Particle size evaluation and its association with feed intake, milk yield and chewing activity in mid-lactation Holstein cows

Abstract

The objective of this study was to determine the associations among fresh and residual fractions of a total mixed ration (TMR), milk production and ruminating proportion of mid-lactation Holstein cows. During March 2002, daily representative TMR samples were collected at 8:00 a.m. from freshly delivered feed on a Holstein dairy in Florida. A sample of the residual feed (weigh-back) was collected at 7:30 a.m., corresponding to the weigh-back of the previous day. Samples were processed daily within 15 minutes of collection. Feed intake (as-fed), maximum and minimum temperatures of the day and individual milk yield were recorded daily. Each day, four hours after the 8 a.m. feeding (12 noon), numbers of cows ruminating and eating were counted. Particle size was evaluated using the Penn State particle size evaluator with three sieves. Dry matter (DM) content of each fraction was evaluated by using a microwave technique. Regression models for different outcomes were conducted. Models were developed using fractions as-fed and as DM basis. Differences in DM content between coarse and medium size were not statistically significant. For all models, predictors were the same for both as-fed basis and DM basis. For dry matter intake (DMI), the only significant predictor was the minimum daily temperature, with a negative association. No variable was associated with weigh-back coarse fraction. However, when coarse and medium fractions were pooled as one fraction, maximum temperature of the day and DMI were predictors of this new outcome. For medium weigh-back fraction, significant predictors were fresh medium fraction proportion and DMI. Dry matter intake was negatively associated with medium fraction proportion. The proportion of cows ruminating was positively related to the proportion of cows eating four hours after fresh feed was placed on the feed bunk. Milk yield was negatively associated with the medium fresh fraction proportion of the day before.