Demonstrating the effect of liveweight on heifer pregnancy rates in northern Queensland

This three year project aims to demonstrate how heifer weight affects puberty and pregnancies. Low pregnancy rates in two-year-old heifers in northern Queensland are common. Typically, it is because heifers go into the mating period under weight, and subsequently don’t reach target mating weights until the end of mating or later.

The CashCow project confirmed that there is a major problem for many producers in the northern forested areas of Australia. An inter-quartile range for heifer pregnancy of between 40–81% was reported and only half of the monitor mobs achieved 67%, demonstrating large scope for improvement.

This supports other anecdotal evidence for low pregnancy rates, even during good seasons. There is general agreement in the scientific community that the major factor is failing to reach puberty by the time of mating. In this northern region, typical weaning weights and annual growth, limit many heifers to little more than 300kg going into their maiden mating as two year olds.

Beef CRC data shows that, on average, puberty is reached in Brahman heifers at 334 +/- 45kg and 751 +/- 152 days. The CRC data also showed that there was a large range in the weights at which heifers reached puberty and therefore plenty of scope for selection. The heritability of age at puberty is 0.57 and rapid genetic progress can be achieved by carefully targeted selection programs.

This project is monitoring a commercial property with below expected heifer pregnancy rates as a Producer Demonstration Site to identify the issues, gain an understanding and discuss solutions which will be common with many other northern producers. The focus will be defining the problem of poor heifer performance (presumably underweight at mating), then look at short term solutions to increase weight (nutrition) and discuss longer term solutions such as genetic selection.

This project proposes to monitor three mobs of heifers until each mob is pregnancy tested:

• No 2012 mob – from the start of mating this year
• No 2013 mob – as yearlings (starting 2014)
• No 2014 mob – as weaners (starting 2014).

When: 15 December 2013 to 31 January 2017

Where: Charters Towers, Queensland

Contact: David Smith

Collaborator: Department of Agriculture and Fisheries

RD&E objectives: Enterprise viability: Increasing cost efficiency and productivity and profitability; Enterprise sustainability: Increasing natural resource use efficiency and managed environmental impacts

Industry priority: Reproduction