94
Dynamics of Culling for Jersey, Holstein, and Crossbred Cows in Large Multi-breed Dairy Herds
The objective of this observational study was to describe and compare the dynamics of reason-specific culling risk for the genetic groups Jerseys (JE), Holsteins (HO), and Jersey x Holstein crossbreds (JH), considering parity, stage of lactation, and milk yield, among other variables, in large multi-breed dairy herds in Texas. The secondary objective was to analyze the association between survival and management factors, such as breeding and replacement policies; type of facilities; and use of cooling systems. After edits, available data included 202,384 lactations in 16 herds ranging from 407 to 8,773 cows calving per year during the study period from 2007 to 2011. The statistical analyses were performed through logistic regression (PROC GLIMMIX, SAS) and by estimation of hazard functions (PROC LIFETEST, SAS). The distribution of lactation records by genetic group was 58%, 36%, and 6% for HO, JE, and JH crosses, respectively. Overall culling rates across-breeds were 30.1%, 32.1%, and 35.0% for JH, JE, and HO, respectively. The dynamics of reason-specific culling were dependent on genetic group, parity, stage of lactation, milk yield, and herd characteristics. Early lactation was a critical period for “died” and “injury-sick” culling. The risk increased with days after calving for “breeding” and, in the case of HO, “low production” culling. Open cows had a 3.5 to 4.6 times greater risk for overall culling compared to pregnant cows (P≤ 0.01). The odds of culling with reason “died” within the first 60 DIM were not significantly associated with genetic group. However, both JE and JH crosses had lower odds of live culling within the first 60 DIM compared to HO cows (OR = 0.72 [P≤ 0.001] and 0.82 [P≤0.002], respectively). Other cow variables significantly associated with the risk of dying within the first 60 DIM were cow relative 305ME milk yield, parity, and season of calving. Significant herd related variables for death included herd size and origin of replacements. In addition to genetic group, the risk of live culling within 60 DIM was associated with cow relative 305ME milk yield, parity, and season of calving. Significant herd related variables for live culling included herd relative 305ME milk yield, herd size, type of facility, origin of replacement, and type of maternity. Overall, reason specific culling followed similar patterns across DIM in the 3 genetic groups.
Keywords: Culling, death, Holstein, Jersey