Effects of a Change from an Indoor-Based Total Mixed Ration to a Rotational Pasture System Combined with a Moderate Concentrate Feed Supply on the Health and Performance of Dairy Cows

SIMPLE SUMMARY: In grazing systems of temperate climate zones dairy cows are often fed with a silage- and concentrate-based diet during winter and are gradually introduced to a pasture-based diet in spring. This housing and feeding change involves many complex nutritional, behavioral, and metabolic adaptions, likely connected with alterations in energy metabolism. In a previous trial, feeding low amounts of concentrate during full-time grazing had not prevented energy shortage during the first weeks on a pasture system. Because of this, further research was needed to determine whether a higher concentrate supply during full-time grazing would have attenuated that energy deficit. In this experiment we were able to show that the transition period is connected with a higher activity due to walking and grazing, associated with changes in red blood cell count. Further parameters like lipomobilization, decreasing milk production, and loss in bodyweight confirm the alterations in energy metabolism. In summary, the present study shows the changes and its impact on the animals during transition to full-time grazing. ABSTRACT: In spring, the transition from a total mixed ration (TMR) to pasture requires metabolic adaptions for the cow. It had been shown that supply of low amounts of concentrate after transition to full-time grazing caused energy deficits, resulting in a lower milking performance and changes in a variety of variables indicative for energy metabolism. The present study aimed to investigate how a moderate concentrate supply (4.5 kg dry matter cow/day) after transition to pasture influences health and production indicators. Over a 12-week trial period dairy cows were observed during transition from confinement to pasture (pasture group: PG) and compared to cows fed TMR indoors (confinement group: CG). On average, the PG consumed less feed and energy than the CG and mobilized body reserves, which is mirrored in a decrease of body condition and various fat depots. These effects were paralleled by elevated serum concentrations of non-esterified fatty acids and ketone bodies as well as an increase in liver fat content. The physical activity (elevated walking, eating, decreasing rumination time) of the PG was significantly higher than that of the CG, which intensified the energy deficiency and resulted in a lower milk yield. In conclusion, the moderate concentrate supply was insufficient to counterbalance the lower energy intake from pasture during transition.