Dairy Cow Biology Makes Rumen-Protected Choline Essential For Optimum Energy Balance
Genetic advancements during the past 50 years have tremendously increased dairy cow productivity. Biological adjustments to support this dramatic production increase have occurred within the cow. At the transition from dry cow to fresh cow, several adaptive challenges can be encountered and are integrated or interwoven. Yet, a successful transition is needed to set the stage for a successful lactation and optimum:
Health and culling.
The dairy cow’s major challenge during the transition period is meeting — or rather coming as close as possible to meeting — her energy (glucose) needs. The cow’s demand for glucose increases 2 ½ times from pre-calving to post-calving, but she cannot physically increase her dry matter intake (DMI) enough to meet that need. Therefore, today’s high producing dairy cows are energy deficit at transition. Nutritionists can help support their biological needs with feed supplements. Dairy cows naturally enter into a period of negative energy balance (NEB) which is not pathology in and of itself, but rather adaptive biology at work to support a dramatic increase in milk production. Transition dairy cows have been experiencing NEB at calving for generations. Most cows under good management and nutrition successfully navigate this time in their life. Yet, protracted periods of severe NEB can have profound adverse effects on them. The keys to successful transition cow management relate to nutrition and the environment. While this paper focuses on nutrition, it is important to recognize that environment and social interactions play a critical role in her performance.
> Social turmoil from frequent pen moves and group changes disrupts eating behavior and directly relates to metabolic problems including ketosis, displaced abomasums, metritis, and retained placentas.
> Waiting to move the animal to the maternity pen when calving has started increases stillbirths, especially among first-calf heifers.
>Proper stocking density is critical, especially as it relates to bunk space. Optimal bunk spacing is 30 inches per cow.
>Overcrowding pre-fresh cows almost guarantees transition problems.
Understanding important aspects of the biology of the transition cow helps guide dairy managers in making management decisions. Naturally occurring hormonal changes cause a huge increase in glucose production and the partitioning of energy to the mammary gland for greater milk production. Energy concerns during the transition period are focused on the liver as only the liver coordinates the processing and conservation of energy supplies. The liver is essentially the only site of gluconeogenesis for the dairy cow and has a role in the metabolism of fat during NEB. For the cow to achieve optimal performance, her liver must be healthy, must be ready to efficiently handle her energy needs. The dairy cow uses three strategies for biological energy management: increase feed intake, increase tissue mobilization (fat and muscle), and cellular adaptations for more efficient glucose use during the transition period. Nutritionists can strategically support her energy needs at transition with select feed additives.
Only during early lactation, do Growth Hormone (GH) levels increase without the levels of Insulin-Like Growth Factor-1 (IGF-1) increasing too. Typically the two move in unison except during early lactation. This causes the cow to enter a catabolic state of tissue mobilization as her major source of energy to support peak milk production. At the same time, the cow’s sensitivity to insulin is reduced allowing her to preferentially partition glucose to the mammary gland for lactose synthesis. The mammary gland is not insulin dependent for the uptake of glucose as are other body tissues. The liver initiates the uncoupling of GH and IGF-1 production as its number of growth hormone receptors (GHR) decrease. This sustains gluconeogensis in the early post partum cow. The liver also initiates the re-coupling of GH and IGF-1 levels when energy balance has returned to a positive state. That is why liver health is critical in postpartum cows as are environmental issues such as grouping and movement strategies. (IMAGE)- cow In dairy cows, the levels of GHR 1A in the liver has changed dramatically among different breeds of cattle. Those with much higher genetic streaming toward milk production, such as today’s North American Holstein as compared to beef breeds or lower producing dairy breeds such as New Zealand Holsteins, have an expression profile of the GHR 1A population which are down regulated starting about two days pre calving and remain low for about one week post calving. This expression of GHR (or lack thereof) is what uncouples the GH/IGF1 axis and puts the cow into the insulin insensitive catabolic state that supports high milk production by preferential partitioning of glucose to the mammary gland. Dairy producers cannot change the uncoupling process or prevent it in high producing cows. They can, however, assist in the re-coupling process with management practices that encourage increased DMI post partum and ensure good liver health. How can dairy management help re-couple GH and IGF-1 post calving? Re-coupling is a function of glucose production catching up with demand and is directly affected by the liver’s capacity to make glucose. The nutritional strategies used should support liver health. The re-coupling of the GH and IGF-1 axis is:
>Linked to nutrition and energy balance. Only rumen-protected choline assists the dairy cow directly with the critical gluconeogenic function of the liver by transporting fat from liver cells. Choline must be rumen protected, however, to prevent degradation in the rumen and to assure delivery to the small intestine for absorption and use.
> Controlled by insulin levels 8 Delayed until either milk production decreases and dry matter intake catches up to the demand for energy which leads to increased insulin levels.
>Begins when the elevation in insulin levels triggers GHR up regulation and an increase in IGF-1 production from the liver. This then down regulates GH production and slows the catabolic state of the cow’s metabolism. Cows return to positive energy balance approximately seven weeks postpartum. The difference between high and low producing milk cows is their DMI, not the time taken to return to positive energy balance. Higher producing cows eat substantially more than lower producing cows.
At approximately day 10 post calving, the cow reaches her nadir or deepest point of NEB and turns in a positive energy direction. Her biology now begins working toward a positive energy balance. The directional change helps the GHR population become more active in the liver, and the cow begins making more IGF-1. The IGF-1 works with follicle stimulating hormone (FSH) and luteinizing hormone (LH) to promote ovarian activity so the early post partum cow can return to cyclicity.
Critical Role Of Choline Any amount of fat deposited in the liver can create impaired levels of gluconeogensis and can negatively influence the cow’s ability to transition to peak milk production effectively. The active synthesis of phosphatidylcholine from choline is essential for the liver to make and secrete very low density lipoprotein (VLDL). TG = tryglyceride NEFA = non-esterified fatty acid AcCoA = acetyl Co A VLDL = very low density lipoprotein TAG = triacylglycerol 4
The dairy cow’s biology adapts to meet the cow’s tremendous demand for energy during the transition period. Glucose production in healthy livers increases dramatically and glucose is preferentially partitioned to the mammary gland for milk production. Rumen-protected choline supports liver health and optimum energy balance. Only rumen-protected choline assists the dairy cow directly with the critical gluconeogenic function of the liver by transporting fat from liver cells. Other feed additives assist in providing precursors for glucose production. Nutritionists who understand the cow’s biology are best prepared to support her biological needs for a healthy liver and optimum energy balance. The most effective feed additives for the transition period promote glucose production in the liver. While some feed additives assist in providing precursors for glucose production, only rumen-protected choline assists the dairy cow directly with the critical gluconeogenic function of the liver by transporting fat from liver cells.
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