Using measurable physical characteristics to forecast beef heifer maturity: The identification of a maturity index

Abstract

A target BW is often used to estimate sexual maturity in beef heifers. The target BW, a percentage of mature BW, is generally an average for the breed, herd, or both. Heifer development is done in groups or herds, and not all heifers respond similarly to the same development regimen. Generally, heifers fed at a higher plane of nutrition gain more BW and tend to have increased pregnancy rates, but this usually increases feed costs. Therefore, determining when increased feed costs exceed the economic gains resulting from greater conception rates is critical and requires the inclusion of economic information and relationships. This research focused on the individual heifer as the decision point, and identification of the individual heifer target BW was based on clearly defined biological relationships observed before breeding. These relationships were captured in a maturity index (MI) identified through a series of steps and guided by current, accepted knowledge of heifer growth and development. Using an in-sample mean absolute percent error comparison, it was determined the MI was more accurate than the current group or herd methods in forecasting actual maturity and target BW. Maturity index demonstrated the flexibility in achieving similar maturities with beef heifers of varying characteristics using alternative nutritional programs. The MI was also the only significant predictor of first pregnancy. These results allow for more precision in determining sexual maturity and probability of first pregnancy in beef heifers and serve as the basis for future studies in determining profit differences among heifers.

Bioeconomic factors of beef heifer maturity to consider when establishing criteria to optimally select and/or retain herd replacements

“…Therefore, MI has an indirect effect on second pregnancy through its direct effect on dystocia. Combining findings from Stockton et al (2013) with those in the current study, there is a link between a lower MI and a reduction in the chance of first pregnancy, an increased rate of dystocia, and, secondarily, a reduction in the chance of second pregnancy. The biology is such that increases in the MI produce a smaller response in pregnancy rates and dystocia with each succeeding incremental increase, diminishing marginal productivity.…”

“…This measure is substituted into the calculation since the heifer's true mature BW cannot be known until long after first parity. More recently, Stockton et al (2013) introduced the MI, which incorporates additional animal-specific information and characteristics. The MI uses heifer BW at breeding, dam mature BW, dam age, heifer breeding age and birth weight, and nutrition level before breeding (Eq.…”

“…Two systems used to indicate breeding readiness (defined here as maturity), measured by the MI proposed by Stockton et al (2013) and the TW approach as outlined by Patterson et al (1992), are tested as predictors of dystocia. This comparison is a step forward in building a systems model to determine the bioeconomic optimal maturity of heifers.…”

“…Costs and revenues are dependent on both physical and economic factors used in producing beef cattle, and any model used to accurately reflect profitability/ productivity must include both. In a step toward this end, the maturity index (MI) developed by Stockton et al (2013) ABSTRACT: Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building a bioeconomic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy.…”

“…Costs and revenues are dependent on both physical and economic factors used in producing beef cattle, and any model used to accurately reflect profitability/ productivity must include both. In a step toward this end, the maturity index (MI) developed by Stockton et al (2013) is used to transform observed physical sam-ple information into usable dystocia and second pregnancy input/output relationships or response functions (Kay 1981). The nature of these response functions provides structure to the economic relationships and, when appropriately applied, may be used to form objective functions such as a profit equation.…”