Recently on June 1st cow-calf pairs were moved onto a grass-alfalfa pasture with a lake as the water source. Within several days, the producer found several dead cows, sick cows with heads and ears down and sunken eyes (showing probable depression and dehydration), and a neurological calf staggering. Gross necropsy of one cow had no significant findings and another cow had some blood-tinged fluid in the abdomen. No significant microscopic lesions were observed in the submitted tissues. The analysis of ocular fluid for nitrates and whole blood for lead were negative. Several water samples were submitted to the NDSU -VDL with a light-green color and putrid odor (typical of the cyanobacteria Microcystis). A heavy bloom of multiple cyanobacteria [Microcystis spp, Dolichospermum spp (Anabaena spp,) and Aphanizomenon spp.] was observed microscopically (see photos) with potential for production and release of multiple toxins (hepatotoxins and neurological toxins causing quick death) into the water. The immediate recommendation was to remove cattle from the pasture and provide supportive treatment for cattle. Alternatively, if practical, the water source could be fenced off and alternative potable water source provided.
Depending on weather (heat and rainfall) an algae bloom or conditions for a bloom could persist throughout the summer/fall. This past year with the early snow fall, formation of a good ice cover was delayed or poor over some of the water sources and potentially cyanobacteria can survive over-winter under ice, and with a quick ice-out in the spring a rapid algal bloom can develop following hot weather. Over the past few days with 90° F days – the conditions for an algal bloom were present in enriched water sources with nutrients of nitrogen and phosphorus.
When placing livestock onto pastures with water sources, check lakes, ponds, sloughs, and slow streams with stagnant water for areas of cyanobacterial – algal blooms. Monitor the water source and cattle frequently (daily if possible) for algal blooms (typically a bluish-green color). Remove livestock from pastures with water sources containing an algal bloom or fence off the water with an algal bloom and provide alternative potable water. Livestock, horses, dogs, cats, fish, some birds, and humans are at risk and carcasses might be observed around the water source. It is critical that water samples be submitted since in many cases tissues from affected animals lack lesions or have no diagnostic changes. Note that the NDSU-VDL can examine livestock water microscopically for toxigenic cyanobacteria but does not analyze for cyanotoxins. Cyanotoxin analysis can be referred to outside laboratories if required.
Learn more about the blue-green algae (cyanobacteria) identification offered at the NDSU-VDL here.
Michelle Mostrom, DVM, PhD, DABVT, DABT
Brett Webb, DVM, DACVP