A comparison of different methods (component trials, systems modelling and whole farm trials) for evaluating dairy farm inputs is made using the example of turnips grown on-farm as a summer forage. Component studies conducted at the Taranaki Agricultural Research Station and at DRC showed respectively increased (P<0.01) milksolids production of 36 and 66 g milksolids (MS)/kg turnip DM. Modelling the use of turnips using a farm management model (UDDER) has shown the practice to be profitable in a dry year if the crop exceeds 8.0 tonne DM/ha and in a normal year, 10.0 tonne DM/ha. A programme designed to demonstrate the value of turnips on summer milksolids production (More Summer Milk) showed on 3 farms over 2 years a decrease of 16 kg MS/ha. The sowing of 7-9% of the farm into turnips (DM yields varied from 6.5 - 11.5 tonne DM/ha) resulted in less pasture conserved (180 kg DM/ha) and, by the commencement of feeding turnips; reduced milksolids production (0.2 kg/ha/day), lower average pasture cover (360 kg DM/ha) and lower cow condition score (0.2 units/cow). Feeding turnips resulted in a small increase in milksolids production, insufficient to compensate for the initial production loss. UDDER simulated the farm situation prior to feeding turnips reasonably well but the response to turnip feeding was higher than occurred on-farm. The results highlight that the impact of a forage crop on dairy production cannot be predicted from short-term feeding trials or currently available farm systems models.

NA, Thomson

Proceedings of the New Zealand Society of Animal Production, Volume 57, , 165-168, 1997
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