Clinical Signs in Cattle Grazing High Molybdenum Forage

Abstract

Revegetation and sustainable cattle grazing are major objectives in the reclamation of mine tailings at the Highland Valley Copper mine in British Columbia, Canada. A total of 84 cow-calf pairs grazed forage extremely high in molybdenum (Mo) for 11 weeks in the summer and fall for 3 consecutive years (1999-2001). The average stocking rate was 0.63 ha AUNT'. The animals' diet consisted primarily of alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) containing 100-400 ppm Mo. Both cows and calves showed adequate daily gains of 0.78 kg head "' day' and 1.33 kg head "' day"', respectively. Uptake of Mo was demonstrated by elevated levels of Mo in rumen contents and feces. Clinical signs of Mo toxicity were observed in less than half of the cows and in only a few calves. Clinical signs included a stiff shuffling gait, watery diarrhea, and a rough hair coat. Lameness, the primary sign, was resolved in all animals by the end of each trial. Diarrhea was also resolved by the end of the trial and hair coats returned to normal by the following spring. The onset and severity of the affliction appeared to be related to prevailing moisture conditions, which may have affected Mo availability in forage. Some affected animals were treated with Cu injections to no avail. Liver biopsies and serum samples showed marginal to adequate copper (Cu) levels but potentially toxic levels of Mo. In the third year of the trial, Cu-containing boluses were employed but they did not prevent the onset of clinical signs.

Geographic determinants of copper and molybdenum concentrations in serum at the end of the grazing season and associations with reproductive performance in beef cows from western Canada

“…Mining can also result in excess Mo in the soil, and forages grown on reclaimed land may be very high in Mo (Gardner et al 2003;Raisbeck et al 2006). Most cases of molybdenosis have been reported in grazing cattle because high Mo plant material is more likely to cause toxicity in cattle when eaten fresh as compared with stored (Ward 1991;Majak et al 2004).…”

Efficacy of Copper Supplementation in the Prevention of Molybdenosis in Cattle

“…The study demonstrated that grazing cows were susceptible to some degree of molybdenosis (Majak et al 2004). Clinical signs of molybdenosis are much varied (Ward 1978;Swan et al 1998), but clinical evaluations at Highmont only revealed signs of lameness, manifested as a stiff shuffling gait, diarrhea, and hair-coat depigmentation (Majak et al 2004). It should be noted that lameness and diarrhea were resolved in all animals by the end of each grazing season without treatment and hair coats returned to normal by the following spring.…”

“…To determine the impact of the high-Mo forage on grazing cattle, a 3-year (1999)(2000)(2001) clinical evaluation was initially conducted at Highmont. The study demonstrated that grazing cows were susceptible to some degree of molybdenosis (Majak et al 2004). Clinical signs of molybdenosis are much varied (Ward 1978;Swan et al 1998), but clinical evaluations at Highmont only revealed signs of lameness, manifested as a stiff shuffling gait, diarrhea, and hair-coat depigmentation (Majak et al 2004).…”

“…Before the commencement of each trial, cattle were held at the Stevenson Allotment (lat 558329N, long 1208519W, elevation 1 050 m) for 12 weeks. The site is near the mine and adjacent to Witches Brook, the holding area used for the clinical evaluation during 1999-2001 (Majak et al 2004). Kentucky bluegrass (Poa pratensis L.), white clover (Trifolium repens L.), pinegrass (Calamagrostis rubescens Buckl.)…”

“…A proposed end land use plan for these areas includes livestock grazing and hay production, thus restoring the terrain to sustainable agricultural use. Studies have shown that residual Mo in the tailings is imbibed by vegetation and can accumulate to extremely high levels depending on plant species and site (Gardner et al 2003;Majak et al 2004). Accordingly, grazing studies were initiated to determine the feasibility of utilizing the tailings areas at HVC for cattle production.…”