Abstract

Selenium (Se) is an important trace element for dairy cattle and deficiencies (0.03 mg Se/kg DM) are associated with lowered milk yields and impaired fertility in grazing cows. As many dairy farms have a comprehensive fertiliser programme the use of Se-amended fertilisers (prills) could be an effective approach to prevent Se deficiency. Three farmlets (6-7 ha) were established and grazed with 13 cows/farmlet balanced for age, calving date and production. The treatments were 1) untreated control, 2) Sel Se prill (Selecote Ultra), and 3) Rav Se prill (Ravensdown Selprill Double). The prills were mixed with 15% potassic superphosphate and applied at 250 kg/ha, in early October, to provide 10 g Se/ha. This is Day 1 of the study. The cows were allocated to treatments 4 weeks later and changes in pasture Se, blood Se, serum Se, milk Se concentrations and blood glutathione peroxidase activity were monitored over the next 12 months. Untreated pasture Se concentrations ranged from 0.03 to 0.04 mg/kg DM, while pastures treated with prills had pasture Se concentrations > 0.5 mg/kg DM within 14 days after treatment, before decreasing to 0.06 mg/kg DM after 121 days, after which they ranged between 0.06 and 0.26 mg Se/kg DM for the Sel prill, and between 0.06 and 0.03 mg/kg DM for the Rav Se prill over the next 251 days. The mean (± SE) blood Se of cows grazing the control pasture was 280 ± 30 nmol/L, while in cows grazing pasture treated with the Sel Se prill blood Se concentrations increased to 1364 ± 112 nmol/L after 372 days. In the case of cows grazing pasture treated with Rav Se prill, blood Se concentrations increased to 1192 ± 66 nmol/L within 60 days, before decreasing slowly to 740 ± 65 nmol/L at 372 days. Blood glutathione peroxidase activity followed a similar pattern to the blood Se. The mean serum Se concentrations of the untreated cows was 151 nmol/L, while in animals on the Sel Se prill-treated pasture they reached a small peak at Day 64, followed by a decrease and then continued to increase to 675 nmol/L at Day 372. In contrast, for cows on the Rav Se prill treatment the serum Se concentrations reached a peak of 920 nmol/L at Day 64, and then decreased to 263 nmol/L at Day 372. Milk Se followed a similar pattern to serum Se. Selenium-amended fertilisers were found to be effective in raising the pasture Se concentrations for 4 or 12 months, depending on Se prill composition, which then in turn increased blood Se concentrations of dairy cows for at least 12 months.

ND, Grace, and DM West

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 182-186, 2006