Introduction
Beef cattle producers are continually challenged with
the need to maintain sustainable production systems.
The most important factors affecting financial viability
of a cow-calf enterprise are reproduction and nutrition.
In reviewing several sources of information, Bellows
et al. (2002) estimated that reproductive diseases and
conditions cost beef cattle producers $441 to $502 million
in lost income yearly (aggregated national cost
>$14/cow). Financial cost associated with feed (4-yr average
= approximately $205/cow) was the greatest factor
influencing profit of commercial beef cow operations,
accounting for over 63% of the variation in total annual
cow costs (Miller et al., 2001). Of the environmental
cues that influence reproduction, nutrition command