Integrated approaches to dairy cow performance: nutrition, reproduction, and production systems
Dairy cow performance in tropical production systems results from complex interactions among nutritional efficiency, postpartum health, reproductive management, and housing environment. Advancing sustainable dairy production therefore requires an integrated understanding of how these biological and management components influence productivity, resilience, and environmental outcomes. This thesis investigated key determinants of dairy system performance through four complementary studies combining controlled experimentation, large- scale retrospective analyses, and on-farm environmental assessment. The first study evaluated supplementation with the live yeast Saccharomyces cerevisiae CNCM I- 1077 and demonstrated improvements in rumen degradability of fibrous feeds, enhanced nutrient utilization, and greater feed efficiency. These findings indicate that optimizing rumen kinetics can improve metabolic efficiency and help mitigate environmental stress without necessarily altering microbial diversity. The second study analyzed retained placenta in commercial dairy herds under tropical conditions using a large retrospective dataset. Retained placenta was associated with cows’ breed, parity, and calving characteristics, and consistently resulted in reduced pregnancy per insemination, increased pregnancy loss, and greater risk of culling. These results confirm that postpartum disorders exert persistent effects on reproductive outcomes and herd longevity, highlighting the importance of preventive health strategies. The third study examined herd-level reproductive performance and showed that management intensity and housing system are major determinants of reproductive efficiency. More frequent reproductive monitoring was primarily associated with improved service rate and shorter intervals between inseminations, whereas compost barn and free stall systems had superior reproductive outcomes compared with dry lot systems. These findings emphasize that reproductive success in commercial herds is strongly related to management rather than fertility itself. The fourth study evaluated manure excretion dynamics in compost barn systems and demonstrated that the concentration of feces and urine within the bedding promotes composting and substantially reduces nitrogen requiring external treatment. This redistribution of nutrient flows enhances recycling efficiency and illustrates how housing design can simultaneously support environmental sustainability and animal welfare. Together, these studies demonstrate that improving dairy production in tropical environments requires a system-level approach integrating digestive efficiency, postpartum health, reproductive management, and production system design. Collectively, these findings highlight how nutrition, reproduction, management, and production system design shape productivity and sustainability in modern dairy systems. Keywords: dairy systems; herd management; reproductive efficiency; rumen function; sustainability; tropical production.