Management to Ensure Adequate Passive Transfer

The effectiveness of passive transfer achieved at a farm level reflects farm management. Best practice colostrum management strategies for dairy and beef calves are presented in Box 19.1 and 19.2.

ENSURING OPTIMAL IMMUNOGLOBULIN CONCENTRATION

Colostrum Collection, Handling, and Storage. Colos­trum collection should occur as close to parturition as possible. Fresh cows should be removed from the calving area and milked out at least twice daily to help ensure optimal colostrum quality. Colostrum collected from cows that have leaked milk prior to calving, have signs of ill health, or have evidence of mastitis should not be fed to neonatal calves.

Colostrum quality is compromised in cows that have leaked milk prior to calving.^87,88 The colostrum from cows exhibiting signs of ill health or mastitis will have increased potential for the presence of infectious pathogens, such as Mycobacterium avium subsp. paratuberculosis, Salmonella spp., Mycoplasma bovis, Staphylococcus aureus, bovine diarrhea virus, and bovine leukemia virus.^161-163 Neonatal enteric pathogens such as cryptosporidium may also be present.^164,165 Consequently, unpasteurized colostrum is a potential risk factor for calf diarrhea and neonatal septi­cemia.^166,167 Unpasteurized colostrum is also a biosecurity risk,

■ BOX 19.1

Best Practice Colostrum Management for Dairy Calves

• Milk cows as soon as possible after calving. Immunoglobulin G (IgG) concentration declines by 3.7% for each hour after calving.

• Remove calves from the calving area at least twice daily.

• Measure quality of colostrum (Brix refractometer). This will determine the quantity of colostrum to be fed. For the first feed, administer colostrum containing 150 g IgG within 4 hours of calving. Feed a maximum of 7.5% of body weight. If calf does not suckle the full amount, top with esophageal feeder.

• Feed an additional 5% to 7.5% of body weight by 12 hours of age. If the calf did not receive 150 g of colostrum in the first feed, it is preferable to supplement 7.5% of body weight at the second feed.

• On farms with a history of Johne's disease, salmonella, mycoplasma, or leukosis, pasteurize colostrum.

• Avoid pooling colostrum where possible. If pooling of colostrum is unavoidable, mix colostrums of similar quality.

• Implement a monitoring program for failure of passive transfer.

■ BOX 19.2

Best Practice Colostrum Management for Beef Calves

• Avoid severe restriction of dietary intake prior to calving; this will reduce volume and make colostrum more difficult to suckle.

• Minimize disruption of calving cows.

• Ensure that calves receive colostrum within 6 hours of calving (active suckling); intervene when there is dystocia or dumb calf.

• Intervention may involve restraining the dam and encouraging suckling or administering colostrum by a nipple bottle. An esophageal feeder should be used only when volumes greater than 1.5 L are available or if the calf will not suck. and the use of colostrum from cows from a different property is not recommended. Pooling of colostrum significantly increases the biosecurity risk, as organisms are disseminated, subsequently infecting a larger number of calves.^167-169 This is exacerbated further if storage is poor, resulting in pathogen prolifera- tion.^166,170 Colostrum with high bacterial levels not only present a significant disease risk, but also affect absorption of IgG by direct blocking of uptake and transport of immunoglobulin molecules across intestinal epithelial cells or by binding free immunoglobulin in the gut lumen.^48,171 Pooling of colostrum will also result in reduced IgG concentrations due to the overrepresentation of high-volume, low-immunoglobulin colostrum and consequently is associated with an increased level of FPT.^44,89 When pooling is necessary for pasteurization, the colostral IgG should be estimated using a Brix refractometer and low-quality colostrum of less than 22% Brix excluded.

Microbial contamination of colostrum compromises colostral quality and subsequently calf health. Bacterial contamination may occur during harvest, storage, or administration.^{161,166,170,173} Possible sources of contamination include cow skin, milking cup liners, hoses, milking buckets, and storage and feeding utensils. Contamination of colostrum with pathogens during harvest can be avoided by careful and hygienic teat preparation in fresh cows prior to applying cups.¹⁶¹ This may involve washing and drying teats and applying a pre-milking teat disinfec­tant.^174,175 Thorough and effective cleaning and disinfection of collection, storage, and feeding equipment is essential. It is important that separate, clearly marked esophageal feeders are used for feeding colostrum and are not used with sick calves, as this may also be a significant disease risk. Milk feeding equipment should not have cracks or scratches that allow for buildup of bacteria. Equipment should be rinsed in lukewarm water and then actively scrubbed in water hotter than 50^o C (122^o F) containing either detergent and bleach (6% sodium hypochlorite) or dry chlorinated detergent to remove any residue. Bottle brushes should be used to clean esophageal feeders, nipples, and feeding bottles. Finally, they should be rinsed in water containing acid or an acid rinse and allowed to dry completely before stacking them upside down for storage.

When there is concern about hygiene practices, plating 10 μL of colostrum onto a blood plate and incubating at 37^o C overnight provides a simple crude assessment of microbial contamination of colostrum being fed to calves and allows identification of the origin of any process failure. Fresh colostrum fed to calves should have a total bacteria count of less than 100,000 colony-forming units/mL and less than 10,000 coliforms/mL.^161,167

Short-term storage of colostrum is necessary in order to deliver known good-quality colostrum to neonatal calves within hours of birth to reduce the risk of failure of passive transfer.

Heat treatment of colostrum is an effective way to control colostrum bacterial load, reducing the risk of infectious disease transmission from cow to calf.¹⁷⁷ Degradation of immunoglobu­lins may be a problem with large-batch colostrum pasteurizers. Calves fed large-batch pasteurized colostrum have significantly lower serum IgG levels than those fed unpasteurized colostrum.⁴⁸ However, pasteurization of small batches of colostrum (57 L) at 67^o C (152.6^o F) or lower for 30 minutes caused a minimal decrease in the immunoglobulin concentration of colostrum compared to pasteurization of large batches (95 L) or batches at higher temperatures (76^o C [168.8^o F] for 15 seconds) and had little effect on the subsequent serum immunoglobulin in calves at 24 hours of age.^178,179 At this temperature M. avium subsp. paratuberculosis may survive.^180,181 Heat treatment of colostrum (at 60^o C [140^o F] for 60 minutes) at a commercial level has been shown to effectively reduce colostrum microbial counts while maintaining IgG concentration.¹⁸² Calves fed such colostrum were also found have reduced morbidity.¹⁸³ This critical temperature and time period appears to significantly reduce the bacterial load while not denaturing the IgG or changing the viscosity of colostrum.¹⁸⁴ Calves fed heat-treated colostrum (in either single aliquots or batch treatment) had significantly improved apparent efficiency of absorption and serum IgG compared to calves fed fresh frozen or fresh refriger­ated colostrum (Kryzer, 2015').^172,184a

The use of ultraviolet (UV) light to reduce the pathogen load of colostrum has been described.

Longer term preservation of colostrum can be achieved by freezing or lyophilization without change in the immunoglobulin and nutritional content.^189-191 However, the cellular content of colostrum is destroyed by freezing, which may have longer term effects on the development of the immune system.¹⁹² In kids the feeding of lyophilized colostrum resulted in higher IgG levels than the feeding of frozen colostrum.¹⁹³ The freeze­thaw cycle is associated with an 8% to 30% loss in IgG1, with the magnitude of the loss dependent on the method of thawing. Thawing at 40^o, 50^o, 60^o, and 70^o C is associated with losses of 8%, 14%, 15%, and 26%, respectively. Thawing in a microwave at 200 and 350 watts causes losses of 20% and 31%, respectively.¹⁹⁴ Thawing larger volumes in a microwave may result in uneven heating and clots and is generally not recommended.¹³⁴ The speed of thawing colostrum can be facilitated by freezing 1- to 4-L aliquots in flat plastic bags or purpose-designed equivalents. Thawing in a rocking heated water bath at 40^o C (104^o F) is recommended; alternatively colostrum may be thawed at room temperature or in a fridge.

Monitoring Colostrum Immunoglobulin Quality. The quality of colostrum has traditionally been measured by visual inspection or by using a colostrometer (a hydrometer). The level of IgG in colostrum cannot be accurately predicted based 88195

on its appearance,^88,195 hence the need for more objective instruments.

Cow-side immunoassay kits for measuring colostral IgG are available and have been shown to have an acceptable sensitiv­ity and specificity for this purpose.²⁰¹ However, their lack of availability on a global scale, along with financial constraints, limit their use.

Optical and digital Brix refractometers can be used to measure the quality of colostrum using fresh and frozen samples.²⁰² For colostrum from Holstein cows, the optical Brix refractometer demonstrated a specificity of 85% and a sensitivity of 90.5% using a cutoff of 22% Brix. A cutoff of 22% Brix was deemed to equate to 50 g/L of immunoglobulin using radial immunodiffusion (RID), thus samples greater than 22% Brix were considered to be of adequate quality.²⁰² In another study the results showed that a cut-point of 21% was estimated in samples greater than 50 g/L, as measured by RID.⁷² Breed influences colostrum Brix readings. The cut point for 50 g/L for Jersey colostrum is lower with a Brix of 18% providing a sensitivity of 92.3% and a specificity of 94.7%.²⁰³

The benefits of the Brix refractometer are that they are not affected by ambient temperature and they are robust, easy, and economical to use at an on-farm level.¹⁹⁸ It has been found that high-quality colostrum samples can yield a “fuzziness” through the viewfinder of a Brix refractometer. Generally this happens in samples greater than 22%. A smaller sample size on the prism can help with clarity in these high-quality samples. The poorer the quality of colostrum, the clearer the value is to read.

Brix refractometers are inexpensive, easily available, and robust, and as such should be standard dairy farm equipment. Farmers are advised to purchase a refractometer that only measure degrees Brix with a scale from 0% to 32%, so that they are easy to read. To get an accurate reading it is necessary to press the cover plate firmly over the prism while looking through the viewfinder, as some thick samples will cause the cover plate to lift off the prism. It is also important that each sample is placed on a clean, dry prism.

Ine Role of Vaccines in Colostrogenesis. A potential approach to achieving an increased level ofprotective immunity in neonatal calves is by vaccination of the dam during the period of colostrogenesis. This practice has frequently been adopted to aid in the control of diarrhea-causing pathogens 204209 such as E. colι, rotavirus, coronavirus, and Salmonella. Calves fed colostrum from vaccinated cows have shown increased serum IgG and reduced morbidity and mortality compared to calves fed colostrum from unvaccinated dams.²⁰⁶ Herd-level vaccination has led to an increase in the colostrum quality observed as determined by Brix refractometry.²¹⁰ The timing of vaccine administration during the dry period is critical, as an increase in dam serum IgG in response to vaccination must coincide with colostrum production in the udder tissue.²¹¹ If a vaccine is administered too close to parturition, there is an inadequate period for a peak IgG response and subsequent transfer of IgG into colostrum. If a vaccine is administered too far away from expected parturition, peak IgG response will not coincide with colostrogenesis. No one generic vaccina­tion protocol fits all vaccines, so the manufacturer’s directions should be followed. Producers should be reminded that the usefulness of vaccines depends on active colostrum feeding and delivery of an adequate mass of IgG to the calf in a timely manner after birth.

Enhancing IgG Uptake. Numerous attempts have been made to artificially augment passive transfer by adding sub­stances to colostrum that aim to increase efficiency of absorption or provide an increased concentration of immunoglobulins. Addition of dried colostrum powder,^110,212 casein, or concentrated whey protein^213,214 had either no benefit or a detrimental effect on colostrum absorption. Feeding colostrum containing 1000 IU vitamin E to calves does not influence uptake of IgG by the calves but did result in higher levels of vitamin E in the calf plasma.²¹⁵ Similarly, the addition of 30 g sodium bicarbonate to colostrum had no effect on uptake.²¹⁶ However some studies have demonstrated positive benefit. The addition of spray-dried bovine serum to lower quality colostrum to provide the equivalent level of IgG as found in a high-quality colostrum resulted in a higher level of IgG at 12 and 24 hours of age.²¹⁷

The addition of 5 g/L of a mineral adsorbent zeolite (clinoptilolite) up to a total of 0.5 g/kg/day has been shown to increase rate of absorption of colostrum in the first 16 hours and in some cases to increase serum IgG at 24 and 48 hours, especially where lower colostrum volumes were fed.^218-220 The exact reason for this has not been explained, but it is thought that clinoptilolite may bind some degradation products of colostral proteins, such as ammonia, in the gut, thus preventing their negative effects on mucosal epithelial cells designated for immunoglobulin absorption. It may also slow the passage rate of digesta through the intestine, allowing increased time for absorption. The addition of 1 and 2 g/kg/day of clinoptilolite has a negative effect on serum IgG concentration at 24 and 48 hours, but when colostrum from cows vaccinated against K99 and F41 antigens of E. coli was fed, calves fed 1 and 2 g/ kg/day had increased blood serum levels of specific antibodies against E. coli at 12, 24, and 48 hours.^221,222 In all of these studies very high-quality colostrum (80 to 100 g/L) was fed, and no more than 2 L was fed at any one feeding and often 0.75 L was fed to a 35-kg calf. The benefits of clinoptilolite when larger volumes of lower quality colostrum are fed have not been evaluated. When clinoptilolite is added to milk replacer as well as colostrum, an added benefit of increased hematopoiesis is seen, presumably as this mineral is high in iron.^222,223

The addition of gut-active carbohydrate (mannan­oligosaccharide) to colostrum has been shown to affect IgG uptake with variable results.^224-226 Again, the mechanisms responsible for this effect have yet to be elucidated. Bacteria in colostrum may directly block uptake and transport of immunoglobulin molecules across intestinal epithelial cells or bind free immunoglobulin in the gut lumen.^48,171 Gut­active carbohydrates have been shown to adsorb pathogens expressing type 1 fimbriae, reducing their ability to colonize the gastrointestinal tract.²²⁷ Thus there is a potential role for gut-active carbohydrates to play in the uptake of IgG from the gastrointestinal tract. However, it is still unclear as to whether the addition of gut-active carbohydrates to colostrum enhances or reduces IgG absorption.²²⁴

These studies demonstrate that it is possible to influence uptake of IgG with specific additives and that further research is required to investigate their potential while accommodating the variation in colostrum IgG concentration and standard management practices within herds.

MONITORING FOR SUCCESSFUL PASSIVE TRANSFER

Calves. Monitoring programs for FPT are an integral step in neonatal calf disease outbreaks and proactive calf health programs. A range of tests have been used to assess passive transfer.^228-230 The RID assay is considered the reference method and is a direct measure of serum IgG. However, its usefulness is compromised by the processing time and expense. There is some variation in the published research as to the level of serum IgG that indicates adequate passive transfer, but most researchers use 10 mg/mL (1000 mg/dL).^{149,228,231,232}

Precipitation Tests. The sodium sulfite and zinc sulfate turbid­ity tests use salts to precipitate serum proteins, in particular the larger molecular weight immunoglobulins. A measured amount of calf serum is added to a standard volume of solution and incubated at room temperature for up to 30 minutes. The test results are quantified according to the degree of cloudiness of the mixture caused by protein precipitation. The sodium sulfite turbidity test has traditionally been described as a three-step semiquantitative test using 14%, 16%, and 18% solutions. The sensitivity, specificity, and degree of association with IgG are similar to measuring serum protein with a refractometer, but the test is more complicated to perform.²²⁸ The sensitivity has been estimated as 85% to 100% and the specificity as 53% to 87% using an 18% solution (1+ end point).^228,232 The zinc sulfate turbidity test can be influenced by hemolysis, making it difficult for routine use.⁸⁹ The standard test is carried out by adding 0.1 mL of calf serum to 6 mL of 208 mg/L zinc sulfate and incubating the mixture for 1 hour at 23^o C (73.4^o F). The test has a sensitivity of 100% and a specificity of 55%, which is lower than serum protein or sodium sulfite turbidity.²²⁸ The specificity of the test can be improved by increasing the strength of the solution to 300 or 350 mg/L.²³³ These solutions resulted in an increase of the specificity to 65% and 76%, respectively, with little decrease in sensitivity.

Recently, ammonium sulfate (immunocrit), previously developed for piglets,²³⁴ was evaluated in dairy calves.²³⁵ The reported advantage of the use of ammonium sulfate is that it only precipitates immunoglobulins and is non-species specific. The test is performed by mixing an equal volume of 55% ammonium sulfate and serum to be tested, followed by collecting the mixture in a microhematocrit capillary tube, and then centrifuging. The capillary tubes are then removed from the centrifuge, and immunocrit values are read with a microhe­matocrit reader card from the top of the capillary tube sealant to the intersection between the precipitated IgG and the remaining serum. Immunocrit values of 11% or greater indicate

^.

235 adequate transfer of immunity.²³⁵

Enzymatic Activity. Measurement of serum gamma­glutamyltransferase (GGT) in calves aged 24 hours can indicate positive ingestion of colostrum but has poor correlation with actual serum IgG levels.²³⁶ A limitation of this test is that serum GGT declines rapidly during the first week of life.²³⁷ Thus accurate records reflecting the age of the calf are vital for this test to be interpreted accurately. Both colostrum and milk contain GGT, but activities in milk are considerably lower than in colostrum.²³⁸ GGT rises quickly after the ingestion of colostrum and then falls rapidly over the subsequent 24 hours, followed by a slow decline for the next 2 months. Calves that do not ingest colostrum have serum GGT activities similar to adult cattle. GGT is a useful test when assessing the passive transfer status of clinically ill calves younger than 21 days of age where disease confounds interpretation of serum proteins; a GGT cutoff of 50 IU/L classifies 93% of calves correctly (sensitivity 93%, specificity 92%).²³⁹

Immunoassay. The on-farm lateral flow immunoassay is 11Γ '1 'C ' 1 '11 1 i r∖ t τ

one method for identifying calves with less than 10 mg/mL serum IgG. It takes approximately 20 minutes to perform and is relatively inexpensive, but it is not commercially available worldwide. The test yields only a positive or negative result as opposed to the actual level of serum IgG. This is considered a limitation of the test.⁴⁸ Published results show that sensitivity ranges from 93% to 99% and specificity from 88% to 89%.²³²,²⁴⁰

Refractometry. An optical handheld clinical refractometer may be used to measure serum protein of calves between 24 hours and 7 days of age. Although it is not a direct measurement of IgG concentration, it is considered an accurate indicator of the

■ TABLE 19.3

Relationship Between Serum Protein and Serum IgG^a (R² = 0.76)¹⁷⁵

^aIt should be recognized that there is variation among refractometers.³²⁶

IgG, Immunoglobulin G.

immunoglobulin status of the animal (Table 19.3).²⁴¹ Studies have compared refractometry to turbidity testing and GGT activity and have shown that it is equivalent or superior to these assays in the proportion of calves classified correctly.^{25,228,236,237} This method is easier to standardize between laboratories and operators than many other indirect methods and is cheaper, quicker, and easier than most direct tests for IgG.²⁵ A minimum of 12 calves need to be sampled; when interpreted on a group level, this method provides a good correlation between serum protein and serum IgG, as measured by RID.⁴⁸ Sick (scouring) calves should not be included in the sample set, as dehydration will falsely elevate the serum protein. It has been suggested that the accuracy of serum protein could be improved if packed cell volume (PCV) is also measured as a proxy for hydration status.²³⁹ The benefits of this method are that it is quick and inexpensive and samples do not need centrifugation.²⁴² This has an added advantage, as this method can be implemented at the farm level on large calf-rearing units to monitor for FPT in groups of calves. A serum protein concentration less than 5.0 g/dL reflects FPT, between 5.0 and 5.5 g/dL reflects marginal passive transfer, and greater than 5.5 g/dL reflects adequate passive transfer. At a herd level the target should be for 80% of calves to have serum protein concentrations greater than 5.5 g/dL. More recently it has been suggested that a serum total protein of 5.8 to 6.3 g/dL should be used to indicate adequate transfer of immunity in dairy calves.¹⁴⁷ Assessment of serum protein using a refractometer is not a reliable estimate of IgG levels in calves that have received colostrum substitutes or replacers.²⁴³ Using the same methodology, a Brix refractometer can also be used to indirectly assess passive transfer using serum protein. A cut-point of 8.3% Brix can be used to estimate FPT (serum IgG and will depend on other components of the epidemiologic triad (agent and environmental factors). Algorithms for predicting passive transfer status of various ages using GGT have been developed in lambs.^245,246 In summary, serum GGT activity and serum protein determination by biuret method are currently the most widely used tests for assessing immunity in lambs. Although determination of serum protein concentration by refractometry is cheaper and practical and test results are readily available, it is likely to misclassify FPT status compared to the other methods.²⁴⁷

Goat Kids. FPT in goat kids is defined as serum IgG concentrations less than 1200 mg/dL.²⁵¹ Practical tests reported as useful in assessing passive transfer status include the 18% sodium sulfite test and serum total protein by refractometry.²⁵¹ Serum total protein concentrations of 5.4 g/dL or higher were considered indicative of adequate passive transfer of immunity.²⁵¹

MANAGEMENT OF FPT. Calves may be managed for FPT by the administration of bovine plasma at a dosage of 20 to 40 mL/kg. The initial rate of administration should be 5 mL/kg/h with close observation for adverse effects, which most commonly include trembling, hives, edema, piloerec- tion, stertorous breathing, and increases in heart rate and respiratory rate. If no adverse effects are noted in the first 30 minutes, the rate can be increased to 10 to 20 mL/kg/h with continued monitoring.²⁵² Whole blood also can be used, but the dosage should be increased to account for the presence of red blood cells.⁸⁹ Calves should be monitored as for plasma transfusions; adverse reactions are very uncommon with first­time transfusions, as there are a large number of blood types in cattle. Plasma or whole blood may also be administered via the intraperitoneal route. An area in the center of the left paralumbar fossa is clipped and surgically prepared. A 14- to 16-gauge, 1.5-inch needle is used to penetrate the skin, abdominal musculature, and peritoneum, and the serum is administered through a giving set.⁸⁹ The benefits of plasma administration in healthy or sick calves with FPT has been questioned. Plasma administrations to healthy calves attained serum IgG concentrations greater than 1000 mg/dL, but the decay of transfused plasma was significant such that by 12 hours post transfusion, the serum IgG concentrations were less than 1000 mg/dL.²⁵³ The half-life of transfused IgG was 4.4 days compared to 17.1 days for colostral-derived IgG.²⁵³ In addition, calves with FPT transfused with plasma were five times more likely to experience mortality compared to calves with adequate passive transfer of immunity.²⁵³ This increased rate of decay of plasma-derived IgG may necessitate repeat plasma transfusions, which might predispose calves to transfusion reac­tions. In another study plasma transfusion had no effect on oxidative and phagocytic activity of neutrophils of calves with FPT.²⁵⁴ Due to high costs associated with plasma transfusions, the procedure should be considered on a case-by-case basis.

Precautions should also be taken to minimize risk factors for infection in calves with FPT, including minimizing potential exposure to pathogens. Colostrum may be fed beyond the period of closure to provide protection at the level of the gut lumen. Where the environment is less than desirable, the prophylactic administration of broad-spectrum parenteral antimicrobials in calves with FPT should be considered.

Navel Treatment associated with bacteremia.²⁵⁷ Prevention of navel ill is based on maintenance of maternity pen hygiene, reducing the resi­dency time of calves in unhygienic maternity pens, ensuring adequate early intake of good-quality colostrum, and navel antisepsis.²⁵8 Literature on the efficacy of navel treatment in reducing calf mortality is divided. In a study of 104 dairy farms, a farm policy of navel treating newborn calves had no significant effect on calf mortality rates. Similarly, spraying the navels of lambs with iodine spray or applying clamps to the navels failed to change the incidence of joint ill in lambs compared to no treatment.²⁵⁹

A significant beneficial effect was observed when the navels of calves that had assisted deliveries were dipped with chlorhexi- dine; other navel treatments such as iodine tended to be associated with increased odds of dying.²⁶⁰ Chlorhexidine has a wide antimicrobial spectrum, long duration of activity, and high efficacy in the presence of organic matter.²⁶¹ In a controlled clinical trial investigating the efficacy of navel dips, a reduction in the incidence of omphalophlebitis was observed in calves when navels were dipped with tincture of iodine (7% iodine), dilute iodine (0.5% or 0.2%), or a commercial product (Navel Guard [NG], Sirius Chemical Group, McDonough, Ga.) as compared to calves with nondipped navels.²⁵⁵ Conversely, navel treatment with iodine was associated with significantly higher mortality in another study of 48 farms; however, the association of navel treatment with mortality on these farms may have reflected the response of producers to high neonatal mortality rather than indicated that iodine navel treatment is a risk factor for high calf mortality.²⁶²

It is interesting to note that navel treatment has been associated with both a reduced²⁶³ and an increased²⁶⁴ risk of respiratory disease. The bases of these associations are unclear.