Effects of monensin and essential oils on immunological, haematological and biochemical parameters of cows during the transition period
The transition period of the high‐yielding dairy cow extends from 3 weeks before to 3 weeks after parturition (Grummer, 1995). It is accompanied by a lowered responsiveness of the immune system which seems to be related to physical, endocrine and metabolic changes of late pregnancy, calving and lactation (Mallard et al., 1998) and leads to the highest incidence of production diseases in early lactation (Ingvartsen et al., 2003). In particular, high‐condition transition cows are at high risk of immunosuppression and periparturient health disorders (Lacetera et al., 2005). This seems to be partly accounted for by the negative energy balance and related metabolic derailment like fatty liver syndrome and ketosis (Trevisi et al., 2011). Commonly, the high energy demand for the growth of the foetus and onset of lactation together with a decreased dry matter intake leads to an unavoidable state of negative energy balance in transition dairy cows (Grummer, 1995). Consequential elevated levels of the serum metabolites non‐esterified fatty acids (NEFA) and ketone bodies seem to be aetiologically involved in an impaired function of neutrophils and leucocytes around calving (Contreras and Sordillo, 2011). High concentrations of NEFA were reported to diminish proliferation, antibody and cytokine secretion of bovine lymphocytes of heifers (Lacetera et al., 2004) as well as viability and generation of reactive oxygen species (ROS) in bovine polymorphonuclear leucocytes (PMN) (Scalia et al., 2006). Similarly, ketone bodies elicit an inhibitory effect on chemotaxis of bovine leucocytes (Suriyasathaporn et al., 1999) and on respiratory burst activity of bovine neutrophils (Hoeben et al., 1997). Oxidative stress is another contributing factor to inflammatory and immune dysfunction in dairy cattle (Sordillo and Aitken, 2009). It describes the imbalance between the rate of ROS production and the antioxidant mechanisms in living organisms and can lead to peroxidative damage of lipids, proteins, polysaccharides, DNA and other macromolecules and therefore alter cell function (Miller et al., 1993). ROS production of PMN is part of the normal host defences against infectious diseases and is mediated by the multicomponent enzyme NADPH oxidase (NOX) (Dahlgren and Karlsson, 1999). However, dairy cows are confronted with massive oxidative stress in the transition period as the enhanced oxygen metabolism increases the rate of ROS production and may lead to a depletion of important antioxidative defences (Sordillo and Aitken, 2009).
To investigate the immune system of high‐condition cows in a ketogenic metabolic status, we formed different animals groups with a diverse extent of post‐partal body fat mobilization by combination of the factors BCS before calving and concentrate proportion in the diet (Drong et al., 2015). We showed that a recently in the EU launched monensin controlled‐release capsule (CRC) indicated for transition cows improved energy status and decreased ketogenesis in high‐conditioned animals likely via an increased provision of ruminal propionate to hepatic gluconeogenesis (Seal and Reynolds, 1993; Drong et al., 2015). Simultaneously we could not confirm analogous effects of the natural intervention essential oils on ruminal fermentation or energy household of the cows (Drong et al., 2015).
Still, different compounds of essential oils have successfully been tested for anticancer, antibacterial, antiviral, antioxidative property and in the treatment and prevention of cardiovascular diseases including atherosclerosis and thrombosis in humans (Edris, 2007) and an enhanced immunocompetence and health of gut and a better performance of broilers and pigs (Michiels et al., 2010; Tiihonen et al., 2010), but studies on the effects on the immune system of cows are very rare. Besides a reduction of the incidence of production‐associated diseases like mastitis, ketosis and displaced abomasum (Duffield et al., 2008), monensin improved chemotaxis of neutrophils obtained from monensin‐treated cows in comparison with control animals (Stephenson et al., 1996).