Dairy cows just don’t have a choice. Due to their biology, they are unable to meet their energy needs during the transition from dry cow to fresh cow. Their body’s demand for glucose (energy) increases approximately 2.5 times from pre-calving to post-calving, with the greatest deficiency occurring one to two weeks after calving.
As cows begin to use large amounts of energy to drive milk production, a lag occurs in dry matter intake (DMI), and they find themselves physically unable to increase DMI enough to meet their needs.
Dairy producers and nutritionists may feel challenged to help cows manage the dramatic increase in the need for energy, but the payoff for doing so is great, as successful transitions set the stage for optimum production, reproduction and herd health.
Energy starts with the liver, particularly glucose production. It is well known that fat accumulation by the liver, during the transition period, inhibits liver glucose production. It is no coincidence that dairy cows with healthy liver function experience fewer energy-related disorders than cows with suboptimal liver function. However, the research also shows that the impact is far beyond disease and that maintaining low liver fat, and therefore, better liver function, can positively impact production and fertility as well.
Research and on-farm experience can guide producers and nutritionists. Research from the University of California – Davis showed that increasing available choline in transition cow diets supports liver function. It demonstrated that supplementing all transition cows with a rumen-protected (encapsulated) choline not only lowered liver fat accumulation post-calving – from moderate to mild – but also resulted in higher post-calving DMI, higher fat-corrected milk yield, less body condition loss post-calving and improved first-service conception rate versus control cows.
When the blood parameters related to energy metabolism were examined as part of the research, cows that consumed rumen-protected choline had higher blood glucose levels and lower blood ketones and non-esterified fatty acids (NEFA). These results indicate that cows consuming rumen-protected choline were better able to orchestrate their energy metabolism in early lactation to achieve improved health, milk production and fertility.
Glucose (also known as blood sugar) conversion to lactose (milk sugar) is the primary driver of milk volume and is required for many metabolic functions. The liver generates glucose from propionate and amino acids. As fat levels in the liver increase, the liver’s capacity for glucose synthesis decreases. It is now understood that efficient glucose metabolism depends upon having low liver fat levels during transition. This is because the liver is the predominant source of glucose for the cow, as very little is absorbed from the small intestine.
The liver’s ability to coordinate energy metabolism and generate glucose is one of the key determinants of milk production, both peak and persistency, and reproductive efficiency, both cyclicity and conception.
Because cows have minimal glucose reserves, their bodies undergo biological changes in early lactation to answer the need for greater glucose supplies. The liver dramatically increases glucose output and peripheral tissues decrease their glucose use for fuel. The ability of the cow to meet her glucose demand is the key to having a successful transition and this in turn, is highly dependent upon the liver.
In addition to producing glucose, the liver metabolizes fat. Here non-esterified fatty acid (NEFAs) are processed after they are mobilized from adipose (fat) tissue in response to the negative energy status of the cow. NEFAs are used to generate energy for metabolic processes and milk fat synthesis. NEFAs are a source of nearly 40 percent of milk fat during the first 30 to 50 days of lactation. However, NEFA cannot replace certain functions of glucose, nor can they be used to make glucose.
The amount of fat the liver can process is limited by certain enzymes and metabolic pathways. Potential fates for NEFA in the liver ( Figure 1 ) include: Complete oxidation for fuel, partial oxidation with the release of byproducts (ketone bodies) into the blood and export of fats to body tissues via a very low density lipoprotein (VLDL), one of the key forms for transport of fat in the bloodstream.
Because the pathways for processing NEFA have limited capacity, triglycerides accumulate as fat in the liver during early lactation when liver NEFA levels exceed use through oxidation and export. These fat accumulations decrease the liver’s ability to synthesize glucose optimally and perform other metabolic processes.
Fat is transported out of the liver by VLDL. A key component in the synthesis of VLDL is choline. Some choline can be synthesized by ruminants from methionine in the rumen and liver, but research has shown that this is often not adequate to ensure optimal liver function and subsequent fertility and milk yield.
Supplementing rations with rumen-protected choline helps reduce fat accumulation in the liver and accelerates fat removal post-calving. Cows receiving supplemental choline show physical indications of better energy synchrony in the form of higher blood glucose and lower blood NEFA and ketone levels. When the cow’s liver performs efficiently, her energy status benefits. Because bacteria in the rumen destroy unprotected choline, the only effective choline supplement for ruminants is a high-quality rumen-protected choline product.
If fat accumulates in the liver, even a small amount can decrease the metabolic functions of the liver and impact overall energy metabolism in early lactation. Liver fat accumulation is generally categorized as normal (less than 1 percent liver fat on a wet basis), mild (1 to 5 percent), moderate (5 to 10 percent) and severe (more than 10 percent). On most dairies, the development of specific feeding and management programs for the transition dairy cow minimizes the occurrence of clinical disorders and excess accumulation (severe category) of fat in the liver of transition cows.
Yet research has indicated that up to half the cows in today’s commercial herds have moderate or severe fat levels in their livers. The greater the fat accumulation in the liver, the more impaired the liver’s ability to orchestrate energy metabolism. Glucose production can be depressed by one-third in cows that have moderate or greater fat accumulation compared to cows with less than 5 percent liver fat on a wet basis. Thus, minimizing fat accumulation and expediting its export or removal from the liver post-calving is an important goal. PD
- Technical Service & Business Development Manager
- Email Ken Sanderson