Optimize crude protein content of the diet
System: Dairy Cattle
Applicability
Mainly applicable for: Intensive and semi-intensive systems, sub-optimal feed ration composition
Not or less applicable for: Fully grazed pastoral systems
Description
Feeding a diet with an as low as possible amount of crude protein, but optimized for metabolizable protein and rumen protein balance based on individual animal requirements for metabolizable energy and protein (i.e., balanced ration). These requirements depend on production level that can be achieved based on basal diet characteristics and feed intake capacity, and production stage.
There is a potential for crude protein reduction in rations as some farmers tend to include more protein than necessary in order to stay on the “safe side” always. Too strong and too abrupt crude protein reduction, may cause erratic feed intake and affect performance and milk quality. If these changes are severe or if feed digestion and utilization diminish GHG emissions per kg product may even increase. Also, differences may exist between breeds or cows may have a different genetic background determining to what extent they are suitable for strategies of dietary protein reduction while maintaining productivity.
Mechanism of effect
Reducing the level of protein in the feed ration can reduce N excretion and hence N emissions from excreta, including direct and indirect nitrous oxide (N2O). In addition, GHG emissions may reduce when less (imported) protein-rich feeds with a high carbon footprint due to land-use change (LUC) are used (see factsheet ‘low-emission feed ingredients’). For scores presented in this factsheet, we assumed no change in LUC. Below-optimal protein provision may lead to health issues, and could increase GHG emission intensity in case of lower productivity. Also, methane emissions from stored manure can increase due to reduction in dietary crude protein if this is accompanied with a poorer digestibility of fibre in particular, and genetic merit of cows (i.e. productivity) needs to be taken into account with this.
To our knowledge, there are currently no papers reporting detailed analysis of the impact of optimization of crude protein content of diets as such LCA studies typically adopted a rather generic approaches not including details on optimization of dietary protein, its consequences for N excretion and N emission from excreta and manure. Therefore, although we expect potentially favorable effects, we do not report on total GHG effects in this factsheet.
Effects on GHG emissions
Reference situation: Average protein level in the diet
Effect on total greenhouse gas (GHG) emissions
| Mean effect and range in kg CO2-equivalents | per kg product | per farm | |||
| Mean | Min-Max | Mean | Min-Max | Level of evidence | |
| Optimize crude protein content of the diet | ? | ? | |||
Legend
| ● – Small effect (<5%) | o – No effect | ? – Effect unknown |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) | |
Effect per emission source
| Mean effect on absolute emission from | Animal | Manure storage | Feed and forage production | Barn | |||
| CH4 | CH4 | N2O | CO2 | N2O | LUC | CO2 | |
| Increase share of silage maize in diet | ●● | ● | ●●● | ? | |||
*risk of an adverse effect (see ’cause of variable or unfavourable effect’)
Legend
| ● – Small effect (<5%) | o – No effect | ? – Effect unknown |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) | |
Cause of variable or unfavourable effect
Optimize crude protein content of the diet
The effect on total GHG depends on whether (imported) protein-rich feeds with a high carbon footprint from land-use change are reduced; ration composition and initial and final CP level of the diet; grazing situation; health and productivity issues due to sub-optimal protein provision; and the manure management on the farm, incl. emission abatement techniques to capture methane from stored manure (e.g. anaerobic digestion).
Other Effects
Effects on yield and cost-effectiveness
| Yield | Labor | Costs and revenues | ||||
|---|---|---|---|---|---|---|
| Animals | Crops | Time | Capital investment | Operational Costs | Revenues | |
| Optimize crude protein content of the diet | o-●●● | o | ●-o | ●●–o | ●–● | o-●●● |
Legend (thresholds differ per indictor and can be found in the tooltip)
| ● – Small favorable effect | o – No effect | ? – Effect unknown |
| ●● – Medium favorable effect | ● – Unfavourable effect | |
| ●●● – Large favorable effect | ● – ● -Variable effect (depending on farm characteristics or way/level of implementation) | |
Effects on other sustainability aspects
| Risks of trade-offs | Potential synergies | |
|---|---|---|
| Optimize crude protein content of the diet | Water quality | Ammonia emission, Water use, Water quality, Biodiversity, Animal welfare |
| Literature references | Reduce crude protein content of the diet |
|---|---|
| Schrade et al., 2023 | Effect of diets with different crude protein levels on ammonia and greenhouse gas emissions from a naturally ventilated dairy housing |
| Krulling et al., 2001 | Emissions of ammonia, nitrous oxide and methane from different types of dairy manure during storage as affected by dietary protein content |
| Kidane et al. 2018 | Interaction between feed use efficiency and level of dietary crude protein on enteric methane emission and apparent nitrogen use efficiency with Norwegian Red dairy cows |
| Sun et al. 2019 | Starch and dextrose at 2 levels of rumen-degradable protein in iso-nitrogenous diets: Effects on lactation performance, ruminal measurements, methane emission, digestibility, and nitrogen balance of dairy cows |
| Morey et al., 2023 | Effectiveness of precision feeding in reducing N excretion in dairy cattle |
| Sajeev et al., 2018 | Greenhouse Gas and Ammonia Emissions from Different Stages of Liquid Manure Management Chains: Abatement Options and Emission Interactions |