Behavior, intake, digestion, metabolism and milk yield of autumn and spring calved Holstein dairy cows with two levels of environmental exposure and feeding strategy

Doctoral thesis abstract

Abstract

High stocking rates and supplemental feeding in intensified pasture-based dairy systems (mixed systems, MS) increase confinement, and with extreme weather events becoming more frequent, environmental exposure and facilities become more relevant. Meanwhile, some dairy producers in Uruguay are replacing low-cost, but complex, MS with total confinement systems (fed with total mixed rations; TMR) to exert greater control over environmental exposure and intake, optimizing production. Holstein cows with autumn calving (ACS, n=48) and spring calving (SCS, n=48) were subjected to three treatments during a full lactation: (a) grazing + mixed ration (MR) during partial confinement in outdoor soil-bedded pens with shade (OD-GRZ); (b) grazing + MR during partial confinement in a compost-bedded pack barn with cooling (CB-GRZ); or (c) total confinement in a compost-bedded pack barn with cooling fed a TMR ad-libitum (CB-TMR). Throughout lactation, intake, milk production and composition, body condition, and blood non-esterified fatty acids and beta-hydroxybutyrate were determined periodically. In early lactation, specifically, behavior, intake, nutrient utilization, and ruminal microbial flow were measured. The results show that cows in well-managed OD-GRZ systems, under moderate climatic conditions, compensated for less favorable housing conditions through behavioral adaptations and achieved an intake, microbial flow, nutrient utilization, and milk production potential comparable to cows in enhanced infrastructure (CB-GRZ). However, when faced severe adverse climatic conditions (SCS), lower production was observed in OD-GRZ cows compared to CB-GRZ (5% throughout lactation and up to 20% during specific episodes of intense rainfall or heat stress). CB-TMR cows greatly outperformed the MS, achieving 20–35% higher milk production and 8–18% better feed efficiency, with no impact on milk components. Production levels surpassed previous studies in the region and aligned with those reported in California dairy systems, USA. The results show that cows in well-managed OD-GRZ systems, under moderate climatic conditions, compensated for less favorable housing conditions through behavioral adaptations and achieved an intake, microbial flow, nutrient utilization, and milk production potential comparable to that of cows in enhanced infrastructure (CB-GRZ).