The effects of feeding different ensiled forages on the minerals excreted from growing lambs - implications for farm nutrient budgets.

Losses of minerals, such as phosphorus (P), from slurry are small compared to nitrogen losses, and slurry is therefore generally mineral-rich relative to plant nutrient needs. Samples from three experiments were analysed to test the hypothesis that the excretion of minerals differs in lambs offered different ensiled forages. Experiment 1 compared lambs offered ensiled forage peas or field beans, Experiment 2 compared lambs offered ensiled red clover, lucerne or birdsfoot trefoil and Experiment 3 compared lambs offered ensiled sainfoin or kale. In each experiment, six Suffolk-cross wethers were allocated to each silage and group-housed for 14 d. Lambs were then adapted to metabolism crates for 7 d before data was collected over 7 d. Daily amounts of silage offered, silage refused and urine and faeces produced were measured and sub-sampled for mineral analysis. Results showed differences in mineral intake or excretion between lambs offered different silages. For example, faecal P output of lambs offered red clover was lower than when lambs were offered birdsfoot trefoil or lucerne (P<0.05). Faecal K output was higher in lambs offered birdsfoot trefoil than red clover or lucerne (P<0.05) but there were no differences in the amount of urinary P or K lost