Selection index for beef cattle that maximizes overall growth yet constrains birth weight and other traits.

Objective: : Maximizing growth throughout the growth period is a practical goal in the beef industry. We developed a novel selection index, called the maximum growth index, that maximizes the growth throughout the growth process and simultaneously achieves the desired weight gain at designated time points by assigning arbitrary values to selection intensity.

Methods: : We used a technique called Lagrange multipliers to maximize overall growth throughout the entire growth process and to restrict weight gains to desired amounts at specific times. We developed a selection index by applying random regression (RR) to the growth curve and using the genomically enhanced breeding values (GEBVs) of the RR coefficients as selection index traits.

Results: : Examples of the developed index was applied based on assumed data in Japanese Black steers. Selection to maximize growth during the growth period and to moderate birth weight yielded an upwardly convex curve for weight gain during the growth process, and the peak daily gain was greater and earlier than achieved without this selection. Under a selection intensity of 0.5, the index that constrained birth weight to decrease by 2.5 kg achieved the pre-selection final weight 8 weeks earlier than occurred without this selection.

Conclusion: : We developed a beef cattle selection index that maximized total weight gain during growth yet constrained birth weight and other traits. The maximum growth index that we developed enables reductions in birth weight concurrent with increases in final weight, thus benefiting the beef industry by increasing final weight and preventing dystocia.