November 8, 2015
This is a detailed account of the experiment. For more data, Click Here.
The rabbits at Windward are kept in elevated or suspended rabbit cages.
We wanted to learn the effects of keeping the rabbits in outdoor colonies, so when a litter of 8 was born Claire and Jonah separated them into a colony and a cage. Midway through the experiment Claire and Jonah left to pursue summer employment, and I took over.
The colony is a 20' by 11' area surrounded by an 8' tall fence made from cattle panels and chicken wire. We dug in the chicken wire to prevent the rabbits from burrowing, so that we could observe them and catch them for weighing. The area was surrounded by trees and included two 10"x18"x14" wooden nesting boxes, which provided shade and shelter.
Our primary goal was to measure each rabbit's weight in both groups and the ratio of commercial feed to rabbit weight. Other goals included comparing the labor involved in taking care of each group and determining the health and safety of rabbits raised in a colony. No measurements were taken for the secondary goals, instead we made qualitative assessments.
- Number of Rabbits: 8 (numbers 1-8 were tattooed in their ears)
- Genders: 7 males, 1 female (#2)
- Breed: New Zealand White
- Date kindled: March 31st, 2015
On May 1st, the rabbits were separated, with five males put into the colony, and two males and one female into a cage.
Initial weights on May 8th (±0.5oz):
The rabbits ate some commercial feed during the month they were with their mother (before we started tracking), but Opalyn estimates that the amount of feed they ate during that month was negligible compared to the amount of feed they ate in the first few weeks of the experiment.
Both cage and colony rabbits were fed the same diet, consisting of commercial feed, alfalfa, and local grasses. While we didn't measure the alfalfa or grass, we gave each group approximately proportional amounts.
On the first day (May 1st), we filled the feeders with commercial feed. We refilled the feeders daily using a 1/3 cup scoop and recorded the number of scoops.
Some feeding issues: on a handful of days we forgot to add feed, but the feeders were never empty so in these cases the record for the next day accounts for the feed eaten during the past two days. On a few other days feed was added but not recorded, for those days I used the average of the feed given on the previous four days and the following four days.
On the morning of the last day (August 14th), I filled the feeders, and removed the full feeders (we didn't want the rabbits to eat on the day of the slaughter).
Between May 8th and August 14th, we weighed the rabbits weekly.
We killed the rabbits by laying each one out on the ground, placing a metal bar over the rabbit's neck, and pulling its hind legs up sharply while holding down the bar to quickly sever the spine. When we butchered the rabbits, we cut off their heads first to let the blood drain, feet (at the ankle) and tail, and skinned and gutted them. The carcass was weighed to determine the carcass weight.
All the rabbits' weights (live, carcass, and meat) were measured on a scale with an accuracy of ±0.5oz.
I next measured the error in the amounts of feed added. I first determined the weight of one scoop of feed by weighing 218 scoops, and dividing the total weight (22lb 1oz) by the number of scoops (218) to get 1.62±0.04oz per scoop.
Using a scale with an accuracy of ±0.01oz, I under-filled a scoop as much as I thought might go unnoticed and weighed that feed, which weighed 1.09oz (33% less than a full scoop). I filled another scoop to overflowing, which weighed 2.19oz (35% more than a full scoop). To cover the additional small errors in these measurements, I took the error for the amount of feed in each scoop to be ±40%.
We began to collect data on May 1st, when the rabbits were 4.5 weeks old. The experiment lasted 106 days (May 1st-August 14th). At the time of slaughter the rabbits were 19.5 weeks old.
Final Weights (±0.5oz)
*This data was extrapolated (in the analysis that follows) because we kept rabbits #2&3 as breeders.
Some Extrapolation Required
Since Windward is not only a research center but also a village, the needs of the community conflict with the demands of science. We wanted to keep two of the caged rabbits as breeders and to preserve the meat of those we slaughtered to eat later. This necessitated some extrapolation.
To help us measure the carcass weight of the caged rabbits we didn't slaughter, we used another litter of 5 New Zealand White/Californian crosses that were both born and slaughtered on the same days as the experiment rabbits. By measuring the carcass weights of the those 5 rabbits and rabbit #4, I got an average carcass weight to live weight ratio of 0.56. I used that number to calculate the carcass weights of the rabbits we didn't slaughter.
I also wanted to determine how much of the rabbit we eat. Since we generally freeze the animals for future use, we cooked only two rabbits (one from the colony, and one of the NZW/Cal crosses). I dried and weighed the bones, and both rabbits had a meat weight to carcass weight ratio of 0.94. I used these measurements to extrapolate the meat weights of the other rabbits.
Weight, Feed, and Costs
The caged rabbits win out in total weight, averaging 1lb 3oz heavier than their colony brethren. This is unsurprising, since the colony rabbits were more physically active, and had things to do other than sit and eat all day. The colony rabbits, however, were better at converting feed into weight. The following chart shows the final feed weight/rabbit weight ratios.
Our commercial feed costs 20$ for a 50lb bag, or 0.4$/lb. The following chart shows the final feed costs/rabbit weight ratios.
It cost us 2.60$ worth of commercial feed for one pound of meat from a caged rabbit, and 2.05$ for one pound from a colony rabbit – 21% less.
Nineteen-and-a-half weeks is a long life for a rabbit raised for meat. Since we measured the weights and feed throughout the experiment, it's possible to extrapolate what would have happened if we had slaughtered them earlier.
Most commercial rabbits are slaughtered at 8-12 weeks, so that's one time to look at. I took the second age between when commercial rabbits are slaughtered and when we slaughtered ours. I extrapolated the results for slaughtering at 10 and 14 weeks old. I assumed that the carcass weight/live weight and meat weight/carcass weight ratios don't change significantly between 10 weeks and 19.5 weeks.
At both 10 and 14 weeks, the colony rabbits have a better feed/meat ratio. In fact, the difference increases as we look earlier. At 19.5 weeks the cost of feed per pound of meat for the colony rabbits was 79% of the cost for the caged. At 14 weeks it's 73%, and at 10 weeks it's 71%.
The feed needed to produce one pound of meat decreases for both caged and colony rabbits as they're slaughtered younger. For both the cage and the colony rabbits the feed/weight ratio at 10 weeks was less than half (40-45%) of the feed/weight ratio at the slaughter time of 19.5 weeks.
Our rabbits gained about half their final weight in the first 10 weeks. For a rabbit that gives four pounds of meat at 19.5 weeks, the last two pounds cost (in terms of feed) over three times more than the first two pounds.
Handling the Heat
The growth rate of the rabbits was somewhat erratic, but three points stand out: 6/12, 7/10, 7/31. During the week preceding each of those measurements the temperature spiked to over 100 degrees Fahrenheit for several days. During these weeks the growth rate of the rabbits dropped. On average the colony rabbits had a smaller drop in their growth rates during the hot weeks compared to the caged rabbits.
Including the caged rabbits from the experiment we had 22 New Zealand White, Californian, and NZW/Cal hybrid rabbits in outdoor cages. We placed ice bottles in the cages, while the colony rabbits were able to use the ground to stay cool. Two caged rabbits (who were not part of the experiment) died from the heat (one before we started using ice bottles), while all the colony rabbits got through fine.
It took around the same time to feed and water the rabbits in the colony as it did for the rabbits in one cage. The main difference came when in got hot. It took 20-30 minutes per day to give all the cages ice bottles, something we didn't need to do for the colony.
Health and Safety
The colony had no problems with predators. There were no noticeable health problems in either the colony or the caged rabbits.
The caged rabbits were spilling some of their feed. When I looked underneath the cages, I found some commercial feed on the ground. I didn't see any feed on the ground in the colony, presumably if it did spill, the rabbits ate it.
Some of the difference in feed/weight ratios between the cage and the colony came from that wasted feed. For all of the difference to be due to wasted feed, over 26 pounds of feed would have to have spilled under the cage during the experiment. I didn't measure the spilled feed but from casual observation I can say that it was much less than that.
We put wood chips under the raised cages to collect the rabbits' wastes, which is periodically collected and used for fertilizer. In the colony the waste sits on the ground, and handling it would be more complicated. Our colony rabbits showed no ill effects, but in a larger or longer term colony we might consider regularly removing the waste.
After 15 weeks old (8/17) the colony rabbits had missing patches of fur on their backs. They most likely tore it out themselves to stay cool, or they may have been fighting with each other (though we didn't see any cuts). Either way, the damage made the pelts less usable.
These results indicate that it is more cost effective to raise rabbits in colonies than in cages. It's also more cost effective to slaughter rabbits at a younger age. Combining those considerations, the cost (in terms of commercial feed) per pound of meat from a colony rabbit slaughtered at 10 weeks is 30-35% of a pound of meat from a caged rabbit slaughtered at 19.5 weeks.
We limit our does to two litters each year, so we might consider having more litters and slaughtering them earlier. That way we could have the same amount of meat at a significantly lower cost. Furthermore, if we slaughter the colony rabbits before they start losing fur, we would be able to use their pelts.
In terms of labor, keeping the rabbits in colonies could reduce the time required to care for them significantly. When not using ice bottles, caring for one colony takes slightly less more than caring for one cage, but more rabbits can live in a colony than in a cage. Additionally, not needing ice bottles during heat waves would be a big saving in time and energy.
Keeping our adolescent rabbits in colonies would reduce their commercial feed costs by up to 66%. And by my qualitative assessment, we could reduce the daily rabbit chores times by perhaps 50%. There are various difficulties involved in keeping rabbits in large groups, many of which I'm still unaware of. But given the potential gains, I think the possibility is worth investigating.