Notes From Nelson

The main goal in a commercial cow-calf operation is to optimize pounds of calf produced per cow as economically as possible. Part of this is a heavy percentage of calves weaned as compared to the number of cows exposed to the bull. There are, of course, a number of things that influence conception rates – many of which we can manage to our advantage.

Nutrition, both before and after calving, has an effect on pregnancy rates. Nutrition that leads to thin cows at calving, results in delays in the onset of estrual activity after calving. Level of energy fed after calving will influence percent of cows cycling but even more dramatically will influence first service and overall conception rates during the breeding season.

Another factor that influences the percent of cows cycling at the start of the breeding season, or conception rates early in the breeding season, is when the cow calved relative the start of the breeding season. If a long calving season is practiced, it is conceivable that some of the cows may not even have calved before the start of the breeding season.

The age of the female can influence first service and overall conception rates. Heifers do not have the added stress or production trauma of nursing a calf and, provided they have reached puberty and are cycling, often have higher conception rates.

Increased calving difficulty will not only increase the length of time required for the cows to cycle after calving, but also decrease the percent of cows conceiving in the first post-partum estrus. Calving difficulty often reduces overall conception rates during the breeding season.

Of course sire selection can have a major influence on conception rates. Using semen-tested bulls with a high libido is a must.

Season of year when breeding occurs will influence conception rates.

There has always been much debate on breed differences in conception rates. The greatest variation, however, will occur within a breed rather than between breeds. Probably the greatest influence of breed on conception rate is the fact that crossbred females will tend to have a higher conception rate and overall fertility by as much as five to eight percent than straight bred females.

Genetic and anatomical abnormalities can have an obvious effect on conception rates. Overall health of the cowherd also will have obvious effects.

Forage or plant toxins will from time to time also cause problems with conception rates.

There are many aspects of reproductive efficiency, but one extremely important aspect is maintaining conceptions rates that will insure that a high percentage of the cows calve early in the calving season.