The GAEC Le Mas d'Illins is located in northern Isere and has 100 dairy cows. The farmers decided to eliminate the maize crop from an area suitable for grazing, and they now run the livestock there as much as possible. However, in the summer, these 50 ha of temporary grasslands are not enough to meet the needs of the dairy cows. For several years, the farmers have been using multi-cut forage sorghum to supplement the cows' diet of summer forage and green feed. Thanks to this solution for the summer, they have decided to focus on increasing spring grass production on the temporary grasslands. The success of the establishment phase, which occurs in late May or early June, after existing grassland has been exploited, is crucial. This timing helps maintain greater soil moisture, promoting rapid grass emergence. The yield then depends on rainfall and heat levels and can reach 5-6 tonnes of DM/ha. The cost of producing forage sorghum for grazing has been estimated at (sic)320 per ha or (sic)53 per tonne of DM for a yield of 6 tonnes before losses. When comparing seasonal averages, only grass that is naturally produced on the farm is cheaper. The cows readily consume multi-cut forage sorghum. When the cows begin to graze in the sorghum field, the plants are at the 50-cm stage, and milk production is 1 to 1.5 litres/cow/day higher than when the cows were grazing on the previous grass. Since growth is fast, the system is often topped up with green feed to avoid any waste in the field. To optimally exploit the sorghum fields, the GAEC is looking for ways to stagger grass development across different plots in order to extend the window during which the forage is consumed at its optimum level of quality.
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