17 Feb 2021
Additional time spent looking at, and helping improve, calf performance can provide satisfying gains on farm, according to Emily Payne.
Emily Payne
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Image: © SGr / Adobe Stock
Replacement calves represent the future of a dairy herd; however, they are often seen as lower priority animals when considering management and time budget allocation.
Heifer rearing represents the second largest expense to farmers (annually, behind feed) and accounts for approximately 20% of production costs for a dairy unit (Boulton et al, 2015). The target age of first calving within the UK is 22 to 24 months; for this goal to be achieved, average daily live weight gain targets must be met (Cook et al, 2013).
The milk-fed calf provides us with the perfect opportunity to do this; when managed correctly, feed conversion efficiency peaks very quickly after birth and is at its highest during this period, decreasing with age (Bach et al, 2013).
Despite this, the period of highest risk for a dairy heifer is within the first few weeks of life; 7.9% of UK calves are born dead or die before reaching 24 hours of age and within 28 days another 3.4% are lost (Brickell et al, 2009). Clearly, the first few hours of an individual calf’s life are critical to its long-term health and survival. However, this article looks to focus on aspects of calf rearing other than colostrum management.
A large proportion of a farm vets’ time is spent carrying out routine fertility visits. These regular visits foster a good working relationship between vet and client, creating a window of opportunity to regularly oversee calf performance.
Calf mortality is an output that should be recorded (and easily found by the vet) on all farms. It can be calculated by either considering the number of calves born (alive) or calvings. The important differences of note here are that when considering number of calvings, stillbirths are included. The ideal window to begin monitoring calf mortality in is from birth to weaning – this indicates early life performance and provides direct feedback on calving and calf management, with a target of lower than 5% frequently quoted (Sherwin et al, 2016).
For a farm vet analysing this information, time of death can offer guidance as to where to begin investigating (perinatal, neonatal or pre-weaned calves). Many diseases of calves have very low mortality, but high morbidity, resulting in significant disease without an apparent effect on mortality rates. Treatment records, or simply looking for sale of calf-specific drugs, often provides a good starting place for assessing disease prevalence.
Target daily live weight gain (DLWG) for replacement heifers is now well recognised at 0.8kg/day (Drackley, 2008). Measuring can help single out underperforming individuals, identify environmental issues leading to suboptimal performance within a group and help exploit feed conversion efficiency.
While calibrated weigh scales will clearly offer the most accurate determination of weight, weigh tapes are a good starting place if scales aren’t available. Weigh tapes measure heart girth and are calibrated to then predict a weight. Provided at least two measurements, on two separate occasions, have been taken then DLWG can be calculated.
Good colostrum management is key and education of clients in this area has a direct influence on calf performance. An easy way to confirm sufficient passive transfer has occurred is by performing serum total proteins on a blood sample using a refractometer. Reliable results can be obtained performing this method in calves up to nine days of age (Wilm et al, 2018), with more than 55g/L or more than 8.4% representing successful passive transfer.
Refractometers cost little and plain samples left to stand will separate without the need for expensive laboratory equipment. Research has demonstrated the sensitivity and specificity of this test to be 88.9% for both (using Brix cut off of 8.4%; Deelen et al, 2014).
Within the UK, vaccination aimed at protecting the calf focuses largely on pneumonia and diarrhoea prevention. Despite vaccination being one of the cornerstones of disease control, a 2014 study of farmer motivators, uptake and communication regarding vaccination showed only 26% were following vaccination protocols because of veterinary advice (Cresswell et al, 2014). When deliberating with clients about vaccines, important considerations include the cost of vaccination protocols (drug and labour costs) and the risk benefit to each unit.
Attention should be paid to several aspects of the calf-rearing process, including, but not limited to, housing, hygiene of the environment, equipment and personnel involved, colostrum protocols and the timing of other events within the calendar, including routine procedures and group changes.
Vaccination is only one aspect of disease control. Without management of immunity, infection pressure and good attention to detail when rearing calves, improvement in performance cannot be guaranteed (Sherwin and Down, 2018). Additionally, it is pertinent to remember vaccines are designed to reduce signs of clinical disease and shedding of infectious agent and, therefore, client expectation should be managed accordingly.
Sick calves are often dehydrated, either as a side effect of the disease process or as a result of simply being too weak/not having easy access to water. Estimation of percentage dehydration, including fluid loss, is notoriously difficult, but common indicators include reduction in skin tenting (or elasticity), degree of eye recession and demeanour changes (Hallowell and Potter, 2009).
An early assessment of this can direct decision-making for the route of fluid administration, and while laboratory assessment analysis often provides a more descriptive deficit analysis, it is not usually practical. Treatment success is often time and facility dependent.
Two types of IV fluid therapy exist: colloids and crystalloids. As a general rule, commercially available colloids are self-limiting when use in farm animal practice is considered (due to volumes required and costings). However, 7.2% of hypertonic saline has the ability to act in a similar manner by drawing fluid from the interstitial space to the intravascular space (Hallowell and Remnant, 2016).
Opinions about using hypertonic saline in dehydrated calves differ within the profession, and a judgement using one’s clinical acumen depends on the individual scenario. Commercially available crystalloids include 0.9% sodium chloride or Hartmann’s; usually replacement of fluid volume alone, with one of these, would be sufficient, with the exception of the severely acidotic calf, which may require additional bicarbonate.
Oral rehydration therapy (ORT) is not as simple as just giving water to rehydrate; many different generations of ORT are available, each with its own appropriate scenario for use. A whole host of differing electrolyte solutions are available, and each farm will likely have one it regularly uses and is familiar with.
First-generation fluids are equimolar; they have no bicarbonate within their preparations. Second-generation fluids do contain bicarbonate, while third-generation fluids are hypertonic, containing glucose and increased concentrations of sodium. Finally, fourth-generation fluids contain glutamine (Pederson, 2013).
Given these differences, it is important to consider what the aim of the fluid therapy is and choose accordingly. It is worth noting, at this stage, that many ORT products can be mixed with either water or milk, although if milk is being restricted the energy requirements of the calf must be calculated and met. This is unlikely to be achieved using third-generation and fourth-generation preparations alone.
Pain in calves can be associated with either common husbandry procedures (for example, disbudding) or with disease or injury. Clearly preventing, rather than reducing, pain is preferable, although when unavoidable managing this is incredibly important to ensure individual calf welfare is met and performance is not hampered.
Cattle are stoic animals and, even at a young age, signs of pain can be subtle. An appreciation of the signs of pain in cattle is required – for example, dull, depressed, ears lowered, teeth grinding, less social interaction. A study of vets suggested use of NSAIDs in routine calf procedures did not match perceived pain, despite an overall increase in use of analgesics (Remnant et al, 2017). Various forms of licensed NSAIDs are available for use in calves, including injectable, transdermal and milk soluble, with preparations available to suit a variety of management systems.
Simply showing an interest in calves can help create a shift in the on-farm attitude towards calves and their performance, with some quick and simple techniques easily employable to assess performance on farm. As with all data, enthusiasm for collection must be maintained by using the data and presenting it back in a helpful manner to the farm.
Vaccination on farm, is a key tool within the veterinary armoury for prevention, as well as fighting disease, and should be considered along with other management factors when offering advice on calf health. When faced with the sick calf, a host of treatments are available, but with responsible use of medicines at the forefront of producer and vet minds, it is important to be confident with the other supportive therapies available.
