Samples of raw milk from bulk cooling tanks were collected in five municipalities of the Southwestern Brazilian Amazon to establish the prevalence of Staphylococcus aueus and Streptococcus agalactiae, as well as to evaluate the milk composition and its correlation with the bulk tank somatic cell count (BTSCC). A total of 250 samples were collected to investigate the causal agents of bovine mastitis in whole milk, from 50 bulk milk tanks in each municipality. Under laboratory conditions, the samples were diluted to 1/10 and 1/100, and samples of 0.1 ml from each dilution were plated in triplicate on selective media for Staphylococcus aureus and Streptococcus agalactiae. To evaluate the correlation between the major milk components (fat, protein and lactose) and the BTSCC, samples were collected for 18 months from 73 dairy herds. The presence of the above-mentioned contagious mastitis pathogens was detected in 97.2% (243/250) of refrigerated raw milk samples evaluated. Analysis of the major milk components and BTSCC demonstrated that during the study period, fat compo-nent showed the largest variance, followed by protein and lactose, which also showed significant variances.
Brazilian dairy production is spread throughout the country. New dairy cattle centers have become established in the Amazon, especially in Rondônia state, located in the Southwestern Amazon. In 2012, the state produced 795,464 million liters, or approximately 2.18 million liters per day [
Mastitis is the most important and economically damaging disease in the dairy industry [
Isolation of microorganisms in whole milk of herds is only possible when mammary gland infection is present in the herd [
Two of the most important objectives of milk analysis are identification of pathogenic microorganisms’ presence and determination of the milk components. The diagnosis of mastitis agents can be done by a culture assay of whole milk samples collected within a herd [
The minimum composition parameters of the cooled raw milk sold in Brazil are established by federal regulations. The minimum composition parameters established for milk production in Brazilian dairy farms are 3.00% fat content, 2.90% total protein content, and 8.40% non-fat solids (NFS) content. In terms of mammary gland health, the maximum SCC levels are being gradually reduced in Brazil. The current limit is 3.6 × 105 SC/ml, which is considered appropriate for sale of milk and its derivatives [
Milk quality studies are incipient for dairy herds established in the Southwestern Brazilian Amazon. The prevalence of the main pathogens involved in mastitis infection is unknown for this region. Thus, the present study attempted to establish the frequency of Staphylococcus aureus and Streptococcus agalactiae infection in the region, as well as to correlate the herd milk composition with the SCC of refrigerated milk samples collected in bulk tanks.
Samples of refrigerated raw milk were collected in bulk tanks located in the municipalities of the main milk-producing area of Rondônia (
A total of 250 raw milk samples were collected, from 50 bulk milk tanks in each municipality. The minimum sample size was determined considering the confidence level of the result, the desired accuracy level and the expected prevalence of mammary infection in the herds, using the formula for simple random samples recommended by Thrusfield [
where: n = number of tanks sampled per municipality,
P = expected prevalence, and
d = desired accuracy (p = 5%).
The procedures recommended by the International Dairy Federation were considered for collection, handling, and maintenance of the milk samples [
The identification of Streptococcus agalactiae and Staphylococcus aureus in the raw milk samples was performed with commercial kits: the Streptococcus agalactiae kit® (Probac do Brasil) and Agar Vogel Johnson kit® (Probac do Brasil) used according to the manufacturer’s recommendations.
Evaluation of the raw milk components and the BTSCC were performed during 18 months during which 73 dairy herds were evaluated. The sampling intervals were about 45 days, resulting in a total of 541 samples evaluated in the period. Means were calculated for fat, protein, NFS, and SCC to evaluate the influence of the dry (May to September) and the rainy (October to April) seasons on milk composition and SSC. The effect of season on the concentrations of fat, protein, and NFS was evaluated by a generalized linear model [
The milk samples analyzed with use of selective media to estimate the prevalence of Streptococcus agalactiae and Staphylococcus aureus (higher than 94%) with good accuracy (lower than 5%) (
Of the total of 250 samples evaluated, agents of contagious mastitis (Streptococcus agalactiae or Staphylococcus aureus) were isolated in 243 samples (97.2%). Streptococcus agalactiae and Staphylococcus aureus together were isolated in 170 samples (68%), while Staphylococcus aureus alone was isolated in 56 samples (22.4%) and Streptococcus agalactiae was isolated alone in 17 samples (6.8%). Only seven milk samples (2.8%) showed no bacterial growth on the selective media for Streptococcus agalactiae or Staphylococcus aureus (
The samples for BTSCC were collected from March 2008 to July 2009. The average concentrations of milk components and the SCC are shown in
Although the milk components and the SCC showed values in accordance with the Brazilian rules on milk quality, some samples were outside the legally established thresholds. SCC was the milk quality indicator with the highest percentage of samples above the limits (19.4%), followed by NFS (13.2%) and fat contents (8.9%). The protein content showed the lowest percentage of samples below the established limits for milk quality (6.4%) (
Isolation on selective media | ||||
---|---|---|---|---|
Municipality | Streptococcus agalactiae | Staphylococcus aureus | Streptococcus agalactiae + Staphylococcus aureus | No isolation |
Ji-Paraná | 0/50 (0%) | 13/50 (26%) | 37/50 (74%) | 0/50 (0%) |
Ouro Preto do Oeste | 0/50 (0%) | 8/50 (16%) | 42/50 (84%) | 0/50 (0%) |
Jarú | 10/50 (20%) | 11/50 (22%) | 25/50 (50%) | 4/50 (8%) |
Presidente Médici | 3/50 (6%) | 0/50 (0%) | 47/50 (94%) | 0/50 (0%) |
Rolim de Moura | 4/50 (8%) | 24/50 (48%) | 19/50 (38%) | 3/50 (6%) |
Total | 17/250 (6.8%) | 56/250 (22.4%) | 170/250 (68.0%) | 7/250 (2.8%) |
Collection Month | Fat (%) | Protein (%) | Lactose (%) | NFS (%) | TS (%) | SCC (cells/ml−1) | |
---|---|---|---|---|---|---|---|
March 2008 | 4.03 | 3.35 | 4.54 | 8.84 | 12.89 | 233 | |
April 2008 | 3.67 | 3.27 | 4.56 | 8.51 | 12.20 | 265 | |
June 2008 | 3.73 | 3.41 | 4.45 | 8.83 | 12.57 | 259 | |
August 2008 | 3.52 | 3.04 | 4.44 | 8.41 | 11.95 | 328 | |
October 2008 | 3.52 | 3.13 | 4.62 | 8.87 | 12.27 | 276 | |
February 2009 | 3.62 | 3.28 | 4.66 | 8.97 | 12.59 | 292 | |
March 2009 | 3.78 | 3.48 | 4.35 | 8.78 | 12.57 | 263 | |
May 2009 | 3.86 | 3.46 | 4.40 | 8.63 | 12.51 | 254 | |
June 2009 | 3.61 | 3.39 | 4.43 | 8.76 | 12.38 | 290 | |
July 2009 | 3.51 | 3.26 | 4.47 | 8.68 | 12.20 | 366 | |
Mean | 3.62 | 3.28 | 4.50 | 8.69 | 12.31 | 289 |
Legal Parameter | Number of samples collected (n) | Samples in accordance with the legal parameters (%) | |
---|---|---|---|
Fat (%) | ≥3.00 | 484 | 91.2 |
<3.00 | 47 | 09.8 | |
Protein (%) | ≥2.90 | 497 | 93.6 |
<2.90 | 34 | 06.4 | |
NFS (%) | ≥8.40 | 461 | 86.8 |
<8.40 | 70 | 13.2 | |
SCC (cells/ml−1) | ≤400,000 | 428 | 80.6 |
>400,000 | 103 | 19.4 |
The average of fat observed in the samples was 3.62% (confidence level of 95%, 3.58% - 3.66%). The SCC results showed significant variation (P < 0.05) in the concentration of milk components (fat, protein and lactose), accounting for 4.0% to 8.0% total variation. The milk fat content was not significantly affected by the season. In contrast, the protein and lactose contents significantly changed according to the season (P < 0.05).
The influence of BTSCC on milk component concentrations can be explained by reduced ability of the breast tissue to synthesize milk components. This situation is caused by lesions caused promoted by mastitis-inducing pathogens in association with the presence of proteolytic and lipolytic enzymes in the udder, secondary to somatic cell migration from the blood into the mammary gland tissue [
Physiological factors can increase the cell count in some cases. In udder health monitoring programs, the use of a threshold of 200,000 cells/ml to denote the prevalence of subclinical mastitis has been reported [
Although microbiological analysis offers advantages, it is important consider that it should not replace the individual clinical assessment of cows’ udders in order to verify the presence or not mammary infections. The isolation of etiological mastitis agents using bulk milk samples can be considered a useful tool for monitoring mastitis in control programs, but the results cannot be used to predict the number of infected mammary quarters in a herd [
However, the Staphylococcus aureus and Streptococcus agalactiae isolation found in this monitoring study of quality milk show that the microbiological analysis of bulk milk samples is an efficient tool to assess the presence of etiological mastitis agents in dairy herds. The results observed by Brito et al. [
The efficiency of BTSCC to detect the variance in the milk contents can be explained by the reduced ability of the mammary tissue to synthesize milk components. Injuries promoted by mastitis-causing pathogens in association with proteolytic and lipolytic enzymes are probably caused by lesions in the udder that occur by somatic cell migration from the blood into the mammary gland tissue. In light of the findings of Schäellibaum [
The present results indicate that the analysis of bulk milk from herds is a viable tool for monitoring udder health in dairy herds. Single samples of bulk milk allowed isolating etiological mastitis agents and tracking the influence of SCC on the composition of milk produced in the analyzed herds. The assessed prevalence of Staphylococcus aureus and Streptococcus agalactiae, as well as the influence of SCC on milk component levels, demonstrates there are important challenges to be overcome by dairy farmers so that the milk produced is in accordance with the sanitary-hygienic limits established by Brazilian regulations. Studies and initiatives aimed at establishing strategies to decrease the prevalence of mastitis and reduce the SCC in dairy herds are promising research fields what will help to ensure the sustainability of dairy farming.
The study received financial support from the National Council for Scientific and Technological Development (CNPq, Process No. 554110/2005-9) and Rondônia Dairy Chamber (Proleite). The authors thank Antonio Xavier do Nascimento of the Embrapa Rondônia Animal Health Laboratory for valuable assistance in conducting the laboratory assays and all the technical staff of Emater Rondônia, who helped in collecting of the milk samples used in the study.
The authors declare there is no conflict of interest regarding the publication of this article.
Brito, L.G., Júnior, J.R.V., da S. Barbieri, F., Rocha, R.B., Figueiró, M.R., da Silva, W.C., Carvalho, G.L.O., de Arimatéia Silva, J. and Souza, G.N. (2016) Evaluation of Milk Compositional Quality and Mammary Gland Health of Dairy Herds in the Southwestern Brazilian Amazon. Open Journal of Veterinary Medicine, 6, 139-148. http://dx.doi.org/10.4236/ojvm.2016.69018