Herd level factors associated with pregnancy success and distribution in beef cow-calf herds

Abstract

Identifying factors that influence pregnancy success is important in order to optimize beef cowcalf
herd management. A logistic regression model was used to evaluate the effect of relevant factors
(categories were: herd size, body condition score, breeding season length, and timing of start of breeding
season) on the probability of pregnancy status at 2 time-points (day 21 and end of the breeding season).
Data were collected by convenience sampling from herds (n = 241) consisting of 8,217 head located in
the Midwest and Great Plains regions of the US from 2012 to 2017. Herds with < 50 head had reduced
probability of pregnancy (51 and 78%) compared to medium-sized (50 - 99 head) herds (63 and 84%).
Cows in thin body condition (score ≤ 4 out of 9) at pregnancy diagnosis had reduced probability of
becoming pregnant (44 and 64%) compared to cows in moderate body condition ([score 5 - 6 out of 9] 62
and 86%) and fleshy condition ([score ≥ 7 out of 9] 66 and 91%). Herds with a short (< 63 days) or
medium (63 - 84 days) breeding season had increased probability of pregnancy (65 and 58%) for the first
21-day interval compared to herds with a long (> 84 days) breeding season (49%). Herds that started the
breeding season in the fall (September 30 - December 31) had higher probability of pregnancy at the end
of the breeding season (88%) compared to spring (April 1 - June 30) start dates (82%). Management
factors (herd size, body condition score, breeding season length, and timing of start of breeding season)
had substantial impacts on the probability of pregnancy.