Prototheca species are achlorophyllic algae that are ubiquitous in soil and aqueous habitats. Prototheca zopfii, mainly, and P. wickerhamii have been reported as etiological agents of intramammary infections (IMI) in cows. Prototheca bacteria generally behave as environmental mastitis pathogens, but can also be spread between cows during milking.

The impact of Prototheca mastitis on milk quality was studied in two New York dairy herds. Dairy A was a closed herd of 60 milking cows, housed in a tiestall barn with a pipeline milking systems. The barn had rubber mats with hay bedding. Cows were pre- and postdipped (0.5% chlorhexidine) with a dipper cup. Prior to the study, the monthly bulk tank milk (BTM) SCC ranged between 200,000 and 300,000 cells/ml while the standard plate count (SPC) was 5,000 - 10,000 CFU/ml.

Dairy B was an open herd of 209 milking cows, mostly housed in a four row tiestall barn. The remaining cows were in freestall housing. A lauricidine postmilking teat dip was applied with a dipper cup. Bedding was chopped hay for tiestalls and sand for the freestalls. Prior to starting the study, the SCC had increased from 260,000 to 780,000 and the SPC increased from 7,000 to 260,000.

In early 1996, Dairy A experienced a rapidly rising SPC. A screening BTM sample yielded pure Prototheca, and the SPC and SCC reached 180,000 and 350,000 respectively. When the herd was sampled, 26 of 53 milking cows (49%) showed Prototheca IMI. A month later, the prevalence in the herd was 50% (28 of 56). Between January 1996 and December 1997, the SPC ranged from 9,000 to 190,000 and the SCC ranged from 120,000 to 660,000, reflecting the chronic nature of P. zopfii IMI.

In Dairy B, Prototheca was first cultured in July 1995 during a whole-herd mastitis screening survey (16 of 229 cows, or 7%, were positive). However, at that time, the BTM sample cultured negative for Prototheca. In April 1997, SPC and SCC reached 260,000 and 780,000, respectively. A whole-herd mastitis screening survey showed 46 cows (22%) had P. zopfii IMI. The owner culled 40 of those Prototheca-positive cows from the herd. The SPC for the BTM sample was 230,000. Four months later, 45 of 192 cows (29%) had Prototheca IMI, 39 of which were newly infected. Between April and December 1997, SPC ranged between 45,000 and 600,000 and SCC ranged between 280,000 and 940,000.

At both dairies, the dry cow lot, splash/puddle areas, fecal samples (from cows with and without Prototheca IMI) bedding and some inflations cultured Prototheca. Two Prototheca species were isolated on Dairy A - P. zopfii and P. stagnora - of which only P. zopfii was isolated from milk. At Dairy B, only P. zopfii was isolated from the environment and milk.

In both farms, cows with either clinical or subclinical IMI did not show signs of systemic illness. Some infected glands were swollen and hard. Several cows were intermittent shedders of P. zopfii. Milk production appeared to decrease and SPC dramatically increased on both farms.

The definite source of Prototheca, predisposition risk factors, and mode of transmission in these herds have not been satisfactorily identified. Bedding or food materials have been suggested as sources of Prototheca outbreaks. Isolation of Prototheca from milk and fecal samples suggests that these organisms can be brought into dairy herds through the purchase of animals with IMI or as residents of digestive tracts of animals of different ages. Furthermore, manure contamination of teats could provide easy access for Prototheca into the mammary gland. The chronicity of protothecal infections occurs because of the lack of an effective treatment as well as the absence of spontaneous recovery.

From the NMC newsletter "Udder Topics" December 1998; Source: AABP 31st Annual Convention Proceedings, pg. 216