NUTRITION AND REPRODUCTION by Mike Mehren Ph.D.

If we use a herd of one hundred cows for an example, having five extra 400 lb calves at weaning time is equal to a 22.5 lb increase in the weaning weight of 90 calves. With all of the variables that affect calf weaning weight, it may be more economical to try to increase the number of calves born. We know that crossbreeding has many benefits, one of them being improved pregnancy rate. Breed Associations have data that show which bulls are the most fertile. Also cows that calve during the first three weeks of the calving season are most fertile. Their daughters are definitely candidates for herd replacements.

We also know that cow body condition has a huge influence on rate of pregnancy. Skinny cows don’t breed back as well as cows in moderate flesh. This is even more pronounced for heifers. Since second calf heifers are the biggest challenge to get bred, this would seem like a group that would respond to a feed program designed to promote weight gain prior to calving. The key word in that last statement is ‘calving’. That should be your target date for achieving the body condition of your cowherd. Obviously, it’s easier to put on weight during the fall than in the dead of winter. Cold winter days require more energy than milder days. This means that the cows will use more of their feed just to maintain themselves when it is cold. Spring-calving cows must also provide nutrients for a rapidly growing fetus. During milder weather early in the fall more of the cow’s diet is available for weight gain. One of the objections to providing extra nutrition to heifers is that it will cause heavy birth weights. Research has found that a ration high in energy (with added fat) increased birthweight of calves from heifers by about 3 lb., calving difficulty was increased by 3.6% and weaning weight was increased by 30 lb.
(Reported by R.A. Bellows, Range Beef Cow Symposium).

Let’s look at three scenarios that show what rations might look like when we hope to change body condition. These rations would be fed the last 60 days before calving.
The first ration will just maintain body condition at a score of 5 (moderate). The second ration will improve body condition from 4-5, while the third will improve body condition
by two scores, 3-5. Each body score equals roughly 90-100 lb. of weight.

Feed	Ration 1	Ration 2	Ration 3
Score	5-5	4-5	3-5
	………..…percent as fed……………………..
Alfalfa Hay	60	100	78 (or grass)
Bluegrass straw	40	--	--
Corn Dstlrs,dry	--	--	18
Total	100	100	100

Note: if feeding wheat straw or baled corn stalks in Ration 1, percent of either of these would be 25, while alfalfa would increase to 75%.
Ration 2 will provide enough nutrients for 1 lb/head/day gain, while
Ration 3 will provide for 2 lb/head/day gain.

All of the above rations have enough protein; the biggest difference is in the amount of TDN or energy. Increasing the amount of energy will do more than any other single protein. Alfalfa/grass or pea hay could replace the alfalfa hay in rations 2 and 3.

Bulls should also be fed to reach moderate flesh (5 score) by the time they are ready to be turned in with the cows. This is especially true for yearlings. Sometime yearlings purchased at a sale in February are carrying too much fat, so they are put on a diet when they are brought home. Check their body condition every thirty days to make sure they aren’t losing weight when breeding season begins. The same nutrients that are important for reproductive performance by cows are also important for bulls.

One thing to remember is that once you have achieved the body condition desired for your cowherd, it’s best to try to maintain that condition between calving and breeding. This would be especially true for heifers or old cows. I’ve encountered instances where the amount of straw fed was increased dramatically after calving. Cows can lose enough weight after calving that they will not breed until they have been out on high quality range for 30 days or more.

How would you determine if your cows are good candidates for A.I.? First, the herd should have a high degree of fertility. Using natural mating, the herd should have an 85-90% calving rate when using a 60 day breeding season. Ideally, more than 60% of the cows should calve in the first 42 days of the calving season. Cows or heifers should be gaining weight prior to starting an A.I. program. Research data has shown that each improvement in body score (such as 5-6 for heifers) increases the number of cows cycling by 18%. A goal of 6 body condition score is best for heifers especially for A.I. There has been variable success when fat was fed to improve conception. It appears that it is most successful when fed to cows or heifers that are thin. The amount of fat fed is important. It needs to be in the range of ½ lb/head/day. Most supplements with added fat are not fed in the amount necessary to provide ½ lb of fat. Some examples of this follow.

Supplement or Feed	amount needed to provide ½ lb fat
Protein Suppl. W/ 10% fat	5 (most fed at 0.5 to 2.0 lb/day)
Corn Dstlrs Grain, 10% fat, dry	5
Whole Cottonseed, 22% fat	2.5
MegALac (fatty acid source) 85% fat	0.6

Note: dairies in the Northwest commonly use the last two ingredients.

A feed additive known as MGA is often used to synchronize heifers for breeding. When fed daily, it prevents the heifers from coming into heat. When removed from the diet the
heifers come into heat in greater numbers than would be expected under untreated circumstances. It’s important to get the required dose into every heifer every day. Do everything that can be done to encourage intake. Give them plenty of bunk space. The MGA might be incorporated into a very palatable supplement that is fed in the bunk. If you have to feed it in a complete ration, feed a small amount that the cows will clean up rapidly, and then follow with the remainder of their daily ration. MGA can be mixed into a free choice product that is designed for ½ lb/head/day intake, but getting uniform intake is pretty tough.

I’ve only commented on energy and protein for reproduction so far, but minerals also play an important role. Those minerals known to be important include Calcium, Phosphorus, Zinc, Copper, Cobalt, Iodine, Manganese, and Selenium. The brutally high cost of phosphorus has caused me to do more forage testing than normal. In many instances we have been able to reduce the phosphorus from the supplement because the forages being fed had a sufficient amount. Most of the time, copper, cobalt, zinc, and selenium are deficient in the forages that have been tested. We also encounter excess iron, and in some instances excess sulfur and molybdenum. If you happen to be feeding corn distillers grain w/ solubles it would be worthwhile to check sulfur content of that feed. Some of the suppliers in the Northwest have much higher levels of sulfur than reported in feed analysis tables. The excess sulfur can lead to copper deficiency, brainer cattle, reduced feed intake and poor performance.

The only vitamin directly related to reproduction is vitamin A. This vitamin is low or absent in many forages fed during the winter. An animal that was on dry feed early in the fall may have little or no vitamin A in its diet until spring grass unless it is added as a supplement. Injectable vitamin A is a good means to raise the level in the body for a short period of time, however an injection in the fall should not be counted on to provide vitamin A through the winter.

Even when supplements are extremely high priced, if they provide the nutrients missing from your feeds, they are a bargain compared to open cows. No amount of management,
synchronization, or bull power will accomplish a high level of reproduction without sound nutrition for the cows and the bulls.

Michael J. Mehren, Ph.D. is a livestock nutritionist who has raised his personal body condition score to 6 this winter. He may be contacted by Email at mehrens@eotnet.net.