Sheep can and do reduce levels of internal parasites by eating plants high in tannins. Offering growing lambs two compounds tannins and saponins is likely to increase food intake, but will it also reduce the number of internal parasites in lambs?
Lambs were 80 days of age at the beginning of the trial. Lambs that were infected with the internal parasite Haemonchus contortus (common names: red stomach worm, wire worm or barber’s pole worm) were fed a: 1) control (C) diet, 2) C plus tannin (T), 3) C plus saponin (S), or 4) a choice of T and S. A fifth group was also fed a choice of T and S, but not infected with parasites.
Animals offered a choice of S and T whether or not they were infected with parasites ate more food and gained more weight than animals offered T or S alone. However, sheep offered a choice had greater fecal egg counts (an indirect measurement of parasite loads) than sheep fed T or S.
In this study, parasite load was considered light, but still required treatment. Offering lambs a choice between saponin- and tannin-containing foods allowed them to increase nutrient intake and gain more weight but did not help them reduce their parasite load. For growing young lambs gaining weight and maximizing nutrient intake may be more important than reducing parasite load provided the parasite infection is not too high.
Reference: Conpani, G, J.O. Hall, J. Miller, and J.J. Villalba. 2013. Plant secondary compounds as complementary resources: Are they always complementary? Oecologia: in press
Below are excerpts from a letter I received from a seed grower who wanted to know if goats could be averted to grass. He did avert the goats on his own with coaching from me. Here’s how it worked.
Part of working the magic with food aversion is giving the animals an experience where they believe a particular food is bad. I compare it to going to the Chinese Restaurant and having the black bean shrimp. If the shrimp makes you sick, you never want to eat black bean shrimp again.
In a corral, I gave the goats a big feed of the grass I wanted them to avoid and then gave them each a very carefully measured dose of LiCl, based on their body weight (200 mg/kg). If you’ve ever had a dose of Ipecac you understand how a sick feeling can be induced chemically. The goats stood around looking morose for a few hours and then resumed normal activities.
The goats ate weeds. They had a preference for the growing tips of kochia, the lambsquarter disappeared and they kept the prostrate knot weed and pig weed suppressed; they had more than they could really eat so they simply gained weight and got fat. The one clump of grass that one of the goats was forced to eat when it was tied up got nipped now and then as the goats traveled through the field.
My Bozoiski II Russian Wildrye gets tall, easily five feet, and the rows are spaced three feet apart. When it got tall, the goats lost interest in going down the little tunnels between the rows. They pretty much stayed out the grass when it was tall. That means that when the seed was close to harvest and ready to shatter the goats were not around; they stayed in the open edges of the field. After harvest they resumed patrolling the whole field looking for weeds.
The mastic tree (Pistacia lentiscus) contains 20% tannins. The tree makes up 17% of the diet of Damascus goats, but only 6% of the diet of Mamber goats. Like many natural chemicals, tannins can be a toxin or a medicine depending on the dose. Mastic tannins can interfere with an animal’s nitrogen balance but also can act as a de-wormer.
Researchers in Israel examined how readily young goats infected with gastro-intestinal parasites ate mastic foliage. Goats with internal parasites typically have a decrease in plasma cell volume value and a decline in growth rate. Mamber and Damascus goats were infected with internal parasites and then fed either hay or hay and mastic foliage.
Fecal egg counts declined sharply in goats that ate mastic foliage compared to the hay diet, but it also impaired the protein balance of the goats, determined by a decrease in blood urea levels.
When given a choice between hay and mastic, infected mamber goats ate 14% more mastic than non-infected Mamber goats. Damascus goats ate the same amount of mastic whether or not they were infected with parasite. Infected goats fed hay, regardless of breed, increased intake of mastic when given a choice between the two feeds.
Goats can passively self-medicate provided they routinely eat high and constant amounts of masticate (tannins). Goats less likely to eat mastic, such as Mamber goats, eat more of the plant only when parasite load increased. Active self-medication can be explained by the neophilic (preferring novel foods) behavior of sick animals. Self-medication of parasite-afflicted goats is a complex process, involving previous foraging habits affected by breed and experience.
For those of you unfamiliar with the term instar. I know I had to look it up.
Most of us don’t really care about the learning and memory of insects, but if caterpillars can learn and remember it’s hard to argue livestock can’t. This study examines whether experiences at the larval stages in the tobacco hornworm can persist through pupation into adulthood.
Fifth instar tobacco hornworm caterpillars received an electrical shock paired with the odor of ethyl acetate to create a conditioned odor aversion. Researchers showed that larvae learned to avoid the odor, and that this aversion was still present in adults. The adult aversion came from training and did not result from carryover of chemicals from the larval environment because neither applying odorants to naive pupae nor washing the pupae of trained caterpillars changed their behavior.
Larvae trained in the third instar still showed odor aversion after two molts, as fifth instars, but did not avoid the odor as adults. Apparently, post-metamorphic recall involves regions of the brain that are not developed until later in the caterpillar’s life.
Reference: Blackiston, DJ, ES Casey, and MR Weiss. 2008. Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned as a Caterpillar? PLoS ONE 3(3): e1736. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0001736
Ranchers in African generally prefer to keep wild grazers like zebras off the grass meant for their cattle. Worldwide savanna rangelands are managed on the premise that cattle and wildlife compete for food. It makes sense, but surprisingly there is little scientific information to support the assumption.
Researchers in Kenya grazed cattle in fenced 10-acre plots of savanna rangeland. Fences excluded wildlife principally zebras. Other groups of cattle grazed with wildlife. Cattle were weighed periodically throughout the year. During the dry season, grazing with wildlife reduced weight gain by cattle, but in the wet season, cattle actually gain more weight when they grazed with wildlife.
During the wet season, grass grows tall and quickly loses its nutritional value. Under these conditions having zebras is beneficial. Zebras are more willing than cattle to knock back the rank grass leaving higher-quality grass for cattle.
It’s not yet clear whether there is a net benefit over a whole year or series of years because conditions vary from year to year. From a management perspective, the positive effect of wildlife on weight gain by cattle during the wet season suggests that wildlife conservation is not necessarily detrimental to, and can at times be compatible with, cattle production.
Reference: Odadi, W.O., M.K. Karachi, S.A. Abdulrazak, and T.P. Young. 2011. African Wild Ungulates Compete with or Facilitate Cattle Depending on Season. Science 333:1753-1755.
Many of the studies on food aversion have used concentrates or food flavors. A few have used shrubs. I’ve often been asked if animals would generalize an aversion to all grasses if they were averted to one grass. My answer has always been: “No not all grasses.” Generalizing the aversion to other grass species would depend on how similar the flavors are between grasses and the strength of the aversion.
A study by Ginane and Dumont answer the question at least between perennial ryegrass and tall fescue. Researchers used a fairly low dose of LiCl (70 mg/kg body weight) to condition an aversion with sheep to ryegrass that was tall in stature. They also looked if animals would avoid a plant based on height. After conditioning, sheep avoided short ryegrass, but readily ate tall fescue that was tall in stature. Sheep did not avoid grass based on height.
Researchers also conditioned sheep to avoid timothy hay but sheep continued to eat red fescue hay after conditioning.
Sheep may use physical characteristics to search out certain foods. But when it comes to eating a food, it’s flavor that matters, not height, not color, or other physical characteristics of the food.
Reference: Ginane, C., and B. Dumont. 2006. Generalization of conditioned food aversions in grazing sheep and its implications for food categorization. Behavioural Processes 73:178–186. doi:10.1016/j.beproc.2006.05.006
I hate social media. When I first start using a new tool, I’m afraid I’ll look stupid or I’ll accidentally signup for something that costs money. So here goes….