While winter feed costs weigh heavily on the mind of most cattlemen, it makes sense that winter feeding programs will be the first place most of us look to preserve what little profit margin remains.
But cattlemen, beware; not meeting wintertime nutrient requirements for spring-calving cows has consequences. Here are three reasons not to cut corners this winter.
Birthweight and calving difficulty
Have you ever heard that you shouldn’t feed gestating cows very much because their calves will get too big? Unfortunately, this is something we hear regularly, but it remains a commonly misunderstood concept.
Phenotype (what we actually observe in the animal, birthweight included) depends upon the interaction between genetics and the environment (in this case, nutrition).
No matter how great the environmental conditions are, an animal’s phenotype will be limited by its genetics. Because of this, it is not physically possible to increase a calf’s birthweight beyond its genetic potential.
So if a calf’s genes say that its birthweight should be 85 pounds under the best environmental conditions, we can’t feed the cow enough to make it 86.
But can we decrease birthweight through nutrient restriction of the dam? Maybe – but at most by only a couple pounds. Does that small decrease in birthweight increase calving ease? Nope.
It actually works against us to increase calving difficulty because the dam calves at a disadvantage; she’s in a poorer state of body condition and may not have sufficient energy reserves to lay down and go to work.
And we may see some of the long-lasting negative consequences of fetal programming come along with it.
The caveat here is that we need to meet her nutrient requirements without over-conditioning. Ideally, she’s wintered to calve in the spring at a body condition score of somewhere between 5 and 6.5. Can we over-condition her to the point where we increase calving difficulty? Sure – but it isn’t a function of birthweight.
Instead, it’s due to accumulation of internal fat. But in order for that to happen, we have to make her obese, calving at a body condition score of 8 or above. If she’s able to put on that much condition between weaning and calving, we probably need to re-evaluate whether or not she’s the best fit for the management setting or if we need to adjust our feeding program.
The bottom line: Nutrient restriction of the dam during late gestation does not decrease calving difficulty. If anything, it increases it. We just need to meet her requirements so that she calves in sufficient body condition without making her obese.
Calf health
Have you ever had that calf that just doesn’t have any energy when it’s born? The calf that the kids stay up all night with in the barn or winds up spending the night on the bathroom floor, but to no avail? Sure – we’ve all experienced that calf. Sometimes every calving season.
But have you ever wondered why some cows can calve in the middle of a sub-zero night on an ice patch and the calf does just fine, but others can’t do the same in more favorable conditions? Nutritional status of the dam tends to be the major contributing factor.
When we don’t meet requirements during gestation and she calves in less-than-ideal body condition, it can have major implications to calf health.
One of the first consequences is the inability of the calf to regulate its body temperature. While I cannot refute the critical importance of nursing and colostrum consumption within the first few hours of birth, this only plays a minor role in temperature regulation.
The major factor that determines the newborn calf’s ability to stay warm during cold weather is its energy status – more specifically, the amount of brown adipose (or fat) that it acquired during fetal development. The calf regulates its body temperature during the first 24 to 48 hours of life by metabolizing the majority of that fat as a source of heat.
If the cow undergoes an inadequate plane of nutrition during middle and late gestation and does not have enough body condition to fill the void, the calf won’t have the fat stores necessary to keep itself warm.
Another consequence of nutrient restriction has to do with the calf’s immune system. Nutrient-restricted cows produce colostrum that is lower in quality. It’s lower in quality because it contains fewer immunoglobulins – the antibodies that the calf uses to populate its immune system.
Not only is her colostrum lower in quality, but she also produces less of it. Insufficient colostrum consumption soon after birth can affect the calf for the remainder of its life. Have you ever had a calf break with respiratory disease? Even if identified early and successfully treated, will that calf ever be the same again?
It sure won’t, but some of that can be prevented by ensuring the cow has been fed appropriately throughout gestation. We can’t expect a calf to achieve a high level of performance if it isn’t equipped with the tools necessary to do so.
Reproductive performance
Last, but not least, we can’t leave reproductive performance out of the conversation.
How she’s managed this winter can play a huge role in her value as a member of the herd next winter. A cow requires a number of progeny to return your initial investment in her as a replacement, regardless of whether she was retained and developed or purchased as a bred heifer or cow.
We’ve known for quite some time that body condition at calving is directly related to the amount of time required for her to have a normal and viable estrus cycle.
Resumption of estrus cyclicity is one of the major factors that determines if and when she conceives during a breeding season. If her body condition is less than ideal, she will require more time to begin cycling than if she calved in better condition.
A cow that calves at a body condition score of 5 or greater begins cycling roughly one-and-a-half to two months after calving. That provides her with adequate time to conceive within the window necessary to calve annually. If she calves at a body condition score of less than 5, she’s going to be much less likely to cycle and conceive within that window.
If we cut corners on winter feeding and she calves in lower condition because of it, it’s likely going to take more time to get her bred back. Or there’s a good chance she will come up open. Based on that, I have to ask: How much of that small profit margin remains if she calves 60 days later next year?
Or how valuable is she if she comes up open? Let me rephrase that: How much does she cost you if she comes up open?
Now does this mean that we shouldn’t be taking a hard look at our feeding programs? Absolutely not. We just need to ensure that we aren’t going to sacrifice performance by doing so. Or at least be certain that any feed savings outweigh the cost of a reduction in performance.
So what’s the best way to do that? For most of us, that’s going to require first evaluating the nutrient content of the base of our feeding program and then using that information to identify the most cost-effective means of filling the nutrient void that remains. 
PHOTO: It’s always a good practice to look at your feeding program, but make sure you don’t sacrifice your herd’s performance by doing so. Photo by Staff.
Jason Smith is an assistant professor and extension beef cattle specialist with the University of Tennessee. Email Jason Smith.
