Impact of Stationary Brush Quantity on Brush Use in Group-Housed Dairy Heifers

Abstract

Our objectives were to evaluate the effect of stationary brush quantity on brush use and competition in weaned dairy heifers naïve to brushes. Sixty-three Holstein heifers (95 ± 5.7 days old) were housed in groups of eight (with the exception of 1 group of 7) with two or four stationary brushes (n = 4 groups/treatment). Brush-directed behaviors of grooming, oral manipulation, and displacements were recorded continuously for all heifers 0-6, 18-24, 120-126 and 138-144 h after brush exposure. Linear mixed models were used to evaluate the effects of brush quantity and exposure duration. Total brush use and competition were not affected by brush quantity, but heifers with access to more brushes used them for longer bouts, suggesting greater opportunity for uninterrupted use. Total brush use was greater in the first and final 6 h observation periods, which was driven by the greatest duration of oral manipulation and grooming in those respective periods. The continued use of brushes by all heifers in the final period indicates the importance of providing appropriate outlets for these natural behaviors to promote animal welfare. The effect of brush quantity on bout characteristics suggests that brush use was less restricted with four compared to two brushes per eight heifers.

Keywords: bout criteria; competition; grooming; oral behavior.

Figure 1

Group-housed heifers were provided with either two or four wash brushes per pen, mounted on two opposite wooden plank walls of the pen. Brush-directed behavior was observed for all heifers via continuous video recordings and coded as (a) oral manipulation, defined as contact between the mouth or tongue and the brush and (b) grooming, defined as rubbing the head, neck, or body against the brush.

Figure 2

Pen diagram for each of the two brush treatments, providing two or four brushes to group-housed, naïve heifers. The yellow boxes represent an individual brush. Solid wooden walls separated the 4 pens in the barn. Note: This diagram is not drawn to scale.

Figure 3

Log₁₀-transformed relative frequency distributions of the intervals between the events of heifers using stationary brushes, fitted with mixture normal distributions. Data presented are summarized for the (A) novel period (0–6 and 18–24 h of exposure, pooled across 63 heifers) and (B) non-novel period (120–126 and 138–144 h of exposure, pooled across 55 heifers). The blue bars represent the frequency of each log₁₀-transformed inter-bout interval. The red lines represent the contribution of individual distributions to the overall probability density (green line).

Figure 4

The mean ± SE duration of brush use for oral manipulation and grooming, averaged per 6 h period of observation, for each brush treatment (2 vs. 4 brushes provided to 7 to 8 group-housed heifers). The error bars represent the standard error of the means.

Figure 5

The mean ± SE duration of oral manipulation, grooming, and total brush use (the sum of the two aforementioned subsets) for each observed period (periods 1–4: 0–6, 18–24, 120–126, and 138–144 h after exposure, respectively), regardless of brush treatment. Letters within the same-colored line indicate significant (p < 0.05) pairwise differences between periods.

Figure 6

Correlation between individual heifer competitive index value (calculated as frequency of initiated displacements (actor role) divided by the total number of displacements she was involved in (actor and receiver roles), multiplied by 100) and the duration of brush use (average per 6 h period). One heifer in the 4-brush treatment was uninvolved in displacements and was excluded. Pearson correlations were performed regardless of treatment (R = −0.07, p = 0.61) and within each treatment (2-brush: R = −0.10, p = 0.58; 4-brush: R = −0.05, p = 0.78).