Energy Balance in Dairy Cows

The period overlapping the end of late gestation and postpartum is the Peripartum / Transition Period, where the animal shifts from a Non-Lactating and Pregnant stage to a Lactating and Non-Pregnant stage. This transition period of a dairy cow comes along with many tags attached. One of these tags is a state of negative energy balance (NEB) which is the most critical with regards to the nutritional / energy demands.

The dry matter intake (DMI) of transition cows is much lower, leading to a difference between the energy gained from feed intake and the energy expenditure associated with different physiological functions resulting in a NEB. NEB is normal during early lactation because the slowly increasing feed intake observed at that stage of lactation does not meet the energy requirements of a quickly increasing milk production. Extensive research has shown that the energy demand peaks ahead of the energy supply in these cows and this lag of about two to four weeks is a natural transient condition.

Negative Energy Balance. Consequences on Animal Production and Reproduction - Image 1

However, in some cows there is excessive body tissue mobilisation during this transition phase, which may take up to 20 weeks to regain a positive energy balance status.

To meet these unfulfilled nutrient requirements, transition cows undergoing NEB will mobilize body tissue (predominantly fat) and convert it to energy. However the energy, and especially the protein, available from body stores can supply only a limited amount of her needs as 1 Kg of fat can provide energy to produce 7 to 8 lit. of milk.

Negative Energy Balance. Consequences on Animal Production and Reproduction - Image 2

All this is accompanied by the priorities of the dairy cow, which utilizes it energy reserves first for its own maintenance, followed by growth, milk production and fetal growth. The priority for breeding / reproduction is the second last on the wish list of the cow followed by storing for its body reserves.

This priority wish list coupled with NEB takes its toll on the productive life span of the cow resulting in grave economic implications.

Effects of Negative Energy Balance

1) Post Partum Metabolic Disorders:

NEB may be associated with health problems when the difference between energy intake and expenditure is very large and sustained over many weeks. The intense lipid mobilization leads to a series of economically important metabolic disorders.

a) Ketosis and Sub-clinical Ketosis - The homeorhetic drive to sustain high levels of milk production necessitating mobilization of body fat stores results in elevated levels of circulating Ketone bodies. Ketone bodies provide available energy to peripheral tissues when carbohydrate levels are limited. Furthermore, betahydroxybutyrate (BHB) is utilized for milk fat synthesis. Therefore, a baseline level of circulating Ketone bodies (BHB, acetoacetate and acetone) is normal in the post parturient dairy cow. However, as the levels of ketones continue to increase and are sustained at an elevated level, an abnormal state of ketosis occurs.

As the period of NEB is prolonged, excess level of circulating Ketone bodies are present leading to Sub-clinical Ketosis. An estimate of the average duration of subclinical ketosis is about 16 days into lactation.

The association between Sub-clinical or Clinical Ketosis and the other common periparturient disease is a complex situation, as these conditions have been linked to Metritis, Abomasal Displacement and Mastitis.

b) Abomasal Displacement - As the concentrations of BHB increase significantly during Sub-clinical or Clinical Ketosis, the likelihood of abomasal displacement is greater. This can be substantiated by the fact that, with the elevated levels of BHB above 1400 mol/L in the first two weeks post-calving, dairy cows were three times more likely to develop abomasal displacement.

c) Mastitis - Cows in NEB period show an impairment of udder defence mechanisms. Hyperketonemia is hypothesized as one of the most important factors leading to reduced udder defences. There are possible explanations for these effects via each of the mechanisms of defence.

Firstly, the capacity for phagocytosis by polymorphonuclear cells and macrophages are reduced in NEB. In cows without intramammary infection (IMI), somatic cell count (SCC) is positively correlated with body condition score (BCS). In transition cows losing weight, SCC is lowered. It is also clear that bacterial killing capacity is impaired in the presence of Ketone bodies. Secondly, there is the capacity for udder leukocytes to induce cell recruitment in IMI. This is due to lower amounts of cytokines produced by lymphocytes in ketotic cows. These cytokines include interferon, interleukins and tumour necrosis factor. Overall, it is likely that the generation of chemoattractant is reduced in hyperketonemic cows.

Finally, the capacity for blood leukocytes to migrate into the infected gland is reduced. Leukocyte chemotaxis is significantly reduced in a Ketone body environment.
Hence leukocytes from hyperketonemic cows have impaired udder defence mechanisms against mastitis.

2) Reproduction:

Cows are in a state of reproductive inactivity (anestrous) during transition period. Although the resumption of ovarian activity is initiated during NEB, there are subsequent effects on fertility that lead to poor conception rates. It has been documented that the energy balance is associated closely with resumption of ovulation and cyclic reproductive activity in lactating cows. The severity and duration of NEB are positively associated with the interval to first postpartum ovulation. NEB impairs fertility by delaying first estrus by limiting the number of estrus cycles occurring before the preferred breeding period.

Studies have demonstrated that the increased secretion of luteinizing hormone (LH) necessary to induce follicular growth and ovulation only occurs after cows start to recover from NEB. In addition, NEB in early lactation exerts latent negative effects on the quality of oocytes ovulated 80-100 days later, reducing conception rates in the first weeks of the breeding season.

a) Metabolic and endocrine changes in the transition cow - The major adaptive changes occur around the time of parturition. The late dry period coincides with the last phase of fetal growth when nutrient requirements for gravid uterus increase. Many metabolic hormones and their receptors also alter in concentration over this critical transition period. In particular, interdependent changes occur in the GH-insulin-IGF-I-glucose signaling pathway. IGF-I is believed to be the main mediator of GH (growth hormone).

Changes in blood metabolites associated with lipid mobilization also affect oocyte quality directly, or indirectly, via alterations in the follicular environment. Profound changes in the liver lead to reductions in the concentration of GH receptor, IGF-I, several of IGF binding proteins and the acid labile subunit whilst IGFBP-2 is increased. This results in a marked decline in the circulating concentration and half-life of IGF-I, which can also impair follicular maturation and steroidogenesis.
The uterine repair mechanisms, after calving, are also delayed.

Negative Energy Balance. Consequences on Animal Production and Reproduction - Image 3

b) Leptin related to reproduction - Leptin is another metabolic hormone of interest in relation to NEB, as its circulating concentrations is strongly correlated to BCS and falls in late pregnancy.

Leptin is a cytokine-hormone secreted mainly by adipose tissue that acts as a direct metabolic signal to the sites in central nervous system that control pulsatile LH release. Leptin accompanies IGF-I in the control of the resumption of ovulation. LH pulse frequency is positively correlated with energy balance and the plasma concentrations of leptin, and also that LH pulse amplitude is correlated only with leptin values. Between leptin production and the reproductive axis is a strong physiological link, that leptin is involved in the control of pulsatile LH secretion as a major factor in the ovulatory process.

In ruminants, circulating leptin concentrations are positively correlated with body fatness, which is directly correlated to energy balance of the transition cow.

Negative Energy Balance. Consequences on Animal Production and Reproduction - Image 4

Hence, the duration and severity of NEB should be minimized to prevent undesirable effects on cow health and reproduction. This depends largely due to factors that impact dry matter intake, cow comfort, diet composition, and farm management.

NEB can be negated by feeding energy / protein rich diets from later part of second trimester, or early third trimester of pregnancy. Studies have demonstrated that these diets do not have an impact, when fed immediately pre partum, as there is a lower plane of metabolism.
Feeding of Gluconeogenic precursors during peripartum is beneficial as these are metabolised by the liver and rumen motility aids in mixing and absorption. A small amount of Gluconeogenic precursors are converted to propionate in the rumen, but most of these are absorbed and metabolized to glucose in the liver, giving an immediate surge to the much needed energy levels. Maximum blood levels of Gluconeogenic precursors occur within 30 minutes of administration, and maximal conversion to glucose occurs about 4 hours after administration.

Thus, it is imperative that a sound transition management program providing a comfortable environment and supporting a consistently high level of dry matter and energy intake should be followed to reduce associated reproductive and health problems, increase milk production and dairy economics.