Effects of stocking rate and supplementation on pasture utilization, cow performance, and rumen environment in a pasture-based and automatic milking syste

Integration of automatic milking systems (AMS) into Midwestern pasture-based systems has been suggested as an alternative low cost and labor efficient dairy system, but proper integration of this technology into a pasture-based dairy system is not well understood. The objective of this thesis was to determine management guidelines for a pasture-based AMS system by examining the combined effect of stocking rate and feeding strategies on cow performance, AMS use, feed degradation, dairy cattle genotype, and pasture utilization. An investigation lasting 8 weeks was conducted using a completely randomized design with a 2 x 2 factorial of two stocking rate systems (high stocking rate (HSR 2.89 cows/ha); low stocking rate (LSR 1.92 cows/ha)) and two genotypes of Holstein cattle, United States Holstein (USH) and New Zealand Holstein Friesian (NZF). The HSR treatment received a partial mixed ration (PMR; 40% ground corn and 60% legume grass haylage) in variable amounts (average: 4.86 kg /cow; +/- 0.14; mean and SEM) to supplement deficits in pasture growth rate and availability. Results indicated no differences in milk production or AMS use between treatments, although differences were found between genotypes. An in situ experiment showed no differences in feed degradation, suggesting that the rumen environment was not affected by PMR supplementation. No differences in pasture utilization or pasture growth were detected between the HSR and LSR treatments. The results of this thesis suggest that dynamic supplementation in the HSR treatment did not affect pasture utilization, cow performance, AMS use, or the rumen environment.