Passive Transfer Of Colostral Immunoglobulins Research Articles

Impact of prepartum administration of a vaccine against infectious calf diarrhea on nonspecific colostral immunoglobulin concentrations of dairy cows.

Passive transfer of colostral immunoglobulins from the cow to the calf is essential for calf health. The objective of this study was to determine if prepartum administration of a vaccine stimulates increased concentrations of colostral immunoglobulins of dairy cows beyond what is explained by vaccine-specific immunoglobulins. A prospective cohort study was conducted on a spring-calving commercial dairy farm that had a policy of only vaccinating cows with even ear tag numbers with a calf diarrhea vaccine, whereas cows with odd ear tag numbers were left unvaccinated. Cows in the vaccinated group (even ear tag numbers, n = 204) received a sensitizer and booster vaccination with a vaccine against bovine rotavirus (serotypes G6 and G10), bovine coronavirus, and E. coli having the K99 pili adherence factor. A sensitizer was given because the study vaccine was different from the vaccine previously used. Cows in the control group (odd ear tag numbers, n = 194) received a 2-mL subcutaneous sterile saline solution. Both groups received two treatments at a 3-wk interval, completing the treatments approximately 2 wk prior to the planned start of calving. During the calving period, technicians separated calves from cows immediately after parturition and prior to suckling, and cows were completely milked out within 6 h of parturition. Vaccine-specific, total, and nonvaccine-specific (total minus vaccine-specific) concentrations of immunoglobulin classes A, G1, G2a, and M (IgA, IgG1, IgG2a, and IgM, respectively) were quantified by mass spectrometry for 20 colostrum samples from each treatment group. Predicted mean non-vaccine-specific colostral IgM concentrations were 8.76 (95% CI = 7.18-10.67) and 5.78 (95% CI = 4.74-7.05) mg/mL for vaccinated and control cows, respectively (P = 0.005). Predicted mean non-vaccine-specific colostral IgG1 concentrations were 106.08 (95% CI = 92.07-120.08) and 95.30 (95% CI = 81.30-109.31) mg/mL among vaccinated and control cows, respectively; however, these means were not significantly different (P = 0.278). It is thus possible that the vaccine, in addition to specifically managing infectious calf diarrhea, may also have non-specific benefits by improving colostrum quality through increased non-vaccine-specific colostrum IgM concentrations. Further research is necessary to determine the mechanism for these preliminary findings, whether the effect may occur in other immunoglobulin classes, and what impacts it may have on calf health outcomes.

Comparison of Different Methods to Determine the Absorption of Colostral IgG in Newborn Foals

The timely diagnosis of abnormalities in the passive transfer of colostral immunoglobulins is important for the health and development of newborn foals. This study investigated three different methods for measuring immunoglobulin G concentration in neonatal foals. Comparison of a commercial SNAP assay, total protein concentration determination, and total globulin calculation by subtracting the albumin fraction from total protein as an indirect parameter was performed on a quantitative ELISA, which served as a reference method. The study included 119 samples from 148 foals between the age of 1 and 6 days. A blood concentration of 800 mg/dL was considered to indicate adequate absorption of immunoglobulins, and a concentration of less than 400 mg/dL was considered to be hypogammaglobulinemia. The sensitivity of the SNAP test was 64.5% and specificity was 94.7% for diagnosing sufficient absorption of immunoglobulin G at a value of 800 mg/dL. A value of 54 g/L was found to be most appropriate for the use of total protein and provided a sensitivity of 67.3% and specificity of 84.2%. For total globulins, the most appropriate value was 27 g/L, which yielded a sensitivity of 74.5% and specificity of 81.6%. At values under 400 mg/dL, the sensitivity of the SNAP test was 89.4% and the specificity was 83.0%. Here, the most suitable value for the total protein was 51 g/L. This provides a sensitivity of 65.2% and a specificity of 76.8%. The most suitable concentration for the use of total globulin was determined to be 24 g/L, which provided a sensitivity of 75.8% and a specificity of 78.1%. The study and its results show that the SNAP test, the TP, and the TP-A method perform similarly well compared to the ELISA in determining IgG concentration of ≥800 mg/dL. Based on the 95% confidence intervals, however, the Snap test and the TP-A method appear to perform similarly well but better than the TP approach for IgG concentrations <400 mg/dL.

EVALUATION OF PASSIVE TRANSFER IN NINE SPECIES OF CERVIDAE

The reliability of packed cell volumes (PCV), total solids (TS), blood glucose (BG), γ-glutamyl transferase (GGT), and glutaraldehyde test in determining passive transfer of colostral immunoglobulins was investigated in nine species of cervids: axis deer (Axis axis), hog deer (Axis porcinus), sika deer (Cervus nippon), tufted deer (Elaphodus cephalophus), Père David's deer (Elaphurus davidianus), pudu (Pudu puda), sambar deer (Rusa unicolor), barasinga deer (Rucervus duvaucelli), and Eld's deer (Rucervus eldii). Individually the parameters evaluated were significant though imperfect predictors of passive transfer status in cervids. Interpreted collectively as a panel along with neonate condition, these tests were clinically helpful in diagnosing failure of passive transfer (FPT). Collectively interpreting test results as a panel along with clinical assessment of the animal is recommended. Some species-specific variations in TS, GGT, and glutaraldehyde test results were identified.

Measurement of transfer of colostral passive immunity in dairy calves

Measurement of transfer of colostral passive immunity in dairy calves

Risk Factors Associated With Failure of Passive Transfer of Colostral Immunoglobulins in Neonatal Paso Fino Foals

A year-long prospective cohort study was conducted in Colombian Paso Fino horse farms to determine the risk factors associated with total failure of passive transfer. The risk factors associated to management, dam, foaling and foal were correlated with failure of passive transfer. Foal's IgG levels were measured using an ELISA test at 24 hours of life; a test agreement to predict failure of passive transfer between the ELISA test and total plasma proteins was evaluated. X2 test and multinomial regression were also performed.

Disease screening profiles and colostrum management practices on 16 Irish suckler beef farms.

BackgroundCalf output is a key element in determining the profitability of a suckler beef enterprise. Infectious agents such as Bovine Virus Diarrhoea (BVD) virus, colostrum management and parasitic challenge can all affect calf output. Prior to the national BVD eradication programme, there was little published information on either the prevalence or effect of BVD in Irish beef herds. There is little published information on colostrum management practices in Irish commercial beef herds and there have also been few studies published on the prevalence of liver fluke or rumen fluke infection in Irish beef herds. Sixteen farms participating in the Teagasc/Farmers Journal BETTER farm beef programme were used in this study. Fourteen herds were screened for the presence of BVD virus in 2010 using RT-PCR. In 13 herds, blood samples were collected from calves (2–14 days of age) in November 2011 - April 2012 to determine their passive immune status using the zinc sulphate turbidity (ZST) test, while in 12 herds, blood and faecal samples were taken in order to determine the level of exposure to gastrointestinal and hepatic helminths.ResultsThe overall prevalence of BVD virus-positive cattle was 0.98% (range 0 - 3% per herd, range 0.6 - 3.0% per positive herd). Eighteen of the 82 calves (22%) sampled had ZST values less than 20 units (herd mean range 17.0 – 38.5 units) indicating a failure of passive transfer. The overall animal-level (herd-level) prevalence of liver fluke and rumen fluke infection in these herds was 40.5% (100%) and 20.8% (75%), respectively.ConclusionsThe potential costs associated with the presence of animals persistently infected with BVD virus through the increased use of antibiotics; the rate of failure of passive transfer of colostral immunoglobulins and the high prevalence of liver fluke infection in these herds highlight that some Irish suckler beef farms may not be realizing their economic potential due to a range of herd health issues. The use of farm-specific herd health plans should be further encouraged on Irish suckler beef farms.

Effect of adding gut active carbohydrates to colostrum replacer on passive transfer of immunoglobulin G in Holstein dairy calves

Early feeding of a sufficient quantity of high-quality colostrum is the key to good colostrum management and obtaining sufficient passive transfer of immunity in newborn calves. Various products have been added to colostrum to evaluate their potential for improving passive transfer of colostral immunoglobulins (lg). Research findings suggest that maternal colostrum supplemented with gut-active carbohydrates (GAC) or mannan-oligosaccharides resulted in higher serum IgG concentrations in young mammals. The aim of this study was to investigate the effects of supplementing a commercial colostrum replacer (CR) with GAC on the serum IgG concentration and preweaning performance of dairy calves in a commercial farm setting.

Bovine immunoglobulin G does not have an inhibitory effect on diagnostic polymerase chain reaction utilizing magnetic bead extraction methods as demonstrated on the detection ofBovine viral diarrhea virusin dairy calves

The objective of the current study was to investigate if the presence of colostral-derived immunoglobulin G (IgG) in blood is an inhibitor of diagnostic polymerase chain reaction (PCR) for detection of Bovine viral diarrhea virus (BVDV). Eleven precolostral and 11 postcolostral blood samples in ethylenediamine tetra-acetic acid (EDTA) anticoagulant as well as serum samples were collected from 11 Holstein bull calves. Calves were fed 3 liters of colostrum once, by oroesophageal tubing. Postcolostral, blood, and serum samples were collected at 48 hr of age. Serum IgG concentrations were determined in the precolostral and postcolostral serum samples using radial immunodiffusion. The blood samples (precolostral and postcolostral) were spiked with BVDV, and 2 diagnostic PCR extraction methods were applied to each sample. The extraction and amplification efficiencies of the 2 PCR methods on the precolostral and postcolostral EDTA blood samples were evaluated. Two of the 11 calves had inadequate passive transfer of colostral immunoglobulins at 48 hr of age based on the serum IgG concentrations. All blood samples from calves were negative for BVDV prior to the spiking with the virus. Evaluation of the 2 different methods among 3 different virus concentrations demonstrated that there was no difference in extraction or amplification efficiency in precolostral and postcolostral samples. The results of this study suggest that bovine IgG is not an inhibitor of PCR used for detection of BVDV in cattle. The methods used in the current study are acceptable for PCR detection of BVDV in cattle.

Effect of colostrum administration by use of oroesophageal intubation on serum IgG concentrations in Holstein bull calves

To determine the amount of colostral IgG required for adequate passive transfer in calves administered colostrum by use of oroesophageal intubation and evaluate the impact of other factors on passive transfer of colostral immunoglobulins in calves. 120 Holstein bull calves. Calves were randomly assigned to specific treatment groups on the basis of volume of colostrum administered and age of calf at administration of colostrum. Colostrum was administered once by oroesophageal intubation. Equal numbers of calves received 1, 2, 3, or 4 L of colostrum, and equal numbers of calves received colostrum at 2, 6, 10, 14, 18, or 22 hours after birth. Serum samples were obtained from calves 48 hours after birth for IgG determination by radial immunodiffusion assay. Effects of factors affecting transfer of colostral immunoglobulins were determined by use of a stepwise multiple regression model and logistic regression models. A minimum of 153 g of colostral IgG was required for optimum colostral transfer of immunoglobulins when calves were fed 3L of colostrum at 2 hours after birth. Substantially larger IgG intakes were required by calves fed colostrum > 2 hours after birth. Feeding 100 g of colostral IgG by oroesophageal intubation was insufficient for adequate passive transfer of colostral immunoglobulins. At least 150 to 200 g of colostral IgG was required for adequate passive transfer of colostral immunoglobulins. Use of an oroesophageal tube for administration of 3 L of colostrum to calves within 2 hours after birth is recommended.

Voluntary Colostrum Intake in Holstein Heifer Calves

An observational study was done to determine voluntary colostrum intake at the first feeding in nipple bottle-fed Holstein heifer calves. Thirty-two Holstein heifer calves resulting from observed births were hand fed using a nipple bottle for a total of 15 minutes at two hours of age. Each calf was offered a maximum of 3 liters (L) total intake. Median colostral intake was 2.34 L with a range of 0.0 to 3.0 L. Ten (31.25%) calves consumed less than 2 L and 14 calves (43.75%) consumed the maximum 3 L offered. Exclusive voluntary intake using a nipple bottle is an inadequate method of colostrum administration unless more rigorous feeding practices than those described are used. Under conditions of limited labor availability, bottle-fed calves should be offered an unlimited volume of colostrum at the time of the first feeding, and tube fed using an oroesophageal feeder if they fail to ingest a minimum of 2 L in a timely manner. This practice improves the likelihood that calves will achieve consistent, adequate passive transfer of colostral immunoglobulins.

Effect of Feeding One or Two Doses of a Colostrum-Derived Commercial Colostrum Replacer on Passive Transfer of Immunoglobulin Gin Newborn Dairy Calves

Colostrum is the single most important management factor determining calf health and survival. Calves experiencing successful passive transfer of colostral immunoglobulins (serum IgG &gt; 10.0 mg/ml) have improved preweaning health and survival, improved growth rate and feed efficiency, reduced age at onset of puberty, reduced age at first calving, and improved first and second lactation milk production. Unfortunately, many producers continue to suffer significant losses related to poor colostrum management. Factors affecting the success of a colostrum management program include 1) Quality of colostrum fed, 2) quantity of colostrum fed, 3) quickness of providing the first colostrum feeding and 4) cleanliness of colostrum (i.e. bacterial contamination). Use of commercial colostrum replacement products may offer multiple advantages, including consistent quality, convenience, and cleanliness. However, it is important to evaluate the ability of commercially available colostrum replacement (CR) products to achieve successful passive transfer of immunoglobulin G (lgG) in calves managed under field conditions. The objective of this study was to describe passive transfer of lgG in newborn calves fed one or two doses ( 100 gm IgG or 200 g IgG) of a commercial colostrum-derived colostrum replacement (CR: Land O'Lakes Colostrum Replacement®, Land O'Lakes Animal Milk Products, St. Paul, MN) or 4 quarts of maternal colostrum (MC).

Screening of the T- and B-cell antigenicity in neonatal calves of the His-tagged Cryptosporidium parvum antigens CP15, CP15/60, P23 and TRAP-C1.

Cryptosporidium parvum Tyzzer, 1912 is the most commonly found enteropathogen during the first weeks of the life of calves, lambs and goat kids and is considered to be an important agent in the aetiology of the neonatal diarrhoea syndrome. Because of the limited availability of effective drugs, hygienic measures and good management are the most effective disease control measures (de Graaf D.C., Vanopdenbosch E., Ortega-Mora L.M., Abbassi H., Peeters J.E. 1999: Int. J. Parasitol. 29: 1269-1287). Immunoprophylactic control of Cryptosporidium infection is still under development and most studies focused on the passive transfer of colostral immunoglobulins from immunized dams to susceptible neonates, with sporozoite surface and microneme antigens being the target molecules of choice (de Graaf D.C., Spano F., Petry F., Sagodira S., Bonnin A. 1999: Int. J. Parasitol. 29: 1289-1306). Although the key position of CD4 T-cell dependent interferon-gamma (IFN-γ) in acquired immunity against C. parvum (Ungar B.L., Kao T.C., Burris J.A., Finkelman F.D. 1991: J. Immunol. 147: 1014-1022) and C. muris (McDonald V., Robinson H.A., Kelly J.P., Bancroft G.J. 1994: Infect. Immun. 62: 2289-2294) is well documented, the development of a T-cell vaccine to be administered to the newborns themselves has so far received only little attention. In previous papers we described the specificity of the IFN-γ response in the Cryptosporidium-infected bovine host (de Graaf D.C., Peeters J.E. 1997: Int. J. Parasitol. 27: 131-134) and the involvement of CD4 T-cells and a low molecular mass antigen preparation (de Graaf D.C., Walravens K., Godfroid J., Peeters J.E. 1998: Int. J. Parasitol. 28: 1875-1880). Further efforts to identify and purify a single parasite-derived antigen that evokes this immune response failed because of the limitations and constraints of the biochemical approach. Here we report the cloning of four known C. parvum surface or microneme antigens in a pBADTOPO-TA expression vector (Invitrogen, Carlsbad, CA, USA) and the evaluation of their Tand B-cell antigenicity in the bovine host. Cryptosporidium parvum oocysts were purified from faeces of infected calves by biphasic diethyl ether/phosphate buffered saline (PBS) extraction and differential centrifugation on Percol. Sporozoites were liberated in prewarmed excystation fluid (37°C) consisting of 0.75% (w/v in PBS) sodium taurocholate with 0.25% bovine trypsine. Cryptosporidium sporozoite DNA was prepared according to a method optimized for the preparation of genomic DNA from bacteria (Ausubel F.M., Brent R., Kingston R.E., Moore D., Seidman J.G., Smith J.A., Struhl K. 1990: Current Protocols in Molecular Biology. Greene Publishing Associates, Brooklyn). PCR primers were designed for the amplification of the complete coding region (stop codon excluded) of the known C. parvum proteins CP15, CP15/60, P23 and TRAPC1 (see Table 1). Amplification was performed in a PerkinElmer model 9600 thermocycler by 30 cycles of denaturation at 94°C for 60 s, annealing at 51°C for 60 s and extension at 72°C for 4 min, with a supplementary annealing step at 72°C for 20 min after the last cycle to ensure that all PCR products were full length and 3’ adenylated. The resulting amplicons had the expected lengths and were subsequently cloned in pBAD-TOPO-TA according to manufacturer’s instructions. Cloning was confirmed by DNA sequence analyses of the retained pBAD-CP15, pBAD-CP15/60, pBAD-P23 and pBAD-TRAP-C1 clones. Indeed, we found a perfect match

Passive Transfer of Colostral Immunoglobulins in Calves

Passive transfer of colostral immunoglobulins has long been accepted as imperative to optimal calf health. Many factors, including timing of colostrum ingestion, the method and volume of colostrum administration, the immunoglobulin concentration of the colostrum ingested, and the age of the dam have been implicated in affecting the optimization of absorption. The practice of colostrum pooling, the breed and presence of the dam, and the presence of respiratory acidosis in the calf also may affect passive transfer. Various tests have been reported to accurately measure passive transfer status in neonatal calves. The radial immunodif‐fusion and the enzyme‐linked immunosorbent assay (ELISA) are the only tests that directly measure serum IgG concentration. All other available tests including serum total solids by refractometry, sodium sulfite turbidity test, zinc sulfate turbidity test, serum γ‐glutamyl transferase activity, and whole blood glutaraldehyde gelation estimate serum IgG concentration based on concentration of total globulins or other proteins whose passive transfer is statistically associated with that of IgG. This paper presents a comprehensive review of the literature of passive transfer in calves including factors that affect passive transfer status, testing modalities, effects of failure of passive transfer on baseline mortality, consequences of failure of passive transfer, and some treatment options. Many previously accepted truisms regarding passive transfer in calves should be rejected based on the results of recent research.

Passive transfer of colostral immunoglobulins in calves.

Passive transfer of colostral immunoglobulins has long been accepted as imperative to optimal calf health. Many factors, including timing of colostrum ingestion, the method and volume of colostrum administration, the immunoglobulin concentration of the colostrum ingested, and the age of the dam have been implicated in affecting the optimization of absorption. The practice of colostrum pooling, the breed and presence of the dam, and the presence of respiratory acidosis in the calf also may affect passive transfer. Various tests have been reported to accurately measure passive transfer status in neonatal calves. The radial immunodiffusion and the enzyme-linked immunosorbent assay (ELISA) are the only tests that directly measure serum IgG concentration. All other available tests including serum total solids by refractometry, sodium sulfite turbidity test, zinc sulfate turbidity test, serum gamma-glutamyl transferase activity, and whole blood glutaraldehyde gelation estimate serum IgG concentration based on concentration of total globulins or other proteins whose passive transfer is statistically associated with that of IgG. This paper presents a comprehensive review of the literature of passive transfer in calves including factors that affect passive transfer status, testing modalities, effects of failure of passive transfer on baseline mortality, consequences of failure of passive transfer, and some treatment options. Many previously accepted truisms regarding passive transfer in calves should be rejected based on the results of recent research.

Failure of Passive Transfer in Calves

Acquisition and absorption of adequate amounts of colostral immunoglobulins are essential to the health of the newborn calf. Calves are born lacking any significant amount of circulating immunoglobulins and relyon antibodies acquired from colostrum for protection against common environmental pathogens. The major immunoglobulin in colostrum is IgG 1, but there are also significant amounts of IgG2, IgM and IgA. Considerable amounts of these immunoglobulins in ingested colostrum are transferred across the epithelium of the small intestine during the first few hours of life and transported via the lymphatic system to the blood. Immunoglobulins in the blood then enter extravascular fluids and external body secretions, depending upon the immunoglobulin class. The absorbed immunoglobulins protect against systemic invasion by microorganisms (and therefore against bacterial septicemias) during the neonatal period. In addition, both unabsorbed immunoglobulins and immunoglobulins re-secreted back into the gut play important roles in protection against intestinal infections for several weeks following birth. Good passive immunity also reduces the occurrence of respiratory disease during the first months of life and may be a determinant of improved lifetime productivity.&#x0D; Partial or complete failure of passive transfer of colostral immunoglobulins is a major determinant of susceptibility to neonatal disease and mortality in calves. Consequently, it is important that calves acquire adequate circulating concentrations of immunoglobulin from the colostral transfer process.

Partitioning the Mortality Risk Associated with Inadequate Passive Transfer of Colostral Immunoglobulins in Dairy Calves

This study developed a method to partition the risk of mortality in dairy calves in the 1st 16 weeks of life. Observed population mortality and the relative risk of mortality in each serum protein concentration stratum were used to determine the population baseline mortality rate and the mortality rate due to inadequate passive transfer of colostral immunoglobulin. A total of 3,479 calves were studied, 8.2% of which died before 16 weeks of age. The population baseline mortality rate was 5.0% and the mortality rate due to inadequate passive transfer was 3.2%. Thirty‐nine percent of the observed mortality was attributed to inadequate passive transfer. This partitioning of risk between passive transfer–related and unrelated sources should prove useful in conducting investigations of calf mortality problems in dairy herds.

Partitioning the mortality risk associated with inadequate passive transfer of colostral immunoglobulins in dairy calves.

This study developed a method to partition the risk of mortality in dairy calves in the 1st 16 weeks of life. Observed population mortality and the relative risk of mortality in each serum protein concentration stratum were used to determine the population baseline mortality rate and the mortality rate due to inadequate passive transfer of colostral immunoglobulin. A total of 3,479 calves were studied, 8.2% of which died before 16 weeks of age. The population baseline mortality rate was 5.0% and the mortality rate due to inadequate passive transfer was 3.2%. Thirty-nine percent of the observed mortality was attributed to inadequate passive transfer. This partitioning of risk between passive transfer-related and unrelated sources should prove useful in conducting investigations of calf mortality problems in dairy herds.

Calf and disease factors affecting growth in female holstein calves in Florida, USA

A prospective cohort study was undertaken to determine calf-level factors that affect performance (growth) between birth and 14 months of age in a convenience sample of approximately 3300 female Holstein calves born in 1991 on two large Florida dairy farms. Data collected on each calf at birth included farm of origin, birth date, weight, height at the pelvis, and serum total protein (a measure of colostral immunoglobulin absorption). Birth season was dichotomized into summer and winter using meteorological data collected by University of Florida Agricultural Research Stations. Data collected at approximately 6 and 14 months of age included age, weight, height at the pelvis, and height at the withers. Growth in weight and stature (height) was calculated for each growth period; growth period 1 (GP1) = birth to 6 months, and growth period 2 (GP2) = 6 to 14 months. Health data collected included date of initial treatment and number of treatments for the diseases diarrhea, omphalitis, septicemia, pneumonia and keratoconjunctivitis. After adjusting for disease occurrence, passive transfer of colostral immunoglobulins had no significant effect on body weight gain or pelvic height growth. Season of birth and occurrence of diarrhea, septicemia and respiratory disease were significant variables decreasing heifer growth (height and weight) in GP1. These variables plus farm, birth weight and exact age when ‘6 month’ data were collected explained 20% and 31% of the variation in body weight gain and pelvic height growth, respectively, in GP1. The number of days treated for pneumonia before 6 months of age significantly decreased average daily weight gain in GP2 ( P < 0.025), but did not affect stature growth. Treatment for pneumonia after 6 months of age did not significantly affect weight or height gain after age 6 months. Neither omphalitis nor keratoconjunctivitis explained variability in growth in either of the growth periods.

Incidence of failure of passive transfer of colostral immunoglobulins to neonatal foals - A field study

Incidence of failure of passive transfer of colostral immunoglobulins to neonatal foals - A field study

Avoidance of Passive Transfer Failure in Calves

Partial or complete failure of passive transfer of colostral immunoglobulins is known to be a major determinant of liability to neonatal disease and mortality in calves. When considering the causes of failure of passive transfer of colostral immunoglobulins the transfer process can be divided into three stages. These are:1. The formation of adequate volumes of high immunoglobulin concentration colostrum in the udder.2. The ingestion of an adequate mass of immunoglobulin by the calf early in life.3. The transfer of immunoglobulins across the gut into the circulation of the calf.&#x0D; Currently we have information on the causes of failure associated with deficiencies in the first two of these stages and there are management strategies that can be used to minimize failure associated with these stages. We have limited knowledge to allow successful intervention strategies associated with the third stage.