Estimation of Probability of Beef Cows Being Culled and Calculation of Expected Herd Life

Abstract

Data from the Livestock and Range Research Station (LARRS) at Miles City for the period 1943 through 1976 were used to calculate the proportion of cows culled for various reasons at each age. The proportions were used to esimate (1) the probability that a cow would remain in the herd to a given age, (2) age distribution of cows culled, (3) age distribution of cows in the herd and (4) expected herd life of a cow of each age. Cows were culled for eight reasons, including physical impairments and management decision criteria (MDC). The pooled estimates of the probability of being culled for physical impairment (including death) increased with age, from .0213 for 2-year-olds to .1191 for 10-year-olds. The probability of being culled for MDC also increased with age, from .1717 for 2-year-olds to .3560 for 10-year-olds, and at each age it was greater than that for physical impairment. Probability of a 2-year-old heifer remaining in the herd through age 10 was .0998. Mean age of cows culled was 5.7 years. Mean age of cows in the herd was 4.8 years. Expected herd life of cows aged 2 through 10 was 3.8, 3.7, 3.4, 3.0, 2.7, 2.2, 1.7, 1.1 and .5 years, respectively.