Department of Agricultural Economics and Business, University of Guelph,
Guelph, Ontario N1G 2W1, Canada
E-mail: howard@agec.uoguelph.ca
Take Home Message
Somatic cell count (SCC) scores for individual cows are more accurate than bulk tank SCC scores for monitoring udder health and milk loss due to mastitis. Comparing the costs and benefits of recommended mastitis control practices indicates that teat dipping after milking, washing, and drying udders before milking, and regular milking machine maintenance are economical. Using a sanitizer in the washing solution and having a service company change inflations is not economical. Dry cow treatment has mixed results: treating all quarters of all cows is economical, but the difference between benefits and costs is even greater when treating selected cows only. However, the selection criteria is not known.
Introduction
Mastitis is a general term referring to an infection of a mammary gland. It is estimated that mastitis costs dairy producers $750/cow/year in terms of lower milk production, cost of medicine, treatment time, and premature culling. Moreover, 70 to 80% of that loss is due to subclinical mastitis, which is nonsymptomatic (6, 7). It is possible that Canadian dairy producers suffer losses due to mastitis without being aware of the problem. Given the nonsymptomatic nature of subclinical mastitis, many producers use the somatic cell count (SCC) as a quick indicator of udder health. While it is not possible to completely eliminate losses due to mastitis, there are recommended herd health practices that minimize the occurrence of mastitis. National and international mastitis councils generally agree on five recommended mastitis control practices: washing and drying udders before milking, regular milking machine maintenance, teat dipping, dry cow treatment, and culling cows with recurrent mastitis (8).
This paper has two objectives:
Additional questions about mastitis addressed in this paper include influence of udder washing and drying practices, whether larger herds have more mastitis problems, and whether regular milking machine and veterinary services are economical. Questions about dry cow treatment are also raised.
Methods
Several recommended control practices have been found to have substantial returns over costs in controlled experiments (7, 8). However, experimental results and the results producers obtain in the field can be substantially different (1). Moreover, differences in herd size, environmental conditions, and production systems (e.g., pipeline vs. Milking parlour) can yield different effects of various control practices on udder health and, subsequently, udder health on milk yield. Therefore, a "farm trial" under field conditions is the preferred way to evaluate the efficacy and cost effectiveness of mastitis control practices.
Survey data were combined with Dairy Herd Improvement (DHI) data; in essence a "farm trial" of the affect of management practices on milk yield and SCC. Dairy producers were surveyed in Texas and in Ontario. Only producers who were on the SCC option of DHI were surveyed. There is possible bias in that the producers surveyed may have a greater awareness and concern about mastitis as evidenced by their enrollment in the SCC option.
A statistical model was estimated of milk yield (MKG) as a function of SCC and producer and production characteristics (P) (e.g., experience and eduction of the farmer, size of herd, etc.) and SCC as a function of producer and production characteristics and management practices (M) (e.g., teat dip, treat all cows with antibiotics at drying off, etc.). The model had the form
MKG = f(SCC, P)
SCC = g(M,P).
The Texas and Ontario data were estimated separately. Over two-thirds of the variables were statistically significant in explaining variation in milk yield and SCC. Details of the studies can be found in Howard et al. (3), Gill et al. (2), Howard et al. (4), and Howard et al. 1992.
Results
Data on management practices, producer and production characteristics, individual cow milk yields, and SCC were collected from 138 herds in Texas and 719 herds in Ontario. Given the wide range of herd size (average herd size was 204 in Texas vs. 55 in Ontario), differences in milking systems (parlour vs. pipeline), and climate, the results from the studies are surprisingly similar and robust.
Only about one-third of the producers surveyed used all five recommended practices. There is a slightly higher frequency of use of the recommended practice in Texas compared to Ontario, as reported in Table 1. The biggest difference in frequency of use - hand-held sprayers used by 4.1% of producers in Ontario compared to 70.3% in Texas - is due to differences in milking systems, which is likely due to the difference in herd size and the much greater use of milking parlours vs. pipelines; the management practices are similar. Even the SCC level at which culling should occur is about the same.
Table 1. Description, frequency, and means of selected management practices and production characteristics for dairy farms in Ontario and Texas.
| Ontario | Texas | |
| Washing Practices
Automated pre-wash Hand-held sprayer Re-usable sponge or cloth Sanitizer used in washing solution |
NA
4.1 14.9 91.1 |
5.8
70.3 8.7 45.7 |
| Drying Practices
Udders always dried Single-use paper towels Newspapers |
57.7
39.9 32.2 |
74.5
58.7 NA |
| Other Practices
Pre-milking check Teat dip after milking Dry cow treatment - all cows - select cows Servicing every 6 months Vet visit on regular basis Inflations changed as needed Mastitis basis of culling SCC level for culling |
39.1
91.5 65.6 28.2 NA 25.0 13.9 89.5 6.00 |
42.0
94.2 77.5 NA 50.0 36.2 NA 71.0 6.56 |
| Herd Size | 55 | 204 |
| Age of Operator | 45 | 40 |
| Education Level | High School | College Grad |
It is somewhat surprising that not all producers are using all of the recommended practices, given that several studies have reported the efficacy and economic benefits of the recommended practices, and that the producers surveyed have indicated their awareness of the importance of udder health by enrolling in the SCC option. As will be discussed, producers may be aware of the difference between results obtained from experiment station herds and commercial operations.
Milk Yield and SCC
Several studies have found a statistically significant, negative relationship between milk yield and SCC. The percentage of milk loss due to increased SCC for both individual cows and for a herd are reported in Figure 1. There is no significant difference in the milk loss function whether milk is modelled as fluid milk or separated into fat and protein components. Also, the loss function did not change significantly between first and later lactation cows. Jones et al. (5) reported a similar loss function, but it was greater for later lactation cows.
The herd model shows a clearly negative relationship, but unlike the cow models, the herd model estimates no appreciable milk loss with herd average SCC scores of four or less. Comparison of the individual cow and herd models indicate that producers who depend on bulk tank SCC as an indicator of udder health may not be receiving full information about the health and production of their herd.
Benefits and Costs of Mastitis Control Practices
The important question for dairy producers is whether the benefit from each mastitis control practice exceeds its cost. Statistical analysis of the effect of management practices on SCC were combined with the estimated effect on milk production to determine the effect of the management practice on milk yield. Specifically, a cow with an average SCC score and average values for the production and producer characteristics was assumed as the benchmark. The effect of implementing a practice on SCC was then calculated, and milk production was recalculated using the new SCC score. The difference in milk yield with and without the practice was multiplied by the price for fluid milk. The cost of implementing the practice was based on cost information from surveys of 11 selected producers in Texas and 12 in Ontario. All values are in Canadian dollars.
Estimated costs and benefits for selected management practices are reported in Table 2. There is a mix of expected and unexpected results. Several questions were asked in Ontario, but not in Texas due to differences in size and type of operating systems. For example, almost all farms in Texas had milking parlours and washed udders using hand-held sprayers. A few Texas farms had automated pre-wash sprayers. Ontario farms used a variety of washing methods and no one had a pre-wash sprayer.
It is recommended that reusable cloth or sponges not be used to wash or dry udders as the cloth or sponge can harbour and spread bacteria. Single-use paper towels are recommended for both washing and drying. As reported in Table 2, there is no difference in the benefit of using single-use paper towels vs. a reusable cloth or sponge to wash udders, but the cost of the cloth or sponge is much less than paper towels. The greatest benefit associated with washing comes from using a hand-held sprayer. The cost of a hand-held sprayer decreases with the number of cows milked, so there is no estimated per cow cost reported.
There is no benefit from using a sanitizer in the washing solution. In fact, both the Texas and Ontario surveys reported higher SCC scores in herds where a sanitizer was used in the washing solution. It may seem counter-intuitive, but when washing udders, plain water is as effective, if not better, than water with a sanitizing solution.
The benefits and costs of drying practices were mixed. Single-use paper towels for drying udders is recommended, but in Texas single-use paper towels were associated with higher SCC scores, and were clearly not economical. In Ontario the practice was economical. What is clear is that drying udders with a reusable cloth or sponge is a low cost drying method, but it is associated with higher SCC scores and is not economical.
Table 2. Costs and benefits of selected mastitis control practices in dairy herds in Texas and Ontario.
| Texas | Ontario | |||
| Cost | Benefit | Cost | Benefit | |
| Individual paper towels used to wash udder | NA | NA | 5.16 | 26.63 |
| Re-usable sponge or cloth used to wash udder | NA | NA | .58 | 26.63 |
| Hand held sprayer used to wash udder | NA | NA | NA | 59.65 |
| Sanitizer used in washing solution | 6.27 | -20.79 | 2.89 | -9.81 |
| Single use paper towel to dry udder | 16.22 | -27.97 | 5.14 | 7.16 |
| Reusable sponge or cloth to dry udder | NA | NA | .58 | -.77 |
| Teat Dipping | 22.00 | 73.34 | 8.87 | 75.53 |
| Milking Machine
Inflations change by company Inflations change by farmer Serviced every 6 months |
NA
NA .98 |
NA
NA 10.83 |
6.62
5.15 |
5.80
5.80 |
| Dry Cow Treatment
- to all cows - to selected cows |
7.85
NA |
-2.68
NA |
8.27
8.27 |
11.06
30.25 |
Teat dipping after milking is clearly an effective and economical way to control mastitis on dairy farms. Given the overwhelming amount of information about the effectiveness and economics of teat dipping, it is surprising that there are still dairy farmers who don't teat dip.
Having a well-maintained milking machine is a recommended way to minimize mastitis. There is a benefit from changing milking machine inflations as needed (i.e., when they slip or "squawk") as opposed to only when scheduled, but the costs are higher than the benefit when a service company does the changing. However, the benefit from servicing the whole milking system at least every six months is much greater than the cost of that servicing.
Dry cow treatment had mixed results. The recommendation is to treat all quarters of all cows at drying off. In Texas this practice was associated with higher SCC scores and was not economical. In Ontario the benefit of treating all cows was only slightly greater than the cost of treatment, but the benefit of treating "selected cows" (the selection criteria are not known) was greater than the costs. The US National Mastitis Council and most veterinarians say that treating all quarters of all cows is the best and safest way to use dry cow treatment to minimize mastitis; however, two studies report that it is more economical to treat "selected cows" rather than the whole herd. Studies of dry cow treatment on experiment station herds report that it is an effective and economical practice. Farm trials and other field studies have had at best mixed results. Further research needs to be done to determine if there are consistent selection criteria that farmers can use to treat only those cows with a tendency to mastitis without increasing the risk of a general flare-up of mastitis throughout the herd.
Other Findings
Regularly scheduled visits by veterinarians (as opposed to emergency or clinical calls only) were associated with lower SCC scores in both studies. The costs of the scheduled visit must vary widely, depending on a number of factors, but the results indicate that herd health maintenance programs are more economical than emergency or clinical visits.
There is some concern that as dairy herds get larger and the number of employees increase that SCC will also increase. The results indicate that herd size and number of employees may cause management problems, but not necessarily mastitis problems. In Texas, SCC decreased as herds got larger, while in Ontario SCC increased with herd size, but at a very slow rate. (The SCC score increased by 0.004 per cow above 55 cows. Everything else being equal, a herd of 110 cows would have an SCC score 0.22 higher than a herd of 55 cows.) Neither study found a significant relationship between the number of employees doing the milking and SCC.
Lastly, dairy farmers who regularly attended extension seminars were associated with significantly lower SCC scores. It may be difficult to measure the costs and benefits of extension seminars, but the benefits are likely much greater than the costs.
References
Gill, Ravinderpal, W.H. Howard, K.E. Leslie and K. Lissemore. 1990. Economics of Mastitis Control. J. Dairy Sci. 73:3340-3348.
3. Howard, W.H., T.O. Knight, C.R. Shumway, R.W. Blake and M.A. Tomaszewski. 1987. Information and Herd Health Management Practices in Texas Dairies. Southern Journal of Agricultural Economics, 19(2):1-10.
Natzke, R.P. 1981. Elements of Mastitis Control. J. Dairy Sci. 64:1431.
Philpot, W.N. 1984. Mastitis Management. Babson Brothers Co., Oak Brook, IL.