Few things are as important as pre-calving nutrition. The last trimester of gestation, particularly the last 45-50 days, is the most critical period in the life of this year's newborn calf and also next year's calf.

What is done for the fetus at this time impacts its survivability and long-term health and performance. Meanwhile, what we do at this time for the cow affects her future breeding performance.

The last 50 days before calving is the most important of two critical periods in a calf's life (the other being just prior to and during weaning). At these times, producers can greatly influence the calf's entire life, regardless of whether it becomes a replacement, a bull or a feeder.

The importance of pre-calving body condition score (BCS) is noted among my clients in drought areas. For the majority of cows with an average BCS (5-6), pregnancy rates were average with a large number performing 3-5% above average despite poor spring and summer range conditions.

I attribute this to an easy winter and good BCS numbers. Thin cows at calving, especially first- and second-calf heifers, never recover the body condition necessary to cycle and breed in poor range conditions, research shows.

It's a common misperception that restricting a heifer's protein intake will reduce calf size and thus calving difficulty. While the calf will likely be smaller at birth, it will also be weaker. And, the heifer will be smaller and less mature.

Producers have told me that high-protein diets cause bigger calves. Perhaps the calves are only reaching their genetic potential, however.

Nonetheless, overfeeding protein is expensive and unnecessary. Pre-calving protein requirements for a 1,100-lb. cow are 1-1.5 lbs./day while post-calving requirements are 2-2.4 lbs./day depending on milk production. This can easily be met with 30 lbs. of an 8% protein grass hay (30 lbs. x 8% = 2.4 lbs.) or 15 lbs. of 16% alfalfa hay (15 lbs. x 16% = 2.4 lbs.).

It's easy to overfeed protein. Often, we can't control the amount due to the variability of protein content in feed. Another factor is the available supplies - the hay you raise is what you feed. In addition, most supplements add some protein to the diet.

Hay should be tested for protein, and cows and heifers should be supplemented accordingly. By-product feeds or straw may be cost-effective in some situations. Some by-product feeds - corn distillers solubles, feather meal, for instance - are high in protein and by-pass protein. This may reduce the need for feeding high-priced protein feeds.

By-pass Protein Has Benefits By-pass protein is one area receiving more interest today. In cows, it's been shown to decrease the time for onset of estrus and may increase calf survivability. In heifers, new research indicates heifers fed by-pass protein had a shorter interval from calving to first estrus with a possible increase in first-service conception rates.

The National Research Council (NRC) now reports protein requirements as metabolizable protein (MP) rather than crude protein. MP is further divided into two components - degradable intake protein (DIP) and rumenally undegradeable intake protein (UIP), commonly referred as by-pass protein.

DIP is broken down in the rumen while UIP escapes the rumen to be degraded in the small intestine. When broken down like this, we have a better picture with which to balance the diet of the animal.

Copper, zinc, manganese and selenium are commonly recognized as the cow's most critical minerals. All minerals are important to the calf, however, since the cow is the single source of nutrients for the calf during gestation and during the first months of the calf's life.

As I've stated in past columns (August, September, October 2000), trace minerals play a crucial role in the immune system, cow fertility, colostrum and other aspects of production.

One important factor to remember in supplementing the pregnant cow before calving is that response time is a key factor. If you are supplementing any nutrient - protein, energy or trace mineral - to reduce stress or correct a problem, it must be fed for an adequate period of time before the problem occurs. Feeding must continue during the entire stress or problem period.

I advise my clients to begin supplementation or feeding a mineral 30-45 days before calving and continuing through breeding.

A plan should be developed early and executed by using recommendations from knowledgeable consultants. But, producers must also rely on their own experience and the history of their cow herd.

Editor's note: For the feed composition values of various feedstuffs, see Rod Preston's "Feed Composition Tables" published in our March 2000 issue. You can also find them at www.beef-mag.com. Click on the BEEF icon on the opening page and go to the "2000 Feed Composition Guide" icon at the bottom of the page.