Controlling Mature Cow Weight
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Douglas Landblom
DREC Beef Cattle and Integrated Systems Specialist
Dickinson Research Extension Center
Office: 701-456-1109; Mobil: 701-690-8245
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Profitability in the cattle business is directly linked to feed cost for maintenance, growth, and reproduction. As beef cows grow in stature over time, mature weight reaches a plateau at approximately five years of age. In regions of the US that are considered to be semi-arid, such as western North Dakota, where the long-term average annual precipitation is 16.0” and growing season precipitation from April to October can often be considerably less (8”-12”), matching cow weight to the environment and feed resource is extremely important. Therefore, by controlling mature cow weight and milk production reproduction does not suffer, because dietary forage energy and protein are sufficient to support maintenance, lactation, and reproduction. Obviously, there are a number of factors that can have a negative effect on reproductive performance, nonetheless, available pasture dietary energy, protein, and mineral nutrition to support milking ability and reproduction are most often the problem when cows fail to become pregnant. As mature cow weight become greater, the dry matter (DM) nutrient requirement expressed as total digestible nutrients (TDN) increases also. For example, comparing a 1,300 lb cow to a 1,500 lb cow with an estimated 25-pound milk production, which is suitable for semi-arid range conditions, gestation and lactation TDN values increase from 54.0% to 59.0%. For the 1,300 lb cow, DM gestation to lactation intake increases from 25 lb to 34 lb/day and for the 1,500 lb cow the DM gestation to lactation increase is from 28 lb to 38 lb/day.
Controlling mature cow weight begins with sire selection for the production of replacement females. Selection tools using EPDs are very effective at identifying sires with the genetic potential to control cow weight. EPDs for maternal weight and maternal height are critical components necessary for controlling mature cow weight. The American Angus Association has developed a Cow Energy Value EPD ($EN) that assesses cow energy requirements for daughters of sires and both maternal and terminal dollar indexes ($). With respect to selecting sires for the production of heifer replacements the $M Index (Maternal Weaned Calf Value) is the correct index to use. This index accounts for calving ease direct, calving ease maternal, weaning weight, milk, heifer pregnancy, mature cow weight, docility, claw set, foot angle, as well as emphasis on maternal height. All too often sires with high $B Indexes, which is a terminal index, are selected from which replacements are kept. The $B Index is the wrong index when selecting sires for potential heifer replacements, because the $B Index takes into account post-weaning growth and carcass value EPDs to include weaning weight, yearling weight, carcass weight, marbling, ribeye area, fat, and residual average daily gain.
In summary, to control mature cow weight select sires with high $M Indexes for replacement heifer selection.
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