Demonstrating the effect of live weight on heifer pregnancy rates in northern Queensland

Abstract

A group of beef producers north of Charters Towers identified low heifer pregnancy rates as a consistent and significant problem, aligning with the regional median from the Cash Cow project of 67%. Results from their Producer Demonstration Site (PDS) over three years monitoring >1,300 heifers clearly demonstrated a highly significant (p<0.001) relationship between proportion pregnant and weight. To achieve rates of more than 75% in high-percentage Brahman type heifers, live weights of at least 400 kg at pregnancy diagnosis (end of mating) was required. Ovarian scanning demonstrated a pre-mating live weight of approximately 340 kg was required for 80% of heifers to be at or near puberty. Neither pestivirus nor vibriosis were shown to be contributing factors in this study. Use of fewer, better bulls (<2% v 4%; selected on scrotal circumference and semen traits) significantly reduced business costs without reducing pregnancies. A 2% bull: female ratio was subsequently adopted by the host property across the entire breeding herd. This project’s findings are relevant to the entire northern beef industry and highlighted the importance of managing for high heifer growth prior to their first mating.