The milk yield of dairy cows has virtually doubled during the past 30 years due to genetic development. The consequence is an enormous physiological burden on the animals. Particularly in the transition period, the shift from late pregnancy to early lactation, the metabolism of the cows is subject to huge adaptation processes and changes.
The transition period covers the phase of 3 weeks prior to until 3 weeks following calving. The significance of this period for health, productivity and profitability has been discussed increasingly in literature. A host of metabolic and microbial imbalances are named: milk fever, metritis, laminitis, acidosis etc. In addition reduced immune competence raises susceptibility to mastitis and other infections. The result is that many cows must leave the herd prematurely. Scientists assume that the negative genetic correlation between milk yield and health could be one of the reasons for the high incidence of health problems during the transition period. On the other hand it is also necessary to consider metabolic stress resulting from the high milk yield at the same time as reduced feed intake at the onset of lactation. The cows are ultimately unable to cover the energy demand for the milk yield. The result is a negative energy balance
Negative energy balance
In order to compensate the energy deficit in the negative energy balance, the cows mobilize body mass, which is primarily fat at the beginning. This leads to a flood of non-esterified fatty acids (NEFA) in the liver. The quantity often exceeds the capacity of beta oxidation in the mitochondria to break down these long-chain fatty acids and transport them into the citrate cycle as a substrate.
This situation is further aggravated by the high glucose requirement of the dairy cow. Around 3.5 to 4 kg glucose is needed per day for a milk yield of 40 – 50 kg in order to synthesize lactose for milk formation. Breeding for high milk yield has thus led to the situation that the glucose needed for lactose formation is virtually all used for milk formation while the remaining glucose regulation and supply in the organism is uncoupled (uncoupling of the somatotropic axis). The consequence of this metabolic imbalance is that ketone bodies are formed from the fatty acids that were not utilized properly and the cows suffer increasingly from ketosis. Carnitine is able to support here as it can make the precursors of ketone bodies reavailable for energy metabolism and thus significantly reduce a ketotic metabolic state.
There is no doubt that immune and inflammatory reactions occur during the transition period. The use of e.g. polyphenols in feed offer a promising opportunity to counteract these reactions. The direct connection between energy metabolism and inflammatory mediators also gives rise to expectation that a combination of both strategies will develop synergetic effects.