Impact of late embryonic and early fetal mortality on productivity of beef cows.

Abstract

Although late embryonic/early fetal mortality (LEEFM) has been extensively researched in the context of reproductive efficiency, its long-term impact on cow productivity over a complete production cycle is poorly described in the scientific literature. This study used a prospective cohort design to evaluate the impact of late LEEFM on the productivity of beef cows. Postpartum cows (n = 2204) were exposed to a fixed-timed artificial insemination (FTAI) protocol followed by natural service breeding for the remainder of the breeding season. Pregnancy status was assessed 28 to 35 and 90 to 115 d after FTAI. Based on pregnancy status, cows were categorized into 1 of 3 cohorts: 1) Cows diagnosed as pregnant to FTAI on both pregnancy diagnoses were considered to have maintained their FTAI pregnancies (MAINT). 2) Cows diagnosed as non-pregnant to FTAI on the first diagnosis were classified as non-pregnant to FTAI (NP). 3) Cows that became pregnant to FTAI and were not pregnant to FTAI at the final pregnancy diagnosis were classified as having experienced LEEFM. Late embryonic and early fetal mortality cows had decreased final pregnancy rates (P < 0.01), calving rates (P < 0.01), and weaning rates (P < 0.01) compared with both MAINT and NP cows. In the subsequent year, LEEFM cows calved later and weaned lighter calves compared with MAINT and NP (P < 0.01). In addition, NP and LEEFM also had decreased (P ≤ 0.03) pregnancy rates to FTAI and final pregnancy rates in the subsequent year compared with MAINT cows. These results indicate that cows experiencing LEEFM exhibited reduced overall performance not only compared to those that maintained their FTAI pregnancy but also to cows that failed to conceive to FTAI, underscoring the detrimental impact of LEEFM on cow productivity.