An Opportunity for Veterinary Involvement in Herd Health
By: Dr. W.Gratwick
This paper will review the implementation and monitoring of a colostrum management program. The emphasis will be on practical interventions that can be easily incorporated into existing herd visits at little extra cost. Such interventions can provide an opportunity to demonstrate the benefit of increased veterinary involvement in herd health management.
A significant proportion of dairy calves will fail to consume an adequate volume of colostrum quickly enough after birth if left to suckle from the dam (Godden 2008). In addition, colostrum from dairy cows contains approximately half the concentration of immunoglobulin G (IgG) than that from beef cows due to dilution (Guy et al., 1994) and dairy calves are often exposed to high levels of both stress and pathogens due to separation from the dam and intensive rearing. As a result, immediate separation of the calf from the dam and hand feeding of a known volume of colostrum is a recommended management practice in dairy herds (Godden 2008). A robust colostrum management plan as well as on-going monitoring of its effectiveness is required to ensure that colostrum management is optimal.
Impact of Colostrum Management on Herd Health and Production
Calves are born with virtually no circulating immunoglobulins and thus rely on the absorption of maternal antibodies from colostrum across the gut wall, also known as passive transfer. Only the milk harvested during the first milking after calving can be considered colostrum, while milk from milkings 2-6 is known as transition milk. Failure of passive transfer (FPT) is defined as a serum IgG concentration of less than 10g/l at 24-48 hours of age (Godden 2008). FPT occurs in 19.2% of dairy heifers in the USA (Beam et al., 2009). In a South African survey carried out on dairy farms in the Eastern Cape, only 10% of colostrum samples were of adequate quality (IgG > 50g/l) with many farmers failing to follow recommended colostrum management practices (Schoombee 2011). This suggests that FPT is likely to be common in South Africa. FPT has been shown to be associated with dramatic increases in both the morbidity and mortality of calves by numerous studies. A large scale survey involving over 3000 dairy calves in the USA found that calves with FPT were 3-6 times more likely to die and that increased levels of disease continued for the full 6 months period for which the calves were followed (Donovan et al., 1998). Further research has demonstrated that the benefits of improved colostrum management can extend far beyond this early phase in the life of a dairy animal. Heifers which had a serum IgG level >10g/l in the first 30-60 hours of life reached their target weight for insemination sooner than herdmates with lower IgG levels (Furman-Fratczak, Rzasa & Stefaniak 2011). Serum IgG levels were shown to be associated with the volume of colostrum ingested in this study. An increase in the volume of colostrum fed to heifer calves has also been associated with higher milk production (Faber et al., 2005). Feeding of 4 litres instead of 2 litres within the first hour of birth, with no difference in subsequent management, lead to an increased milk production of 550kg over the first two lactations.
Multiple factors have been shown to be predictors of colostrum quality, many of which will be out of the control of the farmer (Godden 2008). IgG concentration was found to be higher in colostrum from Jersey and Ayreshire cows than from Holsteins (Muller&Ellinger 1981), which may be partially due to a dilution effect as higher yields of colostrum have been associated with lower quality (Pritchett et al., 1991). Colostrum quality has also been shown to increase with the age of the dam, with heifers tending to produce colostrum with a lower concentration of IgG than multiparous animals (Godden 2008). There are also management factors which have an impact on colostrum quality. Shortening the dry period from 60 to 40 days has no effect on colostrum quality (Shoshani, Rozen & Doekes 2014) but further reduction to < 21 days or completely omitting the dry period has been associated with significantly lower concentrations of Ig (Verweij, Koets & Eisenberg 2014). Vaccination of cows during pregnancy has been shown to increase the concentration of specific antibodies to certain pathogens and can be beneficial to calf health providing management is otherwise of a good standard (Meganck et al. 2015). Colostrum quality deteriorates rapidly after calving due to dilution (Pritchett et al. 1991). As such, it should be harvested as soon as possible after birth and no later than 6 hours.
Measurement of Colostrum Quality
Measurement of the quality of colostrum from each cow is highly beneficial and can be carried out as part of a colostrum management program. Measurement of the specific gravity or total solids of colostrum provides a useful estimate of the IgG concentration, but will also be affected by the fat content of the sample. A colostrometer is an inexpensive instrument which measures specific gravity and can be used to differentiate high quality from low quality colostrum. However, the sensitivity for detecting colostrum with an IgG concentration of <50g/l is only 0.32 (Pritchett et al., 1991). This can be improved by altering the cut-off point of the instrument but this will lead to a reduction in the test specificity and the classification of adequate colostrum as inadequate. A further disadvantage of the colostrometer is that the results are affected by the temperature of the sample. As such, it is necessary to cool approximately 0.5l of colostrum to room temperature before use. The instrument is also fragile and easily broken. An alternative is to measure the total solids of the sample using a refractometer. An inexpensive Brix refractometer designed for use in the food/beverage industry to measure the sugar content of fluids can be used to measure the total solids of a few drops of colostrum with very little effect of temperature (Quigley et al., 2013). A cut-off of 21% Brix to define high and low quality colostrum had a sensitivity and specificity of 93% and 66% respectively. An alternative is a digital handheld refractometer which is even more accurate and easy to use. Colostrum of insufficient quality can be treated as transition milk.
Factors Effecting Passive Transfer
Irrespective of the quality of colostrum fed, there are many calf, management and environmental factors which can have an influence of the success of passive transfer. Multiple studies have looked at the effect of different volumes of colostrum. 100g of IgG is required for successful passive transfer in a typical 40kg Holstein calf (Godden 2008). In theory, this would be provided by 2 litres of good quality colostrum (>50g/l IgG). However, due to variability in both the absorption and quality of colostrum it is beneficial to feed a larger volume. This has been demonstrated by measurement of both the serum IgG of the calves (Morin, McCoy & Hurley 1997) and their subsequent growth and lactation performance (Faber et al., 2005). Increasing the volume as high as 10% of calf body weight has been shown to cause decreased absorption of IgG and results in lower calf serum IgG levels (Conneely et al., 2014). In addition, absorption of colostrum across the intestinal epithelium of the calf declines rapidly after parturition, ceasing almost completely within 24 hours (Besser et al., 1985). As such, the current best recommendation is that 8.5% of body weight of colostrum is fed as soon as possible, by 6 hours after birth at the latest. This equates to 3.4l for a 40kg calf. A further 5-7% of body weight of colostrum should be fed at 12 hours followed by transition milk twice daily until at least 3 days of age. As well as the timing and volume of colostrum feeding, the correct methods of collection, handling and storage are essential to ensure that successful passive transfer takes place (McGuirk&Collins 2004). The efficiency of absorption of Ig is significantly reduced by the presence of bacteria in colostrum due to binding of the free Ig in the gut lumen as well as interference with the transport of Ig molecules across the intestinal epithelium (Godden 2008). For this reason, in addition to the obvious risk of exposure to potential infectious agents such as coliforms and Salmonella spp, it is recommended that colostrum should not be fed with a total bacteria count (TBC) of >100,000 cfu/ml or a total coliform count (TCC) of >10,000 cfu/ml. Samples of colostrum can be routinely collected immediately before feeding, frozen and submitted to a laboratory to determine TBC and TCC as part of the monitoring of the colostrum program. In order to prevent bacterial contamination of colostrum high standards of hygiene should be employed during its collection. Similar practices should be employed as during routine milking, such as proper teat preparation, as well as sanitisation of the collection vessel and feeding equipment. Ideally, colostrum should be collected from the cow and fed directly to her own calf as long as the quality is sufficient.
Storage of Colostrum
When excess good quality colostrum is available from a particular cow it can be stored in aliquots of 2l and labelled with the cow number and date of collection, for feeding to calves whose dams produced colostrum of insufficient quality or quantity. Collection should not be carried out from cows which are known to be carriers of infectious diseases or which are affected by mastitis. Colostrum should be refrigerated within 1 hour of collection. Bacterial counts in refrigerated colostrum will reach unacceptable levels after 2 days. Storage can be extended to up to 6 days by adding potassium sorbate to make a 0.5% solution (Stewart et al. 2005). Alternatively, colostrum can be frozen for up to one year as long as multiple freeze-thaw cycles do not occur as with a ‘frost free’ freezer (Godden 2008). Thawing can be carried out using warm water or slowly in a microwave. Exposure to temperatures over 60˚C will lead to denaturation of Ig. Pooling of colostrum should be avoided due to the risk of increased spread of pathogens, such as bovine leukaemia virus, Salmonella spp. and Mycobacterium avium subsp. paratuberculosis.
Monitoring Passive Transfer on Farm
Various laboratory tests are available to measure serum IgG concentrations in calves in order to monitor the success of passive transfer. Although accurate, these tests are expensive and require the submission of samples to a laboratory, limiting their usefulness for routine monitoring purposes. Assessment of either the total serum protein (TSP) or Brix % using a hand held refractometer provides a useful estimate of the serum IgG concentration, using a cut-off of 55g/l for TSP (McGuirk&Collins 2004) or 8.4% Brix (Deelen et al., 2014). This test is accurate enough for herd-level monitoring of FPT. The test is quick and easy to perform on farm using equipment already available to veterinarians and can be carried out on uncentrifuged serum samples which have been allowed to separate. Calves should be tested between 24 hours and 5 days of age as significant amounts of endogenous IgG will be present in older calves (Godden 2008) and dehydrated calves should not be tested. Regular sampling of calves can be included in routine farm visits and the results monitored on an on-going basis. If >20% of calves are below the relevant cut-off then a problem with FPT is likely to be present and a review of colostrum management practices is warranted (McGuirk&Collins 2004).
Following the diagnosis of FPT in a herd, the implementation of a successful colostrum management program will be of significant and obvious economic benefit to the dairy farmer.
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