Organic milk production: post conversion phase - IGER OF0113

Summary

The main objective of the current project was to improve the understanding of the factors affecting both the physical and financial performance of dairy farms in the post-conversion phase and to compare their performance with comparable conventional dairy farms. An additional objective was to provide a framework for the development and sustainment of organic milk production. The project was based at the Ty Gwyn organic dairy farm at IGER Trawsgoed with ten linked commercial dairy farms also monitored during the study. These farms ranged in size from 45 to 450 ha with the size of the dairy herds ranging from 45 to 260 cows. Among the factors studied during the project were changes in the soil indices, with particular reference to the P and K concentrations in the soil. Estimates of the whole-farm budgets are a useful indicator of the sustainability of agricultural systems and changes in the nutrient balance of the whole-farm system at Ty Gwyn were calculated annually to determine the input/output ratio of nutrients within the system. The effectiveness of a crop rotation to meet the high forage requirements of the organic dairy herd was evaluated, including the effect on the stocking density of the farm, forage yields and forage quality. The performance of the organic dairy herd in relation to managing the farm within the organic standards and the implications on animal health of withdrawing the use of antibiotics on a routine basis were monitored throughout the study. The financial performance of all the farms was recorded during the study with the data compared with comparable conventional farms.
Key conclusions from the study were:
• Nutrient budgets showed the major N-input was from red and white clover, with an average surplus of 141 kg N/ha within the whole-farm system and only 16-28% of the total N recovered in milk and livestock sales.
• The average P and K levels in the soil were higher during the study than the values recorded during the conversion period. However, the values were lower in the third year of the study and the values recorded for the individual farms were influenced by the source of concentrate feeds (home-grown or purchased).
• Large differences were recorded between fields in nitrate leaching, ranging from 15-140 kg N/ha.
• The measurement of N-fixation showed a contribution of 45 and 40 kg N/1,000 kg DM of white and red clover, respectively.
• Herbage yields were 14% higher than the yields recorded during the conversion period and only 9% lower than those recorded pre-conversion when the farm received an annual input of 380 kg N/ha.
• The contribution of forage to the energy requirements of the dairy herd increased to 61 (whole farm) and 76.7 GJ of UME/ha as stocking rates, milk yields and milk quality increased.
• Stocking rates by the third year of organic management were only 8% lower than the rates recorded when the farm was an intensive system with high N inputs.
• No major health problems were recorded in the organic dairy herds. Despite the withdrawal of the routine use of antibiotics the number of cases of clinical mastitis was similar to those recorded in conventional herds. Somatic cell counts in the milk were significantly higher than comparable conventional herds.
The study has contributed to a greater understanding of the physical factors affecting the performance of organic dairy farms. The results have provided quantitative information on many factors that influence the performance of the organic system and have also provided a broad framework on the overall level of production that can be achieved under organic management. The scientific measurements undertaken during the study have been included in Part 1 of the Final Report.