SCC was added to bulk tank testing decades ago to enhance the information gained from Plate Bacteria counts for milk quality. While bacteria counts measure milking environment cleanliness, Somatic Cell counts measure cow health. When one or the other is too high, milk shelf life suffers; when both are high, milk quality (as well as processing yield) suffers as well. USA legal limits for SCC were recently lowered to 400,000 (cells/ milliliter of milk sampled) to conform to an international standard; this aids USA milk handlers in meeting export requirements so we can continue to seek foreign outlets for surplus production.
What is a “somatic” cell?
A somatic cell is any cell of the body except for ovum (female) and sperm (male) germ plasm. Any cell with a nucleus, produced in the cow’s body (of internal or foreign origin) is somatic. Unlike many have been told, or have assumed, it does not mean “mastitis”. The majority of somatic cells found in milk are a result of “immune system” function, and are white blood cells released to fight any infectious challenge, which could be respiratory, bacterial or viral infections, mastitis, uterine infection post-calving, even hoof rot or heel warts. Beyond that you may find epithelial (skin) cells which are shed at the end of milking by higher butterfat% and/or protein% milk, when the bulk of milk solids are released.
What is a “normal” level?
Think of it this way to have perspective—dead cows release “zero” somatic cells in their milk. A cow below 40,000 SCC in milk may have depressed immune function, not producing enough leukocyte cells to fight off an infectious challenge. The optimum level of SCC is probably 50,000 to 100,000 cells based on stage of lactation (very stale cows with low milk production are going to have more cells than healthy fresh cows at their peak milk production). SCC levels will be higher in years following a rainy forage harvest season (such as 2015), when energy values (including sunlight vitamins) are lower in feed. The higher levels of grain supplements fed in such years increase rumen acidity, thus lowering rumen health.
Any environmental situation that lowers cow health can increase SCC even with a total absence of any symptoms of clinical disease. The immune system, when working harder, releases more leukocytes and the udder is the organ that flushes them from the cow’s body once their usefulness is spent.
Can we breed for lower SCC levels?
YES we can, which is why we have always presented our sires in a “health trait” rather than an index rank ordering. In every breed, the “average” SCC level is set at 3.00; bulls whose daughters are better than average score below 3.00, those whose daughters are worse than average score above 3.00.
What is “average”? A couple summers ago, the July milk received by MMPA averaged 266,000 SCC. It is not unusual for spring-summer milk (as it gets hotter) to be a bit higher than fall-winter SCCs. For illustration, let’s assume “average” cows are around 240,000 SCC over their entire lactation. This means that (using logarithmic scales) a 1.00 SCC is around 80,000; a 2.00 SCC is around 160,000, while a 4.00 SCC is around 320,000 and a 5.00 SCC is reaching the illegal 400,000+ level.
The range of SCC today for active AI sires is basically from 2.40 to 3.60. (The worst SCC printed on any bull we ever handled was 3.83 for Shoremar Mason of Semex; the best was 2.44 on Futuraland Zade of Intl Protein Sires.) The worst SCC offenders today disappear from price lists because SCS is a major piece of $NM indexes. 3.80 SCS x 80,000 = 304,000 SCC in Michigan, half his daughters worse…
How heritable is SCS?
The calculated heritability of the PTA-SCS measurement is 15%. Compare this to 25% for milk volume and 30% for butterfat and protein volume; compare this to 10% for linear feet and leg traits. Ignoring this piece of information and assuming you can totally control SCC by milking procedures and higher volume of production (to dilute the cell counts) is asking for trouble over time.
Can we breed for stronger immune systems?
Pfizer Co has a few million dollars betting on this, as they collect Genome data in their contracted “test” herds. University of Guelph (Ontario) patented some research identifying an immune system genome, which Semex markets as “Immunity Plus”. Within the “I+” bulls there is still a range of individual SCS for each progeny group, so these genome links are not (as yet) the total answer.
Understanding that SCS is an aspect of a functioning blood circulatory system, however, does support the “aAa” concept that Strong (code 4) cattle are more likely to have healthy circulation and immunity. In support of this, note that Futuraland Zade (and his sire Carol Prelude Moto) both had aAa “4” strong while Shoremar Mason has his “4” quality down to fifth place (out of six “aAa” qualities). Maintaining levels of Strong quality “4” possession in your cows will produce physiques that are more likely to have higher levels of immune system function. Other qualities [such as Tall (code 2) which improves udder texture on heifers from meaty uddered dams] can also enhance SCC avoidance, as mastitis is known to start with mammary tissue injury, and heavier, meaty udders or udders banged around by narrow hind legs are more prone to mastitis infections. Matings that avoid producing thin-skinned, small, pointed teats (prone to be “leakers”) help avoid bacteria entering the udder when cows lie down in stalls.
Managerial supports to lower SCC levels
Booster heifer vaccinations annually on your cow herd. The cost/benefit ratio on vaccination as a boost to immune system activity is well documented. If you periodically buy in cows, this is hyper-important.
Consider offering kelp mineral free-choice with trace mineral salt, at least in seasons (like spring) where weather changes and moisture levels are higher. “Kelp” is dried ocean seaweed, is packed with mineral elements dissolved in salt water in a balance matching the soils drained into the sea, so is an effective aid to immune function and vitamin synthesis in the rumen. It will mix in your TMR if you prefer that.
Consider using the fresh cow products offered by Van Beek Natural Science that aid in fast and thorough uterine recovery post-calving, support liver enzyme production, and therefore immune system response to any health challenge. Bovi Drop, Cal Caps, as well as Ruma Start add up to a good start for fresh cows.
If group feeding springers, consider Conklin “Fastrack” as a broad-specie probiotic that will have a cow eat her way through calving and fresh-cow transition so that her dry cow reserves are not depleted quickly during her peak production days. Cow health is primarily nutrition. Antibiotics do not help high SCC counts, the cow’s immune system has to finish the job antibiotic therapy starts.
The point is—don’t let your cows “run down”. Keep them “fed up” so their nutrient intake meets their total energy demands (in production, in solids density, in reproduction, in body condition maintenance, in completing growth on young cows so they are “more cow” at maturity). Not all cows utilize feeds equally, so some may need supplementation beyond what the computer says.