Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2002
Publication Date: 6/2/2002
Citation: Taylor, J.B., Strickland, J.R. Appearance and disappearance of swainsonine in serum and milk of lactating ruminants with nursing young following a single dose exposure to swainsonine (locoweed; Oxytropis sericea). Journal of Animal Science. 2002. v. 80. p. 2476-2484. Interpretive Summary: Swainsonine (locoweed toxicant) appeared in the serum and milk of lactating ewes and cows in a dose dependent fashion following a single dose oral exposure; thus, confirming the mammary system to be a route of swainsonine elimination and source of swainsonine exposure to the nursing young. However, detectable levels of swainsonine and(or) subclinical toxicity were not observed in the serum of nursing lambs or calves. Therefore, in order to transfer a sufficient amount of swainsonine to lambs and calves via the milk to subsequently induce detectable levels of swainsonine (>0.025 mg/mL) and(or) subclinical toxicity in the serum, a single oral dose of swainsonine (locoweed extract) greater than 0.8 mg/kg BW to the lactating mothers must occur. Based on this and results of others, the greater risk of swainsonine toxicity seems to be when nursing ruminants repeatedly (daily; subacute exposure) select a diet containing locoweed in addition to ingesting milk contaminated with swainsonine.
Technical Abstract: A series of experiments were conducted to investigate the elimination of swainsonine in the milk of lactating ruminants following a single dose oral exposure to swainsonine (locoweed; Oxytropis sericea) and to assess subsequent subclinical effects on the mothers and their nursing young. In a preliminary experiment, lactating ewes were gavaged with locoweed providing 0.8 mg swainsonine/kg BW (n = 4; BW = 75.8 ± 3.6 kg; lactation = d 45) and lactating cows were offered up to 2.0 mg swainsonine/kg BW free choice (n = 16; BW = 389.6 ± 20.9 kg; lactation = d 90). Serum and milk were collected at h 0 (before treatment), 3, 6, 12 and 24 for ewes, and h 0 (before treatment), 6, 12, 18 and 24 for cows. Swainsonine was highest (P < 0.05) by h 6 in the serum and milk of ewes. Consumption of at least 0.61 mg swainsonine/kg BW induced consistent (> 0.025 mg/mL) appearance of swainsonine in cow serum and milk. In response to the results obtained in the preliminary experiment, a subsequent experiment utilizing lactating ewes (n = 13; BW = 74.8 ± 6.4 kg; lactation = d 30) and cows (n = 13; BW = 460.8 ± 51.9 kg; lactation = d 90) was conducted. Each lactating ruminant was gavaged with a locoweed extract to provide 0 (control), 0.2 or 0.8 mg swainsonine/kg BW and individually penned with their nursing young. Serum and milk from the mothers and serum from the nursing young were collected at h 0 (before treatment), 3, 6, 9, 12, 24 and 48 (an additional sample was obtained at h 72 for ewes and lambs). Serum and milk swainsonine was higher (P < 0.05) in the 0.8 mg treated groups and maximal (P < 0.05) concentrations occurred from h 3 to 6 for ewes and h 6 to 12 h for cows (P < 0.05). Rises in alkaline phosphatase activity indicated subclinical toxicity in the treated ewes (P < 0.05). Following a single dose oral exposure to 0.2 and 0.8 mg swainsonine/kg BW provided by a locoweed extract, swainsonine was detected in the serum and milk of lactating ewes and cows, and rises in serum alkaline phosphatase activity was observed in the ewes. Neither swainsonine nor changes in alkaline phosphatase activity was detected in the serum of the lambs and calves nursing the ewes and cows dosed with swainsonine.