Selection of Heifers and Breeding Bulls for Reducing Calving Difficulties in the First Calvers: An Overview

Abstract

Calving difficulty is associated with cow mortality, calf loss, veterinary and labor costs, and causes delayed return to estrus and lower
conception rate. Dystocia is common in heifers, and the frequency decreases with the increasing age of the cow. Farmers need to
consider both genetics and management factors in an attempt to reduce dystocia. Calf birth weight, the pelvic area of the dam and their
interrelationships are major determinants of dystocia. The weight of the calf is governed by genetic, environmental and management
factors. Genetic factors include sex, length of gestation, breed, inbreeding, and genotype. Non-genetic factors include age and parity of
the dam, nutrition of the dam during various phases of gestation, and environmental temperature and humidity. Dystocia management
must begin with a selection of heifer for mating with respect to the body weight of heifers, body condition score (BCS) and dam’s pelvic
area should be considered before heifer selection. Not only heifer selection but sire selection using an estimated breeding value for
calving ease should also be considered to lessen the dystocia rate in a herd. A combination of culling heifers with small pelvic areas
and using bulls reported to be calving ease sire may reduce dystocia significantly. Apart from all these factors, genomic selection for
reducing calving difficulties is a new tool for dystocia management.