The below content was taken from: "Control Of Calving Difficulty In Beef Industry"
Calving difficulty in beef heifers can be a major source of financial loss, due to a calf death rate of up to 10% in heifer herds and in some cases, loss of the heifer as well. The occurrence of calving difficulty varies between seasons and properties.
Although it is not possible to completely eliminate calving difficulty, a number of steps can be taken to reduce occurrence to a minimum.
Common Causes For Calving Difficulty
The two most important known causes of calving difficulty in heifers are excessive calf size at birth and inadequate size of the birth canal. Large, heavy calves are more difficult to expel than calves of average weight for the breed, and therefore are prone to more difficulty at birth and a greater rate of stillbirths. Male calves need to be assisted at birth much more frequently than females as they are generally heavier.Calves that are heavy at birth require a larger birth canal or pelvic area for normal delivery than lighter calves.
Some of the other common causes for calving difficulty include:
- abnormal calf presentation
- obstruction of the birth canal by fat deposits
- constriction of the birth canal at the vulva, vagina or cervix
- weak labour or poor muscle tone in heifers that are either very thin or too fat.
Prevention Planning Ideas
Bulls of any larger cattle breeds, including Brahmans and European beef breeds, throw heavy calves and may cause high levels of calving difficulty. They should not be mated with heifers of smaller breeds.There are also important differences between the British beef breeds. Hereford bulls normally cause more calving difficulty than either Shorthorn or Angus bulls. The only bull breed which can be relied on to substantially reduce the level of calving difficulty in heifers is the Jersey. However, a beef-Jersey cross doesn't bring much value to the table in terms of the beef industry.
Unfortunately, no simple method of identifying "easy calving" bulls on visually determined characteristics has yet been found. There appears to be little or no relationship between the conformation, degree of muscling or body measurements of a bull and the amount of calving difficulty he causes. The commonly held view that bulls with large heads or protruding shoulders cause higher than normal levels of calving difficulty has not been substantiated by research on the subject.
Apart from progeny testing, the only useful aids to selecting "easy calving" or "low birth weight" bulls are BREEDPLAN "Estimated Breeding Values" (EBVs) or the bull's own birth weight. As birth weight is a moderately heritable characteristic, bulls that had below average birth weight themselves will sire lighter calves than bulls that had above average birth weights.
For obvious reasons a disproportion between sire and dam in frame size and birth weight can lead to increased calving difficulties. So to avoid this problem, in some large Australian herds, heifers are joined with "litter mate" bulls, that is, bulls from the same calf crop as the heifers. This practice ensures that the bulls used are "genetically compatible" with heifers for birth weight and frame size. Ideally litter mate bulls selected should be of below or average birth weight.
Body condition at calving has an important influence on the amount of calving difficulty experienced by heifers. High levels of calving difficulty can be expected in fat heifers due to high calf birth weights, obstruction of the birth canal by fat deposits, poor uterine muscle tone and weak labour. Similarly, in very thin heifers, high levels of calving difficulty are caused by poor uterine tone and weak labour. Heifers should be in medium body condition at calving.
The amount of feed eaten and the growth rate of heifers at any stage of pregnancy is known to affect the birth weight of the calf. High weight gains at any stage are associated with heavy calves and should therefore be avoided. During spring, for example, it may be necessary to run heifers at a very high stocking rate to slow down their weight gains. The aim should be to keep heifers growing at a moderate rate throughout pregnancy (up to 0.5 kg/day).
Exercise is believed to play some part in the avoidance of calving difficulty, although this has not been tested in experiments. Heifers that have had to walk up and down hills, for example, should have better muscle tone and greater calving endurance than unfit heifers. Some producers deliberately feed out hay on hill tops, well away from watering points, to ensure that heifers get plenty of exercise during pregnancy.
With that knowledge this could be why heifers calving in spring invariably experience more calving difficulty than heifers calving in autumn. Or at least this could be said of cold climate farms.
Do Not Disturb:
Experiments conducted in Victoria have shown that calving problems can be induced by excessive disturbance during the calving period. When heifers are disturbed at the time of calving, muscles along the birth canal fail to relax and the birth process may be interrupted by constriction at the vulva and vagina. A compromise must therefore be reached between the need to observe heifers frequently during calving and the need to avoid disturbing them.
Problem Heifers Should Go:
Although calving difficulty is genetically passed down from mohter too daughter, however a heifer who has had several difficult births is a good sign that your breeding heifer is going to continue to have issues and you may want to consider getting rid of problem mama.
Small Heifer Calf = Problem Mama:
Pelvic size is closely related to heifer skeletal size which in turn is related to calf birth weight. By selecting for large pelvic size, calf birth weight would be increased and consequently no improvement in calving difficulty could be expected.
Article Provided By:
Geoff Kroker, Bendigo and Lisa Clarke, Hamilton