AUSTRALIA S PREMIER VETERINARY SCIENCE TEXT. Factors associated with colostrum immunoglobulin G concentration in northern-victorian dairy cows

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1 AUSTRALIA S PREMIER VETERINARY SCIENCE TEXT Factors associated with colostrum immunoglobulin G concentration in northern-victorian dairy cows AJ Phipps, a,b * DS Beggs, b AJ Murray, a PD Mansell b and MF Pyman b Objectives To determine the proportion of first-milking colostrum samples produced on four northern-victorian dairy farms that meet industry standards in terms of immunoglobulin G (IgG) concentration and to identify risk factors that affect colostrum quality. Methods Colostrum IgG concentrations from 442 dairy cows on four farms were estimated using a Brix refractometer and risk factors for colostrum IgG concentration were determined using multivariable logistic regression. Results Only 39% of samples met the definition of high quality. The strongest predictor for colostrum quality was the interval from calving to colostrum harvesting. Colostrum harvested from cows within 12 h of calving was 6-fold more likely to be high quality compared with colostrum harvested later. Colostrum from cows in 4th lactation was nearly twice as likely to be high quality compared with cows entering their 1st lactation. If the calf was not allowed to suckle from the dam prior to colostrum harvesting, the odds of producing high-quality colostrum were nearly 4-fold greater. If the cow had not leaked colostrum prior to harvesting, it was more than 3-fold more likely to produce high-quality colostrum. Conclusions The majority of samples assessed were below industry standard. Herd, lactation number, calf suckling or cow leaking colostrum prior to harvesting and time between calving and colostrum harvesting were factors that influenced colostrum IgG concentration. The results support current industry recommendations of harvesting colostrum shortly after parturition (ideally within 12 h of calving) and testing the quality of all colostrum prior to feeding to dairy calves. Keywords Brix refractometer; colostrum; dairy calves; dairy cows; immunoglobulin G Abbreviations ADCT, antibiotic dry cow therapy; Brix%, Brix percentage; CI, confidence interval; FPT, failure of passive transfer; IgG, immunoglobulin G Aust Vet J 2017;95: doi: /avj The neonatal calf is required to obtain, ingest and absorb an adequate amount of colostrum immunoglobulins (Ig) within the first 24 hours of life to achieve passive transfer of immunity. 1,2 The acquisition of passive transfer of immunity has been well *Corresponding author. a Rochester Veterinary Practice, 72 Lowry Street, Rochester, Victoria 3561, Australia; ashphipps87@gmail.com b Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, Victoria, Australia investigated and has been shown to reduce the risk of morbidity and mortality in the preweaning period. There are also long-term effects on calf health and future production. Under Australian dairy farming conditions, it is common practice to allow the dairy calf to remain with its dam unsupervised for a period of time after birth before being removed from the calving environment to the calf-rearing facilities. 3 It is also common practice to supplement the dairy calf with additional colostrum once the calf has been removed from the dam. An Australian study demonstrated the importance of supplying calves with additional colostrum once they are removed from their dam. 3 Calves that were not supplemented with additional colostrum were 3-fold as likely to have failure of passive transfer (FPT). 3 The process of obtaining colostrum for supplementing calves requires harvesting colostrum from the first milking post calving, storing the colostrum and then feeding it to the dairy calves. It is desirable to feed only high-quality colostrum (defined as 50 g/l immunoglobulin G [IgG]). In many species, including sheep, horses and cattle, Brix refractometry has been used to estimate the IgG concentration of maternal colostrum When measuring liquids that do not contain sucrose, the Brix percentage (Brix%) has been shown to approximate the percentage of total solids in milk. 5 In colostrum this is largely IgG and so the Brix% provides an acceptable estimate of first-milking bovine colostrum. 5 A number of studies have been conducted to investigate the appropriate cut-off Brix% to distinguish between high- and poor-quality colostrum. One study found that the sensitivity and specificity of the optical Brix refractometer was similar for Brix% 21 and 22 cut-off levels in heifers and highest at the cut-off level of 22% for cows in their second lactation or greater. 10 Other studies have reported Brix % cut-offs of 22, and For the current study, it was decided that the appropriate cut-off level would be a Brix% of 22, because 22 equates to 50 g/l of IgG, which is considered to be highquality colostrum. 5 The quality of colostrum can vary greatly between individual cows and is influenced by numerous cow and management factors. There is limited data available on the factors that may affect colostrum quality under Australian dairy farming conditions and whether the quality of colostrum being fed to replacement heifer calves meets industry recommendations. On northern-victorian dairy farms, it is common practice for farmers to select colostrum on the basis of visual inspection, age of the cow and other non-quantitative measures, despite the availability of inexpensive cow-side tests such as Brix refractometers and hydrometers Australian Veterinary Association Australian Veterinary Journal Volume 95 No 7, July

2 The objectives of this study were to determine the proportion of first-milking colostrum samples produced on four northern- Victorian dairy farms that met industry standards in terms of IgG concentration and to identify factors that may affect colostrum quality. Materials and methods Study population The farms selected were commercial dairy herds in the Rochester district of Victoria, Australia, whose herd managers used the services of the Rochester Veterinary Practice routinely, who were known to keep good farm records and who were agreeable to participating. In May 2013, herd managers from eligible herds were invited to take part in the study and fresh colostrum samples were harvested from cows that calved between June and July 2013 on the four farms. This study was conducted with animal ethics approval from the University of Melbourne, Faculty of Veterinary Science Animal Ethics Committee (Ethics ID: ). All participating farmer owners signed a written consent form that detailed the project. Cow management All animals were managed under a pasture-based system. All cows received prophylactic treatment for endoparasites and exoparasites and were vaccinated at dry-off for clostridial diseases, leptospirosis, salmonellosis and Escherichia coli. Herd 1 selectively treated cows with either no intramammary treatment at dry-off, internal teat sealant only, antibiotic dry cow therapy (ADCT) only or internal teat sealant and ADCT together. Herds 2 and 3 routinely used an internal teat sealant and ADCT for all cows and herd 4 routinely used ADCT only. None of the herds used an internal teat sealant or ADCT for their heifers. All animals were calved down in paddocks in groups of 10 and heifers were kept with adult cows for 1 month prior to calving. All calving cows were managed in a similar manner during the colostrum harvesting and sampling process. Colostrum sample collection and evaluation In each of the four herds enrolled in the study, colostrum was harvested at the first milking post calving. All cows enrolled in the study were managed similarly to the rest of the cows in the herd. At the first milking post calving, colostrum was machine-collected into a test bucket in the dairy shed. Using a sterile plastic pipette, 0.5 ml of colostrum was collected from the thoroughly mixed bucket and assessed using a commercially available Brix refractometer (Brix TE-RM32B with Automatic Temperature Compensation from 10 Cto30 C, Test-Equip Pty Ltd, VIC, Aust). In line with industry recommendations, colostrum was considered to be of high-quality if it had a Brix% 22. The optical Brix refractometer has an upper limit on the scale of 32%, so any samples that exceeded 32% were recorded as Brix% 32. Additional information, such as cow lactation number, intramammary treatment at dry-off, date and estimated time of calving, date and time of colostrum harvesting, whether the calf had suckled the cow prior to colostrum harvesting and whether the cow had leaked colostrum prior to colostrum harvesting, was recorded at the time of colostrum harvesting. Data analysis All the raw data was manually recorded in Microsoft Excel 2010 (Microsoft Corp., Redmond, WA, USA) from the on-farm record sheets. Breed, cow lactation number, intramammary treatment at dry-off, calf suckling from the dam prior to colostrum harvesting, cow leaking colostrum prior to colostrum harvesting, the volume of colostrum produced at harvesting, and time post calving and colostrum harvesting were analysed (Table 1). Statistical analysis All descriptive statistics and statistical analyses were performed using IBM SPSS Statistics 2013 for Windows, Version 22.0 (IBM Corp., Armonk, NY, USA). Logistic regression was used to assess associations between potential risk factors that may influence colostrum IgG concentration as estimated by Brix% (dichotomous outcome variable as Brix% < 22 and 22). The categorical variables (herd, breed, lactation, intramammary treatment at dry-off, calf suckle, cow leak, time post-calving colostrum harvested and colostrum volume at first milking) were first tested for association with Brix% in a series of univariate analyses. For multivariable modelling of colostrum IgG concentration as estimated by Brix%, a backward elimination process was used. All univariables with association P < 0.25 were fitted simultaneously. Overall P-values were assessed for each factor and the variable with the highest non-significant P-value was removed. This process was repeated until all remaining variables were significantly (P < 0.05) associated with colostrum IgG concentration as estimated by Brix%. Once a variable had been eliminated it was not re-introduced into the model. Interactions between all significant variables were examined. Least-squared means and odds ratios were compared. Results Descriptive analysis Table 1 summarises each of the variables that affected colostrum IgG concentration as estimated by Brix refractometry of first-milking colostrum. The colostrum Brix% ranged from 9 to 32, with a mean of Only 38.9% of the colostrum samples were equal to or above the desired Brix% of 22. The mean Brix% was highest in herd 3 (Table 1); mean colostrum from Jersey cows had the highest Brix% and Holstein-Friesian cows had the lowest percentage (Table 1). Mean colostrum Brix% for cow entering their 1st, 2nd and 3rd lactation were lower than for cows entering 4th lactation (Table 1). Whether the calf suckled prior to colostrum harvesting had a marked influence on the Brix%. On average, cows that had not been suckled prior to colostrum harvesting had a Brix% > 22. Cows that had not leaked colostrum prior to harvesting had a higher mean Brix % than cows that had leaked colostrum (Table 1). The time between calving and colostrum harvesting ranged from 10 min to 62 h (mean h). Cows having colostrum harvested < 12 h post calving had a higher mean Brix% compared with 12 h (Table 1). 238 Australian Veterinary Journal Volume 95 No 7, July Australian Veterinary Association

3 Table 1. Variables affecting colostrum IgG concentration as estimated by Brix refractometry of first-milking colostrum Variable n Colostrum Brix% (mean SE) a Herd 1 A B B C Breed Holstein-Friesian A Jersey B Holstein- Friesian Jersey C Other crossbred b and dairy breeds AC Lactation 1 A B A C Intramammary treatment at dry-off None A Dry cow therapy only A Teatseal only B Teatseal + dry cow therapy C Calf suckle Yes A No Leak colostrum Yes A No Volume produced (L) < 8.5 A > Time post-calving colostrum harvested (h) <12 A > A,B,C Column means within a classification with different superscripts differ (P < 0.05). a Colostrum Brix percentages (Brix%) are expressed as least-squares mean SE. b Other crossbreds and dairy breeds included Australian Red, Ayrshire, Illawarra Red and their crosses. Ig, immunoglobulin; SE, standard error. Statistical analysis The distribution of the Brix% for the colostrum samples is shown in Figure 1. The colostrum Brix% values were normally distributed, determined by the Shapiro-Wilk test of normality. A scatter plot with a linear regression line was produced to display the relationship between colostrum IgG concentration as estimated by Brix refractometer and time between calving and colostrum harvesting. The linear regression line equation was Brix% (y) = (h), R 2 = It was also found that the Brix% reduced by 0.25 per hour post calving (Figure 2). Univariable analysis The variables selected for multivariable modelling because of their association with colostrum IgG concentration as estimated by Brix% were herd (P < 0.001), breed (P < 0.001), lactation (P = 0.006), intramammary treatment at dry-off (P < 0.001), calf suckle (P < 0.001), leak colostrum (P = 0.014), volume produced (P = 0.002) and time post-calving colostrum harvesting (P < 0.001). The interaction between cow leak and time post-calving colostrum collected was found to be associated (P < 0.25) with the dependent variable colostrum IgG concentration as estimated by Brix%. Multivariable analysis In the final multivariable model of 442 colostrum samples from four herds, five variables remained significantly associated with colostrum IgG concentration as estimated by Brix%: herd, lactation, calf suckle, cow leak and time between calving and colostrum harvesting (Table 2). The final model containing all five parameters was statistically significant (χ 2 (9, n = 442) = , P 0.001). The model as a whole explained between 36.3% (Cox and Snell R squared) and 49.3% (Negelkerke R squared) of the variance in Brix% and correctly classified 79.2% of cases (Table 2). The strongest risk factor associated with quality colostrum IgG concentration as estimated by a Brix% 22 was time post calving to colostrum harvested. Cows from herds 3 and 4, cows in lactation 4, cows that had not been suckled by their calf and cows that had not leaked colostrum prior to colostrum harvesting had greater odds of producing colostrum with a higher IgG concentration (Brix% 22) (Table 2). Other potential interaction between herd and breed, herd and time post-calving colostrum collected, herd and intramammary treatment at dry-off, breed and volume, and intramammary treatment at dryoff and volume were not statistically significant (P > 0.2). Discussion The current study describes a number of the factors and the extent to which they were associated with colostrum IgG concentration in dairy cows on four northern-victorian farms. Colostrum quality In our study, most of the colostrum samples were poor quality, having a Brix% < 22. Only 39% of the colostrum samples had a Brix % 22, equating to 50 g/l of IgG, which is considered to indicate high-quality colostrum. 10 The percentage of colostrum samples from previous studies that were considered to be good quality ranged from 58% to 92%, 5,10 although not all of those studies used a Brix% cut-off of 22. The range of the Brix% in this study was 9 to 32 and the mean was 20, similar to a previous study that reported a range of and a mean of 23.8 (n = 183). 5 The range was also similar to that reported 2017 Australian Veterinary Association Australian Veterinary Journal Volume 95 No 7, July

4 Figure 1. Distribution of the Brix percentages for the colostrum samples from 442 dairy cows sampled between June and November in a different study ( ), although the mean was much greater (26.1; n = 288). 10 This difference may be explained by the fact that 21 of their samples surpassed a Brix% of 32 compared with only three of the samples in our study. The large number of poor-quality colostrum samples in our study suggests that some producers may have difficulty in supplementing all calves with high-quality colostrum. Therefore, we recommend the practice of selecting and storing high-quality colostrum ( 50 g/l) to supplement calves when supply of fresh high-quality colostrum is limited. Herd We found a significant difference in mean colostrum Brix% between herds, but no significant interaction between herd and the other variables (P > 0.05). It is therefore likely that other characteristics of cow management that we did not assess (e.g. periparturient diet, colostrum harvesting, and management practices such as prestimulation of the teats prior to the milking cups being applied to the teats to aid in milk letdown) could have contributed to this result. Further investigation to quantify the effect of these factors on colostrum IgG concentration is needed. Volume of colostrum produced at first milking post calving The relationship between colostrum weight and volume depends on colostrum quality. The specific gravity of poor-quality colostrum is < and that of good-quality colostrum is > Therefore, 1 L of colostrum with a specific gravity of will weigh kg. In the current study, the volume rather than the weight of colostrum produced was measured, as it was easier for the dairy producers to measure and represents what would occur under normal farm conditions. For analysis, the volume cut-off for the Figure 2. Scatter plot, liner regression line (solid line), 95% confidence interval for the regression line (dashed lines) and Brix percentage 22 reference line (bold dashed line) for the relationship between colostrum IgG concentration as estimated by Brix refractometry and time between calving and colostrum being harvested for 442 dairy cows. The linear regression line equation was: Brix percentage (y) = h (x), R 2 = For example, at 20 h post calving, the Brix reading would be (y) = = colostrum that was retained was set at 8.5 L, as this equates to approximately 8.5 kg colostrum weight and is consistent with what has been previously used by other researchers. It should be noted the quality of colostrum produced at first milking post calving was, on average, poor (Brix % < 22%). Predicting the quality of colostrum based on volume produced was not possible. Previous studies have suggested that cows producing > 8.5 kg of colostrum at first milking post calving have a lower quality colostrum than cows that produced < 8.5 kg. 14,15 Although the quality of colostrum was significantly higher if < 8.5 L was produced, the overall effect of the volume of colostrum produced at first milking post calving was not associated with colostrum IgG concentration (Brix% 22) in our final model. The decreased IgG concentration of high colostrum volumes may be explained by a dilution effect as a result of increased lactogenic activity and transport of macromolecules, such as lactose, into the mammary gland. 16,17 However, others have reported no predictable relationship between colostrum IgG1 concentration and the volume of colostrum produced at first milking. 17 Therefore, the practice of arbitrarily retaining and discarding colostrum based on a volume cut-off may result in an unnecessary wastage of potentially large volumes of high-quality colostrum. Breed Although there are limited studies in Australia comparing colostrum Ig concentrations in different dairy breeds, several overseas studies have reported significant herd and/or regional differences in mean Ig concentrations of colostrum for Holsteins and Jersey cows. 14,18,19 In 240 Australian Veterinary Journal Volume 95 No 7, July Australian Veterinary Association

5 Table 2. Adjusted odds ratios (OR) for variables in the final multivariable model of factors that influence colostrum IgG concentration as estimated by Brix refractometry Variable Level Percentage high colostrum IgG concentration (Brix% 22) Coefficient (SE) P value a Crude OR (95% CI) Herd < Reference group (0.35) 1.08 ( ) (0.42) 4.48 ( ) (0.41) 3.04 ( ) Lactation Reference group (0.41) 0.43 ( ) (0.40) 0.92 ( ) (0.34) 1.86 ( ) Calf suckle <0.001 Yes 19 Reference group No (0.29) 3.72 ( ) Leak colostrum Yes 22.4 Reference group No (0.44) 3.16 ( ) Time post-calving colostrum collected (h) <0.001 < (0.30) 6.3 ( ) > Reference group Constant 3.54 (0.84) < a Bold values are the likely ratios test P-values, non-bold values are Wald test P-values. CI, confidence interval; Ig, immunoglobulin; SE, standard error. the current study, breed was not a significant factor associated with colostrum IgG concentration; however, there were breed differences. All breeds in the study produced poor-quality mean colostrum (Brix % < 22). Holstein-Friesians produced the lowest and Jerseys produced the highest mean Brix%. These results do not support a previous study comparing different breeds within a herd that found that Holstein and Jersey cows produced, on average, a higher colostrum IgG concentration than Brown Swiss and Ayrshire cows. 20 The cross-bred cows (Holstein-Friesian Jerseys) in our studies produced the second highest mean Brix%. Findings from our study suggested breed cannot be used in the selection criteria for predicting colostrum IgG concentration and therefore quality. Lactation Primiparous animals entering their 1st lactation produce colostrum of poorer quality in terms of Ig content when compared with multiparous animals entering a subsequent lactation During colostrogenesis, Ig developed from previous antigenic stimulation transfer from the maternal circulation into the mammary secretions. It has been suggested that the greater the parity of the cow, the greater the exposure to pathogens and vaccines (antigens) over time and, therefore, a greater number of Ig transferred into colostrum. This would result in colostrum being produced with a higher IgG concentration. 27 Our study supports this, with cows of greater parity ( 4th lactation), on average, producing colostrum with a higher IgG concentration when compared with cows in their 1st, 2nd or 3rd lactation. However, we found that cows in their 2nd lactation produced, on average, colostrum of the lowest IgG concentration, which was similar to a study from Norway in which the lowest IgG values were found for 2nd-lactation animals. 27 This may be because cows in their 2nd lactation produce, on average, higher volume, therefore more dilute, colostrum at first milking postpartum than primiparous animals. This hypothesis requires further investigation. In our study, the parity of the cow did appear to influence the quality of colostrum. However, the practice of only using colostrum from cows in their 3rd lactation as suggested by some authors, does not necessarily ensure an adequate amount of colostrum Ig will be supplied to neonatal calves, as many other factors influence the colostrum quality. 14,26,28 Intramammary treatment at dry-off It is common practice for dairy farmers to administer an intramammary treatment at the time cows are dried off to cure any existing mammary infection and/or to reduce the incidence of clinical and subclinical mastitis in the dry period and around calving. 29 The intramammary treatments may include ADCT with or without an internal teat sealant or an internal teat sealant alone Australian Veterinary Association Australian Veterinary Journal Volume 95 No 7, July

6 We were unable to find any studies investigating the effect of intramammary treatment at dry-off on colostrum IgG concentration. Our study demonstrated that cows receiving both internal teat sealant and ADCT produced the highest quality colostrum and the cows that received the internal teat sealant only produced the lowest quality colostrum. The reason for this is unclear. It may be hypothesised that the animals receiving an internal teat sealant would consist of a higher proportion of first-calving animals (cows moving into their 2nd lactation) and these animals on average produced the lowest quality colostrum when compared with other lactation groups. Most of the 92 animals that were in the no-treatment group were those entering their 1st lactation and it is not common practice for these animals to receive an internal teat sealant or ADCT and these cows also tend to have lower quality colostrum. Calf suckle prior to colostrum harvesting If calves had not suckled from their dams prior to the dam having her colostrum harvested, these dams had almost 4-fold odds of producing high-quality colostrum when compared with cows that had suckled the calf. In Victorian pasture-based dairy farms, it is common practice to leave the calf with the dam for up to 24 h, 3 during which time the calf suckles from the dam. It has been estimated that suckling calves consume on average 8.3% live weight of colostrum. 31 Therefore, if calves are allowed to suckle poor-quality colostrum from the dam, the calf may reach satiety before consuming the required amount of Ig to achieve passive transfer of immunity. 33,34 In our study, 56% of cows nursed their calf prior to colostrum harvesting, therefore suggesting that these cows are likely to have produced colostrum of poor quality. This may be an important factor when determining a herd mate candidate for colostrum supplementation to feed to a neonatal calf that has not suckled its dam. However, it would be recommended to test all colostrum before feeding it to any dairy calf (all replacement heifer calves, excess heifer calves and bull calves). Cow leaking colostrum prior to colostrum harvesting Cows leaking colostrum prior to colostrum harvesting is a major factor causing low Ig concentrations in the colostrum. 33 We found that 11% of cows leaked colostrum prior to colostrum collection; those that had not leaked colostrum prior to collection had greater than 3- fold odds of producing high-quality colostrum (Brix value 22) when compared with cows that had leaked colostrum. Time between calving and colostrum collection The colostrum collected within 12 h postpartum had a significantly higher Brix% on average when compared with colostrum collected after 12 h postpartum and the Brix% reduced by 0.25 per hour post calving. A reduction in colostrum IgG concentration with an increase in the interval from calving to colostrum harvesting has also been shown by others Delaying the harvesting of colostrum by 6, 10 and 14 h post calving decreased the colostrum IgG by 17%, 27% and 33%, respectively, when compared with colostrum collected immediately postpartum. 36 Two other studies showed that colostrum quality was reduced by 3.7% and 1.1%, respectively, per hour post calving. 37,38 During the postpartum period between calving and colostrum harvesting, mammary gland secretion continues. These secretions contain lower Ig content than that of colostrum and it has been hypothesised that this effect may dilute the colostrum as time increases between calving and colostrum harvesting. 37 Two studies have shown that the volume of colostrum increased with increased time between calving and colostrum harvesting. 36,38 When those authors adjusted for volume they reported that the total Ig amount was significantly lower in the colostrum of cows that had colostrum harvested later when compared with cows having colostrum collected earlier. 36,38 Moore et al. did not support the hypothesis that reduced colostrum quality was caused by dilution and suggested that it may be because the colostrum Ig diffuse passively back into the cow s systemic circulation. 36 An important consideration in relation to colostrum harvesting and feeding to calves is the calf s gastrointestinal ability to absorb Ig. As time increases between birth and the feeding of colostrum, the gastrointestinal tract s ability to absorb macromolecules such as Ig continues to decrease. 39 Therefore, it has been recommended to remove calves from the dam within 2 h of birth prior to the calf suckling and to supplement the calves with an adequate volume of colostrum (3 4 L), containing g Ig, within the first 6 h of life to maximise the efficiency of absorption and reduce the risk of FPT. 40 To achieve this would require the harvesting of colostrum from the cow as soon as possible after parturition to maximise the likelihood of harvesting high-quality colostrum to give to the calves. Such an approach may be practical on intensively run dairy farms where there is adequate labour available. However, on more extensive, pasture-based dairy enterprises with less available labour, meeting that recommendations may not be possible. The current Australian dairy industry guidelines produced by Dairy Australia recommend feeding a volume of good-quality ( 50 g/l) colostrum to calves between 10% and 12% of its body weight in the first 12 h of life (multiple small feeds) and follow up with a similar volume in the next 12 h. 41 This guideline may be more achievable for most Australian dairy herds, but still requires calves to be removed from the calving environment within 12 h of life. Study limitations Other factors that may be associated with colostrum IgG concentration and were not assessed in this study include prepartum nutrition, the season of calving and length of dry period. The voluntary nature of this study may have led to a bias in the herds that participated, which may have influenced colostrum quality because the farms that participated in the study may have been those that pay greater attention to the colostrum harvesting process. There was the opportunity for misclassification of farmer-reported cow-level factors such as the time at which the cows had calved, the time at which the cows had their colostrum harvested, whether the calf had suckled from its dam and whether the cow had leaked colostrum prior to colostrum collection. Without being present on the farms for every cow enrolled in the study at the time of calving through to colostrum collection, this was difficult to avoid. 242 Australian Veterinary Journal Volume 95 No 7, July Australian Veterinary Association

7 Conclusions The results from this study showed that the majority of the colostrum samples assessed in the study herds were poor quality, having a Brix% < 22. Only 39% of the colostrum samples had a Brix% 22, which equates to 50 g/l of IgG, and is considered to indicate high-quality colostrum. Herd, lactation number, calf suckle prior to colostrum collection, cow leaking colostrum prior to collection and time between calving and colostrum collection influenced the colostrum IgG concentration. The results support the current recommendations of harvesting colostrum shortly after parturition (ideally within 12 h of calving) and testing the quality of all colostrum, regardless of the cow breed, lactation number and other nonquantitative measures, before being fed to dairy calves. The practice of selecting and storing high-quality colostrum (> 50 g/l IgG) is recommended to supplement calves when supply of high-quality fresh colostrum is limited. Acknowledgments The authors thank the four participating farm owners for their assistance and involvement in the current research. Conflicts of interest and sources of funding The study was supported in part by Rochester Veterinary Practice, Dairy Australia, Gardiner Foundation and the University of Melbourne, Faculty of Veterinary and Agricultural Sciences. References 1. Bush LJ, Staley T. Absorption of colostral immunoglobulins in newborn calves. J Dairy Sci 1980;63: Quigley JD, Drewry JJ. Nutrient and immunity transfer from cow to calf preand postcalving. J Dairy Sci 1998;81: Vogels Z, Chuck GM, Morton JM. Failure of transfer of passive immunity and agammaglobulinaemia in calves in south-west Victorian dairy herds: prevalence and risk factors. Aust Vet J 2013;91: Phipps A. Colostrum management practices and effects on colostrum quality on commercial northern Victorian dairy farms. MVSc (Clinical) thesis. University of Melbourne, Quigley JD, Lago A, Chapman C et al. 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