Date of this Version
Published in Beef Research Program Progress Report, No. 4, Part 2 (May 1993)
Genetic merit for milk production influences the weight of calf marketed by producers. Higher preweaning weight gains are made by calves from cows that produce high levels of milk. Lactational productivity can influence future levels of herd calf output if the expression of higher genetic potentials for milk production exceeds the nutrient availability for the production environment. For example, if the lactating female energy requirements exceed the available energy resources, then the ability to reinstall the estrous cycle may be delayed. For producers, this delay may result in younger, lighter calves in the following production cycle. Producers using restricted breeding seasons may find that the number of cows conceiving is reduced. If the producer's management strategy includes culling of once open females, more heifers are required to be retained for replacements, thus reducing the number of young animals for sale. Previous research has documented that differences exist among breed crosses or breeds of cattle for characteristics associated with lactation. Yield at time of peak lactation and total milk yield during the lactation period vary. Among dairy animals, research has shown that the higher producing animals tend to be in negative energy balance during the first part of the lactation cycle, Le., in an attempt to achieve their genetic 'potentialor milk production, the cows produce more energy in milk than they can consume. Feeding strategies have been or are being developed to circumvent this problem. It is not argued here that genetic potential for milk production of beef breeds is directly comparable to dairy cattle, rather that the range in feed energy environments in which lactating beef cows produce offers a similar opportunity for a negative energy balance to occur. Current recommended feeding standards make recommendations for supplemental feeding based on level of production but ignore the possibility of breed differences. The object of this study was to quantify breed differences for component traits describing the lactation curve among beef breeds and to characterize the response of these traits to increasing feed energy availability.