The rise in milk production has been accompanied by increasing incidence of health problems, declining ability to reproduce and declining the fertility of modern dairy cows. The transition from late gestation to early lactation is viewed as one of the most challenging elements of the production cycle. Perhaps the most important physiological change occurring during this period is the decrease in dry matter intake around parturition and the sudden increase in nutrients that cattle need for milk production. As a result of these remarkable changes, most of the infectious diseases and metabolic disorders occur during this time. The reducing availability of glucogenic compounds during the negative energy balance period may lead to fatty liver syndrome. Other metabolic disorders may include ketosis, displaced abomasum and hypocalcemia.
Negative energy balance
High producing dairy cows need to mobilize body reserve to be able to sustain their milk production. During early lactation, there is elevated demand for energy for more milk production, but a lag in feed intake creates negative energy balance. Until energy intake assures the requirements, dairy cows, especially high producing breeds, enter a state of negative energy balance (NEB) that leads to economic losses through decreased milk production, decreased reproductive performance and increased risks of disease incidences. The energy expended in producing a lot of milk during peak production is not proportionate to the amount of energy derived from the feed consumed due to increased concentration of sex hormones, early mobilization of lipid and reduced rumen capacity leads to NEB in early lactation. To compensate for the deficit the cow begins to mobilize its energy reserves, although, this does not enable it to meet the requirement and therefore goes to a state of negative energy balance. The amount of energy for milk production and maintenance exceeds the energy derived from the feed intake and body energy reserves. Soon after parturition, the cow’s diet changed from dry cow feed, which is relatively low to a high-energy one, however, the cow’s low appetite and capacity cannot allow her to consume adequate amounts required for energy for production of milk and body maintenance. During this struggle, cows are in a state that is referred to as negative energy balance, where daily energy balance is determined by the amount consumed (feed energy) as compared to the requirements for milk production and maintenance. Negative energy balance (NEB) is of interest in the dairy industry because it does not only affect production and reproduction performances but is also an animal welfare matter. Animals in NEB usually loss body condition after calving usually occurring at 50 to 100 days post-calving, which is a recognized animal welfare problem. There is appearing evidence that high yielding cows which lose body condition during periods of NEB become lame. Lameness is associated with animal welfare and has substantial negative effects on fertility performance and reproductive parameters, which would eventually lead to culling. However, there is a big gap and inadequate compiled information that clearly indicates on negative effect of negative energy balance on dairy cows and available combating strategies. Hence, it is important to revising the negative effect of negative energy balance on dairy cows and postulating ways of combating.
EFFECT OF NEGATIVE ENERGY BALANCE ON REPRODUCTION
Negative Energy Balance 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 Insulin Growth Factor (IGF) plays 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 NEB is negatively correlated with days to first ovulation after calving and cows. Negative energy balance is associated with a greater incidence of irregular cycles that can both increase the interval to first service and reduce conception rates. Problems include a delay to the first ovulation, cycles which are longer than the normal range (Prolonged Corpus Luteum) and long intervals between successive luteal phases, when cows fail to ovulate again at an appropriate time. Uterine involution is a critical component of postpartum reproduction, which involves endometrial tissue repair, myometrial contraction and bacterial clearance. Negative energy balance impedes uterine recovery due to a delay in the clearance of puerperal pathogens. Poor energy balance status is associated with a greater degree of uterine inflammation following calving and a slowing of the repair process.
EFFECT OF NEGATIVE ENERGY BALANCE ON PRODUCTION AND HEALTH
Body condition score decreases as body reserves are mobilized to compensate for negative energy balance in early lactation leading to detrimental effects on the performance of the animal. Animals that suffered negative energy balance failed to reach peak milk production in 16 weeks and eventually lost weight and had reduced conception rates. In dairy cows the onset of lactation causes nutritional and energy requirements to increase dramatically which leads to a state of negative energy balance. Due to this NEB, mobilization of the body’s reserve occurs leading to an increase in plasma ketone levels and is often accompanied by health disorders such as mastitis and endometritis. These problems are reflected in the degree of increase in ketone levels and decrease in glucose. Animals in negative energy balance have a reduced immune response which later results in several negative events like mastitis, lameness, respiratory diseases and metritis. Dairy cows in severe NEB had increased somatic cell count in milk (SCC). SCC in milk, which can act as an indicator of subclinical mastitis, was observed to be higher in animals with four and more lactations. Since animals in a state of negative energy balance eventually lose weight, this could also contribute to the development of lameness. Lameness is painful and will restrict the animals from normal movement and eventually feed intake, especially for pasture dependent feeding, which would lead to a chain of undesirable events including poor animal welfare. Negative energy balance and Left displaced abomasum (LDA) are also positively correlated. Subclinical ketosis is highly associated with several periparturient diseases, including subclinical and clinical mastitis. The mechanisms of udder defense against mastitis are impaired in periods of negative energy balance and hyperketonemia. Nutritional management and monitoring program show promise for alleviation of the impact of negative energy balance on mastitis and other periparturient diseases. Generally, several adverse consequences of NEB have been investigated and documented which include metabolic disorders such as ketosis and acetonemia, reproduction disorders such as anestrous and infertility, and other health problems such as increased susceptibility to mastitis.
Improved energy intake
The diet of high producing crossbred cows is usually deficient in energy during transition period (3 weeks before and after parturition) and early lactation. The animals are not able to eat more during advanced stage of pregnancy; therefore, we need to increase the energy density of their ration with minimal changes in dietary forage to concentrate ratio and fibre intake. If the cows require additional energy, then the supplementation of fats may be useful provided dry matter intake is not compromised. Fat supplementation has little effects on rumen fermentation, as indicated by the acetate to propionate ratio but the fat from different sources had variable effects. If the energy dense ration is not offered to the animals then they may lose more body weight after parturition due to negative energy balance (NEBAL). There is a practice of offering raw vegetable oils to cows by our farmers which is not reasonable. Just 2% vegetable oil in the diet can dramatically reduce rumen fiber digestion. Unprotected fats cause physical and chemical changes in the microbial fermentation of the feed and depress rumen cellulolytic microbial activity. Current practice of using rumen bypass or “protected” fats in fact, the dry fats which are processed to be easily handled and mixed into all animal feeds is best alternative to conventional feeding strategies. Bypass fat is generally used to increase the energy density in the ration of cows. Bypass fat gets digested later in the abomasum or true stomach of ruminants as it is not affected by the rumen microbes. The crossbred cows may be offered bypass fat @100g/d while the buffaloes may be offered @150 g/day during postpartum periods. The bypass fat can be added as 1.5-2.0% of the feed intake of animal. This is sufficient to increase the energy density that meets all the requirements of the body. Animals that have not any previous exposure to these fats may require an adaptation period. In addition to this, a care should be taken to ensure the mixing of products thoroughly into the ration, so that the feed intake is not affected. Most classes of bypass fats are handled and mixed into dairy feeds with relative ease. Glucogenic diets fed during the transition period and early lactation decreased milk fat and milk energy output and tended to stimulate the partitioning of energy to body reserves and improve the energy balance in early lactation compared with lipogenic diets.
Computer modeling through rationing software allows educated guesses to be made about how likely a diet is to induce excessive negative energy balance. Using a reputable nutritionist to formulate dry and early lactation diets will help prevent feeding errors that lead to undersupply of metabolizable energy. Regular sampling & analysis of conserved forages are a vital part of reducing feeding errors caused by variation in nutritive qualities within the clamp.
If accurate clinical records are kept, monitoring metabolic disease incidence can gives some indication of how well transition cow management is functioning. Herds with high incidence of metabolic disease or culling within the first 60days should certainly involve veterinary surgeon for further investigation.