Dairy cows adaptation to integrated strategies of grazing and supplementation management, grazing behaviour, ruminal fermentation and production

Doctoral thesis abstract

Abstract

The objective of the project was to identify feeding strategies under grazing, to improve the efficiency of the use of feeding resources, especially the pasture. The research strategy involved 4 experiments, where effect of access time to pasture and time of grazing allocation and timing of corn silage supplementation on productive and ruminal fermentation variables was studied. Milk yield and herbage dry matter intake (HDMI) was higher for cows that grazed 8 h compared to 4 h, and there were no differences for the time of grazing allocation. However, cows that grazed from 11-15 h (T11-15) spent less time grazing with a greater bite mass and intake rate than cows that grazed from 7-11 h, and could explain the higher milk protein production. Ruminal pH of T11-15 dropped faster than T7-11 cows, which was in line with the higher VFA and ammonia concentrations observed in T11-15. Milk fat concentration and yield were higher in cows that received corn silage divided twice a day than those who received it at one time consistent with the higher HDMI observed. The timing of corn silage supplementation related to grazing session affected ruminal kinetics in terms of pH, ammonium and VFA concentration, and liquid/solid ratio fractions. Corn silage before grazing worked as a buffer for ruminal fermentation, but at the same time as a satiety signal and impact on rumen fill and fermentation due to changes in grazing and ruminating pattern and total DMI. The research strategy allowed us to understand how the grazing dairy cows modify ingestion and digestion on a daily basis, when they are exposed to a limited amount of feeding resources in different setups, showing high plasticity and adaptation on both: ingestion and digestion. A new window of opportunities has been opened after these results, to improve efficiency of the use of feeding resources applying alternative feeding strategies.