Mjölk på bara vall och spannmål

When producing milk according to the rules for organic production one of the problems is the supply of protein. There is a general shortage of organically produced protein-rich feeds and the prices for these feeds are high. Therefore it is interesting for the producers of organic milk to evaluate the effect of offering the cows a diet of home-grown feed only. In most cases cereals in combination with high quality grass silage is a diet can be produced entirely on the farm. Milk production for cows on such a diet would be lower compared with a diet where a protein-rich supplement also is included but there is a lack of information about how large the production drop would be. With this knowledge it would be easy for the producers to utilize current prices for organically produced milk and feed and calculate if it would be economical to exclude the protein rich supplement from the cows’ diet. The high price of concentrate feeds in combination with comparatively low milk prices during the last year has made the following question highly relevant: Which diet is economically most favourable? Within a program that has been granted money from the research fund for organic research at Swedish University of Agricultural Sciences (EkoForsk), production experiments were performed. The objective of these experiments was to study the effect of excluding the protein-rich components in the concentrate at two levels of crude protein in the grass silage. The effect on milk yield, milk composition, feed intake, nitrogen balance and methane production was studied. Based on experimental results, economic calculations of milk revenue minus feed costs have also been performed using current prices paid for organic milk and for organic feed components. In two production experiments, a diet with only cereals and grass silage to dairy cows was compared to a diet where protein-rich supplements, such as soybean and rapeseed products, were also included. In the first experiment (Exp 1) these two diets were combined with two grass silages with different content of crude protein (13 % and 17 %) in a factorial design using 37 cows of the Swedish Red (SRB) breed during 20 experimental weeks. In the second experiment (Exp 2), only one grass silage quality was used (18% crude protein) and the diet with and without the protein-rich supplement was studied using 32 SRB cows during 12 weeks. In Exp 1 only cereals, or cereals together with protein supplement were offered in combination with ad libitum access to silage (13% or 17% crude protein). In Expt 2, the diet was designed to offer the same amount of metabolizable crude protein (AAT) to cows in the two treatment groups i.e. with or without the protein supplement in the diet. This was possible up to a production level of 37 kg energy corrected milk (ECM). Above that level, cows with only cereals and grass silage in the diet were somewhat underfed with regard to AAT. The results of both experiments were similar and showed that milk yield without protein supplement gave a significantly lower milk production and a significantly higher milk fat content. In Expt 1, the yield with- and without protein supplement was 35.3 and 30.9 kg ECM, respectively. In Exp 2 the corresponding figures were 40.0 and 37.3 kg ECM for the treatment with- and without protein supplement, respectively. The diet without protein supplement gave an increase in nitrogen efficiency of 20 % and 12 % compared with the diet with the protein supplement in Exp 1 and Exp 2, respectively. In a separate experiment evaluating the effects on methane production of the different diets, no significant differences in methane production (g methane per cow and day and g methane per kg ECM) between the diets were found. From milk production and feed intake data obtained from the experiments, the milk revenue minus feed costs for these diets were calculated using current feed prices in Sweden (February 2013). For organic milk the price was 3.76 SEK/kg ECM, and for cereals, protein supplement mix and grass silage the cost was 3.40 SEK/kg, 6.06 SEK/kg and 1.30 SEK/kg dry matter, respectively. The results of the calculations showed that the diet without the protein supplement gave a lower net income in Exp 1 (-8.20 SEK/cow and day) and a higher net income in Exp 2 (+6.04 SEK/cow and day). With prices from the previous year the results come out differently. The conclusion is that it is important to continuously follow the prices of milk and feed components and calculate the outcome to see if it is economical to exclude the protein supplement from the diet. The experiments that were performed give the basis for making these types of calculations. To regularly perform this type of calculations is economically interesting not only for producers of organic milk but also for conventional milk producers.