Wednesday, April 24, 2024

Live calves drive profitability

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The number of live calves on the ground in relation to the number of cows put to the bull or wintered is what drives profitability in a commercial beef cow operation. The national calving percentage during the past 20 years has hovered around 83%, so there is plenty of room for improvement.
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At the recent Beef + Lamb New Zealand AgInnovation Beef Genetics workshop in Feilding, well-known vet, Angus breeder and embryo transplant specialist Neil Sanderson said our stubbornly low national calving percentage was the result of a combination of factors such as: 

  • Low fertility in our cow herd
  • Bull fertility issues
  • Calving difficulty. 

While he acknowledged that the first two contributors to this national problem were serious, his presentation focused on the third, calving difficulty and particularly the genetic component. 

The calving ease EBVs: Sanderson said there were two calving ease EBVs. The first was known as “calving ease direct” which is the ease with which a bull’s calves are born, and “calving ease maternal”, the ease with which the bull’s daughters calve. He also pointed out that the model used by Breedplan to evaluate calving ease was different to the model used for developing other EBVs in that it used a calving ease score of 1 – 5 to indicate the degree of difficulty a female had in delivering its calf.

Because so many factors are involved in the birth process that cannot be measured, assigning a score to each birth is an attempt to account for the combined effect of all these immeasurable factors. 

Components of calving ease: If a calf is born without any difficulty and there are no signs of the mother having experienced any difficulty during the birth process, like the effects of a pinched pelvic nerve, the birth will be recorded as having a score of 1. If the female on the other hand has experienced a slight degree of difficulty or has needed slight assistance, the birth will receive a score of 2.

A difficult birth which requires considerable assistance receives a score of 3, a calving ease score of 4 is recorded when veterinary assistance is needed, and a 5 relates to malpresentations. The last score is not used to produce the EBV and scores 3 and 4 are combined.

The other two components of the calving ease EBVs are birth weight and gestation length. Birth weight has a significant influence on calving ease because as a calf gets heavier before birth a greater mismatch develops between the size of the calf and the pelvic area of its mother, creating a greater chance that some form of difficulty will be experienced.

Gestation length has an effect on birth weight in that generally the longer the gestation length the heavier the calf will be at birth and vice versa, but there are always exceptions to these relationships. Arguably the ideal combination at birth is a big calf that is born without assistance.

“Breeders need to concentrate more on the calving ease direct EBV rather than the birth weight EBV as a way of improving calving ease in their herds,” Sanderson said. 

A living example: Sanderson used an example of a bull whose “calving ease direct” EBV is poor compared with other Angus bulls on Breedplan.

In the example, the bull in question had himself been born 8kg heavier than the average birth weight of all other bull calves born on the property that year. No calving ease score was recorded for him. When he became a sire and was used in six other herds his calving record showed that out of 231 progeny born, 212 had been born unassisted, 10 had a calving ease score of 2, and two had a calving ease score of 3. Of the 10 with a score of 2, eight were out of two-year-old heifers, which is bad, and two were out of older cows, which is even worse.

When the computer is developing the calving ease EBVs it is particularly severe on bulls who create any form of calving difficulty and particularly if it occurs with older cows. It is not surprising, therefore, that this bull’s “calving ease direct” EBV took a pounding. He is ranked in the bottom 1% in Australasia for this EBV with an accuracy of 97% and in the bottom 5% for gestation length with a slightly lower accuracy. 

Summary:

  • The calving ease EBVs are the best EBVs to use for improving calving ease in cattle
  • There are two calving ease EBVs – Calving Ease Direct and Calving Ease Maternal.
  • Calving ease is a combination of birth weight, gestation length and a calving ease score
  • The calving ease EBVs refer to the ease with which calves are born to two-year-old heifers and the ease with which two-year-old heifers calve.
  • Higher more positive calving ease EBVs are more desirable.
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