Reproduction, mastitis, and lameness in housed and pasture-based systems: Associations with parity

Dairy farming systems can be broadly classified as either housing-based dairy (HOUSED) or pasture-based dairy (PASTURE) systems. System-level differences in diet, housing, management, and milk production may influence health and reproduction of cows and the interaction of parity with these outcomes. This multi-site prospective, observational study investigated risks of pregnancy, mastitis, and lameness for different parities and housing systems (HOUSED and PASTURE). There were 15 HOUSED and 14 PASTURE Australian dairy farms enrolled, with health, reproduction, and production data collected from each farm between Feb 2022 to Jan 2026. Linear regression, logistic regression, and Weibull parametric survival models were used to assess the effects of parity, production system, and season on measures of pregnancy, mastitis and lameness. Robust sandwich estimators controlled within-farm correlation. The 100 d in-calf rate (100DICR, logistic regression) was not significantly different between PASTURE (34.0%; 95%CI: 28.0, 40.0) and HOUSED (32.9%; 95%CI: 28.9, 36.9) farms. The hazards of pregnancy (HPREG) assessed with a Weibull model were not different between PASTURE (1.04 HR, 95%CI: 0.82, 1.25) and HOUSED [1.08 hazards ratio (HR); 95%CI: 0.70, 1.45] farms. There was a monotonic decrease in the 100DICR and HPREG with increasing parity regardless of system. Cows breeding during Summer or Spring in PASTURE farms and Spring in HOUSED farms had reduced reproductive efficiency compared with other seasons. The effect of season was greater in PASTURE compared with HOUSED. There were 34,890 mastitis events across 129,039 lactation records. The crude incident rate of mastitis in HOUSED was 42.6 per 100 cows per 365 cow-days (95%CI: 41.9, 43.3) and 34.9 (95%CI: 33.7, 36.3) in PASTURE. The hazard of mastitis was numerically greater in HOUSED (2.85 HR, 95%CI: 1.10, 4.61) compared with PASTURE (2.13 HR, 95%CI: 1.62, 2.64) farms. The hazard of mastitis increased monotonically with parity. There were 9,495 cases of lameness across 125,362 lactation records. The crude incident rate was 8.75 per 100 cows per 365 cow-days (95%CI: 8.43, 9.07) in HOUSED and 10.7 (95%CI: 9.97, 11.4) in PASTURE. The hazard of lameness was similar in HOUSED (1.04 HR, 95%CI: 0.24, 1.84) and PASTURE (1.19 HR, 95%CI: 0.92, 1.44) farms. The hazard of lameness were unchanged in the first 3 (PASTURE) and 2 (HOUSED) parities but increased with parity thereafter. The association of increasing parity was far greater on health and reproductive outcomes than that of housing system. These results suggest that to support cow health and longevity we must address the impact of increased parity on health and reproduction of cows.