Effect of milking systems on the milk somatic cell counts and composition

A K Dang and S K Anand

National Dairy Research Institute, Karnal - 132 001 (Haryana), India
rajadang@rediffmail.com

Abstract

The objective of this study was to investigate the relationship of milk somatic cell counts, with regard to the milking practices followed under organized farms, under peri-urban systems and in single holdings under rural conditions. Milk samples were collected from 32 crossbred (CB) cow; 16 each milked under the Flat barn and Vario-Tandem Parlors, and were analyzed for SCC and milk composition. Distinction was also made between samples collected from bucket milked and hand milked CB cows. The operations at the time of milking were recorded along with milk yield of individual animals. Milk samples collected from CMT negative animals were analyzed for fat, protein and lactose.

Average values of SCC were higher (P<0.01) in hand milked animals than machine milked cows. Lactose was found to be significantly lower (P< 0.01) in hand milked cows, whereas, changes in fat and proteins were not significant. Milking practices followed by farmers need improvements to obtain clean milk production under field conditions.

Key words: Bucket milking, flat barn, hand milking, milk composition, milking parlor, milking practices, SCC, Vario-Tandem

Introduction

Somatic cells of milk are white blood cells and epithelial cells, which slough off from the lining of the mammary gland during normal course of milking (Harmon 1994). They are widely used as marker to determine the mammary health and quality of milk (Dohoo and Meek 1982 and Eberhart et al 1982). Milk from healthy mammary gland has about 10⁵ somatic cells/ml and values higher than this indicates secretary disturbances (Dang and Singh 2006). Hamann (2002) termed the word "Gold Standard" for a cell count of up to 100 000 cells/ml and values of milk above 100 000 cells/ml results in reduction in the milk production and processing properties of milk. Considerable literature is available on normal values of SCC in organized dairy herds, but information on the relationship of various farm management practices with the composition of milk under different production system is not available. Therefore, the purpose of the present study was to evaluate differences in management practices amongst herds with low and high SCC and their effect on milk composition.
 

Materials and methods

Milking set-ups

The present study was conducted both in the Institute's herd, in an organized dairy farm and under village conditions with single animal holdings. The method of milking varied with the type of production system; machine milking in the Flat Barn and Vario-Tandem parlor was practiced in the Institute's farm. The Flat Barn parlor was modified from the existing hand milked parlor where milking equipment was mounted. In this type of parlor, the cows entered in a group, and the milker washed coat and udders of individual cows. The cows were then provided feed concentrate according to their milk yield followed by attachment of milking unit (Photograph:1).

Under this system space was provided between cows for mounting equipment and between milkers. Milking equipment also has to be protected from damage by any movement caused by cows. Milking units were removed and cleaned manually.

On the other hand, in the Vario-Tandem parlor, each cow was admitted through an entrance gate. The cows were washed under the sprinkler systems and each cow entered an individual pen. This system not only provided safe and correct cow positioning, but there was also good visibility of the animal's udder to the milker. The cows were provided with feed concentrate, and the milker wiped the udder with cloth and put on the milking cluster (Photograph:2).

Milking units are cleaned automatically using a CIP system. Thus there was comparatively less human involvement in this type of milking parlor as compared to Flat-Barn parlor.

The progressive farmers of the organized farms practiced bucket system of milking. In this type of milking, the milking units and ancillary equipment were carried from cow to cow and the milk was transported, lifted and tipped manually. All the milking equipment was also cleaned manually. In contrast to this, cows were hand milked (Photograph:3) under the rural/village conditions.

Sampling

A total of 32 crossbred cows were selected from the Institute's herd, 16 each from Vario-Tandem and Flat Barn parlor. 12 Crossbred cows each were selected from progressive farms and from village level respectively. In progressive farm all the cows belonged to a single farmer, whereas under village conditions samples were collected from three farmers having 4 cows each. All the cows selected were multiparous and were in their mid-lactation. Milk sampling was done only once from each animal. All the lactating cows were fed with additional concentrates according to their milk yield. Information regarding management practices followed at the organized farms and under village conditions by the farmers was determined by means of a questionnaire. Questionnaire was filled in duplicate after interviewing the farmer and than by personally recording the management conditions practiced under each group. Six samples were also collected from the bulk milk tank of the institute in which milk samples of vario-tandem and flat-barn milks were pooled together. Udders of experimental animals were screened for mastitis using California Mastitis Test. None of the cows had any history of clinical mastitis. Only those milk samples, which were found negative for mastitis, were collected. Calf suckling was not practiced in the Institute farm, where all the calves were weaned at birth.

Counting of somatic cells in milk

The fine smear slide of somatic cell counts was prepared using 10 ml fresh milk sample by spreading it over a glass slide. The fine smear was dried in an oven at 30-40°C cooled and then dipped in xylene for 2 minutes to remove fat globules. Subsequently, slides were stained using methylene blue dye and excess of stain was removed from the smears with tap water. For preparation of methylene dye, to stain somatic cells and leukocytes, ethyl alcohol (54 ml) and tetrachloroethane (40 ml) were mixed in a bottle and heated in a water bath at 60 to 70°C for 15 minutes. Methylene blue dye was added to the solution carefully and kept in a refrigerator at 4°C for 30 minutes and then glacial acetic acid was added. The dye solution so prepared was filtered using a filter paper with a pore size of 10-12 micron and stored in a colored bottle. Only those cells, which possessed a blue stained nucleus, were counted. The SCC was measured under a microscope with a magnification of 40 x 10 X in 50 fields and average number of cells per field was multiplied by the microscopic factor (0.882). The microscopic factor was determined by using ocular and stage micrometer. Somatic cell counts/ml of milk (lakh) = Average cells count in one field x 0.882. (Singh and Dang 2002)

Aliquots of milk samples from each milking were composited in proportion to yields for milk analysis. Fat, protein and lactose were analyzed using a milk analyzer.

Statistical analysis

Somatic cell counts (after being transformed to log₁₀), milk yield and composition  were analysed using the GLM option in the ANOVA program of the Minitab software (Minitab 2000). Differences between means were identified using the Tukey test in the same software. .
 

Results and discussion

Management practices

A brief account of various management practices followed in the Institute's farm, at the organized farm and under village conditions have been presented in Table 1.

It may be noted that under the milking practices followed in the Institute's herd. Before every milking all the cows were washed under the sprinkler system. Their udders were thoroughly cleaned and teats wiped with towel. Milkers also washed their hands before milking. Milk was finally pooled in the bulk tank and stored in a refrigerated tank until transportation.

Similarly, progressive farmers also bathed and cleaned their cows before every milking. Cows were machine milked by the bucket system and udders were also washed after every milking. Milking practices being followed by the farmers under rural conditions indicated that washing of udder was also done before milking. Although farmers practiced full hand milking, hands were not being washed before milking in most cases. In addition to this, calves were allowed to suckle first few drops of milk. If there was no calf under the cow, the milk was added to the milking bucket. Milk of all the animals managed by a farmer was being collected in a single stainless steel or aluminum bucket irrespective of the health condition of animal. The above practices under the village conditions were found to be in total disagreement to our previous recommendations regarding clean milk production which advocated the discard of fore milk due to high microbial counts (Dang et al 2004). Also, for clean milk production sick or treated animals should be milked at last and their milk should not be collected in vessels with the milk of normal animals.

Regular screening of udder using the CMT and dipping of teats with iodophor solution after each milking was practiced in the Institute's farm. However, under the village conditions, although udders were washed after milking but practice of teat dipping was not being followed. It was also noticed that most of the farmers washed the udders of their lactating cows only in newly calved cows and that to for the first ten days after parturition. Regular screening of udders was not being practiced either under the organized farm or village conditions. The reasons for not following post milking udder washing were mainly related to awareness levels. It may be an important factor in influencing udder health. There are several previous report supporting teat dips like Neijenhuis et al (2001) observed that teat wall and cistern respectively were recovered only after 6 and 3 hours of milking, whereas, complete recovery of the teats took more than 9 hours. In a later study, the group also reported that post-milking teat dipping reduced the somatic cell counts of milk (Neijenhuis 2003).

On comparing the sanitary conditions under different milking systems. It was found that the milking places were having proper drainage and disposal system for both dung and urine under both the institute and at the progressive farmers level. However, under village system the floor were of mud type and there was lack of drainage system

Somatic cell counts

The average values of SCC of milk under different milking systems are presented in Figure 1.

Minimum values of milk SCC in Flat barn were 0.68 x 10⁵ and maximum values were1.66 x 10⁵ cells/ml of milk, whereas, minimum milk SCC values in Vario-Tandem parlor were almost similar to flat barn i.e., 0.60 x 10⁵ , but maximum values were higher i.e., 2.20 x 10⁵. In comparison to this, the values of SCC in organized farms under Bucket milking system were found to be higher and ranged from 1.11 to 2.12 x 10⁵ cells/ml of milk. SCC was found to be highest ranging from 1.27 to 2.27 x 10⁵ cells/ml of milk under the hand milking systems. Differences in these values were highly significant (P<0.01) with Flat Barn and significant (P<0.05) with Vario-Tandem parlors. On the other hand, SCC in bulk milk samples ranged from 0.42 to 0.80 x 10⁵ cells/ml of milk. For comparing the statistical treatments between various milking systems and bulk tank, samples collected from cows under different milking systems were compared with 6 samples collected from bulk tank and analysis of variance (ANOVA) was done by the method of Snedecor and Cochran (1994).

Statistically significant relationship was also found between management practices and SCC as previously reported by Barkema et al 1998. Similarly, Ohtani (1994) also reported that in the case of herds with mean lower SCC, dairymen kept their environment clean, had experience of milk hygiene practices and recognized the importance of the role of milking machines in the spread of pathogens. However, in herds with higher SCC, dairymen, in general, did not examine cows' teats and had little knowledge of milk hygiene practices and milk quality. Similarly, in the present study, SCC were found to be higher under village conditions as compared to other milking systems but all the values of SCC were within physiological range in the different milking systems.

Milk yield and composition

The average values of milk yield omposition under different milking systems are presented in Figure 2.

It may be observed that the values of fat and protein content ranged from 3.82 to 5.12 % and from 3.02 to 3.99 % respectively in all the milking systems. However, differences in the values of Fat and Protein were non-significant among different milking systems. Contrary to this, Hamann (2002) reported a decrease in 6 to 8% of protein in milk content in very high SCC herds (> 4.0 lakhs).

In the present study, values of lactose were found to range from 3.86 to 4.97 % respectively in CMT negative milk samples. Minimum values of 3.86 were reported under village conditions and differences in these values were highly significant (P<0.01) with Flat Barn and significant (P<0.05) with Vario-Tandem parlors. Most of the changes in milk composition in high cell count were related to decreased synthesis or increased leakage due to damage to udder tissue Schultz (1977). Similarly, Harmon (1994) also affirmed that there is a linear inverse relation between SCC and milk production. Higher SCC values also characterized some infection and resulted in a reduction of lactose between 5 and 20 %. As all the values of SCC under different milking systems were within physiological limits in the present study, therefore, not much change was observed in the overall composition of milk.

Although conducted at a small scale, present study provides the preliminary evidence that different types of machine milking may help in improving the quality of milk without affecting the composition of milk. At the Institute's herd where more attention was paid to hygienic milking practices, that helped in maintaining lower limits of SCC as compared to higher SCC values of rural conditions where all the recommended practices were not followed. In the machine milking systems, human interference was also comparatively less than hand milked which may be the reason for less milk SCC under these systems. The reasons for not following procedures like regular screening of udders or post milking teat dipping were found to be due to low awareness levels and economic reasons. Major concern under rural conditions is that even the minimal values of milk SCC are on the higher side indicating that mammary gland is under stress in these conditions. The work values vary between 1.26 and 1.54 x 10⁵ between organized and unorganized (rural) farms but it has been seen that this small difference due to poor management practices is very critical because more influx of milk SCC not only disrupts the mammary epithelium but also decreases milk quality (Singh and Dang 2002) which in turn leads to lower returns. Several of these issues can be addressed if we are able to link milk quality with payment. In a previous study also, Bailey and Heald (2000) reported that each load of milk picked up at the farm was tested for SCC and premiums or deductions were made on the milk prices based on the SCC quality. Similarly, Hamann (2002) also emphasized the need to combine payment of milk for quality not only with SCC but also with the changes in milk composition. So far there is no such practice being followed in the developing countries like India, where farmers are paid for their milk according to the fat percentage of milk. As consumers are becoming more health conscious and general awareness to produce clean milk is increasing, there is a need to educate dairy farmers to follow clean milk production and management practices, so that they get a good price for their milk and it matches international quality. In the end it can be concluded that better milking practices improve milk quality by keeping milk SCC to minimal levels.
 

References

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Received 26 February 2007; Accepted 5 May 2007; Published 1 June 2007

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