We have all heard the adage "A dead calf has a very poor growth rate." Those of us who breed Murray Grey Cattle, we
do so in part due to the ease of calving and moderate birth weights for which the breed is known. However, it is still
necessary for us to understand the factors which contribute to calving problems.
The following are management and genetic factors associated with calving difficulties:
- Calf Birth Weight
- Dam's Pelvic Area
- Sex of Calf
- Gestation Length
- Age of Dam
- Dam's Size
- Sire's Size
- Size of Dam's Sire
- Nutrition and Body Condition of Dam
- Geographic Region
- Season of Year
Calf Birth Weight
Birth Weight is the major factor causing calving problems. Genetics of the sire play the most important
role in determining calf weight; however, the maternal genetic influence should not be overlooked. The
heritability of birth weight is nearly 48%. By putting selection pressures on bulls for birth weight
and calving ease, it should be possible to alleviate many existing calving problems within a herd.
Calving ease is an important trait in both the cow's and bullšs genetics.
Producers need to emphasize the following performance traits when selecting a bull for calving ease
(particularly for first calf heifers):
While breeders must kept in mind that many factors cause birth weights to vary, procedurally
a producer should:
- EPDs for birth weight
- EPDs for calving ease
- Actual birth weight of the bull
- Shape of bull (smooth in the shoulders, not too thick)
Dams Pelvic Area
- Decide which traits are important in their program
- Set the range of EPDs to accomplish these goals
- Select bulls that meet this EPD criteria
- Eliminate any with individual birth weights that are too high
- Eliminate bulls that are not correct in physical appearance
Calving problems occur largely because the size of the calf is too large for the pelvic opening
of the dam. Pelvic area appears to be highly correlated with heifer size. By selecting for larger,
growthier heifers, producers are indirectly selecting for a larger pelvic area. Unfortunately, when
larger, growthier heifers are selected, there is a tendency for these heifers to have heavier birth
weight calves. So, the use of pelvic size has not been shown to be as clear cut a criteria in
predicting which heifers will experience calving difficulty, as was once thought.
The need to check pelvic size does exist. This, plus the fact that heifers need to be cycling by 12
months of age, leads to the recommendation that all heifers should be palpated at a year of age for
three criteria: 1) Adequate pelvic size 2) Physical abnormalities of the pelvis 3) Functioning reproductive tract.
Sex of Calf
Bull calves tend to outweigh heifers by up to 10 pounds. Calf losses are higher in males. Calving problems in
mature cows carrying male calves is twice that of cows carrying female calves. This is partly because bull
calves tend to have a longer gestation length which contributes to heavier birth weights.
Gestation length appears to have an indirect influence on calving problems. As gestation length increases,
birth weights increase as much as a pound a day. Gestation length is a trait that can be selected for.
This means the potential exists to select cattle for shorter length and subsequently lighter birth weights.
Another indirect benefit of a shorter gestation length is that cows calving at an average gestation length
of 280 days as compared to 287 days have an additional 7 days after calving to start cycling for rebreeding.
Although selecting for shorter gestational periods is possible, selecting for growth and moderate birth weight
is more effective as a means of increasing growth rate with a simultaneous increase in birth weight than
selection for growth and shorter gestation.
Age of Dam
Once a cow has had calves, she is less likely to have calving problems. First and second calf heifers experience
Body size (frame) is highly correlated with pelvic area and pelvic dimensions determine birth weight limitations.
The larger cows will tend to have larger pelvic areas and produce heavier birth weight calves.
Selecting replacement heifers out of bulls with low EPDs for birth weight should help reduce birth weight and
calving difficulty. Research shows that selecting heifers out of low birthweight sires tend to result in
females with a lower mature size, which may, or may not, be desirable.
Selecting bulls with low birthweight EPDs is very desirable for first calf heifers and can be important in
reducing calving losses in the entire herd.
Nutrition and Body Condition Score
Supplemental dietary energy fed for 90-100 days prior to calving will increase birth weight but does not
have adverse effect on calving. Incidence of calving problems is actually lower in moderate to high energy
fed cows than in low energy fed cows. "You cannot starve calving difficulty out of cows and heifers."
When low energy feed is fed 90 days prior to calving, it will take 2 to 6 weeks longer for the animals to
start cycling. Underfeeding protein to pregnant cows in an effort to reduce calving problems will result in
deceased calf vigor, increased time to cycling and decreased conception rates following calving. These
problems are compounded when energy is also deficient.
Studies have shown calf birth weight increases in colder environments compared to warmer, southern climates.
Northern states tend to experience a higher rate of calving problems than their southern neighbors.
Exercise improves muscle tone in heifers and cows which will lead to easier calving.
Fall-born calves usually are lighter and born with less assistance than spring calves. This is because hot
summer temperatures tend to reduce birth weights, whereas cold temperatures increase birth weights.
Information from Oregon State University Calving School Handbook (Dr. Don Hansen, Bill Zollinger)