The liver of a dairy cow performs so many essential functions that we cannot overemphasise its importance in maintaining a healthy and high-performing cow.
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Liver health problems are often caused by metabolic imbalance resulting from dietary inadequacy, or other nutritional and environmental factors.
Most common is the accumulation of fat in the liver during transition period, when cows mobilise excessive body fat.
Research has shown there is a link between high accumulation of fat in the liver, ketosis (high NEFA and BHBA) and low milk production (Figure 1).
Figure 1. Average milk yield, liver fat content, blood beta hydroxybutyric acid (BHBA) and blood non-esterified fatty acid (NEFA) in healthy and ketotic cows. Adapted from Xiliang et al., 2017.
So, if we can keep the liver healthy by preventing excessive fat accumulation, there is a very good chance the cow will stay healthy, productive, fertile and profitable.
Let’s look at the key functions of the liver and how nutritional solutions like B vitamins can support a healthy and functioning liver.
Energy metabolism
Glucose is the main energy source for a dairy cow, and most of her glucose requirement is derived from a process called gluconeogenesis — a metabolic process of producing glucose from non-carbohydrate sources like fatty acids and proteins (amino acids).
Early research suggests up to 90 per cent of glucose requirement of ruminants may be derived from gluconeogenesis, occurring mostly in the liver.
Gluconeogenesis also occurs in the kidney.
The liver is also a major storage organ for excess glucose as glycogen, which is drawn upon when there is low blood sugar due to low dietary carbohydrate or low dry matter intake. The process of converting glycogen back to glucose is called glycogenolysis.
Given the importance of energy in dairy cows, it is important to maintain a healthy liver for it to continue to function properly and produce the energy the cow needs.
Fat metabolism
Dairy cows continuously metabolise fat, but during transition period — four weeks before and four weeks after calving — intake is depressed, and cows will mobilise more body fat (as NEFA, non-esterified fatty acids) for energy.
A healthy liver will convert the NEFA to a usable energy for the cow and/or to a non-toxic form of fat.
These two processes will prevent or minimise fat accumulation in the liver and improve glucose (energy) production.
Protein metabolism
Many essential protein-based compounds like hormones are produced in the liver.
For example, an essential hormone called insulin-like growth factor-1 (IGF-1), which plays a key role in follicle development and resumption of a regular oestrous cycle, is produced in the liver.
Many other hormones that regulate reproductive functions are produced in the liver.
Detoxification
The liver functions in breaking down toxic compounds such as ammonia (from rumen fermentation) into non-toxic urea.
Excess amino acids in the system are not stored, instead they are converted to urea in the liver. Urea formed in the liver is excreted in the urine or recycled through the digestive tract.
Some toxins from dietary source can also be detoxified by the liver.
Immune defence
The liver produces antibodies against infections and other molecules to respond to challenges of infections, inflammations and stress.
Dairy cows are always challenged throughout their production cycle, so the liver must be healthy to be able to respond adequately to these various challenges.
B vitamins and a healthy liver
The B vitamins are involved in the metabolism of fatty acids to prevent or reduce the accumulation of fat in the liver and maximise glucose production (gluconeogenesis).
They are essential in the process of converting NEFA to energy and/or non-toxic fat that is easily transported out of the liver for use in other tissues or secreted into milk.
Figure 2. Supplementation with rumen protected B vitamins (RPBV) reduced liver triglyceride (TAG, fat) in transition dairy cows (Morrison et al., 2019).
Although B vitamins are naturally present in the diet and produced in the rumen, research has shown they are significantly broken down in the rumen (up to 99 per cent degraded, depending on the vitamin), therefore, dairy cows need supplementation to optimise their health, production and reproduction.
Several studies have shown that supplementing transition cows with rumen-protected B vitamins reduced liver fat and subsequently improved production and reproduction (Figures 2 and 3).
It is important to note that for supplementation to be effective, B vitamins must be in the diet and in a rumen-protected form.
Figure 3. Supplementation with rumen protected B vitamins (RPBV) increased milk yield in transition dairy cows (Morrison et al., 2019).
Conclusion
The liver, in addition to being an organ that produces essential molecules such as glucose, also acts as a filtering system.
If it is clogged due to accumulation of fat, its capacity to function will reduce and many important metabolic processes will be hampered.
A healthy liver is critical to a healthy cow, as this will ensure your dairy cows are healthy and perform to their genetic potential.
Nutritional solutions like rumen-protected B vitamins can support liver health and contribute to the resilience, health and performance of your cows.
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