UPDATE ON NUTRITION: SOLUBLE VS INSOLUBLE GRITUPDATE ON NUTRITION: SOLUBLE VS INSOLUBLE GRIT
Grit has traditionally been added to passerine (Finch, Canary, etc.) and small psittacine (Parakeet, Lovebird, etc.) diets as a digestive aid. It has been a long held belief that grit will increase digestibility of feeds by mechanically helping the gizzard (ventriculus) break down seeds and grains provided in the diet. In poultry, the benefits of grit have been well researched for over 50 years. Adding grit to the diet was shown to increase digestibility of feed by 10- as far back as 1955 (Titus,1955)1
Although many pet stores will readily promote the use of grit, many avian veterinarians have a more cautious approach to its use. The concern about grit is that some birds will binge on it. Over ingestion is believed to be the cause of grit impaction, a condition were the intestines are blocked by a mass of grit. Since there have been no research studies in pet bird species that prove or disprove the tenet that grit is beneficial to pet birds, it is difficult to make accurate recommendations. Most of the information we have about the use of grit in pet birds comes from two studies performed at the Waltham Centre for Pet Nutrition. The first study failed to show an increase in feed digestibility in Canaries provided with grit vs. those that were not provided grit 2. Unfortunately, this study did not take into account the type of grit that was provided. The second study focused on the difference between soluble and insoluble grit and its effect on feed digestibility in Canaries3.
Grit can be composed of soluble and insoluble minerals. Insoluble grit is composed primarily of quartz or silica (sand). These are minerals that the body cannot digest. They are eliminated in the feces unchanged from when they were eaten. Soluble grit is composed of minerals (usually calcium based) that the body can digest and utilize. Oyster shells, limestone, marble and gypsum are all composed of calcium and are forms of soluble grit.
The findings from the second study were surprising. There was no difference in feed digestibility for energy fat or carbohydrates in birds offered either soluble or insoluble grit. However, birds that were fed only insoluble grit had lower digestibility of protein than birds fed soluble grit. The birds fed only insoluble grit also consumed more cuttlebone than those fed only soluble grit. These findings suggests that the original digestibility study bares further investigation.
This new information permits avian veterinarians to begin to make accurate recommendations in regards to the use of grit. We now know that soluble and insoluble grit may have different effects in the digestive tract of birds. If an owner chooses to provide grit to their Canary, then it should be soluble grit or at least a combination of soluble and insoluble grit. Similar recommendation cannot be accurately made for other species at this time. Future studies are needed to shed light into this area. As always.....if you have any questions, please consult with your avian veterinarian.
1 In Taylor E. Jean. An Evaluation of the Importance of Insoluble versus Soluble Grit in the Diet of Canaries. Journal of Avian Medicine and Surgery, 1996; 10(4): 248 25l .
2 Taylor E. Jean, Nott H.M.R., Earle KE. The Nutrition of the Canary (Serinus canarius). Journal of Nutrition, 1994; 124: 2636S 2637S.
3 Taylor E. Jean. An Evaluation of the Importance of Insoluble versus Soluble Grit in the Diet of Canaries. Journal of Avian Medicine and Surgery, 1996; 10(4): 248 251.
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