More milking days with lower yields : sustainability impacts of short or no dry periods in dairy cows

Summary

Farmers traditionally stop milking a cow 6 to 8 weeks before next calving. This ‘dry period’ (DP) maximises milk production in the next lactation. The resulting high milk production in early lactation, however, results in a negative energy balance and is associated with reduced health and fertility. Shortening or omitting the DP improves the energy balance in early lactation at the cost of milk production. This project aimed to evaluate and integrate sustainability impacts of shortening or omitting the DP, with a focus on cow welfare, cash flows at farm level, and greenhouse gas (GHG) emissions per unit milk. Welfare was addressed by monitoring lying and feeding behaviour of 81 cows with no DP or a 30-day DP in weeks -4 and 4 relative to calving. On average, cows with no DP had a 1 hour per day shorter lying time in week -4 than cows with a DP, but the absolute daily lying time (12.6 h) and relatively constant feeding rate suggest that welfare of cows with no DP was not impaired by milking in late gestation. Moreover, cows with no DP had a 1 hour longer lying time and a greater feed intake in week 4 of lactation, suggesting a better adaptation to the start of the next lactation. The number of meals, feed intake, and lying time of dairy cows were associated with physiological indicators of high metabolic load during this period. To compare milk yield between cows with different DP lengths, accounting for extra milk before calving and possible changes in calving interval, the ‘effective lactation yield’ measure was developed. The impact of DP length on effective lactation yields of second and greater parity cows was assessed over multiple lactations. The reduction in effective lactation yield compared with a standard DP was larger for no DP than for a short DP, and did not differ between the first and a subsequent shortening or omission of the DP, although the timing of milk yield changed. The overall impact of DP length on milk production, cash flows and GHG emissions were modelled based on production data of dairy farms that voluntarily managed cows for a short or no DP. First, introduction of no DP resulted in a dip in milk production of the herd in the second year the strategy was applied. On average over 5 years, applying a short DP reduced milk yield of the herd by 3.1%, and applying no DP reduced milk yield of the herd by 3.5%. Moreover, short and no DP reduced partial cash flows by €12 and €16 per cow per year, and increased GHG emissions per unit milk by 0.8% and 0.5%, respectively. These relatively small negative impacts of short and no DP on cash flows and GHG emissions can be offset by improved cow health and lifespan, which could result from the improved energy balance in early lactation (more pronounced for no DP than for a short DP) when these strategies are adopted. In conclusion, both shortening and omitting the DP can improve cow welfare with a small negative impact on cash flows and GHG emissions, which may be offset by improved cow health.