The Association between forage particle size at initial feeding and the weigh-back and chewing activity in dairy cattle

Abstract

A field trial was conducted at the University of Florida Dairy Research Unit (USA) to determine the relationship between initial coarse portion (ICP) particle size of a total mixed ration (TMR) and orts (weigh-back coarse portion, WBCP) of the same TMR. Additionally, the relationship between the ICP of a TMR and the proportion of cows chewing their cud 2.0 hours after feeding was determined. A random representative sample of TMR was taken from the feed bunk at initial feeding and 8 h later (weigh-back) every day from the same barn for 75 days. Samples were analysed for particle size content using a particle size evaluator. Proportion of the largest particles of the TMR was recorded. Additionally, the proportion of cows ruminating 2.0 hours after the morning feeding was recorded each day. Correlation and regression models between ICP and WBCP, and between ICP and the proportion of ruminating cows were calculated. The mean and standard deviation for ICP, WBCP and proportion of cows cud chewing were 14.2ñ6.6, 29.9ñ13.2 and 18.4ñ5.0%, respectively. The Pearson correlation coefficient between ICP and WBCP was 0.53, and the correlation coefficient between the proportion of cows chewing their cud and ICP in the TMR was 0.19. Initial coarse proportion was a predictor for WBCP (p<0.01), but was not a predictor of the proportion of cows ruminating 2 h after the morning feeding (p>0.05). These findings are suggestive of sorting of the TMR by the cows. Sorting was significantly higher (p<0.01) as the coarse proportion at the initial feeding increased, but this difference was likely of little biological significance.