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Individual study: Conditioning of ewe/lamb pairs to spotted knapweed Centaurea maculosa increases post-conditioning knapweed consumption by lambs but not ewes, Fort Ellis, Montana, USA

Published source details

Whitney T.R. & Olson B.E. (2006) Conditioning ewes and lambs to increase consumption of spotted knapweed. Applied Animal Behaviour Science, 100, 193-206


In the northwestern United States, spotted knapweed Centaurea maculosa (native to Eurasia) is an invasive plant that alters vegetation composition and reduces grazing value of rangelands. The abundance of spotted knapweed may be reduced by livestock grazing, with areas repeatedly grazed by yearling sheep exhibiting lower densities of plants than ungrazed areas. The objectives of the study described here were to determine if mature ewes and their lambs consume more spotted knapweed when previously conditioned to eating it (summarised below), and secondly, if lambs conditioned to spotted knapweed consume more of it than non-conditioned lambs when grazing without their mothers (see Case 469).

In theory, conditioning livestock to plants containing aversive chemicals, as present in spotted knapweed, should increase tolerance to such plants by altering rumen microbial populations and increase detoxification mechanisms within the animal, thereby increasing intake.

Feeding trials: The sheep feeding trials took place at Fort Ellis, near Bozeman, Montana, (USA) using 34 white-faced ewes with their single lambs (around eight weeks old). These were randomly selected from the Montana Agricultural Experiment Station Red Bluff Research Ranch. Experimental procedures were approved by the Institute for Animal Care and Use Committee at Montana State University.

Conditioning to spotted knapweed: Conditioning was conducted over 17 days (22 June – 9 July 2004). Ewe/lamb pairs were randomly assigned to one of four treatments:

T1 - ewes and lambs not conditioned to fresh-cut spotted knapweed (9 pairs)

T2 - conditioned ewes with non-conditioned lambs (9 pairs)

T3 - non-conditioned ewes with conditioned lambs (7 pairs)

T4 - conditioned ewes and lambs (9 pairs)

During the daily 30-min conditioning period when fed with hay or a hay and knapweed mix(see below), lambs were temporarily separated from their mother, being reunited afterwards, moved to a dry-lot and fed grass hay (about 4% of ewe body weight). Sheep had continuous access to fresh water and mineral.

Ewes from Treatments 1 and 3 each received 285 g of chopped oat hay/day with zero knapweed.

On days 0 and 1, each ewe from Treatments 2 and 4 received 35 g of fresh-cut, chopped knapweed (leaves and stems) mixed with 250 g of chopped oat hay. From days 2 to 13 and 16 to 17, each received 40 g of knapweed mixed with 245 g of chopped oat hay. On days 14 and 15, sheep were fed smooth bromegrass Bromus inermis.

Non-conditioned lambs were fed as a group and received the equivalent of 57 g chopped oat hay each (presented in six troughs). Conditioned lambs (also fed as a group), received 7 g of fresh-cut knapweed mixed with 50 g of chopped oat hay each.

Fresh-cut spotted knapweed, collected nearby, was chopped and fed within 2 h. Sheep were allowed 30 min to consume their assigned treatment. Left-overs were weighed and discarded.

Feeding after conditioning: From July 12 – 16 July 2004, each day around 12:00 h, 1 kg each of fresh-cut, chopped knapweed and fresh-cut, chopped smooth bromegrass per ewe/lamb pair was placed in three piles (to minimize agonistic feeding behavior). For 30 min after being given forage, an observer recorded whether an animal was feeding from a knapweed or brome pile, so that time spent feeding on each forage type could be assessed. After 30 min, uneaten fodder was collected, weighed and discarded. At the end of each day, perennial grass hay was provided to each ewe/lamb pair at approximately 4% of ewe body weight. The sheep and had continuous access to water and minerals.

Time spent by ewes eating fresh-cut spotted knapweed and bromegrass was similar among treatments, although T3 and T4 ewes were eating less knapweed and more bromegrass at the end of the trial.

T2 ewes spent more time eating knapweed than T3 ewes, and T2 ewe/lamb pairs consumed more knapweed than T3 ewe/lamb pairs. T4 ewes spent less time eating knapweed and more time eating bromegrass than T2 and T3 ewes. T2 ewes spent more time eating knapweed and less time eating bromegrass than T3 ewes

Conclusions: Conditioning ewes to knapweed had limited, if any, effect on enhancing subsequent knapweed consumption. Non-conditioned ewes and lambs spent similar amounts of time eating spotted knapweed to those previously exposed to it. Thus, even without prior experience, they ate spotted knapweed quite readily. The amount of knapweed provided represented about 20% of their daily requirement (3% body weight for 60 kg ewe), thus they may have had plenty of other feed to buffer any negative consequences associated with this novel food. Lambs of conditioned ewe/lamb pairs spent more time eating knapweed than treatment 2 and 3 lambs, especially later on in the trial, indicating that mentoring, in addition to conditioning, enhanced time spent eating knapweed. Time spent eating knapweed remained similar during the trial for ewes, but increased over days for lambs indicating lambs were increasing their acceptance of this plant.

We did not see a pronounced increase in intake by ewes with conditioning, possibly because: (1) we did not condition long enough, although they had 16 days, (2) we did not provide enough spotted knapweed during the conditioning phase, and/or (3) the ewes self-limited their intake of this plant to avoid toxicosis, and (4) they had a choice.

Note: If using or referring to this published study, please read and quote the original paper. Please do not quote as a case as this is for previously unpublished work only.