The aim of this study was to evaluate the effects of M. elsdenii (Me) dosing on dairy heifer performance. A secondary set of data (feed intake, heifers birth weights, age and Weight at insemination, and first lactation milk performance) of heifers (dosed and not dosed with Me) was obtained from the dairy herd of the Agricultural Research Council – Animal Production. Data were arranged in a complete randomised design and analysed as repeated measures. Milk, pre-weaning starter and metabolised energy intake did not differ between the control and the Me groups. Post-weaning starter feed intake was higher (p=0.03) for Me fed heifers than control heifers. The post-weaning metabolisable energy intake was also higher (p=0.03) for heifer fed Me than control heifers. The average daily weight gain of heifers dosed with Me was higher during the pre-weaning period (0.66 kg/day; p=0.04) and after weaning (1.12 kg/day; p=0.03) compared to control (0.60 and 0.65 kg/day, respectively). At 42 and 70 days old, the BW of Me-heifers was greater (75.8 ± 2.6 and 91.2 ± 4.6 kg) than control heifers (61.9 ± 2.6 and 77.2 ± 4.6 kg) (p<0.05). There was no difference (P>0.05) in BW at insemination, number of insemination and milk yield between the two groups of cows (p>0.05). Early feeding of Me to heifers in the present study positively affect heifer growth during and early after milk feeding period, confirming previous report. Animal weight at puberty and the subsequent milk production were not influenced by feeding Me. It is possible that Me did not survive long after weaning to continue to express its influence on animal performance. / Agriculture and  Animal Health / M. Sc. (Agriculture)