The effect of fouling on herbage intake of dairy cows on late season pasture

During three years (experiments 1-3) short-term grazing experiments were performed to study late season herbage intake by dairy cows. Change-over designs were used during experiments 1 and 2 while a continuous design with a covariate period was used in experiment 3. The effect of fouling on intake at a herbage allowance of 30 kg dry matter (DM) per cow and day was studied by comparing herbage intake on clean, grass-dominated pastures (treatment CG), with herbage intake on fouled grass-dominated pastures (treatment FG), in experiments 1-3. In experiment 2, a third treatment was included, consisting of grazing a clean clover-grass ley (treatment CC). Pastures on treatment CG were cut and those on FG were grazed and then immediately topped at the same times throughout the grazing season until the start of the experiment. In experiment 2, the grazing area of treatment CC was the regrowth after an early season harvest. The herbage intake on treatment FG was 13.0, 13.8 and 14.2 kg organic matter (OM) per cow and day in experiments 1, 2 and 3, respectively, while corresponding intake values for treatment CG were 13.7, 15.5 and 14.8 kg (OM). In experiment 2, the herbage intake of cows on treatment CC was 15.1 kg OM. The increases in intake observed on clean pastures were statistically significant (p < 0.01) in experiments 1 and 2 but not in experiment 3. Herbage intake was approximately 5-10% higher when animals were offered clean pasture compared with fouled. Sequential estimations of areas fouled were also made in experiments 2 and 3. Dung pat sizes in 15-25% of the total experimental area were measured. The area fould per cow and day increased from an average of 0.7 m(2) during the first rotation to 1.8 m(2) during later rotations. In a similar manner, the proportion of the paddock covered by dung increased from approximately 0.7% after the first rotation to 1.2% after later rotations, although the average stocking density was higher at the first rotation compared with later rotations: 92 and 77 cows per ha, respectively. Topping of pastures in experimental paddocks increased the fouled area considerably and, at the start of the experiment in late August, approximately 6% of the total experimental area had been covered by dung after three rotations.