Effects of origin, experiences early in life, and genetics on bitterweed consumption by sheep
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Bitterweed is one of the most detrimental poisonous plants to sheep production in west central Texas. Sheep typically avoid the plant unless alternative forage is limited. When consumption does occur, some flocks and individuals are able to consume bitterweed and avoid toxicosis. Our objective was to determine the importance of site of origination (long-term exposure), experiences early in life (short-term exposure), and sire selection on the ability to avoid bitterweed toxicity. In Trial 1, we compared bitterweed intake of 15 ewes originating from bitterweed-infested and 15 ewes, from bitterweed-free rangelands. Bitterweed intake of their half-sib offspring was compared in the subsequent year. Ewes from bitterweed-infested rangelands ate more (P < 0.05) bitterweed, but lambs born to ewes from bitterweed-free rangelands consumed more (P < 0.05) bitterweed. In Trial 2, we compared intake of 40 lambs from two separate ewe flocks (20 from each flock). One flock of ewes originated from bitterweed-infested rangelands, the other from bitterweed-free rangelands. Each flock was divided in half so that irrespective of origin of the ewes, lambs from both flocks would be born and reared (birth to weaning) in each habitat. Lambs from flocks originating from bitterweed-free rangelands consumed more bitterweed than lambs from bitterweed-infested rangelands, regardless of site of rearing. During Trials 2 and 3, we also assessed the influence of sire on bitterweed intake. Offspring from three sires in Trial 2 consumed differrent (P < 0.05) amounts of bitterweed, but sires were confounded with origin. In Trial 3, offspring from five unrelated sires consumed similar amounts of bitterweed. Thus, the ability to consume bitterweed does not appear to be strongly influenced by the sire's genetic characteristics. Likewise, experience with bitterweed early in life does not appear to lead to greater consumption later in life. Thus, manipulating feeding behavior does not appear to be a viable management option at this time for reducing the likelihood of bitterweed toxicosis. 2003 Elsevier B.V. All rights reserved.
