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Extended lactations in dairy production: Economic, productivity and climatic impact at herd, farm and sector level

Lehmann, Jesper Overgård, Mogensen, Lisbeth, Kristensen, Troels
Livestock science 2019 v.220 pp. 100-110
beef, cash crops, dairy cows, economic impact, economic sustainability, farm area, farmers, farms, fermentation, greenhouse gas emissions, heifers, herd productivity, herds, insemination, lactation, markets, milk, milk yield, models
The management concept “extended lactation” whereby farmers deliberately delay time of first insemination allow them to utilise the high milk yield potential of modern dairy cows for longer. The main objective of this study was to quantify the effect of different extended lactation strategies on herd productivity, farm economics and sustainability at product level with focus on greenhouse gas emission. The herd model SimHerd simulated cow state, production, replacement and herd dynamics that supported a quantification of the effect of managing either first lactation, older or all cows for calving intervals of either 15 or 17 months compared with 13 months. The initial herd was self-sufficient with replacement heifers, and the extended lactations were achieved by only changing time of first possible insemination while keeping insemination and conception rates as well as all other production and management parameters unchanged. The different extended lactation strategies reduced annual milk production and herd feed use up to 4.1 and 7.1%, respectively, which combined caused herd milk production per kg DM herd feed use to increase with up to 3.5%. Replacement rate per annual cow (per cow per year) was reduced with up to 13.6% points and the number of youngstock per annual cow with 27%. Managing only first lactation cows for extended lactations resulted in close to negligible production effects compared with baseline scenario and positively affected farm contribution margin whereas the other strategies had a negative effect on farm contribution margin per cow of up to 3.2%. The reduction in herd feed use reduced farm area for feed production, and the economic effect of using this area to either feed more cows or grow a cash crop was greater than the negative economic effect of the extended lactation strategy itself. Hence, the overall economic effect depends on the ability of the farmer to realise savings and utilise a potential freed area. Finally, the extended lactation strategies reduced greenhouse gas emissions with up to 8.1% per annual cow where less feed production and less enteric fermentation were determining factors.However, the weight ratio between milk and meat increased up to 34.7% across scenarios, which affected the allocation of emissions. Hence, emissions were reduced per cow but unchanged per kg milk. If the market requires an unchanged supply of milk and beef meat, then these extended lactation strategies caused an indirect emission from production of substitute beef meat, which can lead to an increased total emission. In conclusion, managing dairy cows for extended lactations can be an economically viable production strategy if the farmer is able to realise potential savings and gains. Emissions are reduced per cow but the sector level effect for milk and beef meat can be unchanged or even increased.