13 Oct 2021
Phil Elkins
Job Title
The transition period remains a key area of interest for dairy veterinary advisors – and probably will remain so for the duration of many careers.
A 2006 paper in the Journal of Dairy Science stated that “transition cow management promises to be the foundation for progress in maintenance and enhancement of the health of dairy cows in the next 25 years”1.
When disease incidences are considered on most dairy herds, it is clear to see why – approximately 75% of clinical disease in dairy cattle occurs in the first month after calving and can, therefore, be attributed to the transition period.
As the paradigm of production veterinary medicine has shifted from clinical disease, via subclinical disease to disease prevention – and now with some within the field targeting optimisation of health, welfare and production – it is clear to see that significant attention must be targeted towards the transition period.
The transition period refers to the process of a late gestation cow becoming an early lactation cow, which involves a number of physiological changes, including:
Figure 1 shows the complexity of the adaptations in metabolic pathways that occur within a dairy cow around the time of calving affecting metabolism of lipids, nucleotides, energy and proteins/amino acids2. Significant deviations from these adaptations can have significant consequences in performance and disease risk.
A number of definitions of the specific time period referred to as the transition period exist, based on the time during which external factors can be shown to have a direct influence on disease and performance.
It is likely that the effective transition period in fact changes with each cow, with some less affected by specific factors than others; however, for simplicity some agreement exists on a transition period being from 60 days pre-calving to 30 days post-calving. During this time, the changes listed increase the susceptibility to three biological failures during transition:
Figure 2 shows how a failure of calcium metabolism is inherently linked with apparent failures in the other two categories3. The same is true whichever of the three may be seen as the initiating factor.
To identify whether the transition control is suboptimal on a farm, performance must first be assessed.
Monitoring individual disease incidences, while potentially useful and sometimes relatively easy to do, is not without issue. Diseases such as clinical milk fever, left displacement of the abomasum and retained placentae generally occur on individual farms with a low incidence. As such, understanding the significance of apparent changes in incidence is difficult.
Other symptoms of transition issues such as delay of return to normal cyclicity and cystic ovarian disease show a long lag period, and as such do not allow for proactive monitoring. Biological indicators of transition management – such as blood beta-hydroxybutyrate or calcium assessment, and early identification of purulent vaginal discharge – are minimally invasive, but even so do require consideration as to their justification. Considering the inter-related nature of transition diseases, it is the author’s approach to consider the rate of transition success rather than of individual disease.
A cow is deemed to have successfully transitioned if she has:
Milk production is an important component of this – for every additional litre of milk at the first milk recording, a cow will give on average 125 litres more milk throughout lactation4. A target for farm-level transition success rate must be specific to the farm situation, but the author’s experience is that those farms achieving 70% or higher success rate are either doing an extremely good job, or are not very good at identifying disease.
Transition success rate is a holistic output parameter. If it is acceptable, no further action may be needed other than continued monitoring of this parameter. Otherwise, a combination of disease incidences and assessment of the appropriate input parameters can identify which of the three biological parameters is worthy of further attention. Once in the system of regular transition success rate monitoring, those input parameters can act as early warning system.
Dry matter intake is the first key input parameter to be aware of. Dry matter intake in the precalving period is inherently linked to the incidence of disease and production; those animals that develop metritis post-calving have significantly lower dry matter intake up to 14 days before calving5. Also, a strong predictive relationship exists between dry matter intake pre-calving and the following parameters:
So it is clear to see that maximising dry matter intake, or rather minimising the reduction in dry matter intake around calving, is essential to achieving transition success. Monitoring fresh weight intakes is a moderate proxy for dry matter intakes, but a food dehydrator is a relatively inexpensive way to assess the dry matter percentage of the ration.
Three major influencing factors in dry matter intake exist – ration formulation, feed management and feed availability. The “Goldilocks” approach is the most successful in supporting high dry matter intakes – diets with high energy density reduce dry matter intake as the inherent “desire” to consume is suppressed, and increase over-conditioning, whereas low energy density diets are associated with poor milk yield and low dry matter intakes through unpalatability. The aim is for a low-to-moderate energy density diet with high palatability.
It is the author’s opinion that the introduction of hammer-mill or tub-ground straw into transition diets had led to significant improvements in transition success. These allow relatively high inclusion rates of up to 6kg of low energy density straw without affecting palatability or allowing sorting of the ration.
The diet should also have relatively high levels of metabolisable protein – heifers, in particular, produce more milk, fat-corrected milk, butterfat and milk protein with more supply of metabolisable protein up to 1,100g per day. The effects in multiparous cows are more modest, and limited beyond 800g per day6.
Feed must be mixed appropriately, presented in an appropriate manner and troughs maintained at an adequate level of cleanliness. The management of feed to transition cows will have a large potential effect on performance, and as such veterinary advisors should familiarise themselves with well-presented food, as well as examples of poorly presented food.
It is not always essential to have the solutions, but being aware of the issues is key. For example, value exists in identifying sorting in the feed trough, even if you cannot identify the solution.
Feed availability is closely linked with dry matter intake. A plethora of published data shows that when feed space per cow in the transition yard is below 90cm per cow, dry matter intakes, yields and health suffer. This is a simple calculation that can be made.
One approach can be to calculate feed space, and identify a maximum stocking density for the shed on the basis of this. This number then will not change, and simply regularly counting the number of cows in the shed will give an indication of feed availability.
Calcium homeostasis is also a key component of the transition ration. In multiparous cows, reducing dietary cation-anion balance to 100meq/kg has positive impacts on milk yield, fat yield, fat-corrected milk yield and dry matter intake post-partum through the reduction of subclinical hypocalcaemia7. No positive significant effect exists in primiparous calvings.
The efficacy of the ration in supporting calcium homeostasis can be monitored through observing either urine pH pre-calving or blood calcium levels post-calving, or indeed both. This can be combined with post-calving beta-hydroxybutyrate monitoring to monitor the success of energy metabolism and disease monitoring for immunity. Therefore, the three biological failures can be closely monitored for ongoing success.
So, in conclusion, by monitoring transition success rate, the veterinary advisor can assess the impact of the transition period on disease holistically. This can be supplemented with observations of pre-calving dry matter intake, stocking density and nutritional competency as early warning indicators, and urine pH, blood calcium and blood beta-hydroxybutyrate as biological indicators of success. From this, potential biological failures can be identified and corrective action taken.
