Producers know intuitively that calves born by caesarean or those that have difficult births are more likely to die than those delivered naturally.
In fact, calf death rates are 12.5 percent in
C-section calves and only 5.2 percent in calves born naturally.
These numbers reflect deaths only, not the economic losses associated with weak calves that become ill.
This data came from a study of dairy herds, but comparative death rates will be similar in beef production, although the percentages will be lower overall.
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Uterine contractions cause a significant decrease in blood flow through the uterus. This leads to a brief period of hypoxia, or lack of oxygen, to the fetus. If the hypoxia is sustained, as it can be with the continued contractions associated with prolonged labour, the calf becomes acidotic due to a buildup of lactic acid.
In response to the lactic acidosis, the fetus redistributes blood flow from its muscles, intestines and kidneys to its brain, heart, and placenta. This helps maintain sufficient blood and oxygen flow to the vital organs. Unfortunately, the organs that receive less blood and oxygen shift to anaerobic metabolism, which results in the production of more lactic acid.
Uterine contractions also increase placental and fetal blood pressures. This causes the fetus’ heart rate to drop temporarily during a contraction. The rate then returns to normal
between contractions.
If a calf is acidotic, its heart is less able to recover after the decelerations. As the acidosis worsens, the calf’s heart rate will not rise between contractions and starts to plummet.
Obstetrical procedures have a significant effect on these physiological events. Manipulations cause an increase in the level of oxytocin, a hormone that triggers stronger and more frequent uterine contractions. Obstetrical manipulations also cause the cow to strain more, which increases pressure on the uterus. This can reduce the oxygen supply to the fetus, worsening the acidosis.
When the obstetrical procedure is short, the total effect on fetal heart rate is minimal. With longer manipulations, however, or if traction is applied to the fetus, the uterus’s contraction frequency increases. The fetal heart rate stays low and the placental blood flow is decreased so the fetus gets less oxygen. Under these conditions, the calf quickly becomes acidotic.
Acidosis has a direct effect on a calf’s vitality at birth. Though most calves are born with a mild degree of acidosis, normal breathing will reverse the problem.
Calves that do not recover, even though they are breathing well, may be acidotic. These calves will have a low heart rate, slow breathing, pale mucous membranes and poor muscle tone.
If a calf takes more than 15 minutes to get upright on its chest, there is an 84 percent chance it will need intensive veterinary care. Calves that are acidotic require treatment with sodium bicarbonate to reverse the buildup of lactic acid.
Newborns that experience sustained acidosis will suffer a higher mortality rate than normal calves and they may develop medical problems later in life. The muscles of their hindquarters may be permanently stunted due to degeneration. These calves can also suffer from diarrhea due to damage to the cells that line their intestines. As a result, more medications will be needed.
