Abstract

Ideally, the forage portion of a manatee feed should be composed of aquatic plants and grasses that are likely more digestible than terrestrial plants. However, in order to produce a low-cost feed, we used terrestrial plants in our feed. Grinding, cooking, extruding and keeping the lignin content low were techniques used to enhance digestibility of the feed. We have now prepared a floating, specific-pathogen-free, manatee pellet to assist caregivers in maintaining rescued, rehabilitating manatees.¹ The manatees at Mote Marine Laboratory, Homosassa Springs State Park and Lowry Park Zoo readily accept the pellets. Digestibility, expressed as total digestible nutrients (TDN), was calculated using digestion coefficients determined for the manatee² and the available energy value of the pellets was estimated using percent TDN for ruminants and percent acid detergent fiber for horses. Forage quality of the pellets as defined by TDN and crude protein would be considered high when compared to terrestrial grass for either a horse or ruminant.³

Some caregivers believe that the feed should contain sufficient water to meet the animal's requirements, even though manatees are aquatic animals. The water requirements of a manatee are unknown; therefore, our feed was designed to meet the needs of a milking cow. A milking cow will drink from four to five kg of free water for each kg of dry matter eaten; therefore, our feed was dried to contain less than 12 percent moisture and expanded so it would take up four to five times its weight in water. The dry feed was stored for over one year at room temperature.

An optimum feed protein concentration for the manatee is not known, but it can be estimated to lie between the 12 percent concentration recommended for horses and the 17 percent concentration recommended for high-producing dairy cows in lactation. Mean protein concentration of stomach contents from recently deceased manatees was determined to be 17.9 percent,² but forage protein concentration at ingestion is probably lower than the crude protein level of stomach contents. Protein content of the manatee feed can easily be increased by the addition of protein-rich feedstuffs. We adjusted the protein content of our finished feed to approximately 16 percent protein.

Manatees have been maintained and have even gained weight on diets consisting entirely of romaine lettuce or water hyacinths; thus, we believed that either of these two forage materials met both the vitamin and mineral requirements of the manatee. Therefore, a vitamin/mineral mix was added to the feed to approximate the greater individual vitamin or mineral concentration found in either romaine lettuce or water hyacinths on a dry matter basis.

The daily energy requirement for manatees kept in fresh water at approximately 72°F was estimated from the daily consumption by individual animals being fed a single forage (romaine lettuce) ration. A 300 kg manatee consumed about 1.5 kg of lettuce on a dry matter basis or 4.12 Mcal of gross energy and approximately 3.3 Mcal of digestible energy. The energy requirements of a manatee this size could be met with approximately 1.2 kg of our maintenance feed.

Almost the entire natural diet of a manatee consists of freshwater plants and sea grasses. These aquatic forages supply fiber and all the nutrients previously discussed. Fiber is necessary for normal gastrointestinal function in the horse and presumably the manatee. It provides enough bulk to prevent feed compaction and constipation in the horse. Fiber stimulates intestinal motility, provides substrate for fermentation in the large intestine, and satisfies the psychological need of a horse to chew and feel "full." Forages also apparently help the horse maintain fluid balance. Correct fiber length is believed to be important for good gut motility in the horse and seems to be more effective than ground, pelleted fiber in reducing the incidence of colic. The lignin component of the fiber is virtually indigestible in the manatee, as is the case with terrestrial animals.² Aquatic plants are reported to have lower lignin content than terrestrial plants;² therefore, the lignin content of our feed was maintained at levels lower than those found in the stomach contents of deceased manatees.²

Our pellets have been fed to nine adult manatees at Homosassa Springs State Park for more than one year at increasing percentages of the ration, which has been increased to about 1.1 lbs per animal for the last six months. We believe this amount meets more than 30 percent of the nutrient requirements of these manatees. The animals obtain approximately 70 percent of their required nutrients from fresh vegetable forages. We have been cautious in changing the amount and source of fiber for these animals, since a rapid change is known to cause problems occasionally for horses. At this time we have observed no digestive problems in the Homosassa State Park colony.

We plan to monitor the health status of the Homosassa State Park colony by means of feed consumption, morphometrics, blubber thickness, clinical values and any indications of feed compaction or constipation. Ultimately, many of the captive manatees will be returned to free-ranging status. It is assumed that the manatee may be similar to the horse in requiring slow changes in the fiber source and our pellet should not hinder caregivers in their ability to return their manatees to free-ranging status. Thus, the fiber in our feed should be compatible and readily interchangeable with the fiber found in the aquatic forages available to manatees.

Acknowledgments

Mr. Wayne T. McClellan and Mr. Joseph P. Cardeilhac provided technical assistance. The authors wish to thank all the caregivers for their valuable contributions to this project. This project was supported by a grant from the Florida Fish and Wildlife Conservation Commission.

References

1.  Cardeilhac PT, HM Dickson, R Larsen, P McGuire, M Lowe, C Manier. 2002. Proceedings International Association for Aquatic Animal Medicine. 33: 158-159.

2.  Burn DM. 1986. The Digestive Strategy and Efficiency of the West Indian Manatee, Trichechus manatus. Comp. Biochem. Physiol. 185A: 139-142.

3.  Jurgens MH. Animal feeding and nutrition 6th Ed. 1988. Evaluating Feedstuffs for Farm Livestock. Kendall/Hunt Publishing. Pp 49-72.