The Effects of Summer Heat on Meat Rabbit Growth Rates

It is quite common to see somewhat slower growth rates and weight gain in meat rabbits during the summer. In fact, it is to be expected.

While this will be most noticeable in meat rabbit grow outs, there can be impacts on older rabbits and breeders, too.

This is not an issue to be overly stressed or concerned about, but it is a factor to be aware of so that you know what to expect, know what is normal, and know what you can do to prepare for and minimize the impacts of summer heat on the growth rates for your meat rabbits.

This will all help you to maintain a healthy, productive, and efficient meat rabbit program.

Jump to:

• Why Summer Can Slow Meat Rabbit Weight Gain
• The Ideal Growing Temperatures for Meat Rabbit Grow Outs
• Impacts on Nursing Does
• Impacts on Nursing Kits
• Impacts on Grow Outs
• Impacts on Breeding Stock, Bucks, and Does
• The Importance of High Quality Feed in the Summer (And All Year Round)
• VIDEO: Summer Can Change Meat Rabbit Growth Rates. How?
• Water: The Most Important Nutrient
• Watch for Digestive Issues Throughout Summer and High Heat
• What Does All Of This Mean for Raising Rabbits in the Summer?
• Steps to Take to Mitigate Summer Growth Rates

Why Summer Can Slow Meat Rabbit Weight Gain

There are two major reasons why meat rabbits may gain weight more slowly in the summer. They are both related to heat:

1. Rabbits tend to eat less in the summer and take in lower amounts of feed
2. Rabbits expend more energy into cooling themselves off (panting, etc.) -- more of their calories and resources go to cooling

One of the main reasons that rabbits eat less in the summer is that fiber, which is digested through fermentation in the cecum, produces heat. That heat needs to be dispelled. The only way rabbits dispel heat (whether from the gut, body, or environment), is through heat radiation through ear capillaries (blood vessels) and through panting.

If a rabbit is already taxed with cooling, it will reduce food intake in an effort to also reduce bodily heat production.

Simply put -- rabbits eat less so they stay cooler to begin with.

(In the winter, the converse can be true -- rabbits may eat more to warm themselves through hind gut fermentation, and yet still experience a slower than optimal rate of gain simply because more energy from the feed goes into warming the body).

The Ideal Growing Temperatures for Meat Rabbit Grow Outs

Rabbits are most comfortable and perform the best at moderate temperatures of 60 to 65℉ (15.56 to 18.33℃). This is the range in which they will grow the best and convert feed the most efficiently, thus resulting in the best and most efficient growth rate. This is why we say spring is the best time to raise rabbit litters! (While a topic for another post, winter can slow growth for other temperature-related reasons.)

We cannot control the weather, the climate, or temperatures. But we can be aware of this being the case, manage and adjust accordingly, and at least know what to expect; then we know when not to stress or worry over unexplained phenomena.

When the temperatures outside start to rise above this ideal, especially when they consistently and significantly rise above it, we can see reduced growth rates as a result. This is normal and is to be expected.

This happens to rabbits all throughout the rabbitry -- to breeding stock, does, kits, and grow outs.

Impacts on Nursing Does

Milk production and nursing require a lot from a doe. Does should be free fed their normal diet when they are nursing so that they can intake all that they need to produce milk for their litter and keep themselves healthy, well-maintained, and in good weight and condition.

Nursing does are just as likely to eat less in high heat periods as your other rabbits are. If they reduce their feed intake, they may also reduce their milk production. This can have impacts on the doe and the kits, as it may be more difficult to provide for all of their needs for good growth and for maintaining her body condition.

Extended high heat in the summer may be a time to consider some of the additives and supplements that meat rabbit growers give to nursing does to boost or support milk production (even if you don’t typically need to provide them for your does).

Some recommendations include:

• Calf manna (this is a powder sprinkled over the feed so it can be good to use because it doesn’t translate into a lot of bulk, which your rabbit may be reluctant to take in)
• Black oil sunflower seeds (BOSS)
• Rolled, crimped, or whole oats
• Alfalfa hay or hay cubes

Impacts on Nursing Kits

If the doe is not producing enough milk because she is not eating enough, then there is a clear impact on the kits.

• Nursing kits may not intake enough milk
• You may see weaker kits failing to thrive if there is not enough milk to go around, and they are not able to fight to get enough of their fair share
• Kit's growth can slow down
• Kits are at risk for dehydration, especially in the first two to three weeks, because they are totally dependent on their mother’s milk for both nutrients and hydration

The solution to these problems is to support the doe in her comfort and feed intake. Keep her as cool and comfortable as possible so that she is more likely to eat more feed. Supplement as needed, as outlined above, to support her milk production.

Keep daily checks on kits during high heat and look for signs of dehydration. These include

• Failure to thrive
• listlessness
• dry skin
• skin that lacks elasticity and stays pinched if you pinch it (gently) without smoothing back into shape
• dry eyes and nose
• skinny, bony kits that do not gain weight

Also, make sure the nest box stays clean, even if you have to remove pulled fur and replace it with shavings or hay. Do not allow an environment in which bacteria, flies, and maggots can proliferate!

You can expect the weight at weaning time to be less than your average in the summer. As long as the kits are in otherwise good condition, this is simply something you will need to accept.

Impacts on Grow Outs

The growth of summer grow outs can be impacted by heat in a couple of ways:

• They may enter weaning at a somewhat reduced size or weight if the doe’s milk production was reduced, as above
• They may eat less because they are also hot and expending energy in keeping themselves cool, and so they may gain more slowly

For grow outs, the things to look for are

• Steady, if lower, feed consumption
• Regular water intake (hopefully increased)
• Good hydration and skin tone
• Moist eyes and nose
• Generally healthy and steady rate of gain, even if it is slower than normal
• Good body condition, even if they gain more slowly
• Regular urine and fecal output (poop!)

Even though we can expect that grow out growth rates and weight gain may be slower, it should not stop completely. You should still see a pretty steady upward climb in growth and weight.

If one week was much hotter than another, this may be a more jagged growth curve than the typical smooth arc, but again, if the condition and health are otherwise good, take it as a sign of summer growing.

Impacts on Breeding Stock, Bucks, and Does

Typically, noticeable impacts on breeding does and bucks are minimal. It would be logical to expect some slight weight loss if heat persists for several days or weeks.

You will probably notice your bucks and does don’t eat quite as much as they do at other times of the year. This will result in some reduction of weight.

As long as the bodies remain in good condition and the weight loss is not significant to the point of boniness or malnutrition, this is not a problem. In fact, if you have bucks or does that are overweight, it could be helpful to maintain them at a weight that is more optimal for good reproduction.

It is best if your breeding rabbits go into summer at a healthy weight, one not outside their mature adult weight for that breed.

Bucks and does, because they are larger and older, can be expected to be more susceptible to the effects of heat. This is another reason to keep your breeding bucks and does reasonably young and to rotate stock out before they get too old to be able to handle heat and weather fluctuations.

The Importance of High Quality Feed in the Summer (And All Year Round)

Feeding a steady, consistent diet of high-quality feed is important all year round, but it takes on added importance during the summer months.

The reason this is true is that when the heat is high, you can expect your rabbits to take in less food. So it is highly important that the food that your rabbits eat offers a lot in terms of nutrition. When they reduce the quantity of food, the quality takes on added significance, so that your rabbits are still getting a good balance of protein, fiber, vitamins, and minerals as needed.

Even if they’re not gaining at as high a rate as they do in other times of the year, with a good, quality, balanced feed, your rabbits will still access adequate nutrition. When the weather moderates and their appetites return, they’ll be in good condition and ready to get growing again. (Or maintaining optimal health in the case of breeding stock.)

“A rabbit will get accustomed somewhat to the heat and eventually eat more, however it will never eat as much when it is hot as it does when it is in a comfortable temperature zone. This means that it is very important to feed a high-quality feed that will continue to provide adequate nutrition, even when intake is reduced.” -- Purina Mills website

Don’t skimp on fiber in an effort to keep rabbits cool

In the first section, we talked about how fiber is fermented and then turned into heat in the rabbit’s body. This may logically, but erroneously, lead us to think we should reduce fiber in the meat rabbit’s diet during the summer or in periods of high heat.

Fiber is critical to good rabbit digestion, health, and growth. We do not want to deny our rabbits fiber. Fiber always needs to be available. It is what keeps the gut moving and active.

When rabbits’ digestive systems stop moving, stasis can result. That will quickly kill a rabbit. Rabbits are more predisposed to GI stasis when they are stressed. Heat is stressful.

So, maintain good sources of available dietary fiber. Make feed and fiber available to them as you normally would. Leave it to the rabbit to decide and intake the food and fiber that it needs.

While it is true that an argument could be made to feed quality pellets and remove hay (if you feed hay), it would be best to avoid abrupt dietary changes because of the stress involved. It might be smarter to just feed less hay if you feel like you need to force your rabbits to eat more calorie-dense and protein-dense pellets during those times when they are eating less.

Consider increasing protein in the feed

This may be a time of year when you consider feeding a higher protein feed. This may help even out growth rate drops. Generally speaking, though most meat rabbits will grow very well on a 16% feed, they would perform better on an 18% pellet.

It would also help stabilize and concentrate protein intake. So, if your rabbit is not eating as much, a higher protein feed may help them get more protein to make up for the decrease in feed intake.

Often, higher protein feeds, even from the same feed company, will be slightly different in formulation and may be of a somewhat higher quality feed. For example, if you look at the feed label, you may find a higher prioritization of better quality ingredients in the higher protein feed.

Compare the feed labels to see if a difference in protein in your pellet also translates into a better overall feed ratio. Feeding a pellet that may be higher in both protein and nutrition can provide more to your rabbits if they are eating less to begin with.

Though higher protein translates into more expensive feed, the cost may moderate and even out as well (or close to it), because your rabbits are probably eating less of it than they normally do. And if it also speeds up your summer growth rate, then again, there is another opportunity for the increased feed cost to pay for itself.

All of this, of course, depends on costs, summer growth rates, consumption, and what is available to you locally for feed options. It is something to weigh and consider.

If you decide to change to a higher protein feed

If you are changing feed for the summer months, try to do this as early as possible, before high heat sets in. Make the change gradually by mixing the feeds over the course of a week or two, until the new feed constitutes most, and then all, of the ration.

And know your rabbits. If you have rabbits that are more sensitive to high protein, this may not be a switch worth making.

VIDEO: Summer Can Change Meat Rabbit Growth Rates. How?

https://youtu.be/l5l4xeyLf6g

Water: The Most Important Nutrient

The University of Michigan says that water is the “single most important nutrient” for rabbits (and other animals, too).

It is easy not to think of water as a nutrient, but clearly, it is the most important for life.

Water is essential for meat rabbit hydration, digestion, and gut function. It is also critical in cooling.

Without adequate water, rabbits cannot cool themselves.

In hot weather, rabbits can drink four times the amount of water that they normally do; so, it is important to have a plan to refresh their water as many times a day as they need it refreshed, or to provide extra waterers (a drip system, extra bottles, more crocks) so that they have water in front of them at all times.

• Water should be fresh
• Rabbits are less likely to drink stale water, which is why fresh water daily is essential
• Water should be cold or cool (and hence may need replacing two, three, or four times per day in high heat)
• Waterers (such as bottles, crocs, cage cups, and even automatic watering lines) need to be regularly cleaned to reduce the growth of bacteria, algae, and pathogens

Watch for Digestive Issues Throughout Summer and High Heat

Because they are grazers and hind gut fermenters, rabbits need fibrous foods to continuously move through their digestive system. If rabbits slow or stop eating because of high heat, this can cause bigger problems, like GI stasis.

This is why it is especially important to observe your rabbits in periods of high heat. Even one day of not eating can put a rabbit into stasis.

While it’s not advisable to try to force feed a rabbit that has simply slowed its eating because of the weather, do pay attention and look for signs of digestive stress, like:

• Seriously reduced fecal pellets (poop)
• No poop pellets at all
• No urine output
• Not eating any food at all
• Bloated gut
• Pain or distress
• Lethargy
• Hunched posture
• Little to no movement
• Raised head, gasping for air

If you suspect GI stasis, support your rabbits with this first-line protocol.

What Does All Of This Mean for Raising Rabbits in the Summer?

As long as your rabbits are healthy and thriving and dealing with the heat without too many issues or heat stress, the main takeaway here is that it is not uncommon for your meat rabbits to eat less and to grow more slowly during the hottest summer months.

One of the reasons, probably the most common reason, for achieving high growth rates is to grow fast, feed efficient meat. Slower feed intake will result in a slower growth rate. However, that doesn’t necessarily translate into a poorer feed conversion; at least, not a significantly poorer feed conversion.

In the end, even though it may take a little longer for your grow outs to reach the desired harvest weight, or, if harvesting by age, even though the carcasses may be a bit smaller than those harvested in cooler and more moderated months of the year, they still probably didn’t eat a significant amount more feed to get there. The variable is more in time, and less in feed inputs.

And so, since we can’t control the weather, this is not something we should stress too much about. It is something to simply be aware of, to manage to the best of our rabbit raising abilities, and to perhaps plan breedings around.

It is also something worth knowing so that we don’t unnecessarily stress over the fluctuations in the rabbitry when the answer is quite simple, natural, and even.

Steps to Take to Mitigate Summer Growth Rates

1. Feed a high-quality, nutrient-dense feed
2. Feed early or late in the day so the rabbits are more energetic and willing to get up and eat and drink
3. Maintain a consistent feed program so that rabbits are not also dealing with digestive stressors
4. If you are changing feeds or using a higher protein feed for summer growth, try to make the transition before the stress of summer heat
5. Always have fresh, clean, cool water available
6. Ice cubes in water can help keep it cooler and fresher for longer
7. Plan for increased water consumption and figure out how you can accommodate for increased watering
8. Keep rabbits as cool and comfortable as possible
9. Limit stress and excitement in the rabbitry, especially throughout the hottest parts of the day
10. Plan breedings, if possible, to circumvent high growth periods during expected periods of high heat and humidity
11. Plan breedings to avoid having does having to nurse kits at peak milk demand (first two to three weeks) when you expect your heat to be highest
12. Consider other supports and adjustments for good summer care for all of your meat rabbits
13. Selectively breed for heat tolerance, with year-round climate tolerance in mind
14. Don’t be overly concerned about lower weights and growth rates through the high heat periods of summer