Meeting the energy requirement of transition dairy cows is particularly important when fresh cows are coming into lactation and several weeks after calving. Unfortunately, not all energy requirements can be met only from feeding a well-balanced diet. Most cows at this time are drawn into a state of “negative energy balance” (NEB) for several weeks after calving. It is how well, we handle this natural situation that dictates the short- and long-term success of milk production, health and reproduction in the dairy barn.
The magnitude of post-partum NEB is mainly a function of how much energy can be consumed by these high-milk producers. That’s because good dry matter intake, which is interchangeable with good energy intake, peaks a few weeks later than peak energy demands by early lactation. Because of this lag time between energy required and energy consumed by lactating dairy cows; most high-producing dairy cows are drawn into a period of NEB for about five to six weeks during early lactation. To bridge this energy gap, the cow will naturally mobilize and break down her own body fat, which can supply a substantial amount of energy to support high milk production.
University of California (Davis) research shows a natural benchmark for bodyweight loss during early lactation is about 80 kg. Given a natural body loss of two kg per day for about six weeks will supply 400 Mcal of necessary net energy of lactation (Nel) which is enough to support 13 kg of milk production for this period. Once energy intake catches up (after peak milk production), feed energy intake match production requirements and the process slows enough to where the animal stops losing bodyweight altogether.
- From the Canadian Cattlemen: You can learn a lot about grazing yearlings from a dairy man
Risk of ketosis
For many reasons, some early-lactation cows do not meet universally accepted dry matter intake benchmarks (set forth by sound dairy trials). They have a rapid rate of fat mobilization that leads to the dire consequence of ketosis that often parallels the first six to eight weeks after calving.
There can be clinical signs for advanced cases of ketosis, but most affected NEB cows are usually not detected because ketosis will show up in other subtle ways such as an increased incidence of displaced abomasums, retained placentas, mastitis, or a weakened immune system. It has also been linked to milk fever and unexplained reproduction problems. Cows with subclinical ketosis on average lose about 25 per cent of their potential milk production per lactation.
Ketosis usually relates to a complex chemical imbalance that occurs when dairy cows cannot get enough of a basic energy block called glucose. It is the simplest sugar in cattle metabolism, but it essentially drives all energy-requiring maintenance and production activities. When dietary carbohydrates (containing glucose) are in short supply, the dairy cow burns her own body fats to produce energy; yield non-esterified fatty acids (NEFAs), which are reconfigured back into energy-rich glucose.
The same serum (blood) concentrations of NEFAs and ketone bodies such as Beta-hydroxybutyrate (BHBA) are used as current markers by many dairy specialists and veterinarians to measure the potential of ketosis (and associated severity of NEB) in early lactation cows. NEFA levels are thought to reflect the degree of body fat mobilization, while BHBA levels indicate completeness of oxidation of NEFA in the liver. The theory being that unhealthy and rapid breakdown of body fat in the early lactating cow increase the supply of NEFA from body fat and if it exceeds the liver’s capacity to turn it into available energy for the milking cow, the level of BHBA rises.
Sound field research shows NEFA levels of 0.3 mEq/l or higher in close-up dry cows are two times more likely to suffer from a post-partum disorder (re: ketosis, displaced abomasum, retained placenta and metritis). Post-partum NEFA levels of 0.6 mEq/l were five times more likely to suffer from similar post-partum disorders. BHBA levels that is greater than 1400 umol/l warns of subclinical ketosis in post-calving dairy cows.
Prevention is preferred
Nobody should disagree that preventing ketosis is a much better option than controlling it once identified. One should implement a proper transition-feeding program (three weeks before cows calve and three weeks post-partum) in order to promote good dry matter intake and a body condition score of 3.0-3.5 early lactation dairy cows.
Such close-up dry cow diets should ideally dovetail into early lactation rations; both diets formulated with the central idea of maintaining good rumen function (by providing adequate effective forage fiber) and yet carry enough availablae dietary energy to meet respective vital and production needs. Another goal is to maintain adequate DMI in dairy cows prior to calving (re: 12 kg, DM basis), while building feed intake in early lactation to about 3.5 to four per cent of their bodyweight at about nine to 10 weeks post-partum.
When pre- and post-partum dairy diets are fed, good transition bunk management is also necessary to minimizing NEB. Common sense dictates enough bunk space and adequate time to eat is always provided. A properly mixed ration should also be put in front of the cows, pushed up frequently and old feed removed, daily. It is a matter of implementing sound practices that will get dairy cows, before and after calving to eat an extra kilo of feed.
That particular kilo feed might just help many cows in their close-up and/or early stage of lactation maintain optimum dry matter intake and thus minimizes “negative energy balance” or NEB. Some fat mobilization is acceptable, but if left unchecked leads to dangerous ketosis. As recommended above, a good transition feeding program should be invested for every milk cow; to yield not only high milk production, but keep them healthy for the current and future lactations.