Nutritional Balance of Feed
(For a less technical article on feed nutrient balance and why our vet doesn't recommend feeding too many treats or hay on a regular basis along with our commercial rabbit pellets, see our page on Feeding Supplements.)
I did some reading about rabbit nutrition recently, and learned some interesting things. One is that the balance between various nutrients and their ratio to each other is at least as important as the levels of individual components. For example, calcium absorption and utilization is strongly affected by the phosphorus and vitamin D content; and even sodium, sugar and phytate levels can affect calcium absorption (at least in humans--I didn't find anything specific to rabbits about that last point).
The problem I'm finding is that most feed companies don't label the amounts of most nutrients. Generally you'll get max/min quantities for a few key elements such as protein, fat, fiber, sodium, calcium and phosphorus. If you want more info. than that, you often have to contact the company and ask--and then you may or may not be able to get information on things like magnesium and potassium content.
In my reading, I was looking mostly at phosphorus, calcium and potassium levels. Protein and fiber levels are also important, and the fiber should be equal to or (preferably) greater than the protein in a pelleted feed. Most resources recommend 15% to 17% protein for adult rabbits that are not in production, and 17% to 18% protein for lactating and growing rabbits. We find that satins seem to be particularly sensitive to protein levels, and do not produce and grow nearly as well on 16% protein feed as they do on 17% to 18% protein.
One thing that is included on most feed labels is the amount of calcium and phosphorus. This is one key indicator of the nutritional balance of the feed.
According to my research, the ideal calcium to phosphorus ratio for rabbits is 2:1, which means there is about twice as much calcium as phosphorus. Some sources say that ideal can be anywhere between 1.5:1 and 2:1 Ca/P ratio.
One reason this is important is that rabbits do not process calcium in the same way as most other animals do. Rather than their body absorbing only the calcium it needs and excreting the rest in the stools, they absorb almost all available calcium and excrete the excess primarily in their urine. This is why you see white calcium deposits, sludge, or sometimes even bladder stones--this excretion tends to be increased in rabbits that are absorbing more calcium than their body needs. Calcium carbonate crystals can also be one possible cause for reddish-brown colored crystals in rabbit urine.
Interestingly enough, researchers Cheeke and Amberg found that calcium carbonate is much more readily absorbed and excreted by rabbits than calcium oxalate--a good illustration of the fact that the form of the vitamin or mineral is also important.
Phosphorus is also an important nutrient for health and growth in rabbits. The need for phosphorus is significantly increased for nursing does.
First-cut orchard grass and whole oats are particularly good sources of phosphorus, both being higher in phosphorus than in calcium (the grain more significantly so than the hay). However, you have to be careful about whatever you add to the diet potentially messing up the balance of other nutrients. It's always a good idea, if feeding pellets, to check with the feed company to see what their recommendations are as far as feeding hay or other supplementary foodstuffs. It would be a good idea to check with a vet also if you can find one that's knowledgeable about rabbit nutrition. Remember that nursing does need more phosphorus than the rest of the herd, so they may be the only ones that need such supplementation if you do decide to suppment.
Alfalfa hay has high levels of calcium with a badly unbalanced calcium to phosphorus ratio of 5.6/1. This is one reason that alfalfa hay is not recommended when you are feeding commercial rabbit pellets--the calcium and phosphorus levels need to be carefully balanced for rabbit health, and it's almost certain to result in excess calcium and deficiencies in phosphorus when you add alfalfa hay to a pellet diet.
This link has info. on the Ca/P ratio of various hays and grains:
http://www.shady-acres.com/susan/Calcium-Phosphorus.shtml
Several researchers have estimated that for meat-breed rabbits in production, particularly nursing does, a phosphorus level of about 0.5% to 0.8% of the diet is ideal. It's hard to find a rabbit feed in my area that actually has that much phosphorus, but I have found a few that have 0.4% to 0.6% phosphorus and close to a 2:1 ratio.
Here are some links and excerpts from resources on the dietary levels of calcium, phosphorus, and potassium, since that's what I've been mostly focusing on researching recently.
Hopefully this information will be helpful.
-----------------------
Scientific and nutritionist recommendations Re: Calcium/Phosphorus balance
Here are my notes from various references:
Rabbit calcium metabolism, "bladder sludge," and urolithiasis (Proceedings)
Aug 1, 2009
By: Dan Johnson, DVM
CVC IN KANSAS CITY PROCEEDINGS
"The unusual calcium metabolism of rabbits makes it essential to maintain a diet that is well-balanced with appropriate calcium concentration, calcium to phosphorus ratio, and vitamin D content. If too little calcium is consumed, secondary hyperparathyroidism and bone resorption may result, while if too much calcium is present, the risk of urolithiasis and bladder sludge is increased. A dietary calcium level of 0.22% supports normal growth, but 0.35-0.4% calcium is required for optimal bone calcification and growth rates in young rabbits. There should be less than 25 �g (1,000 IU) cholecalciferol/kg food to prevent soft tissue mineralization. The pet rabbit's diet should be chosen carefully to prevent selective feeding. If the rabbit rejects pellets and whole grain,
calcium intake may be insufficient. Most commercial rabbit feeds contain calcium from alfalfa hay and calcium carbonate, which are very absorbable. While many vegetables are high in calcium, they often contain calcium oxalate, which is not metabolized by rabbits, and thus cannot contribute to urinary sludge or stones.
The ideal diet for pet rabbits should contain at least 15-16% fiber, 12-13 % protein, 1-3 % fat, 0.6-1.0 % calcium, calcium to phosphorus ratio of 1:1 - 2:1, and less than 1000 IU/kg vitamin D."
http://veterinarycalendar.dvm360.com/avhc/article/articleDetail.jsp?id=648133&sk&date&pageID=6
Nutrient requirements of rabbits
By National Research Council (U.S.).
Subcommittee on Rabbit Nutrition:
"Hove and Herndon (1955) . . estimated the potassium requirement for growth to be at least 0.6 percent of the diet. . . . It has been reported that high levels of potassium (0.8-1.0 percent) may induce nephritis in rabbits (Surdeau et al., 1976)"
http://books.google.com/books?id=z9AtAmWYzDkC&pg=PA5&lpg=PA5&dq=calcium+phosphorus+ratio+rabbit&source=bl&ots=if8iHJ4gaw&sig=eQemi1qohEDThYSXtDmiUS7F4Wc&hl=en&ei=oDWcTbPlIoissAP1vaCCBA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCoQ6AEwAw#v=onepage&q=calcium%20phosphorus%20ratio%20rabbit&f=false
Nutrition of the Rabbit By Carlos De Blas, Julian Wiseman (p. 122),
"Excess calcium is more detrimental to rabbit health if marginal levels of phosphorous are used . . . Assane et al. (1993) observed an increase of phosphorus and magnesium in the blood at the end of the gestation period when the calcium to phosphorus ratio in feed was 1:1 as compared with 2:1 (Table 7.2). Assane et al. (1994) reported positive calcium and phosphorus balances with dietary calcium to phosphorus ratios of 2:1 and 1:1. However, calcium retention increased in both non-pregnant and pregnant does with the higher calcium level. Moreover, the best reproductive performance was obtained when the calcium to phosphorus ratio was 2:1.
" Practical recommendations on dietary levels of calcium and phosphorus vary according to age, breed, productivity and diet composition. For growing-fattening rabbits, the recommendations vary from 4 to 10 g for calcium and from 2.2 to 7 g for phosphorus. . . . Calcium and phosphorus requirements are higher for lactating does than for growing rabbits or non-lactating does . . . Practical recommendations in doe feeds vary from 7.5 to 15 g for calcium and from 4.5 to 8 g for phosphorous . . . "
Regarding potassium, it says that "practical recommendations" for the amount of K+ in feed "range between 6.0 and 10 g kg-1."
http://books.google.com/books?id=YdSfvj79DPoC&printsec=frontcover&dq=rabbit+nutrition&hl=en&ei=_recTefuAoSssAOH1KSKBA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CEMQ6AEwAQ#v=onepage&q=calcium%20phosphorus%20ratio%20rabbit&f=false
Nutrient Requirements of Rabbits (linked above) says,
"Kennedy (1965) also suggests a possible role of vitamin D in stimulating the high urinary calcium excretion.
"Dietary requirements for calcium and phosphorous for rabbits have been estimated. Matheiu and Smith (1961) estimated the phosphorus requirement for growth to be 0.22 percent of the diet. . . . Chapin and Smith (1967b) reported that a diet with 0.37 percent phosphorus and 0.45 percent calcium was adequate for gestation and lactation. In view of the secretion of these elements into milk (Lebas et al, 1971), tentative requirements of 0.75 percent calcium and 0.5 percent phosphorus are recommended for lactation. . . . Chapin and Smith (1967b) found that diets containing as much as 4.5 percent calcium and a calcium/phosphorus ratio of 12:1 did not depress growth and resulted in normal bone ash."
(Note from Shiny: this would make the phosphorus level in the cited Chapin/Smith experiment 0.375%)
Rabbit Feeding and Nutrition by Peter R. Cheeke, Tony J. Cunha
Although the National Research Council (NRC) (1977) recommends dietary phosphorus levels of 0.22% for growth and 0.5% for lactation, these values were obtained with Dutch rabbits and seem too low for commercial production. Lebas (1980) recommended 0.8% phosphorus for does and fryers fed the same diet. Lebas and Jouglar (1984) found the optimal level to be about 0.64-0.67%, with reduced litter size with 0.42% or 1.0% phosphorus levels." (p. 112)
"Hope and Herndon (1955) . . . estimated the potassium requirement to be about 0.6% of the diet. . . . French workers have found that high dietary levels of potassium (0.8-1.0%) may induce nephritis in rabbits (Surdeau et al., 1976). Evans et al. (1982a) observed slight growth depression with 1% dietary potassium as compared to 0.6%. (p.115)
http://www.amazon.com/Rabbit-Feeding-Nutrition-Animal/dp/0121706052#reader_0121706052
This preview also includes tables 16.1 and 16.2 on pgs. 296-297 of Rabbit Feeding and Nutrition, which provides a chart of recommended amounts of various vitamins and minerals for optimum health at different stages of rabbit production.
I did some reading about rabbit nutrition recently, and learned some interesting things. One is that the balance between various nutrients and their ratio to each other is at least as important as the levels of individual components. For example, calcium absorption and utilization is strongly affected by the phosphorus and vitamin D content; and even sodium, sugar and phytate levels can affect calcium absorption (at least in humans--I didn't find anything specific to rabbits about that last point).
The problem I'm finding is that most feed companies don't label the amounts of most nutrients. Generally you'll get max/min quantities for a few key elements such as protein, fat, fiber, sodium, calcium and phosphorus. If you want more info. than that, you often have to contact the company and ask--and then you may or may not be able to get information on things like magnesium and potassium content.
In my reading, I was looking mostly at phosphorus, calcium and potassium levels. Protein and fiber levels are also important, and the fiber should be equal to or (preferably) greater than the protein in a pelleted feed. Most resources recommend 15% to 17% protein for adult rabbits that are not in production, and 17% to 18% protein for lactating and growing rabbits. We find that satins seem to be particularly sensitive to protein levels, and do not produce and grow nearly as well on 16% protein feed as they do on 17% to 18% protein.
One thing that is included on most feed labels is the amount of calcium and phosphorus. This is one key indicator of the nutritional balance of the feed.
According to my research, the ideal calcium to phosphorus ratio for rabbits is 2:1, which means there is about twice as much calcium as phosphorus. Some sources say that ideal can be anywhere between 1.5:1 and 2:1 Ca/P ratio.
One reason this is important is that rabbits do not process calcium in the same way as most other animals do. Rather than their body absorbing only the calcium it needs and excreting the rest in the stools, they absorb almost all available calcium and excrete the excess primarily in their urine. This is why you see white calcium deposits, sludge, or sometimes even bladder stones--this excretion tends to be increased in rabbits that are absorbing more calcium than their body needs. Calcium carbonate crystals can also be one possible cause for reddish-brown colored crystals in rabbit urine.
Interestingly enough, researchers Cheeke and Amberg found that calcium carbonate is much more readily absorbed and excreted by rabbits than calcium oxalate--a good illustration of the fact that the form of the vitamin or mineral is also important.
Phosphorus is also an important nutrient for health and growth in rabbits. The need for phosphorus is significantly increased for nursing does.
First-cut orchard grass and whole oats are particularly good sources of phosphorus, both being higher in phosphorus than in calcium (the grain more significantly so than the hay). However, you have to be careful about whatever you add to the diet potentially messing up the balance of other nutrients. It's always a good idea, if feeding pellets, to check with the feed company to see what their recommendations are as far as feeding hay or other supplementary foodstuffs. It would be a good idea to check with a vet also if you can find one that's knowledgeable about rabbit nutrition. Remember that nursing does need more phosphorus than the rest of the herd, so they may be the only ones that need such supplementation if you do decide to suppment.
Alfalfa hay has high levels of calcium with a badly unbalanced calcium to phosphorus ratio of 5.6/1. This is one reason that alfalfa hay is not recommended when you are feeding commercial rabbit pellets--the calcium and phosphorus levels need to be carefully balanced for rabbit health, and it's almost certain to result in excess calcium and deficiencies in phosphorus when you add alfalfa hay to a pellet diet.
This link has info. on the Ca/P ratio of various hays and grains:
http://www.shady-acres.com/susan/Calcium-Phosphorus.shtml
Several researchers have estimated that for meat-breed rabbits in production, particularly nursing does, a phosphorus level of about 0.5% to 0.8% of the diet is ideal. It's hard to find a rabbit feed in my area that actually has that much phosphorus, but I have found a few that have 0.4% to 0.6% phosphorus and close to a 2:1 ratio.
Here are some links and excerpts from resources on the dietary levels of calcium, phosphorus, and potassium, since that's what I've been mostly focusing on researching recently.
Hopefully this information will be helpful.
-----------------------
Scientific and nutritionist recommendations Re: Calcium/Phosphorus balance
Here are my notes from various references:
Rabbit calcium metabolism, "bladder sludge," and urolithiasis (Proceedings)
Aug 1, 2009
By: Dan Johnson, DVM
CVC IN KANSAS CITY PROCEEDINGS
"The unusual calcium metabolism of rabbits makes it essential to maintain a diet that is well-balanced with appropriate calcium concentration, calcium to phosphorus ratio, and vitamin D content. If too little calcium is consumed, secondary hyperparathyroidism and bone resorption may result, while if too much calcium is present, the risk of urolithiasis and bladder sludge is increased. A dietary calcium level of 0.22% supports normal growth, but 0.35-0.4% calcium is required for optimal bone calcification and growth rates in young rabbits. There should be less than 25 �g (1,000 IU) cholecalciferol/kg food to prevent soft tissue mineralization. The pet rabbit's diet should be chosen carefully to prevent selective feeding. If the rabbit rejects pellets and whole grain,
calcium intake may be insufficient. Most commercial rabbit feeds contain calcium from alfalfa hay and calcium carbonate, which are very absorbable. While many vegetables are high in calcium, they often contain calcium oxalate, which is not metabolized by rabbits, and thus cannot contribute to urinary sludge or stones.
The ideal diet for pet rabbits should contain at least 15-16% fiber, 12-13 % protein, 1-3 % fat, 0.6-1.0 % calcium, calcium to phosphorus ratio of 1:1 - 2:1, and less than 1000 IU/kg vitamin D."
http://veterinarycalendar.dvm360.com/avhc/article/articleDetail.jsp?id=648133&sk&date&pageID=6
Nutrient requirements of rabbits
By National Research Council (U.S.).
Subcommittee on Rabbit Nutrition:
"Hove and Herndon (1955) . . estimated the potassium requirement for growth to be at least 0.6 percent of the diet. . . . It has been reported that high levels of potassium (0.8-1.0 percent) may induce nephritis in rabbits (Surdeau et al., 1976)"
http://books.google.com/books?id=z9AtAmWYzDkC&pg=PA5&lpg=PA5&dq=calcium+phosphorus+ratio+rabbit&source=bl&ots=if8iHJ4gaw&sig=eQemi1qohEDThYSXtDmiUS7F4Wc&hl=en&ei=oDWcTbPlIoissAP1vaCCBA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCoQ6AEwAw#v=onepage&q=calcium%20phosphorus%20ratio%20rabbit&f=false
Nutrition of the Rabbit By Carlos De Blas, Julian Wiseman (p. 122),
"Excess calcium is more detrimental to rabbit health if marginal levels of phosphorous are used . . . Assane et al. (1993) observed an increase of phosphorus and magnesium in the blood at the end of the gestation period when the calcium to phosphorus ratio in feed was 1:1 as compared with 2:1 (Table 7.2). Assane et al. (1994) reported positive calcium and phosphorus balances with dietary calcium to phosphorus ratios of 2:1 and 1:1. However, calcium retention increased in both non-pregnant and pregnant does with the higher calcium level. Moreover, the best reproductive performance was obtained when the calcium to phosphorus ratio was 2:1.
" Practical recommendations on dietary levels of calcium and phosphorus vary according to age, breed, productivity and diet composition. For growing-fattening rabbits, the recommendations vary from 4 to 10 g for calcium and from 2.2 to 7 g for phosphorus. . . . Calcium and phosphorus requirements are higher for lactating does than for growing rabbits or non-lactating does . . . Practical recommendations in doe feeds vary from 7.5 to 15 g for calcium and from 4.5 to 8 g for phosphorous . . . "
Regarding potassium, it says that "practical recommendations" for the amount of K+ in feed "range between 6.0 and 10 g kg-1."
http://books.google.com/books?id=YdSfvj79DPoC&printsec=frontcover&dq=rabbit+nutrition&hl=en&ei=_recTefuAoSssAOH1KSKBA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CEMQ6AEwAQ#v=onepage&q=calcium%20phosphorus%20ratio%20rabbit&f=false
Nutrient Requirements of Rabbits (linked above) says,
"Kennedy (1965) also suggests a possible role of vitamin D in stimulating the high urinary calcium excretion.
"Dietary requirements for calcium and phosphorous for rabbits have been estimated. Matheiu and Smith (1961) estimated the phosphorus requirement for growth to be 0.22 percent of the diet. . . . Chapin and Smith (1967b) reported that a diet with 0.37 percent phosphorus and 0.45 percent calcium was adequate for gestation and lactation. In view of the secretion of these elements into milk (Lebas et al, 1971), tentative requirements of 0.75 percent calcium and 0.5 percent phosphorus are recommended for lactation. . . . Chapin and Smith (1967b) found that diets containing as much as 4.5 percent calcium and a calcium/phosphorus ratio of 12:1 did not depress growth and resulted in normal bone ash."
(Note from Shiny: this would make the phosphorus level in the cited Chapin/Smith experiment 0.375%)
Rabbit Feeding and Nutrition by Peter R. Cheeke, Tony J. Cunha
Although the National Research Council (NRC) (1977) recommends dietary phosphorus levels of 0.22% for growth and 0.5% for lactation, these values were obtained with Dutch rabbits and seem too low for commercial production. Lebas (1980) recommended 0.8% phosphorus for does and fryers fed the same diet. Lebas and Jouglar (1984) found the optimal level to be about 0.64-0.67%, with reduced litter size with 0.42% or 1.0% phosphorus levels." (p. 112)
"Hope and Herndon (1955) . . . estimated the potassium requirement to be about 0.6% of the diet. . . . French workers have found that high dietary levels of potassium (0.8-1.0%) may induce nephritis in rabbits (Surdeau et al., 1976). Evans et al. (1982a) observed slight growth depression with 1% dietary potassium as compared to 0.6%. (p.115)
http://www.amazon.com/Rabbit-Feeding-Nutrition-Animal/dp/0121706052#reader_0121706052
This preview also includes tables 16.1 and 16.2 on pgs. 296-297 of Rabbit Feeding and Nutrition, which provides a chart of recommended amounts of various vitamins and minerals for optimum health at different stages of rabbit production.
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