Infection with gastrointestinal nematode parasites, particularly Haemonchus contortus, a voracious blood-feeder, is the most important constraint to profitable small ruminant production in the southeastern United States and worldwide. Lambs and kids are more susceptible to infection than older animals, but haemonchosis can rapidly lead to lost production and even death at any age. Anthelmintic drugs (dewormers) have been over-used in attempts to control this problem, which has resulted in high levels of anthelmintic resistance in nematodes throughout the Southeast. The problem is so severe that it is threatening viability of small-scale and limited-resource small ruminant farm operations in this region despite continued high demand for sheep and goat products. A more sustainable approach to parasite control involves integrating targeted, limited use of anthelmintics with non-chemical, novel control methods that reduce nematode numbers in the host animal and lower pasture contamination with eggs and larvae. This project evaluated one alternative control method, condensed tannin containing forage (AUGrazer cultivar of sericea lespedeza, ASL) fed as ground hay (Trial 1) and pellets (Trial 2), for effect against experimentally induced existing and newly acquired infection (Trial 1) and naturally acquired infection (Trial 2). For both trials, infection, based on fecal egg count (FEC), decreased significantly during the period of ASL feeding. In Trial 1, FEC increased after ASL feeding was stopped which indicated an effect on female worm fecundity. Also in Trial 1, worm burden at necropsy was substantially reduced in ASL fed animals. Results indicate that ASL, fed as ground hay or pellets, has the potential to help control H. contortus infection in lambs.
Gastrointestinal nematode parasitism is arguably the most serious constraint affecting ruminant production world-wide. Economic losses are caused by decreased production, cost of prophylaxis, cost of treatment, and the death of infected animals (Barger, 1982; Donald and Waller, 1982). Problems with nematode parasitism are often classified as production disease (i.e. chronic subclinical condition affecting productivity). The most recent surveys by the United States Department of Agriculture (Animal and Plant Health Inspection Service, Veterinary Services) revealed that 62% of 5,174 sheep producers surveyed in the United States identified stomach/intestinal nematodes as a major concern (USDA, 1996a). These losses were compounded in the southeastern region because climatic conditions are generally more conducive to the growth and establishment of large nematode parasite populations. Seventy-five percent of 467 sheep producers surveyed in this region identified stomach/intestinal nematodes as a major concern (USDA, 1996b). The nematode of particular concern is Haemonchus. contortus (Craig, 1986). The tremendous egg-laying capacity of H. contortus is maintained by feeding on blood by both immature and mature nematodes. Severe blood loss can occur, resulting in anemia, anorexia, depression, loss of condition, and eventual death.
The control of nematode parasites traditionally relies on grazing management and/or anthelmintic treatment. However, grazing management schemes are often impractical due to expense or to the hardiness of infective larvae on pasture. In addition, the evolution of anthelmintic resistance in nematode populations threatens the success of drug treatment programs (Craig, 1993; Waller, 1994; Prichard, 1994; Condor and Campbell, 1995; Sangster, 1999). There is an urgent and increasing need to develop alternative strategies for control of nematode infections. A more sensible, sustainable approach to controlling nematodes is to reduce exposure of susceptible nematodes to anthelmintics, which in turn would maximize effectiveness of existing anthelmintics. Developing and utilizing alternative, non-chemical technologies will augment control with minimal drug use.
This project was part of an overall approach to develop and test small ruminant control methods that will eventually be integrated for routine use on-farm. This reseacrh effort is being directed by a group of scientists and extension personnel who formed the Southern Consortium for Small Ruminant Parasite Control (SCSRPC) in 2000. In addition, producer education will continue to be one of the goals as this is a critical component to changing paradigms and increasing adoption of new technologies. The validity of this approach of testing and validating new technology and then emphasizing producer education to increase adoption of the technology has been demonstrated with the previous work using FAMACHA which was successfully tested on sheep and goat farms throughout the southern United States and the US Virgin Islands (Kaplan et al., 2004). The FAMACHA system uses a card with 5 colors representing level of anemia where 1 is healthy (red) and 5 is very anemic (white). Scores of 4-5 indicate that deworming is necessary. The card colors are matched to the color of the lower inside eyelid. Producer training workshops on proper use have been conducted across the southeastern United States. The response has been encouraging in that continual requests are being made for more workshops.
The overall strategy for controlling nematode parasites will be to build on the successes of previous work of the SCSRPC, including the dissemination of smart drenching and FAMACHA technology through producer and “train the trainer” workshops in order to reduce dependence upon chemical anthelmintics, and to test alternative, non-chemical control methodologies eventually resulting in incorporating them into producer application (workshops) as they are validated. This approach has already impacted sheep and goat producers throughout the southeastern United States and Puerto Rico by changing thinking about control from eradication of nematodes (i.e. the next anthelmintic “silver bullet”), to managing them with what works and is available, thus, keeping producers in business. Information has been and will continue to be disseminated through scientific and popular publications, through the SCSRPC web site (SCSRPC.org), and through producer workshops. Producer interest in these methodologies is growing rapidly, and feedback from producers that have used the FAMACHA system has been very positive. Developing integrated control programs that incorporate smart use of anthelmintics and alternative, non-chemical strategies along with producer education through extension on implementation of such management systems, has the potential to redirect parasite control paradigms in small ruminant production systems, increasing viability and profitability.
The focus of the SCSRPC is to help sustain the small ruminant industry across the United States by developing and testing environment-friendly, non-chemical methods for controlling infection by parasitic nematodes. Educating producers to the dangers of over-use of anthelmintics and testing alternative, non-chemical control technologies that target different stages of the parasite life cycle for use on-farm is paramount to success. It is anticipated that recommended practices will be applicable to a wide geographic area. The main emphasis is on simple, effective, inexpensive techniques which will be expected to lead to producer-friendly methodologies that will be both affordable and sustainable by reducing dependence upon anthelmintics while improving animal health. Use of natural deworming agents will also reduce potential chemical residues in the animal and the environment.
A number of new control methods are being developed which include nematode-trapping fungi, copper oxide wire particles, hidden-gut vaccines and condensed tannin containing forages. The later is the focus of this proposal. An initial report, using goats grazing common sericea lespedeza, indicated that there was an effect on reducing the fecundity (egg-laying capability) of nematodes (Min et al., 2004). Subsequently, the Auburn University cultivar of sericea lespedeza (AUGrazer, ASL) fed as hay was shown to reduce fecal egg count (FEC) in goats (Shaik et al., 2004) and sheep (Lange et al., 2005), but this method has not been tested with grazing sheep, or with goats or sheep on-farm. Cultures made from feces of ASL hay-fed goats has also shown a reducing effect on egg and larval viability compared with feces from non-sericea lespedeza hay (Shaik, unpublished data). This could reduce pasture contamination and reduce the infection rate of grazing animals, although this hypothesis has not been tested in field trials. Reducing parasitic nematode larval levels on pasture would be particularly helpful for limited resource farmers who may not have the option of moving animals to “safe” pastures.
The original objective was to determine the effect of feeding the condensed tannin containing forage ASL, in a pellet formulation, on parasitic gastrointestinal nematode infection in lambs. However, at the time of the first study, pellets were not available; therefore, the new objective was to determine the effect of feeding ASL, as ground hay, on parasitic gastrointestinal nematode infection in lambs. Ground hay was evaluated to determine if it was just as efficacious as hay. Subsequently, pellets became available for the second study.
Sericea lespedeza (ASL). Hay was ground and some of the ground hay was processed into pellets.
Trial 1. Twenty-eight mixed sex lambs with essentially zero fecal egg count (FEC) were randomly allocated to 4 treatment groups of 7 animals each. Lambs were kept in cement floored pens. Two groups received a bolus of 5000 H. contortus infective larvae (L3) once (existing infection). The remaining 2 groups received trickle infections of 500 H. contortus L3 3 times a week for 3 weeks (establishing infection). ASL ground hay was fed over a 35 day period (days 0-35) to one of the existing and establishing infection groups while the other groups were fed bermudagrass ground hay (BG, control). All groups were fed BG for an additional 14 days (days 35-49) at which time all animals were necropsied.
Feces, for FEC, and blood, for packed cell volume (PCV), were collected weekly to monitor infection level.
If any individual animal’s PCV dropped below 15, they were dewormed.
Trial 2. Twenty mixed sex lambs with naturally acquired infections were randomly allocated to 2 treatment groups of 10 animals each. Lambs were kept in cement floored pens. ASL pellets were fed over a 35 day period to one group while the other group was fed BG hay (control). Both groups were fed BG hay for an additional 14 days.
Feces, for FEC, and blood, for PCV, were collected weekly to monitor infection level. Weight was taken at the beginning and end to access weight gain.
If any individual animal’s PCV dropped below 15, they were dewormed.
Trial 1. During ASL feeding (days 7-35), FEC was significantly reduced in the existing infection ASL fed group (Figure 1) and was lower in the establishing infection ASL fed group (Figure 2), but that difference was not significant. After ASL feeding was terminated, FEC increased in both existing and establishing infection groups which indicated that there was an effect on female worm fecundity. There was no difference in PCV between groups which remained >25 (data not shown). No animal’s PCV dropped below 15, so no dewormings were necessary. At necropsy, there were fewer worms in both ASL fed groups (Figure 3), but the differences were not significant. However, in both ASL groups there was one animal that did not respond to treatment. In a group feeding situation, it is not uncommon that one animal will not be able to consume their share of the ration. This is usually attributed to the aggressive nature of the others not allowing that one animal (usually the weakest) access to the feed. Or, one animal may just not eat as much as the others and therefore, does not ingest enough to achieve the desired effect. If those two are dropped from the analysis, then worm burden was significantly reduced in both ASL groups (Figure 3).
Trial 2. During ASL feeding (days 7-35), FEC was significantly reduced in the ASL fed group (Figure 4). After ASL feeding was terminated, FEC remained low and did not increase as expected in the ASL group, and the control group FEC decreased to the level of the ASL group. Four control animals required deworming, one each on day 14, 21, 35 and 42. Because there was no reinfection, these dewormings probably accounted for the observed decrease in the control group FEC by the end of the trial. Necropsies were planned to determine worm burdens, but since infection levels were similar at the end of the trial, that was not done. The lack of a FEC increase in the ASL group when put back on BG hay during the last 14 days was not consistent with previous studies that showed an effect on female worm fecundity. The reason for this is not known, but it could be that the worm burden was reduced to the extent that the majority of worms remaining were males. PCV of the ASL group was significantly higher than the control group from day 7 through day 28 (Figure 5), which supports a decrease in worm burden. From day 35-49, the control group PCV increased and was greater than the ASL group on day 49. This shift can be accounted for by the 4 animals that were dewormed whose PCVs increased substantially after infection was reduced. There was no difference in weight between groups at the beginning or end of the trial or weight gain (data not shown). However, both groups gained about 9 lbs which suggested that ASL pellets were equivalent to BG hay in nutritional value.
It is known that the level and reactivity of condensed tannins in plants decreases at each stage of processing, i.e. fresh forage > hay (long stem or ground) > pellets. The processing to make pellets in most circumstances involves heat (>80 C) which was been shown to dramatically reduce the effect of some condensed tannins. The pellets for this study were made with a low heat (about 65 C) process in an attempt to retain activity which the results indicated occurred.
Educational & Outreach Activities
Chafton, L.A., Miller, J.E., Mosjidis, J.A., Terrill, T.H., Burke, J.M., 2006. The effect of the condensed tannin containing forage sericea lespedeza fed as a meal on existing and establishing infection of Haemonchus contortus in sheep. Proc 51stAnn Meet Amer Assoc Vet Parasitol: 38.
Results were reported at the annual meeting of the American Association of Veterinary Parasitologists held in Honolulu, HI in July, 2006 and at the annual meeting of the Southern Section of the American Society of Animal Science held in Mobile, AL in February, 2007. Results are also being presented at various producer meetings.
A manuscript is in preparation which will be submitted to Veterinary Parasitology for publication.
ASL, fed as ground hay or pellets, has the potential to help control H. contortus infection in lambs.
ASL fed lambs grow just as well as BG fed lambs.
Although this study was not intended to evaluate farmer adoption, once ASL products are available, it is expected that many will adopt this method for controlling H. contortus with the added benefit of it’s nutritional value.
Areas needing additional study
The next step in this line of investigation is to test various methods of using ASL products in the field under controlled conditions and then follow up with on-farm evaluation.