential buyers of the cattle before including ionophores in the diets. Heifers that fail to conceive are likely to end up in feedlots to be fed out as Select, Choice, or Prime beef.