Written by Chris Balemi An overweight cow is more exposed to an increased risk of ketosis in early lactation. This is particularly prevalent in pasture fed cows as there can be limited options for balancing the diet. There is much debate around exactly what the ideal body condition score should be in largely pasture-based feed systems. Under this management system there is a fine line between cows having an adequate condition score or being overweight, which runs an increased risk of ketosis and fatty liver disease.
HOW DO FARMERS AND HERD MANAGERS MAINTAIN OPTIMUM CONDITION, WITHOUT THE RISKS ASSOCIATED WITH OVER CONDITIONING THEIR COWS?
Fat cows wouldn’t be an issue if they weren’t subject to a higher risk of metabolic diseases, particularly ketosis. Maintaining herd condition and holding it at the correct level can be a very fine line. To successfully manage the conditioning of our herds, we first need to understand the processes at play and the nutritional factors that govern and balance it.
Ketosis in dairy cattle is triggered by an energy deficiency in early lactation. When blood glucose levels reach a low point, the body then begins to mobilise body fat as an alternative energy source. The downside to mobilising large amounts of fat is that it risks clogging the liver, which can run the risk of catastrophic liver failure, or what is termed as fatty liver disease. Stored fat is also considered an inefficient means of creating energy, and in some instances mobilising it can use more energy than it creates.
Under the right circumstances converting fat to energy should be a normal, healthy, and efficient process. As mentioned earlier, this process can be extremely beneficial in times of short term food shortage or stress periods. In this way it can be utilised when extra energy is required to plug gaps, such as calving and early lactation.
Science is now showing us that if the body is nutritionally balanced, the process of converting fat to energy can be more efficiently managed without experiencing the negative downsides. In order to prevent fatty liver and maintain general liver health, nutrients play a paramount role. The key nutrients in this process are defined as methyl donors, which are the amino acids; choline, methionine, and betaine. These methylated compounds contain a one-carbon group), which have the ability to play a fundamental role in hundreds of metabolic reactions. A deficiency of any one of these elements can jeopardise the health and the economic performance of the early lactating cow.
Towards late gestation, the requirement for methionine increases in dairy cows due to inadequate DMI, as well as the increased protein demand to support foetal growth and the onset of the next lactation. Milk contains a high amount of methylated compounds (choline and methionine) as components of milk fat micelles or proteins. At the beginning of lactation, a dairy cow has a high demand for these compounds due to high metabolic need. The availability of ready-to-use methyl groups is low in ruminants because of the extensive rumen degradation that takes place at this time, as well as the reduced DMI at the onset of the lactation. This creates a shortage of methylated compounds, particularly in the lead up to calving and in early lactation
OVERCOMING THE DEFICIT
To overcome this deficit in methyl groups, ruminant animals rely on methyl-neogenesis. These processes depend on an adequate supply of B vitamins as co-enzymes. These vitamins are also fundamental in the energy supplying metabolic pathways. In this way up to 50% of the total methionine used by the cow comes from homocysteine remethylation. Certain minerals such as zinc, copper, selenium, and iodine are also important in underpinning the process as they also play an important role for the liver. It’s important that each element is in the correct form and combination for the system to work most efficiently.
One of the best known amino acids, methionine constitutes 5.5% of the total EAA in bovine milk and between
2.48% and 3.32% of casein. The most visible effect of a deficiency is the decreasing milk protein synthesis because of its status as a limiting AA, but it also results in limited utilisation of other circulating
AA. Upon pathogen challenge, as is the case in newly calved cows, a good availability of methionine allows a higher neutrophil and monocyte oxidative burst capacity, which increases effective protection against invading pathogens in dairy cows.
Also known as PtdChol, one of the most important and high-demand methylated compounds in dairy cows during the transition period. Apart from the demand for PtdChol in milk, transition dairy cows also need high PtdChol availability for very low density lipoprotein (VLDL) synthesis in order to prevent fatty liver.
Therefore without sufficient levels of these nutrients, what would normally be a natural, efficient process of converting fat to energy, can instead cascade out of control, ultimately leading to impaired energy supply and issues such as ketosis, and fatty liver disease.
In order to supply the amino acids to fuel the methylation process, the feeding of a good quality bypass source is required. Feeding a good bypass protein source is expensive and may not always supply the correct amino acids at the desired levels. Recently companies have developed ways of protecting these key amino acids and vitamins from rumen degradation within a single protected micro prill matrix. This system effectively targets all of these key elements directly into the metabolic pathways.
In dairy cattle, liver function is critical in maintaining the energy pathway during the lead up to calving and early lactation. Balancing these key methyl donor elements allows the liver to function at an optimum level by efficiently mobilising the excess fat, creating energy at key times. With good rumen protected methyl donor support, farmers now have the potential to more effectively utilise condition levels in their animals for more production during stress times.
Methionine and choline regulate the metabolic phenotype of a ketogenic diet
Pavlos Pissios et al
Methyl Donor Nutrient Intake and Risk of Type 2 Diabetes: Results from 3 Large US Cohorts (OR15-02-19
Kim V E Braun
Importance of methyl donors during reproduction1,2,3,4
Steven H Zeisel
Multifaceted role of one-carbon metabolism on immunometabolism control and growth during pregnancy,
lactation and the neonatal period in dairy cattle
Danielle N. Coleman