Lifetime profitability assessed through multivariate health index measured on primiparous Italian Simmental cows

The herd life is of major importance in dairy cattle. Direct or indirect indicators of health, fertility, feed efficiency, etc. are often used for selecting animals for reducing input costs. Many factors affect both the efficiency and the short/long-run profit of the dairy herds. The broad idea behind this contribution may be defined by the highlight ‘the healthier is the cows the higher the longevity and the profit in the long run’. Thus, breeding for healthier cows can accommodate both animal welfare and a sus¬tainable system of milk production. This study aimed at develop¬ing a health index on primiparous cows and to study its relationship with cows’ longevity. Data were from the Italian Simmental breeder association (ANAPRI). From an initial set of 957716 individual lactation records (11476 herds) a set of 131317 (5959 herds) of primiparous cows, born between 1992 and 2018, were extracted (90–600 DIM). Each cow was scored for: milk (MY), fat (FY), protein yield (PY) and fat:protein ratio (F:P) (effective or within the first 90 DIM), somatic cell score (SCS), days open (DO), size (SZ), muscularity (MU), udder (UD) and feet and legs (FL) scores. Moreover, for each cow retrospectively were computed the number of lactations (NL) performed, the longevity as the difference between the date of the last test day and date of first calving (LON, d), lifetime milking days (LMD, d), lifetime MY (LMY, kg) and lifetime daily average milk produc¬tion (LAP, kg/d). Multivariate factor (F) analysis of scored traits was performed. The longevity (LON & LMD) and lifetime produc¬tion (LMY & LAP) were analysed with the following mixed linear model: random effect of the herd (5959 levels); fixed effects of year of calving (27 levels) and classes of F scores (3 levels: high, medium, low) built according to their distributions. The NL ranged from 1–13 (mean 2.81 ± 1.73). Average LON, LMD, LMY and LAP were 1116 ± 666 d, 848 ± 509 d, 19203 ± 13069 kg and 22.15 ± 4.98 kg/d, respectively. Four common F were retained (64% σ2). F1–F4 were associated with production, size, health and NEB, respectively. The F3 (22% σ2) is regarded as a health index since its positive association with SCS (0.65) and logDO (0.58) and negative correlation with AP (−0.48) and UD (−0.56). The health index (F3) exerts a statistically significant effect on LON, LMD, LMY and LAP (p < .001). For instance, LON raises from 1039.7 ± 11.17 d to 1225.56 ± 11.18 d (+0.78 ± 0.81 NL and +1.44 kg/d of LAP) passing from the favourable to unfavourable health scores classes.