Prediction of the energy balance and milk production of grazing cows in the Azores for autumn and spring calving

Abstract

The climatic energy demand (CED) of cattle was modelled for Azores climate conditions. A deterministic model of the bioenergetic system of lactating and pregnant cows (TERCOW) was used to predict the energy balance and milk production of grazing cows for 3 classes of maternal live weight (400, 550 and 620 kg), respectively with 4000 kg, 5300 kg and 7000 kg milk production, for two calving periods (autumn and spring). Model simulations considered diets based on fresh grass supplemented, or not, with grass silage and commercial concentrate in accordance with the availability of grass in the pasture, the animal energy requirements and the case studies (Autumn calving, AC: a) grass, grass silage and barley; b) grass and maize silage; c) grass, grass silage and concentrate; d) grass, maize silage and concentrate; Spring calving, SC: e) grass; f) grass and barley; g) grass, maize silage and concentrate). It was concluded that thermoneutral heat production was higher than the CED all year-round in all weight classes studied and for autumn and spring calving. Under Azores production conditions it was possible to sustain the milk production target of 4000 kg with 400 kg live weight cows feeding grass only. Spring calving may have economic advantages in relation to autumn calving. Production costs can be 0.01 € kg −1 milk lower than those obtained with autumn calving, but economic benefits are masked by the seasonal differences in the milk price paid by local cooperatives.