The energy requirements for maintenance of modern dairy cattle is higher than in 1975, the year in which the Dutch net energy system (the VEM system) for dairy cattle was developed: lactating cows on average require 16% more metabolizable energy for maintenance, and dry cows even need 26% more energy for maintenance. These are the conclusions from an experiment with Holstein Friesian cows in climate respiration chambers carried out in 2018.
Results from this experiment, combined with data from literature, also suggest that the conversion of ME in body reserves proceeds less efficient during the dry period than during lactation. Wouter Spek of Wageningen Livestock Research (WLR) showed that the conversion efficiency depends on the dietary ME source (fat, starch or protein) on the one hand, and on the body tissue that is accreted (fat or protein) on the other hand.
In 1975, Van Es determined a ME requirement for maintenance (MEm) of 488 kJ/d/kg metabolic body weight (BW0,75). Around 2015, studies in the USA and the UK revealed a higher MEm requirement, of around 700 kJ/d/kg BW0,75. The increase in MEm is accompanied with an increase in the efficiency of which ME is utilised for milk production (kL). In the experiment of Spek a MEm requirement of 700 kJ/d/kg BW0,75 with a kL of 0,70 for dairy cows with a high milk production was estimated. For cows with a low milk yield a MEm requirement of 534 kJ/d/kg BW0,75, with a kL of 0,60 was estimated, and for non-lactating cows a MEm requirement of 614 kJ/d/kg BW0,75 was estimated together with an efficiency of which ME is converted in body energy reserves of 0,57.
The milk production of dairy cattle has increased over the past decennia, the digestive tract of the cows per kg of body weight has become larger, and the blood flow to organs and tissues has increased. The energy requirement for maintenance has, therefore, significantly increased since 1975. Time to update the Dutch VEM system. In follow-up research, the data of this experiment will be combined with data of other recent climate respiration chamber research. This combined dataset will then be used for updating the Duch net energy system for dairy cattle.
This study was financed by ZuivelNL and the Dutch Topsector Agri&Food. Results will be implemented in the CVB tables.