RT Dissertation/Thesis
T1 The influence of L-carnitine on hematology and functional blood parameters of dairy cows with special focus on high resolution data around parturition
A1 Kononov,Susanne Ursula
WP 2023/08/16
AB The transition period, defined as three weeks before to three weeks after parturition, is one of the most critical times in the production cycle of dairy cows. On the one hand, cows have to cope with increased energy demand, while on the other hand, feed intake decreases due to stress and pain during parturition. This results in an negative energy balance and, consequently, at the beginning of body fat tissue mobilization. Lipomobilization increases the blood concentration of NEFA. This is accompanied by an increase in the blood concentration of ketone bodies, such as BHB. In addition to changes in energy metabolism, alterations in the immune function of dairy cows occur during the transition period. Stress and pain during calving lead to elevated blood levels of glucocorticoids, such as cortisol, which affect the immune system. Furthermore, the immune system is affected by increased concentrations of NEFA and BHB. At the same time, oxidative stress occurs due to an imbalance between the production of reactive oxygen species (ROS) and the activity of the antioxidative system. In general, the period around calving and its consequences constitute a very complex process influenced by many interdependent factors. One key factor in energy production is the quaternary amine L-carnitine (LC), which is necessary for the transport of short-chain fatty acids from the cytosol to the mitochondrial matrix. Furthermore, several studies have demonstrated the antioxidant and membrane-stabilizing effects of LC.
This study aimed to investigate the effects of dietary LC supplementation on energy metabolism, hematology, and immune functions of dairy cows during the transition period. In addition, the first 72 h after calving were observed at high resolution to show the characteristic courses of the examined parameters, which, to the best of our knowledge, have not yet been analyzed.
To attain this aim, 60 pluriparous Holstein Friesian cows were assigned to two groups based on their lactation number, body weight, body condition score, and fat-corrected milk yield from previous lactation. The LC group (CAR) received 25 g of rumen-protected LC. The study started 42 days before excepted calving and ended 110 days after parturition. 
To evaluate the performance and health of the animals, feed and milk samples were collected regularly, and feed intake, milk yield, body weight, and BCS were documented (Manuscript I). Additionally, NEB was calculated, and NEFA, BHB, and triglyceride concentrations in the blood were determined (Manuscript I). Also, the concentration of LC in the blood as well as that of the precursors γ-butyrobetaine (γBB), Nε-trimethyllysine (TML), and acetylcarnitine (ACA) was examined (Manuscript I). Red blood cell counts and antioxidant enzyme activity were measured to obtain more information on the oxygen supply and antioxidant status of the animals (Manuscript II). To evaluate the immunological status and inflammatory response, white blood cell count, phagocytic activity, ROS production, and lymphocyte populations were analyzed (Manuscript III). 
Dietary supplementation with LC increases blood LC, γBB, and ACA concentrations. Furthermore, LC supplementation resulted in better utilization of NEFA and TG. This was manifested by an increased blood concentration of triglycerides and a lower concentration of NEFA. Moreover, increased levels of platelets and eosinophils were detected in the CAR group, confirming the membrane-stabilizing effect of LC and the associated longer cell lifespan. 
Additionally, immunological functions were affected by LC supplementation. The ability of polymorphonuclear cells (PMN) to phagocytose bacteria was analyzed by the mean fluorescence intensity (MFI) of ROS-producing PMN, and the phagocytic capacity decreased compared to the CON group. Simultaneously, the efficiency of ROS production by PMN increased in CAR cows. These results suggest an altered immune function around calving, but not suppression, as is often described in the literature.
In addition, this study showed that calving affected almost all analyzed data. The strongest changes in hematology and cell function were found four hours after calving. Furthermore, the influence of LC supplementation on immunological parameters was observed in the first few hours after parturition, indicating that LC supplementation may have an effect at energetically critical times.
In conclusion, the present study showed that dietary LC supplementation affected energy metabolism, cell vitality, and cell function during the critical period around calving. However, this study also showed the clear influences of calving, which may be even more pronounced than animal-specific differences. Future studies should record the LC supply of cells to enable a more detailed description of the energetic situation of cells such as blood cells.
K1 Milchkuh
K1 Levocarnitin
K1 Energiestoffwechsel
K1 Hämatologie
K1 Leukozyt
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2023/2202