by Tamara Scully

Researchers at the University of New Hampshire have been exploring the use of kelp supplementation in milking cows. A survey conducted in the Northeast showed that 59 percentage of organic dairy producers are using kelp, either supplementing the ration with two to four ounces, or sometimes making it available free choice. In the Midwest, 83 percent of Minnesota organic dairy farmers, and 49 percent of Wisconsin’s organic dairy producers are using kelp.

The reasons given for using kelp are many: increased body conditioning score; decreased somatic cell counts; decreases in pinkeye; enhanced fly control; and improved reproductive health. But are these anecdotal accounts of kelp’s powers accurate?

Andre Brito, Associated Professor of Dairy Cattle Nutrition and Management at UNH and his team set out to determine what benefits kelp supplementation may actually have, and to find out what level of supplementation — if any — is advantageous, and why.

Kelp, a brown seaweed, is “high in minerals and that’s one of the reasons farmers adopt kelp meal,” Brito said in a Penn State Extension Dairy Grazing Management webinar.

Pasture alone often cannot meet the needs of lactating dairy cows, and kelp can help with some deficits. Its crude protein is about 10 percent, and phosphorous and sulfur levels are similar to pasture. Even pasture supplemented with kelp might not provide all the calcium and phosphorous needed. While potassium and iodine levels fluctuate among brands, as kelp is a wild-harvested product and there are differences in varieties and processing techniques, these minerals are found at high levels in all kelp.


The UNH Burley-Demeritt Organic Dairy Research Farm is home to a 55-head milking herd, which is rotationally grazed. Cows are milked twice per day and moved to fresh pasture after each milking. Twenty Jersey cows, producing 45 lbs./milk per day and weighing about 972 lbs. each were fed either no kelp, or supplemented with four ounces of kelp meal. Both groups were supplemented with a total mixed ration (TMR), and moved to fresh pasture after each milking.

The study showed that in some months, the kelp-supplemented cows produced a statistically insignificant higher amount of milk per day than the control group, while in other months, they produced a significantly insignificant lesser amount. The cows on the kelp meal supplementation consumed a slight bit more pasture each day.

“Cows that are on kelp consume a bit more pasture, and that may be why they produce a bit more milk,” Brito said.

The total dietary dry matter intake for the kelp-supplemented cows was slightly increased from that of the control. There was no effect of kelp on the milk composition.

Higher milk Somatic Cell Score, SCS, which is the based off of the Somatic Cell Count, SCC, is associated with lower milk production. In the kelp supplemented cows, the SCS dropped during July and stayed lower than the control until the cows were taken off of pasture in October, when the levels in both groups equalized again.

“It may be a situation where kelp, either (via) anti-microbials or those high levels of iodine transferring to milk, somehow can prevent infection,” Brito hypothesized. “Something seems to be happening.”

Researchers also measured serum cortisol levels. Cortisol levels increase under stress, and it has been thought that kelp might decrease cow stress. However, the kelp supplemented cows actually showed increased cortisol levels — but no statistical difference — compared to the control group when cows were grazed on pasture.

Researchers fed groups of cows diets of either no kelp, or two, four, or six ounces of kelp meal supplementation. Serum cortisol levels did decrease in a statistically significant, linear manner as the amount of kelp supplementation increased. These results were similar in winter or summer studies of confined cows. It is hypothesized that kelp may help to regulate body core temperature, and therefore reduce stress responses.

The amount of methane released on kelp-supplemented cows was also measured. Using a portable GreenFeed gas emission system, cows on pasture were able to graze while in the equipment and being monitored. Only 10 cows were in the study. The amount of methane produced per day, the yield of methane per pound of dry matter intake, and the intensity of the methane, in grams per kilogram of energy corrected milk, were all measured.

Statistically, there was no effect when cows were supplemented with four ounces of kelp as compared to the control. However, in another study, confined cows fed kelp demonstrated a consistent decrease in methanobrevibacter spp., the microbe that is in rumen fluid, when fed higher amounts of supplemented kelp. Biologically, this slight decrease is probably not associated with a drop in methane production, Brito said.

Iodine concerns

One major concern with feeding a kelp meal supplement is the large amount of iodine kelp contains. The researchers wanted to measure milk iodine levels at different levels of supplementation throughout the grazing season.

They measured the total iodine intake during the grazing season on pastured cows fed TMR and a four-ounce kelp meal supplementation. September had the highest iodine intake, but August had the highest levels of iodine found in milk.

In July, and again in September, the pasture forage featured species which were high in glucosinolates, which can bind iodine. In August, these forages — primarily the brassicas and clovers — were not as prominent. In October, when pasture intake decreased and glucosinolates were absent from the diet, the four ounces of kelp supplementation caused a large increase in iodine levels in the milk.

“Cows on kelp produce milk with high concentrations of iodine,” Brito said.

Iodine interferes with metabolic pathways, and either too much or too little causes goiter in humans, so there is serious concern about high levels of iodine in milk. The researchers found iodine levels in one eight ounce serving of milk, produced from grazing cows supplemented with four ounces of kelp meal during the month of October, to be 230 mg. This is extremely high for children, and even too high for adults, except lactating women, whose iodine needs are much greater than normal at 290 mg per day.

“Kelp meal supplementation effectively increases the concentration of iodine in milk,” Brito said, and the level varies throughout the year in pastured cows. “Depending on the concentration of the glucosinolates…you may have higher or lower levels of iodine in milk.”

The research at UNH also examined canola as an alternate forage for dairy cows. This crop could provide forage later in the season, and contains glucosinolates, potentially lowering iodine levels in milk from grazing cows. The canola is highly digestible, but has less fiber than annual ryegrass, and more sugar. It can be grazed for several weeks after the first frost.

Kelp is a high-cost supplement, with pricing of $50-$60 per 50 pound bag. Because of the concerns with iodine levels and toxicity to humans, more research is needed. Feeding brassicas or canola can help to lower the iodine levels in milk from kelp-supplemented, grazing dairy cows.

“Kelp meal may provide farmers with opportunities to improve animal health, but further research is needed,” Brito concluded.