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Beef cattle fertility and milk production potential is shaped to a large degree by the body fat levels of your bull and heifer calves during their adolescent sexual development.
What you do in the pasture or feed yard during your cattle's adolescence has as much impact on lifelong fertility and milk production potential as the sum of all the other genetic factors that are normally considered when selecting cattle breeding stock. Too much body fat during the adolescent sexual development stage will prevent your growing cattle from achieving the maximum beef cattle fertility and milk producing potential written into their genetic DNA.
This article is going to focus specifically on the adolescent stage of your young breeding stock's lives - the time when bull and heifer calves are reaching sexual maturity and developing the building blocks of their future fertility. What happens at this critical stage of their lives determines whether their beef cattle fertility will realize its full genetic potential or forever be limited by developmental deficiencies that occurred during adolescence.
Body fat is important to maintain normal healthy body functions. Insufficient body fat is dangerous and unhealthy. All animals, including your cattle, need to maintain a certain minimum level of body fat to stay healthy. This minimum amount of body fat is identified as a Body Condition Score (BCS) of 5 on the 9-point BCS scale.
A BCS of 7 is the upper limit of the safe and healthy normal body condition range. That's how much body fat your cattle should have when they are finished for slaughter. That's also how much body fat your cows and bred heifers should have before they calve and when they begin producing milk.
But while your cattle's body condition is considered safe and healthy anywhere within this range from 5 to 7, there is one time in your cattle's lives when a BCS of 7 is too fat - one time when you'd prefer to see your cattle's body conditions closer to the lower end of this healthy range - during their adolescent sexual development stage.
There are two important things that develop during the brief adolescent stage in your young cattle's lives:
Intramuscular fat cells are formed within the animals' muscle tissues. These are the microscopic fat cells that are found deep within the actual muscle fibers, not the large easily-visible fat deposits that you can see with your naked eye. These intramuscular fat cells are the fat cells that will be filled later on during the grass-finishing stage of your cattle's lives and are primarily responsible for the flavour and tenderness of your beef.
These intramuscular fat cells are formed at the same time as your young cattle develop their sexual maturity - the time when the bull's testicles and the heifers ovaries and mammary glands mature.
This developmental stage starts when the calves are approximately 45% of their mature body weight and lasts until they reach approximately 65% of their mature body weight. Once this stage ends (typically around the the time the calves reach 10 months of age), they will no longer develop new intramuscular fat cells and their sexual maturity will be locked in place. What they end up with at the end of this development stage determines the beef cattle fertility that they are stuck with for life.
Once this developmental stage ends, the calf can only fill its existing intramuscular fat cells (like balloons filled or emptied of water), but it cannot grow additional new intramuscular fat cells. Nor can it get rid of intramuscular fat cells that it has formed during adolescence. Whether empty or full, these cells remain in place. They are like tiny balloons, which are either filled with fat when food is plentiful or emptied in order to supplement their diet when there is a calorie-shortfall in their diet.
Likewise, the DNA inside the sexual organs is locked in place once this development stage ends. For example, if insufficient DNA-rich mammary tissue formed during adolescence, the heifer cannot grow additional mammary tissue later in life to boost milk production. An udder full of fat instead of DNA-rich milk producing cell tissue will not produce more milk no matter how plump the udder looks because of the extraneous fat.
Fat absorbs important hormones. And once the hormones have been absorbed by the fat, they become useless - completely incapable of completing tasks in the body for which they were designed.
If your young cattle are too fat during this key adolescent development stage, some of those intramuscular fat cells will form inside the sexual organs and mammary glands where they will absorb (inhibit) important hormones. And those fat cells will remain there forever and continue to cause hormonal problems for the rest of the animal's life.
However, if the calves don't get too fat during adolescence, they will only form intramuscular fat cells in the right places. Location matters. As long as these key intramuscular fat cells only form where they are meant to form, the animal can get extremely fat later in life without that fat causing hormonal issues in the reproductive organs of the animal.
So, it's all about what body condition score your young heifers and bull calves have during adolescence sexual development.
When excess fat cells are formed inside the mammary glands (udders) of heifers during this key developmental stage, their ability to produce milk will be compromised for the rest of their lives.
The wrongly-placed fat will absorb much of the hormones that are responsible for developing the mammary tissues, which will impact every single one of this heifer's future calves. Less DNA-rich mammary tissue means this heifer will have lower milk production throughout its entire adult life, which will affect the growth rates of every single one of their calves.
Less milk for their future calves = slower weight gains and slower growth = lower profits for the farmer. Period.
Excess fat cells in the ovaries during sexual development will also absorb the hormones that are responsible for the healthy development of the ovaries, which control the beef cattle fertility of the heifer throughout her lifetime. Excess fat in the ovaries during this adolescent stage of sexual development will mean lower fertility throughout her entire lifetime.
Bull calves that are being raised as cattle breeding stock fare no better if they are too fat during this crucial stage of sexual development. Excess fat in the testes during this crucial stage will absorb the testosterone required to fully develop the testicles, which will reduce the future beef cattle fertility of the bull calf for the remainder of its life.
Furthermore, the excess fat cells that form in the scrotum will act as an insulator around the testes for the rest of the bull's life, preventing him from regulating the temperature of his sperm.
Sperm cannot survive if the temperature is too hot, so the excess fat around the scrotum leads to lower fertility or in many cases completely destroys the beef cattle fertility of an otherwise perfectly normal looking bull, regardless of the bull's pedigree or genetic potential. This is a dramatic illustration of how often-overlooked environmental factors can completely override the genetic potential of an animal.
You can read about the detrimental effect on bull fertility when bull calves are fed in bull feed test stations during this crucial stage of their sexual development in "The Cattle Year on Grass" chapter of Grass-fed Cattle.
In view of how excess fat affects the future fertility of adolescent beef cattle, the timing of when most calves are born is completely wrong because most calves are born in early spring or late winter.
Calves born in early spring before the growing season starts will reach adolescence and begin their sexual development stage towards the end of the growing season while they are still on lush growing pasture and their body fat levels are at their highest. Which means they will be too fat as they begin their adolescent sexual development.
While too much fat during adolescent sexual development is a bad thing, once this phase of the young heifers lives it complete, they should then get the absolute best nutrition to prepare for their first breeding season.
But in a conventional early-spring or late-winter calving cycle the cattle breeding season typically is scheduled to start in late spring or early summer, at the beginning instead of at the end of the growing season. This means that the young heifers must fatten up and prepare for their first breeding cycle on stored cattle feed instead of the much more lush, vitamin-rich, and nutritious growing pasture. This puts them at a clear disadvantage compared to heifers that spend all summer on lush growing pastures in advance of a breeding season scheduled to start in the autumn (when summer calving programs breed).
There is a simple, effortless 2-part solution to fixing these timing issues so your young breeding stock have the correct body fat levels during adolescent development and so the heifers have optimal nutrition after this short but crucial phase as they prepare for their first breeding season.
Calve on pasture 3 weeks to a month after your cattle begin grazing on the fresh new grass of the new growing season, timed to coincide with the calving season of the deer, moose, or antelope in your area.
Graze as long as possible during the winter, allowing your cattle to use up some of their body fat reserves to supplement the calories available from their winter pastures.
It's all about timing...
The crucial adolescent sexual development stage is a very short stage in your cattle's lives. The date of your calving season determines the time of year when your calves reach this crucial developmental stage.
By calving during the growing season and continuing to graze during the winter, your calves sexual development stage will naturally begin shortly after the winter grazing season begins, which naturally ensures that their body fat levels will be lower during this crucial development stage.
This timing also ensures that as autumn begins and this crucial development phase approaches, the calves' mothers will naturally slowly begin reducing their milk production in response to the lower cattle nutrition available from the winter pastures. This is a natural survival response that cows use to protect themselves against excessive weight loss during the winter, but it is also Nature's way of protecting the bull calves and heifer calves from being too fat during adolescent sexual development.
Essentially, without any further effort on your part, simply by adjusting your calving season and focusing on managing a safe and effective winter grazing program, you are able to strike the delicate balance between too little and too much body fat during the sexual development of your future cattle breeding stock.
And the beauty of this timing doesn't end there. As I mentioned earlier, this crucial stage in your calves development ends when the calves reach 65% of their mature body weight, right around the time they reach 10 months of age. And, right on cue, this is the time when the next growing season begins. The calves can gorge themselves on lush growing pasture without any risk whatsoever to their future beef cattle fertility or future milk production potential.
In fact, now the fresh grass growth allows them to grow quickly and fatten up as much as possible so they are as prepared as they can possibly be for the upcoming cattle breeding season at the end of the growing season. That's perfect timing.
The image below shows the timing of an ideal summer calving season versus the timing of an early-spring or late-winter calving season. As you can see, even a modest shift in timing dramatically affects the cattle nutrition and consequently the body fat levels of your growing future breeding stock during their adolescent sexual development stage, which will have lifelong consequences to their beef cattle fertility.
Body condition during adolescent sexual development is just one of the many innovative ways that you can make dramatic changes to beef cattle fertility, simply through using timing to your advantage.
"The Cattle Year on Grass" chapter of my book Grass-fed Cattle also shows you how timing can take advantage of powerful effect that photo-period (hours of daylight) has on conception rates during breeding season.
This important chapter also discusses how the timing of the calving season can dramatically improve calf survival rates during calving season, significantly increase the number of unassisted births on your farm, and vaporize the majority of your post-calving disease pressures, all while reducing your workload. Timing really is everything!
What innovative strategies do you use to improve beef cattle fertility on your farm? What challenges do you face in your breeding herd?
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