Particle size distribution consistency in mixed rations on UK commercial dairy farms

Total mixed rations (TMR) and partial mixed rations (PMR) are now commonplace on UK dairy farms due to ever-increasing herd size and lactation yields. Rations should meet the cow’s nutritional requirements although research has shown differences exist between the formulated and the delivered ration because of on farm mixing. This inconsistency, including particle size is a key factor in the effective fibre aspect of the ration, has a negative effect on the performance and health of the cow. There is very little research on the initial particle size variation in mixed rations and the reasons for such variation. Therefore, the aim of this study was to investigate the extent of particle distribution variation in the initial dispensed ration to dairy cows and the possible causes for this.

Sampling took place over five farms that fed either TMR or PMR, for a selection of different lactation groups. Ten samples were taken equidistance along the feed face of each of the loads and a Penn State Particle Separator used to determine particle size distribution. Coefficient of variation (CV%) was calculated for each mixed ration load based on a three-day average. SPSS was used for data analysis. Correlation relationships between CV% and influencing factors were examined. Results showed there was no significant correlation with either dry matter%, forage%, forage NDF% or wagon fill (fresh weight). Comparison between horizontal and vertical mixer wagon type was made using a t-test. This revealed a significant difference (P=0.004), where the vertical wagon type had a lesser CV% (6.8%) compared to the horizontal mixer type (13.5%). Particle distribution inconsistency of the initial feed-out was noted to be far higher than North America values. This suggests either more can be done to improve the consistency of mixed rations on UK dairy farms or the recommendations advised need to be further refined for Penn State Particle Separator use in the UK; given the higher proportion of grass silage included within UK rations. Dairy farmers need to consider mixer wagon choice and implement a monitoring system that is suited for UK forage production type to minimise initial spatial variation. This in turn will reduce the risk of poor rumen health and promote improvements in production