The development of organic milk production systems

Summary

The main objective of the 4-year project was to provide both qualitative and quantitative information on the development of two contrasting organic dairy systems, including the benefits and limitations of each system and also the opportunities for improving the systems. The first system (SS system) was based on an extensive and sustainable system, with the objective of achieving a high level of self sufficiency and sustainability by minimising the importation of nutrients into the system. Therefore, the cropping rotation for the system included forage crops for grazing and conservation and also cereal crops to provide both grain (for feeding as a concentrate) and straw for bedding. The main objective of the second system (PC system) was to change from a cropping strategy that was based on a rotation to the establishment of multi-species leys and also maximise milk output per cow and per hectare by importing concentrate feeds into the system to maintain a more productive enterprise with an increased milk output from feeding larger quantities of concentrate feeds.
The two systems were based at the IGER Ty Gwyn farm in West Wales, with the Holstein-Friesian dairy herd in each system managed on a land area of 30.45 (SS) or 28.0 ha (PC). Each herd was housed for six months of the year from mid-October to mid-April when diets were based primarily on grass+ clover silages, with the herds grazing the herbage from swards of both grass + clover re-seeded leys and permanent pastures during the other six months. Soil samples were taken from all the fields in each system at 2-yearly intervals. Monthly samples were taken from the grazing fields to measure both the yield and botanical composition of the herbage in the different swards, with the changes in the mineral and nitrogen concentrations also measured in four of the fields. Crops grown for conservation or combining were sampled prior to the cutting date. In addition the potential of new crops and plant mixtures was evaluated, including their yield potential and the relative cost of production. The physical performance and health of the individual cows within the herd was measured to provide a comparison between the systems in milk yields, milk quality, the efficiency of forage utilisation, efficiency of the conversion of nutrients into milk, incidence of specific health problems and reproductive efficiency. The farm-gate’ nutrient budgets were also calculated annually for each system.
During the first two years of the project the performance of the cows in both systems was severely affected by the occurrence of liver fluke (Fasciola hepatica) which also led to a reduction in the reproductive efficiency of the two herds. In the 2004/05 period both herds returned to higher performance levels and acceptable pregnancy rates.
No significant differences were recorded between the systems in either soil or herbage mineral concentrations, despite the contrasting ‘farm-gate’ nutrient budgets which showed both a lower annual N-surplus and increasing deficit in the P & K balance in the SS system. This compared with an overall high annual N-surplus and small, but increasing, P & K balance in the PC system due to the importation of concentrates and straw for bedding. In both systems the concentrations of the majority of minerals (and also nitrogen) increased during the growing season and the mineral concentrations were within the ranges that have been published for conventionally-grown herbage. Despite large variations between fields in both the grass to legume ratios and soil P & K concentrations, no relationship was found between these parameters and annual yields.
Growing both forage and concentrate feeds in the SS system led to a stocking density that ranged from 1.08 to 1.28 cows/ha, with c.17% of the total land area used annually for grain production. The annual total grain production from the barley and triticale crops determined the quantity of concentrates that was available for feeding to the herd with 0.329-0.666 t fed per cow, leading to the milk yields ranging from a rolling average of 4,301-4,755 litres/cow, annual milk yields from 5,192-6,492 litres/cow and 4,817 to 6,695 litres being produced per hectare. Between 73.4 and 86.0% of the annual milk output was produced from forage (i.e. grazed herbage, silage).
As fields became due for re-seeding in the PC system, a multi-species ley was sown to replace the existing crop rotation. The key objectives of these leys were to sow species that were adaptable to the different soil types within the system, reduce forage costs, avoid the long periods in a rotation between the harvesting of the previous crop and initial production of the succeeding crop, and also provide a 10-year ley suitable for both cutting and grazing. The results from the multi-species leys, currently in their early-development stage, showed: (a) increased species diversity when compared with the standard organic leys that are widely established, (b) a non-uniform establishment of the species due to variations in the soil profile and water-retention capacity and (c) yields comparable to those recorded from leys with limited species diversity. Multi-species leys have the potential to improve the compatibility between soil type and plant species and also the need to respond to the changing climatic conditions in the UK.
Purchasing concentrate feeds in the PC system, rather than growing grain crops within the system, and also the option of purchasing additional feed when annual forage yields were inadequate, allowed a higher stocking density to be maintained (1.54 to 1.96 cows/ha) compared with the stocking density recorded in the SS system. The output of milk was also higher with the rolling average yield ranging from 5,204 to 6,810 litres/cow, annual milk yields from 5,893 to 8,086 litres/cow and between 8,743 to 12,532 litres being produced per hectare. The level of concentrate feeding was determined by the actual daily milk yield of the individual cow and led to an average of between 1.341 and 1.743 t/cow being fed, leading to 35.4 to 53.2% of the total annual milk being produced from forage. The efficiency of feed energy utilisation for milk production was higher in the PC system (33.7-39.8%) compared with the SS system (26.6-29.8%), attributable to the greater proportion of feed used for milk production rather than body maintenance. The yield of milk fat + protein ranged from 392 to 487 kg, markedly higher when compared with the yields of 331 to 420 kg in the SS system.
The Holstein-Friesian dairy cows were well suited to the PC system where the concentrate input was >1.0 t/cow/annum. However, in the SS system where the quantity of concentrates fed was dependent on the annual grain yields from the cereal crops there was insufficient feed energy in the total diet during the early lactation period leading to problems of reduced milk persistency during lactation, lower milk protein concentrations and either delayed conception or a failure to conceive that resulted in reduced pregnancy rates. The results show that in a system where the quantity of concentrates fed is low a different type of cow (e.g. dual-purpose breed, cross bred) would have the potential to improve the balance between the cow’s nutrient requirements and the quality of the diet and also lead to an improvement in the quality of milk that is produced for both the liquid and processing markets.
The incidence of liver fluke adversely affected the cows in both systems during the early part of the project and led to the routine use of a preventative treatment. The cases of clinical mastitis and lameness were higher than in the previous study (during which period the systems were established), but the total number of cows in each herd was relatively small for carrying out this type of analyses on specific ailments. The reproductive performance was low immediately following the liver fluke problems, but re-covered to a satisfactory level at the end of the study.
Compared with the PC system, the SS system achieved a high level of self sufficiency but required a more complex crop rotation and was less flexible in relation to meeting the total annual feed requirements for the herd and also more limited when diets were formulated to balance the energy to protein ratio and meet the cow’s nutrient requirements. While the stocking density of the PC system was markedly higher than in the SS system, if the area of land that would be required for producing the concentrate feeds is calculated, then the stocking density and output of milk per hectare in the system would be sharply reduced.
To date there have been no adverse physical effects recorded in the SS system in relation to both the growth and yield of the crops or animal health, despite the exporting of nutrients from the system. However, the time period since the establishment of the system is relatively short (i.e. seven years); therefore the effect of the increasing magnitude of the decline in nutrients may not have yet reached a critical point when problems will be apparent in crop and/or animal performance and health.
Analysis of the combined data collected from both the two Ty Gwyn systems and the six stakeholder farms shows a wide range in both the size of the individual enterprises and the approach to the management of the farm, with the source of the concentrate feeds (i.e. home-grown or purchased) one of the key factors. The cropping strategies were also diverse including the proportion of permanent pastures, short-term leys and medium-term leys on the individual farms. There was a wide range in the performance of the different systems, including the efficiency of nitrogen utilisation for milk production. Despite the diversity within the eight systems, analysis of the data that was collected suggest all to be viable in relation to the physical management of the farms and also financially viable providing a satisfactory price was received for the for the milk being sold from the system.
The results from the study show that aiming for a high level of self sufficiency in an organic dairy system (SS system) can be achieved by producing all the feed for the dairy herd within the system and via a crop rotation that includes both combinable and forage crops. The ratio of N-demanding to N-fixing crop is s a critical factor in ensuring there is adequate nitrogen for optimal crop production. The system was markedly influenced by the seasonal effects on total crop production and the proportion of land allocated for combinable crops. A failure to grow and feed sufficient grain within this type of system leads to low energy diets, reduced milk persistency, lower milk protein concentration and reduced herd fertility when Holstein-Friesian cows are managed within the system. The PC systems are less sustainable, more vulnerable to market trends in both the supply and price of purchased feeds but easier to manage, they do not necessarily require the implementation of a crop rotation, have the potential to both produce a higher output of milk per unit area of land and also improve the supply of feed energy to the cow in the critical early lactation period.