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Immunoglobulin G Concentrations in Temporal Fractions of First Milking Colostrum in Dairy Cows
Douglas Hostetler, DVM, MS*
Vicki L. Douglas, DVM, PhD†
Jeff Tyler, DVM, PhD†
Julie Holle, LVT†
Barry Steevens, PhD‡
*Department of Veterinary Pathobiology, Mississippi State University
†Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, Missouri
‡Department of Animal Science, University of Missouri, Columbia, Missouri
KEY WORDS: colostrum, IgG, cattle,
The objective of the described research was to compare the immunoglobulin G (IgG) concentration of colostrum fractions collected throughout the first milking after calving in dairy cows. Composite colostrum samples (25 mL) were obtained at the initiation of the first milking from a bucket collected during the first milking and at the end of the first milking from 23 dairy cows. Colostral IgG concentrations were determined by radial immunodiffusion. Colostral IgG concentrations for premilking, bucket, and postmilking colostrum were 86, 81, and 67 g/L, respectively. The premilking and bucket colostrum fraction IgG concentrations were significantly (P <.05) greater than those of postmilking fractions. Premilking and bucket colostrum IgG concentrations did not differ significantly. Because the IgG concentration is significantly higher in the initial temporal fractions of colostrum collected and significantly lower in the last fraction of colostrum collected, the volume of colostrum needed to meet IgG intake goals might be decreased if only the first fraction is collected. It should be noted that an adequate mass of colostral IgG probably would be provided by postmilking colostrums if recommended volumes (4 L) were fed.
The ingestion and absorption of colostral immunoglobulins is critical for the health and survival of neonatal calves.1 Inadequate passive transfer of maternal antibodies dramatically increases the risk of mortality.1–7 Unfortunately, inadequate passive transfer is common in dairy calves. In one recent study, approximately 35% of 3479 dairy replacement heifers had inadequate passive transfer.1 Recognition that dairy cows produce large volumes of colostrum with a low concentration of immunoglobulin G (IgG) has led to more aggressive colostrum administration strategies.8 One source has suggested that dairy calves should receive 4 L of colostrum using an oroesophageal feeder within the first 12 hours of life to ensure a goal intake of 100 g of IgG.9 However, this practice is not widespread and many clients resist implementation of the procedure.
Methods, including specific gravity determination, have been proposed as strategies to screen colostrums for adequate IgG concentration. Unfortunately, the distribution of specific gravities for high and low IgG concentrations overlap greatly.10 Consequently, this procedure is probably not suitable for farm use. Pritchett et al. observed that larger-volume first-milking colostrums had significantly lower IgG concentrations and advocated that large-volume colostrums should be presumptively classified as having low IgG concentrations and, therefore, discarded.10
It has been demonstrated that the immunoglobulin concentration of colostrums decreases rapidly after parturition. By the fourth milking postpartum, the immunoglobulin of colostrums is equivalent to milk. Consequently, recommendations for colostrum administration to calves emphasize the administration of first-milking colostrums.4,6,11,12
The purpose of this study was to compare the concentration of colostral IgG at different times during the first milking. If the IgG concentration of the initial fraction of colostrum is greater than subsequent fractions, then collecting only the volume that will be fed to the calf will decrease the total volume required for adequate passive transfer. Although one previous study attempted to determine compositional changes, including colostral IgG concentrations, occurring during the course of the first milking, the study included only 12 cows. Consequently, that study probably lacked power, and the absence of statistically significant differences is not surprising.13
MATERIALS AND METHODS
Colostrum Sample Collection
Colostrum samples were collected from 23 dairy cows housed on the University of Missouri, Foremost Dairy. Samples were collected from 5 Guernsey and 18 Holstein cows. Only cows in which parturition was directly observed were included in the study. Calves were immediately separated from their dam and hand-reared. Three separate colostrum samples were collected from each enrolled cow within 4 hours of observed parturition. Initially, 10 mL of colostrum was collected from each functional quarter by hand-milking into a 50-mL conical tube. This composite sample was defined as the premilking colostrum sample. Thereafter, each cow was mechanically milked using a portable bucket milking machine. A 40-mL aliquot of colostrum was collected from the bucket. This sample was defined as the bucket colostrum sample. After mechanical milking, a third colostrum sample was collected by hand-milking 10 mL of colostrum from each functional quarter into a 50-mL conical tube. This final sample was defined as the postmilking colostrum sample.
Colostrum IgG Determination
Colostral IgG concentrations were measured using a previously reported procedure.12 Briefly, IgG concentrations were determined using radial immunodiffusion (RID). RID plates measuring colostral IgG were prepared by dissolving 1% agarose (Sigma Chemical Co., St. Louis, MO) in a sodium barbital buffer (Sigma Chemical Co.) containing 0.1% sodium azide (Sigma Chemical Co.). Rabbit–antibovine IgG (Organon Technika Corp., West Chester, PA) (1%) was added to the thawed agarose solution. Eleven milliliters of the agarose solution was added to 10-cm Petri dishes. After the agarose solidified, 3-mm wells were cut in the agar. Colostrum samples were diluted 1:100 using a barbital buffer and 5 UL was inoculated in each well. The diameter of the zone of precipitation was recorded after 72 hours of incubation at 23˚C. Colostral IgG concentrations were determined by comparing the diameter of zones of precipitation with a standard curve generated using serial dilutions of a bovine IgG standard (Sigma Chemical Co.). The regression equation generated in this manner accurately predicted inoculum IgG concentration (r2 = 0.965).
Initially, mean and standard deviations were calculated for premilking, bucket, and postmilking IgG concentrations. Thereafter, premilking, bucket, and postmilking colostral IgG concentrations were compared using one-tailed t-tests for paired comparisons. Each of the 3 possible comparisons, premilking versus bucket, bucket versus postmilking, and premilking versus postmilking, was performed separately. The null hypothesis that each mean difference was 0 was rejected when P <.05.
Mean and standard deviations colostral IgG concentrations for premilking, bucket, and postmilking colostrum were 86 ± 51, 81 ± 42, and 67 ± 36 g/L, respectively. Mean and standard deviations of differences between premilking versus bucket, premilking versus postmilking, and bucket versus postmilking colostral IgG were 5 ± 55, 14 ± 39, and 19 ± 49 g/L, respectively. Premilking colostral IgG concentrations did not differ significantly (P >.05) from bucket milk colostral IgG concentrations. Postmilking colostral IgG concentrations differed significantly from both premilking and bucket colostral IgG concentrations (P <.05).
Recommendations regarding the volume of colostrum that should be administered to calves have evolved over the last 2 decades. Older reports recommend the administration of 2 L of colostrum shortly after birth and feeding a second 2-L aliquot 12 hours later.11 Based on the observation of 19.3% failure of passive transfer rates in nipple bottle-fed calves and 61.4% failure of passive transfer rates in naturally suckled calves, many authors have advocated more aggressive colostral management practices.6,9 These recommendations are supported by reports describing relatively low colostral IgG concentrations in dairy cows.8 Pritchett et al. advocated oroesophageal administration of large volumes of colostrum.8 Recommendations that calves should receive 4 L of colostrum in the first 12 hours of life have become frequent and widespread.8,9
Premilking and bucket milking colostrum had significantly higher mean IgG concentrations than did postmilking colostral samples. However, it should be emphasized that colostrum collected after the first milking still had an IgG concentration that was 84% of bucket milk. The observed difference, although statistically significant, probably is not biologically significant and is insufficient in magnitude to warrant dramatic changes in colostrum administration practices.
This study did not examine at what point during milking the colostral IgG concentration begins to decrease. Consequently, we propose no dramatic change in current colostral management recommendations. The absence of a significant difference in the IgG concentration of various temporal fractions in a previous study by Stott et al. might have related to the small sample size (n = 12) and the fact that no postmilking colostrum was evaluated.13
The colostral IgG concentrations observed in this study were substantially higher than those observed in some previous studies,8,14 however similar to concentrations reported by others.13,14 Several potential explanations are available for this apparent discrepancy. First, the methodology used to measure colostral immunoglobulins varied among studies. In the present study, a radial immunodiffussion assay was used to measure total IgG, including both IgG1 and IgG2 isotypes. Pritchett et al. and Besser et al. specifically measured IgG1.8,9 The vast majority of colostral IgG is of the IgG1 subtype; consequently, measured immunoglobulin concentrations should have been similar. Secondly, colostrum collection methodology differs among studies. Pritchett et al. and Besser et al. completely milked out cows and then collected a representative bucket sample,8,9 and Tyler et al. collected small volumes of “foremilk” colostrum from each teat.12 Finally, many previous studies did not standardize the lag time between calving and colostrum collection, raising the possibility that colostral IgG might be transported or leak back into the cows’ circulation.8,9,12 The present study addressed these differences by standardizing the timing of colostrum collection. Because colostral IgG concentration varies throughout the first milking, differences in sampling strategy could have an effect on measured colostral IgG concentration.
Gay proposed a goal of 100 g intake of IgG in the first hours of life and recommended that dairy calves should receive 4 L of colostrum through an esophageal feeder at an early age.4 Volumes smaller than 4 L of colostrum would have provided 100 g of colostral IgG in the majority of cows studied. However, this study did not directly examine calf serum immunoglobulin concentrations. Consequently, a degree of caution should be exercised before less rigorous colostrum administration practices are adopted. In the present study, the increased colostral IgG concentration of the initial fraction of colostrum were relatively small in magnitude.
The importance of failure of passive transfer was well illustrated by the observed failure of passive transfer rate of 35% in a recent study.1 Clearly, the management practices currently used on most dairies do not make adequate provision for passive transfer of colostral immunoglobulin. Future studies should examine more temporal fractions of the first milking to determine at what point of the milking cycle colostral IgG concentration falls.
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