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Passive transfer of immunity (PTI) is a metric used on farm to assess colostrum management. With multiple colostrum replacers available differing in composition, classical total serum protein cut points may not apply to all products. The aim of this analysis was to determine whether calves fed a whey-based colostrum replacer that successfully achieved PTI (serum IgG ≥10 mg/mL) would have been classified as having PTI using typical benchmarks (total serum protein <5.0, 5.2, or 5.5 g/dL or Brix% <8.4).
Materials and Methods
In total, 1,220 calves were assigned to 1 of 2 treatments: (1) maternal colostrum (MC) or (2) whey-based colostrum replacer supplying 150 g of IgG (CR). Serum samples were collected at 0 and 24 h of life to determine serum IgG, total serum protein, Brix%, and apparent absorption efficiency.
Results and Discussion
When comparing serum IgG values with current on-farm cut points, the proportion of calves incorrectly classified as having PTI failure was greater (P < 0.01) for the CR treatment compared with the MC treatment. The proportion of calves incorrectly classified for CR versus MC using current total serum protein or Brix% cut points were as follows: 5.0 g/dL (31.2 vs. 8.8%, P < 0.001), 5.2 g/dL (52.5 vs. 15.5%; P < 0.001), and 5.5 g/dL (82.0 vs. 34.0%, P < 0.001) or serum Brix 8.4% (73.2 vs. 29.2%; P < 0.01).
Implications and Applications
These data suggest when analyzing serum on farm from calves fed a whey-based colostrum replacer, traditional cut points for PTI should be revised.
). Colostrum contains a high content of antibodies, or Ig, designed to be absorbed by the newborn calf to provide passive transfer of immunity (PTI). This is of extreme importance in newborn mammals because in many mammalian species, placental transfer of Ig does not occur (
). As recently as 2011, the USDA conducted a survey and determined that 100% of US dairy operations were feeding colostrum to calves. Among farms surveyed, 64.3% were feeding colostrum originating from the dairy, whereas 53.8% of farms used a colostrum replacer in some capacity (
). Additionally, this survey found roughly 40% of farms were monitoring PTI rates on farm.
Monitoring PTI on farm is a way to gauge colostrum program effectiveness. Total serum protein (TSP) and, in some cases, Brix% are methods used on farm for estimating serum IgG levels and PTI for calves. It is generally accepted that TSP >5.5 g/dL is equivalent to serum IgG >10 mg/mL (
), calves were fed maternal colostrum or a whey-based colostrum replacer shortly after birth. Mean TSP (5.84 g/dL) was acceptable for gauging PTI in maternal colostrum–fed calves, but the mean TSP for calves fed colostrum replacer was lower than traditional benchmarks. The lower TSP readings when feeding a whey-based colostrum replacer may be due to (1) removal of casein during the manufacturing process of whey-based colostrum replacer, (2) concentrating of IgG during the manufacturing process resulting in a lower feeding rate, or (3) the lower feeding rate resulting in less total protein consumption by the calf. Therefore, the study objective was to determine whether there is a difference in the number of calves fed maternal colostrum or a whey-based colostrum replacer that have serum IgG values greater than 10 mg/mL at 24 h of life but would be classified as calves experiencing failure of passive transfer on farm based on traditional PTI cut points. These calves are referred to as “false failures.” We hypothesized that casein absence in the whey-based colostrum replacer, resulting in less total protein intake, would lead to a greater proportion of calves being classified as PTI false failures compared with maternal colostrum–fed calves.
MATERIALS AND METHODS
DairyExperts Inc. provided suitable orientation, appropriate materials, adequate resources, and training to enable research personnel to carry out their respective duties consistent with the Guide for the Care and Use of Agricultural Animals in Research and Teaching (
A total of 1,220 calves (1 d of age) were used in the experiment and fed 1 of 2 treatments: (1) maternal colostrum (MC; 178 g of IgG intake) or (2) a whey-based colostrum replacer (CR; 150 g of IgG intake, 96% DM, 47% CP, 15% fat). A subset of calves was randomly selected from the population and bled for determination of serum IgG (n = 300 and 292 calves for CR and MC, respectively) and TSP (299 and 294 calves for CR and MC, respectively) at 24 h after feeding and used for the present analysis.
A more detailed explanation of methods can be found in a previous publication (
) that used the same calves. Briefly, the trial was conducted on a commercial, freestall dairy farm in California, using both Jersey and Jersey × Holstein cross calves. The colostrum replacer fed was a commercially available product (First Day Formula, Accelerated Genetics, Baraboo, WI). Calves were randomly assigned to their respective colostrum treatment at birth and were either fed 2.8 L of MC or CR mixed into 1.9 L of water. All treatments were administered within 1 h ± 5 min of birth via an esophageal tube to ensure the entire colostrum treatment was consumed.
Maternal colostrum used was harvested twice daily before onset of trial, pooled, and stored until feeding. Colostrum was sampled after collection for quality (n = 53 samples) and averaged 63.6 g of IgG/L (1.96 minimum to 96.9 g/L maximum,
). Before feeding, colostrum was warmed and fed at 41°C. The bucket used to mix the colostrum replacer was filled with 1.9 L of warm water and a package of colostrum replacer (500 g of colostrum-replacer powder providing 150 g of IgG) was added. Mixing occurred for 40 to 60 s until complete dispersal of the colostrum replacer into the water, and the solution was fed at 41°C.
Logistic regression models using the SAS LOGISTIC PROC version 9.2 (SAS Institute, Cary, NC) were constructed for each of the TSP (5.0, 5.2, and 5.5 g/dL) and Brix (8.4%) cut points. The effect of treatment and a dichotomous variable representing the serum IgG results (serum IgG ≥10 or <10 mg/mL) as a function of the TSP or Brix cut point used were modeled to determine how accurately a given cut point would correctly classify PTI compared with serum IgG for a given treatment. Other explanatory variables such birth weight, calving ease, and single versus twin were included in the model in a forward stepwise selection method where a variable was included when significant at P < 0.05.
RESULTS AND DISCUSSION
Health, growth, and performance as they pertain to the current study are presented in a companion publication to this study (
) and are only discussed when relevant to the current work. Colostrum treatment affected the likelihood that a calf was classified as a false failure when compared with a variety of TSP cut points (Table 1). A false negative in this example would be a calf that had a serum IgG value above 10 mg/mL at 24 h after feeding but a TSP value less than 5.0, 5.2, or 5.5 g/dL (classified as failure-of-passive-transfer calf on farm). For all TSP cut points evaluated, feeding CR versus MC resulted in more calves being classified as false failures (P < 0.001; 31.2 vs. 8.8%, 52.5 vs. 15.5%, and 82.0 vs. 41.0% for TSP <5.0, 5.2, and 5.5 g/dL, respectively). The magnitude of difference was 3.55-, 3.39-, and 2.05-fold for TSP values less than 5.0, 5.2, and 5.5 g/dL, respectively. One cut point for Brix% was evaluated as Brix cut points have been evaluated with less frequency (Table 2). When the Brix% cut point of 8.4 was evaluated, CR-fed calves were 2.05-fold more likely to be classified as a false failure (P < 0.001; 73.2 vs. 35.7% for CR vs. MC). Both TSP and serum Brix were correlated with serum IgG in this study regardless of colostrum treatment (P < 0.01; see Figure 1). In general, TSP was more correlated than serum Brix with serum IgG at 24 h. Additional MC generally resulted in better correlations for TSP or serum Brix with serum IgG than CR.
Table 1Effects of feeding a whey-based colostrum replacer (CR) or maternal colostrum (MC) on the proportion of calves with serum IgG ≥10 mg/mL but falling below 3 established total serum protein (TSP) cut points
Although serum IgG can be considered a direct measure to evaluate PTI and immune status after colostrum is fed, TSP and Brix% both are merely estimates of serum IgG and not exact measures of serum or blood IgG content (
). The clear difference in the ability to use traditional TSP cut points to correctly classify PTI in calves fed MC versus CR should call into question whether traditional TSP cut points are valid for colostrum replacer, particularly, whey-based colostrum replacer. From a practical standpoint, consultants, veterinarians, and on-farm personal should not blindly trust traditional TSP cut points to appropriately estimate PTI in calves. This appears especially true for calves fed colostrum replacer, unless published data exist to confirm the validity of the cut points or provide valid new cut point estimates.
In the case of CR versus MC (or possibly dried maternal colostrum), the potential explanation of these results may be a function of protein intake or nutrient profile. Although both colostrum treatments result in adequate levels of IgG at 24 h of life (
), the amount of non-IgG protein present in MC should be greater than in CR. Therefore, it is likely that additional protein consumption may provide additional protein for absorption, thus diluting the IgG content of the serum with excessive non-IgG proteins. The non-IgG proteins may not provide additional immunity protection to the calf but could falsely elevate TSP readings. As a result, lower TSP readings would be expected to estimate the same level of IgG among calves fed whey-based colostrum replacer. This hypothesis seems to be at least partly confirmed by recent work (
). In this study, a similar product to that used in the current work was used and a similar feeding rate of IgG employed (150 or 110 g). No calves in the referenced study experienced failure of passive transfer when fed 150 g of IgG from colostrum replacer, but average TSP was below traditional TSP cut points (4.45 g/dL). It was concluded that a TSP of 4.2 g/dL was a better indicator of PTI than traditional cut points such as 5.2 g/dL (
). It should be noted, however, that previous work conducted with whey-based colostrum replacer was done before and did not take into account recently published work suggesting updated benchmarks for assessing PTI on farm (
). The inhibitory effects of casein may require greater feeding rates of other colostrum-replacer sources to supply the same level of IgG as a whey-based colostrum replacer. The number of animals in the present work combined with other recent reports (
) seem to indicate differences in colostrum diet composition may have effects on absorption of IgG and the ability of PTI to be evaluated on farm using traditional metrics.
From these results, it is clear that standard TSP cut points may not apply to calves fed colostrum replacer. This appears to be especially true for whey-based colostrum replacer, although both TSP and serum Brix positively correlated with serum IgG in CR-fed calves. Therefore, calf-side estimates of PTI for calves fed colostrum replacer should be viewed with skepticism and not used as the sole metric for evaluation until additional research is conducted. More work is needed in this area to further define appropriate TSP cut points for calves fed various forms of colostrum replacer.
Financial support for this research was provided by Accelerated Genetics (Baraboo, WI), Milk Products Inc. (Chilton, WI), and Zinpro Corporation (Eden Prairie, MN).
Quigley III, J.D.
Addition of casein or whey protein to colostrum or a colostrum supplement product on absorption of IgG in neonatal calves..