Submitted to: Small Ruminant Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/12/2005
Publication Date: 11/14/2005
Citation: Pfister, J.A., Astorga, J.B., Panter, K.E., Stegelmeier, B.L., Molyneux, R.J. 2005. Maternal ingestion of locoweed. i. effects on ewe-lamb bonding and behaviour. Small Ruminant Research. Interpretive Summary: The maternal behavior of sheep during parturition is well documented (Herscher et al., 1963; Arnold and Morgan, 1975). Hormonally-regulated maternal behavior is triggered by parturition (Poindron and Le Neindre, 1980; Poindron and Levy, 1990). Maternal-infant bonding must occur within 12 hours of birth if a bond is to be established (Poindron and Le Neindre, 1980; Alexander, 1988). The initiation and maintenance of maternal responsiveness following parturition are partially dependent upon neonate activity and sensory information from the young (Alexander, 1977; Vince et al., 1987). Ineffective udder seeking by newborn lambs is related to hypothermia and increased mortality (Slee and Springbett, 1986; O’Connor and Lawrence, 1992). Maternal interest soon fades when poorly reinforced with weak infant responses (Alexander et al., 1990; Dwyer and Lawrence, 1999). Disruption of ewe-lamb bonding during parturition is detrimental to lamb survival (Alexander et al., 1983b; Dwyer, 2003). The bonding process allows the mother to discriminate her own young, and fosters stable ewe-lamb pairs within a herd, ensuring lamb survival ( Herscher et al., 1963; Poindron and Le Neindre, 1980). Locoweeds (Astragalus and Oxytropis spp.; legume family) are toxic range plants that are often consumed by pregnant sheep. These genera are closely related, and both are called locoweeds because they contain the same toxin, the indolizidine alkaloid, swainsonine (Molyneux and James, 1982). Ingestion of either Astragalus or Oxytropis causes the same clinical signs (Stegelmeier et al., 1995). Swainsonine disrupts glycoprotein processing in cells, resulting in vacuolation and cell death (Elbein, 1989). Pregnant animals ingesting locoweed often abort (Van Kampen and James, 1971). Chronic locoweed intoxication leads to abnormal behavioral patterns, including loss of motor control, lack of proprioception, and anorexia (James and Panter, 1989; Pritchard et al., 1990; Pfister et al., 1996). Lambs from intoxicated mothers have reduced birth weights and may require assistance in nursing (James, 1971, 1972a). Maternal ingestion produces lesions in the fetus parallel to those in the mother (Hartley and James 1975; James, 1971, 1972b). The objective of this study was to examine maternal-infant bonding and related postpartum behavior in ewes fed locoweed. Our hypothesis was that maternal locoweed ingestion would impair maternal-infant bonding, and disrupt the ewe’s ability to discriminate her own from an alien lamb.
Technical Abstract: This study investigated whether exposure of ewes to locoweed (Oxytropis sericea Nutt. In T. & G.; Leguminosae) during gestation would affect ewe behavior during parturition, ewe-lamb bonding and related behaviors post partum, and maternal responsiveness of ewes to alien and own lambs. Twenty-nine nulliparous Columbia-Targhee ewes bearing a single fetus were divided into two feeding treatments: (1) locoweed (L, n=15), fed as 10% locoweed pellet at 3 kg/day from day 100 to 130 of gestation, or (2) controls (C, n=14) fed 3 kg/day of alfalfa hay. Lamb birth weights were reduced about 25% (P<0.001) from maternal locoweed ingestion. There was a distinct lack of maternal-infant bonding due to locoweed intoxication of lambs. Only 1 lamb born to L ewes was able to nurse without assistance within 120 min. Lambs born to L ewes took longer to stand (P<0.05), to initiate teat-seeking behavior (P<0.03), and to suckle (P<0.0007). The behavioral toxicosis did not persist in lambs, as behavioral anomalies largely disappeared within 10 days following parturition. Locoweed-intoxicated ewes in general had an increased propensity (P<0.1) for locomotor activity, notably during fetal expulsion, and longer fetal expulsion times (P<0.1). There were few behavioral differences induced by locoweed up to 30 min post partum, when L ewes became inattentive to lambs (P<0.1). After the first (human assisted) suckling bout, L ewes were attentive toward their own and alien lambs. Both L and C dams were equally aggressive toward alien lambs. These results indicate that lamb survival after maternal locoweed exposure will depend greatly on human intervention. If locoweed-exposed lambs survive the first 24 to 48 hours after birth, then the prognosis for survival improves greatly.