CONCEPT OF NEGATIVE ENERGY BALANCE (NEBAL) IN DAIRY CATTLE & ITS EFFECT ON HEALTH & REPRODUCTION
Energy balance (EB) in dairy cows is defined as the difference between energy intake from feed and energy required for body maintenance, production and gestation . NEB results in animals losing body condition. Metabolic and calving stress is thought to affect the fat-protein ratio (FPR) in milk. The FPR differs between cows and depends on the lactation stage. It is often high in early lactation when NEB is most likely to occur . The nutrient demand of lactation typically exceeds the dietary intake potential in the early postpartum period which often results in a varying extent of NEB . High producing dairy cows mobilize their body fat, and to some extent, protein reserves in order to sustain their milk production which leads animals to enter a state of NEB until energy intake meets the output requirements . Loss of energy in feed reduces the ability of rumen microbes to digest plant proteins and synthesise animal proteins, thus reducing the protein percentage in milk. The mobilisation of body fat increases non-esterified fatty acids (NEFA) in the liver and consequently the percentage of fat in milk. As the percentage of fat in milk increases and that of protein decreases, the FPR increases. The resulting NEB and metabolic demands influence the postpartum interval to first ovulation and thereby affecting the interval to conception which eventually affect the reproductive potential of the affected cows. Conception rates are thought to be low in animals that experienced NEB prepartum and early postpartum because of the poor quality of oocytes generated during this stage . Many studies have shown that while feed intake and milk production both increase after calving, maximum feed intake is only achieved some weeks after maximum milk yield . A relationship that involves three components of dry matter intake (DMI), live weight and milk production comes into play throughout lactation. It is therefore biologically plausible that cows lose weight in early lactation as milk production increases rapidly and DMI cannot cope with the rising production demand. The energy status after calving is lowest at the time of peak milk production.. It would therefore be a challenging task to prevent NEB in cows that are naturally high producers because of the interplay of these factors. Several adverse consequences of NEB have been investigated and documented which include metabolic disorders such as ketosis and acetonaemia, reproduction disorders such as anoestrous and infertility, and other health problems such as increased susceptibility to mastitis . Some of the methods proposed to diagnose NEB include estimating the difference between energy intake and energy requirements, body condition scoring and analysis of milk fat and milk protein especially in early lactation. NEB is believed to have an influence on several production and physiological parameters in dairy cows .It would therefore be of paramount important to identify animals at risk of this condition and take mitigating action.
Relationship of NEB with cows’ health status—–
Further research has suggested that animals in NEB have a reduced immune response which later results in several negative events like mastitis, lameness, respiratory diseases and metritis . A study of effects of NEB on udder inflammation in Holstein dairy cows concluded that animals in severe NEB that had increased SCC in milk . SCC in milk, which can act as an indicator of subclinical mastitis, was observed to be higher in animals with four and more lactations . A study on expert opinion identified high SCC as one of the risk factors associated with preceding or subsequent subclinical mastitis in dairy animals . Animals with FPR greater than 1.5 were at greater risk to be in NEB especially in early lactation. It is therefore justifiable to assess the relationship between NEB and SCC because very low SCC on the other hand has been identified to be a strong risk for the development of clinical mastitis which becomes costly for the affected dairy enterprise due reduced production and cost of treatment. Since animals in a state of NEB eventually lose weight, this could also contribute to the development of lameness. It has been demonstrated that animals with excessive weight loss postpartum had an increased risk of subsequent lameness . Lameness is painful and will restrict the animals from normal movement and eventually feed intake, especially for pasture dependant feeding, which would lead to a chain of undesirable events including poor animal welfare. Left displaced abomasum (LDA) is a disorder that occurs mainly in high producing dairy cows postpartum (Esposito et al.), often without causing observable clinical signs. Studies have also shown a relationship between NEB and LDA postpartum . The causal pathway for LDA is not certain but thought to involve disorders of NEB, hepatic lipidosis and ketosis. Clinical ketosis leads to recumbency and is a consequence of an excessive mobilization of body fat by a cow. It is common in early lactation and characterised by hypoglycaemia and hyperketonemia (Esposito et al.) that later induce a decline in plasma insulin and mobilization of triacylglycerol deposits as NEFA. Amounts of both NEFA and β-hydroxybutyrate (BH) in early lactation are believed to be normal . However, excessive amounts have been observed to increase the risk of disease, decreased reproductive efficiency and lower milk production. While being a strong contributor, NEB is only one of several possible causes for poor reproduction outcomes because other herd management factors are also involved, such as low DM availability through pasture prior to calving, insufficient maintenance of cow races, poor silage quality or other diseases. Both NEFA and BH at concentrations greater or equal to critical thresholds were seen to increase the risk of LDA by up to 10 times . Uterine diseases after calving have been seen in some studies to be higher in cows that experienced a greater degree of NEB postpartum and had decreased glycogen levels of intracellular polymorphonuclear neutrophils ,which could be a major predisposing factor for disease. Since NEB has effects on milk production, reproduction and immune system in dairy cows as outlined in the literature review above, dairy farmers should be on the look-out so as to reduce the impacts of these conditions especially in cows at high risk. The farmer should ensure availability of enough DM and provision of optimal and well balanced nutrition during the transition period as well as during early lactation. This could be done by providing animals with energy dense rations in beginning of lactation to alleviate as much as possible fat reserve mobilization. Efforts should be made to check in the stable to determine whether the calculated amounts are really being consumed by the cows and veterinarians should use their expert knowledge to determine the general health status of the animal and intervene when necessary
Relationship of NEB with Reproduction——
Reproductive efficiency in cows plays a crucial role in ensuring profitability of the dairy enterprise because it determines the length of the inter-calving period and the productive lifetime. In the strictly seasonal calving system which is typical for over 90% of dairy farms in New Zealand, conception within planned or optimal times is a major determinant of culling, which contributes to financial losses. NEB during early lactation in dairy cows leads to alterations in metabolic state that has major effects on the production of insulin-like growth factor (IGF) and related metabolites . Since IGF play an important role in follicular growth and embryonic development it becomes evident that reproduction potential is affected in animals that enter a state of NEB. High producing dairy cows have been observed to be more prone to NEB shortly after parturition, a situation that can impair reproductive recovery because EB is negatively correlated with days to first ovulation after calving . Therefore cows in NEB during early lactation would generally conceive later than expected. Ovulation after parturition is usually first observed within three weeks in about 50% of healthy cows . Early resumption of ovarian activity should lead to high fertility which would increase the chance of cows achieving the 365 days reproduction cycle. The delays in onset of postpartum ovarian activity eventually limit the number of oestrous cycles before breeding, which could account for the decrease in fertility . NEB therefore would be thought to act in a similar manner as under-nutrition in which ovarian activity is delayed which later affects secretion of follicular and luteinizing hormones . The magnitude and duration of the prepartum NEB status has a detrimental effect on reproduction and production performance in high producing dairy cows . The changes in biochemical, endocrinological and metabolic pathways are associated with delay of the first visible signs of oestrus, increased calving to first ovulation interval, decreased conception rates and prolonged calving interval . An increased calving to first ovulation interval would definitely affect PSM to conception interval at the herd level since the PSM date would arrive with some animals not yet physiologically ready for servicing. Body condition score decreases as body reserves are mobilized to compensate for NEB in early lactation leading to detrimental effects on the performance of the animal . In as much as every dairy farmer would like to have high producing cows in his herd, care has to be taken in order to maintain a balance between production and reproduction performances. This is important to consider since cows would usually be kept in the herd until they are in parity five or sometimes higher. If then conception rates are way below expectations, culling and replacements increase, thus herd productivity in the subsequent season may get seriously affected. Some studies have shown that animals that suffered NEB failed to reach peak milk production in 16 weeks and eventually lost weight and had reduced conception rates . Efforts and strategies to reduce negative effects of NEB should therefore be made before calving.
The consequences of a negative energy balance—-
Starting at two weeks before calving, dairy cattle can already get in negative energy balance due to the growth of the calf, start of the colostrum production and a strong decrease in dry matter intake. Especially fat cows with a Body Condition Score of 4 or greater are at risk. Dairy cows in negative energy balance will start to mobilise body fat. Massive mobilisation of body fat reserves can result in metabolic problems, related to the fact that the liver can’t cope with the high amounts of fatty acids mobilised from the fat tissue.Modern high-yielding dairy cows enter a state of negative energy balance (NEB) around calving when the energy demand for maintenance and lactation exceeds that of dietary energy intake . Cows with excessive body tissue mobilisation at this stage may take up to 20 weeks to regain a positive energy balance status . Although the resumption of ovarian activity is initiated during NEB
Dairy cows in negative energy balance have an increased risk to develop clinical or sub-clinical ketosis. Ketosis in dairy cows will have a negative impact on dry matter intake, health, fertility and production of the lactating cow. Recent evidence suggests that sub-clinical ketosis in cattle is much more common than clinical ketosis.
Signs of ketosis in dairy cows
Signs suggestive of sub-clinical ketosis in dairy cows are:
• A drop in body condition score of more than 1,0 point
• A disappointing milk production in combination with a fat:protein ratio above 1.5
• A reduction of dry matter intake
• Reduced fertility
Managing the negative energy balance correctly can therefore have a strong positive effect on farm profitability
Dry cow management————
Most of the problems occurring in the first few weeks after calving are related to dry cow management. Aim at a dry cow period of 8 weeks. During the first 6 weeks (far-off period) feed intake should be reduced to ensure the body condition score does not increase above 3.5.
During the last two weeks (close-up period), the diet should be similar to what is fed after calving. Ensure energy density of the diet is high, this compensates partly for the lower dry matter intake immediately after calving. A higher concentrate level will increase total dry matter intake. Provide sufficient levels of glucogenic energy. Feeding sufficient levels of glucogenic energy will increase insulin levels. One of the effects of insulin is that it decreases fat mobilisation. Ensure good structure and palatability of the diet and ensure it contains sufficient effective fibre.
Calcium intake during the last two weeks before calvingshould be reduced as much as possible by adding something to the diet that reduces calcium intake. Magnesium supply should be optimised.
Negative energy balance is a major nutritional factor affecting reproductive performance. When excessive BCS loss occurs, first ovulation after calving is delayed, conception rates decline and days open increase. Dairy producers must strive to optimize DMI and energy intake for cows throughout the transition period to minimize the level and duration of NEBAL and BCS loss during early lactation.
A Return to Positive Energy Balance (PEB)-—-
Return to positive energy balance occurs quickly when fed nutritionally adequate diets
to be accomplished through successful metabolic adaptation and feeding rather than through decreasing or preventing a rapid increase in milk yieldnEnergy balance is more likely to be related to energy intake than energy output (milk yield) Minimizing negative energy balance is most likely
Success in management of energy metabolism during the transition period depends upon excellent management in a number of different areas to manage the dynamics of DMI and body condition mobilization along with optimize performance. Our understanding of the metabolic regulation underpinning the changes that occur in energy metabolism of cows during the transition period is increasing, and with this understanding has come new potential opportunities for enhancing transition cow health and performance. Controlling energy intake of cows during the prepartum period (both far-off and close-up) is an important factor that predisposes cows to smoother adaptations to lactation. Furthermore, available information suggests that feeding higher energy diets (or not feeding a diet lower in energy than the high cow diet) promotes higher energy intake and milk yield along with better metabolic status during the postpartum period.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development) Image-Courtesy-Google Reference-On Request.
