As reported elsewhere , a significantly higher proportion of calves fed pooled-MC (70%) suffered from FPT (serum IgG < 10 g/L) in comparison to calves fed lacteal-derived CR (11%). Failure of passive transfer of immunity is a well-recognized predictor for increased preweaning calf morbidity [5–8]. It is therefore not surprising that calves fed raw pooled MC in this study were more likely to be treated with antibiotics or experience preweaning event of diarrhea compared with calves fed lacteal-derived CR in the study herd.
Bovine specific pathogens (Salmonella sp., Escherichia coli, Mycoplasma sp.) are frequently shed in colostrum of infected fresh cows either during an epidemic or intermittently during the peripartum period . It is possible that the higher proportion of diarrhea in preweaned calves fed pooled MC (vs. lacteal-derived CR) was a consequence of direct ingestion of such pathogens in pooled MC. However, this theory could not be further investigated given that culture of the pooled MC samples for specific pathogens (example Salmonella sp., Escherichia coli, Mycoplasma sp.) was not performed in the current study.
Our results indicate that only 21% of diarrhea cases and 12% of antibiotic-treated calves would be eliminated in this population if the pooled MC feeding program was replaced by 200 g IgG/ calf delivered in a lacteal-derived CR product. This should not be surprising given that in replacement heifer rearing, improved preweaning health is a function of several factors including reducing calf exposure to risk factors (infectious agents inclusive). This can be accomplished through proper housing, ventilation, and general hygiene; increasing levels of specific and non-specific immunity through providing good quality colostrum, balanced nutrition, stress minimization; and boosting specific resistance through preventive vaccinations of either the dams or newborn calves against specific pathogens [22, 25, 26]. Calves in the present study were housed in raised individual wooden hutches up to 60 d of age and maintained on preweaning diets of milk replacer, calf starter grain, and fresh water ad libitum. While a number of calf management practices were in place to reduce calf exposure to risk factors for disease in the current herd, it is possible that some yet unidentified factor (unrelated to pooled MC) may have contributed to the additional risk of diarrhea (e.g. compromised sanitation) leading to increased antimicrobial use on this specific farm.
The overall finding that calves fed raw pooled MC (vs. lacteal-derived CR) were more likely to be treated with antibiotics or experience preweaning diarrhea differed from a previous report . Swan et al. reported no difference in post-feeding morbidity risk observed between calves fed a plasma-derived CR compared with calves fed individual maternal colostrum (i.e. non-pooled colostrum) . In contrast, another study found significantly lower morbidity risk for calves fed MC (46.9%) compared with calves fed a lacteal-derived CR (67.3%) . Although not statistically significant, Priestley et al. reported that a greater proportion of calves fed a lacteal-derived CR experienced diarrhea (44.9%) compared to calves fed MC (28.6%) [27, 28]. Although some studies have found no link between FPT and the risk of treatment for diarrhea in beef calves, a possible reason for the difference in findings could be the higher proportion of FPT in calves fed MC in the current study, and in calves fed a lacteal-derived CR (vs. MC) in the Priestley et al. study [27–29]. The difference in FPT is likely to be due to better quality MC fed to calves in the aforementioned studies compared to the current study [22, 27]. In a recent survey, 41% of individual colostrum samples met industry recommended colostrum quality benchmarks (IgG >50 g/L and TPC <100,000 cfu/mL) compared with only 26% of pooled colostrum samples [30, 31]. The mean IgG mass in the pooled MC fed to the calves in this study was approximately 21 g/L compared with approximately 69.7 g/L of IgG reported for non-pooled colostrum in the recent survey of colostrum quality [24, 30].
While there were no differences in the proportion of preweaning respiratory disease, omphalitis or death in calves fed lacteal-derived CR compared to those fed pooled MC, mean daily weight gain was significantly higher in the former. This reflected perhaps a general benefit accruing from the improved preweaning health outcomes associated with feeding lacteal-derived CR rather than a direct role in enhancing daily weight gain in the study calves . Such a link between reduced morbidity and increased weight gain was also reported in a Florida study, although unlike in the current study, the Florida study reported reduced morbidity in calves fed MC compared to those fed a lacteal-derived CR [27, 28].
In the current study, type of colostrum fed (CR versus MC) had no effect on mortality risk between birth and weaning in the study calves. These results are consistent with results from an earlier study in which feeding a plasma-derived CR (vs MC) had no effect on preweaning mortality ; however they differed from the Florida study which found a significantly lower proportion of mortality in calves fed MC compared to calves fed a lacteal-derived CR . These contradictions may reflect the fact that in concert with passive transfer of immunity, calf survival in the preweaning period is a function of several herd factors including housing and nutrition.
Although a major strength of this study included its randomized assignment of treatment, the results presented here must be interpreted cautiously. It is possible that the ability to correctly assign a disease diagnosis (i.e. diarrhea, respiratory disease, omphalitis) varied among the study personnel involved in the care of the calves during the follow-up period. This potential bias, if present, was likely to be non-differential because the study personnel were blinded to treatment group assignment (lacteal-derived CR vs. pooled MC). Moreover, a veterinarian (SA) cross-validated each recorded diagnosis and treatment with the herd veterinarian’s drug protocols. The extent to which this study’s results can be extrapolated to a wider population of dairy herds is limited by the use of a single herd to evaluate the current study objectives. While approximately 57% of large dairy operations in the US routinely feed pooled MC , the current herd was not representative of this wider population with respect to FPT risk profiles and quality of pooled MC fed. Recent findings  suggest that approximately 23% of calves in US operations that fed pooled MC experienced FPT compared with 70% of calves fed the pooled MC in this study. In addition, the mean IgG mass in the pooled MC fed to the calves in this study was 3-fold lower than similar estimates of IgG concentration in nationally representative samples of pooled MC . The lower quality of the pooled MC fed to calves in this study compared to comparable US herds likely biased the morbidity outcomes in a direction suggestive of a better efficacy for the lacteal-derived-CR for improving preweaning health in calves. Hence, it is possible that the benefits of feeding lacteal-derived CR (vs. pooled MC) on preweaning health may not be similar in dairy herds managed under a different husbandry system.
The findings reported here indicate that producers should adopt colostrum management strategies that improve colostrum quality. To achieve this, producers can begin by pooling only colostrum with acceptable immunoglobulin concentration (>50 g/liter IgG). This can be achieved by testing individual cow colostrum samples prior to pooling and by properly identifying dams so that first milking colostrum is pooled separate from colostrum harvested from subsequent milkings. Alternatively, pooling colostrum can be replaced by feeding a colostrum replacement product with a known immunoglobulin concentration. Other recommendations identified from previous research should also be followed such as observing proper sanitation and hygiene during harvesting, processing, and storage of colostrum, feeding colostrum replacement products or heat-treated colostrum [2, 3, 33].