Producers’ goals are to maximize returns and this could be achieved through least-cost rations that provide the desired performance (gain). With recent corn prices, it is appealing to include as much corn as possible into cattle diets. Corn is a cheap and high quality source of energy.
Balancing Feed Rations
A balanced ration based on performance goals and the composition of feeds in the ration dictates the appropriate amount of corn to include. Heifer development strategies fall into three categories: 1) Maintaining steady gain (ADG) throughout the development phase, 2) Low ADG early followed by high ADG late in the development phase, 3) High ADG early and low ADG in the latter part of the development phase. Remember, within each of these development strategies, heifers need to reach the selected target by the start of the breeding season. The amount of corn included in each ration for each of these strategies would differ.
Successful rations provide the nutrients required to support muscle development and growth, but not too much energy resulting in excessive fat deposition. Research has shown that excessive body condition negatively affects reproductive efficiency. Previous researchers have reported that overfeeding results in weak estrous expression, reduced conception rates, high embryonic mortality, decreased mammary gland development, and decreased milk production (Patterson et al., 1992).
Reduced conception rates and increased embryonic mortality will result in easily seen differences in the number of open (non-pregnant) replacement heifers. Impacts on mammary gland development and milk production are more difficult to assess but are very important because those changes affect productivity throughout the cow’s entire life.
Cassady and co-workers (2009) developed replacement heifers to a body condition score (BCS) of 7 or 5, and then restricted nutrients until all heifers entered anestrous. They then increased the amount of feed until the heifers began cycling. Heifers that were developed to reach a BCS of 7 resumed cycling at a score of 6 compared to a score of 5.2 for the heifers developed to the lower score. In this study, initial BCS had no effect on days to recommencement of estrous cycles but did influence the degree of fatness required to resume estrous cycles.
Bottom Line Implications
Producers should start with feed testing and setting the right performance targets in order to successfully use higher corn inclusion in replacement heifer diets. The cost for providing either too much or too little energy can impact producers’ bottom-line due to losses in reproductive efficiencies.