Reproductive efficiency and survival of Holstein-Friesian cows of divergent Economic Breeding Index, evaluated under seasonal calving pasture-based management

摘要

The objective of the current study was to examinephenotypic fertility performance and survival, and togain insight into underlying factors that may contributeto greater fertility performance in 2 divergent geneticgroups (GG) of Holstein-Friesian, selected using theIrish Economic Breeding Index (EBI). The GG wereevaluated across 3 spring calving pasture-based feedingtreatments (FT) over 4 yr. The 2 divergent GG were(1) high EBI; representative of the top 5% nationally(elite), and (2) EBI representative of the national average(NA). In each year, 90 elite and 45 NA cows wererandomly allocated to 1 of 3 FT: control, lower grassallowance, and high concentrate. No interaction betweenGG and FT was observed for any of the measuresof fertility investigated. The elite cows achieved significantlygreater pregnancy rate to first service (+14.9percentage points), and significantly greater pregnancyrates after 21, 42, and 84 d of breeding (+17.3, +15.2,and +9.6 percentage points, respectively) comparedwith NA. The number of services per cow was fewerfor elite (1.57) compared with NA (1.80). The intervalfrom mating start date to pregnancy was significantlyshorter for elite cows compared with NA. The elite cowsmaintained greater mean body condition score than NAthroughout the study (2.91 vs. 2.72), and had greaterbody condition score at calving, artificial insemination,and drying off compared with NA. The elite cows hadgreater mean circulating concentrations of insulin-likegrowth factor-1 compared with NA. No significant effectwas observed of GG on commencement of lutealactivity, or progesterone profile variables. Greater survivalto the start of fifth lactation was observed for elitecows. The elite cows were 43% less likely to be culledthan NA by the beginning of the fifth lactation. Theresults highlight the success of the Economic BreedingIndex to deliver reproductive performance and longevityconsistent with industry targets across a range ofseasonal pasture-based FT. The results also clearlydemonstrate the potential of appropriate genetic selectionto reverse negative fertility trends incurred duringprevious decades of selection for milk production alone.