Morning and evening pasture access - comparing the effect of production pasture and exercise pasture on milk production and cow behaviour in an automatic milking system

Although pasture is low-cost feed, many farmers find it difficult to maintain high milk yield when using pasture for high-yielding dairy cows in automatically milked herds. Therefore, a seven-week experiment with 40 cows in early to mid-lactation was performed to evaluate a management model for including pasture in the diet without jeopardizing milk production. Within a part-time grazing system with morning and evening outdoor access, we compared a group with ad libitum grass silage indoors combined with access to a small grass-covered permanent paddock for exercise and recreation (group EX) with a group offered production pasture at a high allowance per cow and day combined with restricted grass silage allowance at night (group PROD). Both groups had the same outdoor access times and the same concentrate allowance based on pre-experimental milk yield. Milk yield and milking frequency were recorded daily in the automatic milking unit. Milk recordings and samplings for determination of milk composition took place weekly and outdoor behaviour of cows was recorded during pasture access hours on six observation days, evenly distributed over the experimental period. During the experiment, average metabolisable energy concentration was higher in the grass silage offered both groups than in pasture herbage. However, our results showed no significant difference in daily milk yield between treatments. Furthermore, no significant differences between treatments were found in energy-corrected milk, milk fat production, or body weight change. Milk protein production was, however, significantly higher in group PROD. In early lactation, no difference in milking frequency was observed between treatments while for cows in mid- to late lactation, milking frequency was significantly higher in group EX than group PROD. Over the entire experiment, group EX cows spent significantly less time outdoors than group PROD. In conclusion, offering high yielding dairy cows in automatic milking systems high-quality pasture at a high allowance for a few hours in morning and afternoon appears to be an interesting alternative to exercise paddock with full indoor feeding, as it can reduce costs for supplementary silage, facilitate natural behaviour, and encourage cows to spend more time outdoors, while maintaining milk production at a level comparable to that of full indoor feeding.