Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Beef cattle rank first in cash receipts in 21 states and are among the top "five income-producing agricultural commodities in 47 of the 50 states. Estimated losses from infertility in cattie exceed by more than 5X the cost of the next most costly bovine disease problem. The 37 million beef cows in the U.S. in 1978 weaned only 27.4 million calves, or 74% of the total possible. The goal of beef cow/calf production is to maximize the net calf crop--the pounds of calf produced per cow in the herd--in the most economical manner possible. Many factors influence productivity, but one of the keys is to achieve a high level of reproductive performance, and a very important part of successfully accomplishing this is a sound nutrition program.
Johnson, Kirk E. and Evans, Thomas J.
"Effect of Energy and Protein on Reproductive Performance in Beef Cattle,"
Iowa State University Veterinarian: Vol. 53
, Article 10.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol53/iss1/10