Troubleshooting Records to Determine Udder Health Problems
Allen J. Young
Extension Dairy Management Specialist

Mastitis is a costly disease of the mammary gland. It has been estimated that each incidence of mastitis costs the dairy producer $105 - 110; primarily in lost milk sales. Summers are the time of the year when the incidence of mastitis goes up on most farms. That means now is the time to evaluate your herd health program and make sure it is in good working order. This will help prevent the incidence of mastitis from becoming unmanageable. If you are currently having a problem, now is the time to fix it before summer gets here.

How do you know if you have a problem right now? If you are not on DHI, you can use processor records or your on-farm record system. If you are on DHI, you have at least one tool each month that will help. It is called the Herd Summary. On row two of the summary you will find a section entitled Somatic Cell Summary. The level of somatic cells in the milk is a window to the amount of mastitis in your herd. Most mastitis is sub-clinical, which means you don't see any flakes or clumps in the milk, but mastitis is still there. A copy of this section is shown below in Table 1. How can you use this section to evaluate your herd?

Table 1. From Herd Summary (row 2).

L a c t	Somatic Cell Summary
	Low 0-4	Med 5-6	High 7-8	% L	% M	% H	Avg L2	Avg SCC	30 Day Loss	Chg SCS		1st Test	45 - 180	181 - 305	> 305
										% UP	% DN
1	42	1		98	2		1.3	64	0.37			2.0	1.2	1.4	1.7
2	25	4		86	14		2.6	114	1.97	7		3.1	1.4	3.0	4.2
3	60	12	1	82	16	1	2.2	168	2.36	8	3	5.0	1.4	2.4	3.6
T	127	17	1	88	12	1	2.0	130	1.80	6	1	3.7	1.4	2.3	3.3

The table is divided according to the percentage of cows which fall into three categories or levels of somatic cells in the milk: low, medium, and high. Your goal is to have the highest percentage of your herd in the low (0-4) category. The greater the incidence of mastitis in your herd, the higher the percentage of cows which will fall in the medium and high groups. Herds with excellent udder health will have greater than 88% of their herd in the low (0 - 4) category. Values of 65% or less in the low category are considered poor and should be corrected immediately.

The second thing to look at is where the problem is occurring. You can look at this in two dimensions. The first is which groups of animals are having a problem (1, 2, 3+ lactation) and second, at what point in their lactation (1st test, 45 - 180, 181-305, or >305 days in milk) is the problem occurring. To understand this you need to understand a little about how the Linear Score (LS or L2) scale works.

The LS (L2) is a mathematical way of converting the raw Somatic Cell Count (SCC) to a linear scoring system. For each increase of 1 unit of Linear Score, the Somatic Cell Count doubles (see Table 2). At the lower linear scores, that isn't as much of a change in the somatic cell count for each unit change as at the higher scores. For example, going from a LS of 1 to a 2 is only a difference of 25,000 SCC, while going from a 4 to a 5 is 200,000. I generally consider a herd with a LS of 4.5 and above to be having problems. Currently there are proposals to lower the legal limit of somatic cells from 750,000 down to 600,000 (LS 5.5) or 400,000 (LS 5). If these proposals are approved, then the LS at which herds approach the trouble zone will also decrease. My advice is to stay away from the line.

Table 2. Somatic cell count as related to linear score and milk losses.

Somatic Cell Count (Thousands)			Milk Yield Losses
Linear Score (LS)	Average	Range	Per Day		Per 305 Lactation
			1st1	2nd(+)2	1st1	2nd(+)2
0	12.5	0 - 17
1	25	18 - 34
2	50	35 - 68	Pounds of milk loss relative ot LS 2.0
3	100	69 - 136	0.75	1.5	200	400
4	200	137 - 273	1.5	3.0	400	800
5	400	274 - 546	2.25	4.5	600	1200
6	800	547 - 1092	3.0	6.0	800	1600
7	1600	1093 - 2185	3.75	7.5	1000	2000
8	3200	2186 - 4371	4.5	9.0	1200	2400
9	6400	4372 or more	5.25	10.5	1400	2800

¹ Refers to 1st lactation animals.
² Refers to 2nd and older animals.
From Cornell University mimeo series # 124, 1987.

Now back to the example herd. Generally this herd is doing an excellent job with the lst lactation animals and very good with the 2nd and 3+ lactation animals in terms of % cows in the low (0-4) category. The average LS or L2 is generally good. If you look at the LS by stage of lactation, 1st lactation animals are doing really well. The 2nd lactation animals are getting into the danger zone in late lactation (>305 DIM). The biggest problem here is that the 3+ lactation cows are calving in at a very high LS (5.0), then dropping. In this case, this is a herd that looks good at first glance, but does have one area which could be improved. This herd could help itself by looking at the calving area (possibly also the dry cow area) to make sure it is clean and sanitary. One last thing to look at is the %UP or %DN. This is a measure of the percentage of cows, by lactation #, that had an increase in SCC from below a LS of 5.0 from the last test day to above LS 5.0 on this test day. The % DN is just the opposite; above a LS of 5.0 on last test day to below LS 5.0 on this test day. If you start seeing an increase in the %UP, then immediately start evaluating your udder health program and do something now before it becomes a big problem.

Why should you care or put any effort into keeping the SCC low? I have three reasons: MONEY, MONEY, and MONEY. It is less costly to prevent mastitis, than treat it. It costs money to treat mastitis cases and dump milk, it costs money in lost quality bonuses, and it costs money in decreased milk production per cow. The herd summary computes this for you in the column called "30 Day Loss" (Table 1). In our example, they are losing, on average, $1.80 per cow per 30 days. For a 100-cow herd this would be $180 milk per month. Assuming you maintained this level for one year, it would come to $2160. This herd has a low SCC and is losing a relatively small amount of money, but in herds with problems the amount of money being lost is quite large. This doesn't include lost quality bonuses, the possibility of dumping milk, possible loss of milk license, or the aggravation of dealing with the problem. Table 2 gives another perspective of how much can be lost due to mastitis.

In conclusion, your records can give you a window to how your herd is doing. Take time to get your money's worth out of them. For further questions or help, contact your county extension agent.