The Effect of Leucaena Supplementation on Conception Rates of Heifers In Northern Australia

This project investigated the perceptions and trends related to the use of leucaena (Leucaena leucocephala) supplementation ad libitum in northern Australia. Leucaena is a long-lived tree legume that contains up to 25% of crude protein (CP) and up to 15 kJ/g of metabolisable energy (ME), with a range of uses including forage for cattle, shade, green manure, firewood, and erosion control. As a legume species, leucaena fixes atmospheric nitrogen in the soil and has other environmentally favourable benefits such as increased sequestration of carbon. A survey questionnaire was distributed to determine how leucaena is used in the management of breeder herds and the current perceptions by cattle producers in northern Australia. The hypothesis was that cattle producers in northern Australia do not use leucaena as a supplement for female cattle. However, the evidence found in this experiment contradicted the notion that cattle producers in northern Australia are not using leucaena for female cattle, as (n = 31) of respondents acknowledge using leucaena as a supplement in breeder herds. Moreover, a field experiment was undertaken in central Queensland to collect data on the conception rates of heifers (n = 234) (Bos indicus and Bos indicus crossbreed) with a completely randomised design by stratified by liveweight, fed with and without leucaena ad libitum supplementation over a 90-day period at the commencement of the breeding season in October, 2023. A trans-rectal examination was conducted to determine the percentage of heifers that became pregnant using fetal age or evidence of fetal loss, to assess the effect of feeding leucaena supplement in female cattle. At the same time, the fat depth (P8) was measured in cm, and heifer liveweight (LW) was recorded. The specific objective of this activity was to understand how leucaena as a supplement could improve conception rates. The hypothesis was that conception rates of heifers grazing leucaena ad libitum are lower than heifers grazing pasture with a protein supplement in northern Australia. Nonetheless, there was no effect of leucaena on conception rates, evidence of fetal loss, or significant difference in the likelihood of pregnancy occurring for heifers in the current study. As a result, heifers can be used for breeding as early as yearling-mated, accelerated reproductive maturity through leucaena offered ad libitum to increase liveweight gain (LWG) since the weaner period, reducing the time window to have mature reproductive heifers in a breeder herd in northern Australia.