Heifers Growing and Growth
Growing Bred Replacement Heifers
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 are presently approved for use with growing programs for replacement heifers.
Research conducted in Texas and Wyoming 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. Similar data is available for lasalocid.
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
Bred replacement heifers that will calve in January and February need to continue to
grow and maintain body condition. Ideally, two year old heifers should be in a body condition score 6 at the time
that their first calf is born. This allows them the best opportunity to provide adequate colostrum to the baby,
repair the reproductive tract, return to heat cycles, rebreed on time for next year, and continue normal body
growth. From now until calving time, the heifers will need to be gaining 1 to 1 1/2 pounds per head per day,
assuming that they are in good body condition coming out of summer.
Heifers will need supplemental protein, if the major source of forage in the diet is
grass or native pasture or grass hay. If the forage source is adequate in quantity and average in quality (6 - 9%
crude protein), heifers will need about 2 pounds of a high protein (38 - 44% CP) supplement each day. This will
probably need to be increased with higher quality hay (such as alfalfa) or additional energy feed (20% range cubes)
as winter weather adds additional nutrient requirements. Soybean hulls or wheat mids may also be used to insure
adequate energy intake of pregnant heifers.
Wheat pasture (if adequate rainfall produces growth) can be used as a supplement for
pregnant replacement heifers. Using wheat pasture judiciously makes sense for pregnant heifers for two reasons.
Pregnant heifers consuming full feed of wheat pasture will gain at about 3 pounds per head per day. If they are on
the wheat too long the heifers can become very fat and cause dystocia. Also the wheat pasture can be used for gain
of stocker cattle or weaned replacement heifers more efficiently. If wheat pasture is used for bred heifers, use it
as a protein supplement by allowing the heifers access to the wheat pasture on at least alternate days. Some
producers report that 1 day on wheat pasture and two days on native will work better. This encourages the heifers
to go rustle in the warm season pasture for the second day, rather than just stand by the gate waiting to be turned
back in to the wheat. What ever method is used to grow the pregnant replacement heifers, plan to have them in good
body condition by calving so that they will grow into fully-developed productive cows.
OSU Cow/Calf Corner
Heifers Breeding Weight