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Calving Difficulty and its Association with Subsequent Productivity in Herefords¹

Colorado State University, Fort Collins 80521

Abstract

PARTURITION records of 2,733 Hereford calves sired by 123 bulls and out of 778 dams were analyzed by least squares procedures to determine factors which affect calving difficulty. Calves were born during a 16- year period at the Colorado San Juan Basin Experiment Station. Births were scored for ease of calving on a scale which ranged from 1 through 6 with 1 being most difficult and 6 being a normal, unassisted birth.

Analyses I (all calvings) and III (2-year- old calvings only) considered calving difficulty as a trait of the calf. The effects of year, sex of calf, age of dam, day of calf birth, line of sire of calf, sire within line, sex x age of dam and age of dam x level of dam inbreeding were highly significant (P<.01) sources of variation in Analysis I, but all factors included in the model accounted for only 17.0% of the variation in calving difficulty. Many of the same factors were significant sources of variation in Analysis III, where all factors in the model accounted for 15.6% of the variation.

Calving difficulty was treated as a trait of the dam in Analysis II (all calvings) and Iu (2 year-old calvings only). All factors included in the two analyses accounted for only 16.1 and 15.3% of the variation in calving difficulty.

Heritability estimates were calculated by the paternal sib method and were low in all cases. As a trait of the calf, heritability was estimated at 0.069±.022 in Analysis I and 0.126±.109 in Analysis III. As a trait of the dam, the estimates were 0.134±.029 and –.003±.097 from Analyses II and IV. A repeatability estimate of 0.045 was obtained from heifers calving both as 2- and 3-year-olds.

Heifers experiencing calving difficulty as 2-year-olds weaned 11% fewer calves of those born the first year and 14% fewer calves per cow exposed the second year when compared to contemporaries that had no difficulty at first parturition. The calves from 3-year-olds that had calving difficulty at 2 years of age were born an average of 13 days later and were 21 kg lighter at weaning than calves from 3- year-old dams that experienced no difficulty at 2 years of age.

¹ Published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series Paper No. 1717.

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