The study was undertaken as bull costs are a significant component in the Cost analysis of a breeding enterprise. The cost of capital tied up in bulls can be substantial and can be reduced if non working bulls can be identified and sold. The hypothesis is that bulls contribute more than given credit for in the differential diagnosis of causes of lowered branding rates in northern Australian beef herds. Our estimates from limited data with Bos indicus cattle, is that 20-25%of bulls mated in multiple sire herds do not contribute to any of the following year's progeny. This could be due to a combination of structural defects, inability to serve, testicular or reproductive tract abnormalities or social dominance.
Evidence from some Bos taurus herds would suggest that the average working life of a bull is 2.5 to 3 years. Earlier studies by P.W. Ladds from James Cook University confirm this for Bos indicus bulls with -an increasing prevalence of testicular and reproductive tract abnormalities in slaughter bulls greater than 5 years of age. However the 1990 North Australia Beef Producer Survey indicated that the majority of herd bulls were kept in excess of this age and that selection of breeding stock, particularly superior bull selection was one of the consistently identified issues important for improving profitability over the next 5 - 10 years. It would seem that there could be considerable wastage of effort in identifying genetically superior sires if our estimates are correct of up to 25% of bulls being non contributors of progeny.
The project sought seed funding to allow scientists from a number of organisations and locations to meet, review and discuss existing knowledge on bull fertility and if considered necessary, to develop a co-ordinated research program whose progressive outcome will be the means of improving the efficiency of bull reproduction performance in tropical Australia by 1999. The objectives of the project were by March 1993: (i) to identify gaps in research knowledge that limit the ability to select more fertile bulls for herds in northern Australia; (ii) to assess the feasibility of making significant gains in these identified areas; (iii) depending upon the outcome of (i) and (ii): (a) make recommendations to the NAP2 Management Committee for technology transfer of existing knowledge on the subject; (b) to identify research needs and develop strategies for commencement in July 1993 that will progressively address bull reproduction efficiency.