Current Status and Progress of Research on Porcine Ophthalmic Diseases
Researchers in veterinary medicine at the University of Florida in the United States used pigs as experimental subjects and specially treated the feed provided so that it created a zinc-deficient condition. As a result, this treatment group may have caused chronic damage to the pigs' retinas, and it may be related. Veterinary ophthalmology experts have completed monitoring changes in blood, skin, body weight and major organs in young piglets and older pigs. The pig eye is very similar in structure to the human eye. This group of researchers has been able to identify the relationships among those changes.
There is a professor of ocular anatomy, Dr. Don A. Samuelson, who said that in the treatment group whose feed contained zinc at 25%-50% of the recommended amount, the most dramatic changes could appear in the eyes and liver. When this feed lacked zinc supply for a long period of up to one year, we could repeatedly find changes in the eyes, as well as lesions in other major organ tissues including the liver, skin, pancreas, esophagus and bones.
In the studies by Dr. Samuelson and his colleagues, the treatment group with low zinc content in the feed showed mild swelling in the retina, and along this retina the pigmented epithelium showed mild enlargement. This pigmented epithelium is one layer of eye tissue, and it is related to the aging process and to macular degeneration. It causes blindness in humans apparently more than in the eyes of humans over 70 years of age.
In the authors' animal model experiments, it was found that in the above treatment group the height of these cells consistently increased by 10%, and the overall cell size increased by 20%. The authors said that at present we are concentrating all our efforts on determining what changes occur in the pigment in this melanoma, and whether those changes are related to this retinal pigment epithelium. He explained that the total amount of this zinc in eye pigment appears to play a very important role. When zinc is deficient, this pigment becomes damaged, which affects the normal characteristics of light control.
Dr. Patricia J. Smith is a veterinary ophthalmology expert, and he is conducting research on how the appearance of light interacts with this zinc to affect changes in pigment. It includes the retinal pigment epithelium and the choroidal pigment epithelium. He used 30 pigs for the experiment to determine the effect of light intensity on the eyes. He kept half of the pigs (15) in an artificially controlled light environment, so that there were 18 hours of artificial light per day and 6 hours of darkness. The other 15 pigs were kept under 24 hours of light per day.
The results showed that in the group of pigs given 24-hour light all day, more retinal damage could definitely be seen. When the feed contained excessive zinc, the initial results might make this retina perform worse.
Since 1986, Mr. Samuelson and others began to study whether the amount of zinc contained in feed is sufficient, and to study the risks caused by containing too much or too little zinc. Therefore, based on the findings of this study, the authors have established the baseline level of zinc deficiency in sows during pregnancy, and established the standard zinc requirements for the feed of piglets, growing pigs and pregnant sows.