Abstract
In early lactation, an energy deficit leading to a negative energy balance (NEB) is associated with increased susceptibility to disease and has been shown to be an important factor during transition in dairy cows. L-carnitine as a key factor in the mitochondrial transport of fatty acids and subsequently for β-oxidation and energy release is known to modulate mitochondrial biogenesis and thus influence metabolism and immune system. In the current study, we characterized hematological changes around parturition and investigated the potential effects of dietary L-carnitine supplementation on immune cell functions. For this approach, dairy cows were assigned either to a control (CON, n = 30) or an L-carnitine group [CAR, n = 29, 25 g rumen-protected L-carnitine per cow and day (d)]. Blood samples were taken from d 42 ante partum (ap) until d 110 post-partum (pp), with special focus and frequent sampling from 0.5 to72 h post-calving to clarify the impact of L-carnitine supplementation on leukocyte count, formation of reactive oxygen species (ROS) in polymorphonuclear cells (PMN) and peripheral mononuclear cells (PBMC) and their phagocytosis activity. Blood cortisol concentration and the capacity of PBMC proliferation was also investigated. All populations of leukocytes were changed during the peripartal period, especially granulocytes showed a characteristic increase up to 4 h pp. L-carnitine supplementation resulted in increased levels of eosinophils which was particularly pronounced one day before to 4 h pp, indicating a possible enhanced support for tissue repair and recovery. Non-supplemented cows showed a higher phagocytic activity in PBMC as well as a higher phagocytic capacity of PMN during the most demanding period around parturition, which may relate to a decrease in plasma levels of non-esterified fatty acids reported previously. L-carnitine, on the other hand, led to an increased efficiency to form ROS in stimulated PMN. Finally, a short period around calving proved to be a sensitive period in which L-carnitine administration was effective.
Highlights
During the transition period dairy cows have to cope with physiological consequences of calving and with metabolic consequences of a negative energy balance (NEB) due to high energy requirements for beginning milk production and an inadequate feed intake [1–3]
Ability to cope with the onset of milk production and the physiological stress of parturition by means of sufficient energy supply and fast recovery are critical for health stability and consistent performance in dairy cows
The aim of the present study was to investigate the hypothesis that L-carnitine supplementation affected the leukocyte population of the cow around calving with consequences on the function of polymorphonuclear cells (PMN) and lymphocytes
Summary
During the transition period dairy cows have to cope with physiological consequences of calving and with metabolic consequences of a negative energy balance (NEB) due to high energy requirements for beginning milk production and an inadequate feed intake [1–3]. Dietary L-carnitine supplementation in transition dairy cows was described to increase milk yield in early lactation and milk fat percentage in the first week of lactation, assuming an improved peripartal energy metabolism [13]. In these Lcarnitine supplemented cows the export of triglycerides (TG) from liver into blood seemed to be increased during the last 14 days ante partum (ap), whereas non-esterified fatty acids (NEFA) tended to be lower in supplemented cows directly before calving compared to non-supplemented cows [13]. It can be hypothesized that insufficient endogenous synthesis of L-carnitine could lead to affected cellular energy metabolism and impaired cellular functions which may compromise immunological processes Evidence for this can be found in studies describing a suppression of the immune system during the peripartal period [4, 17, 18]. Like PMN and lymphocytes are important effectors of the innate as well as the adaptive immune system and are challenged during time of parturition as frequently described for humans [32] and in some studies on dairy cows [33]
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