Monensin reduces consumption of urea supplement blocks

[Extract] Monensin has been demonstrated to reduce the intake of self fed energy supplements (Muller et al. 1986). In contrast to self fed energy supplements, which are often fed to growing cattle, dry season breeder supplements in northern Australia are typically urea based and targeted at maintaining body condition. Desired intakes are 0.1-0.2 kg/day and the regulation of supplement intake is an important cost and management consideration for graziers. The objective of this study was to determine the effect of including monensin on the supplement intake of cows consuming a high urea block. Methods: Sixty one Bos indicus cows were allocated on the basis of parity and pregnancy status to either of two supplement treatments and grazed in a common buffel grass (Cenchrus ciliarus) paddock at Fletcherview, Charters Towers, between September and December 2009. Cows accessed a single watering pOint via entry and exit spear gates. A remote automated drafting unit (CAWD Engineering Pty. Ltd.) was located at the exit spear to draft cows into the treatment supplement yards consisting of molten, high urea blocks (Rumevite® 30% Urea + P; R30U) either with, or without monensin. Mean monensin concentration in blocks was 896 ± 4.9 mg/kg (as fed). On 3 occasions, treatment blocks were replaced with lithium spiked blocks and blood samples collected 24 hours after initial access to provide an estimate of daily individual and group block intakes. Results and Discussion: There were effects of treatment and time, but no interaction, on supplement block intake. Cows with access to monensin blocks had lower supplement intakes compared to control cows at all measurement intervals (Table 1). Supplement intake at first sampling was lower than at the second and third sampling (P