The performance and nutrient use efficiency of two contrasting systems of organic milk production

During a four year study, two contrasting systems of organic milk production were studied to determine differences in soil nutrient status, crop production, milk output and quality, efficiency of feed conversion and the effect on animal performance. The key aim of the first system was to increase the levels of both self-sufficiency and sustainability of the system by establishing a balanced crop rotation and minimizing the imports of nutrients. The second system was based on increasing the output and flexibility of the system by establishing a forage-only cropping strategy and importing purchased concentrate feeds into the system. The results showed that increasing the level of self sufficiency led to an improved nutrient input/output balance and improved efficiency of milk production from forage but not an increased efficiency of total feed utilization. This type of system is dependent on the production of high-energy forage to meet the cow's nutrient requirement and avoid problems of reduced milk persistency during early lactation, lower milk quality and reduced fertility. In the system based on purchased concentrate feeds, higher levels of both crop energy and milk output were recorded without any adverse effects on milk persistency during lactation. The flexibility of the system ensured that any potential deficiency or imbalance in the availability and quality of the forages produced within the system was avoided by the import of concentrate feeds. However, the reliance on purchased rather than home-grown concentrate feed reduced the sustainability of the system and also led to both a lower efficiency of forage utilization and reduced milk output from forage.