Effect of Group Composition and Feeding System on Behaviour, Production and Health of Dairy Heifers in Deep Bedding Systems

Abstract

An experiment was conducted in eight Danish commercial dairy herds, using 168 Danish Friesian heifers for 5 months, from November 1995. Three groups were established in each herd: two small, homogeneous groups (SHom) with five light heifers (130-250 kg) or five heavy heifers (250-380 kg) and one large, heterogeneous group (LHet) with ten light and heavy heifers (130-380 kg). The space allowance per heifer was 4.5 m2 including a 2.7-m2 resting area (deep litter). Four herds were fed restrictive amounts of concentrate per pen and ammonium-treated straw ad libitum (RCS) and four herds were fed one ration of either silage or total mixed ration (TMR) ad libitum (OR). The group composition had no general affect on the live weight gain (LWG). When using the RCS feeding system, the daily LWG in the LHet groups compared with the SHom groups decreased by 95 g for the light heifers, whereas it increased by 31 g for the heavy heifers. The average feed intake was 7% lower in the LHet groups than in the SHom groups (P=0.02). When heifers were fed RCS, light heifers spent less time eating concentrates (P=0.01) and for heavy heifers, there was a tendency to spend more time eating concentrates (P=0.10) in the LHet groups compared with SHom groups. The effect of group composition on synchronization of resting behaviour (when all heifers lie down simultaneously) revealed a tendency towards less synchronization in the LHet groups when fed OR (P=0.09), but not with RCS feeding (P=0.16) compared with the SHom groups. For heavy heifers, the aggression was decreased (P=0.02) when fed RCS, whereas it increased when heifers were fed OR (P=0.001) in the LHet groups compared with the SHom groups. Grouping criteria regardless of the feeding system did not influence the heifers' health. Whereas productivity was not decreased by increasing group size and group heterogeneity, the welfare of light heifers seems to some extent to be affected negatively by housing in a large heterogeneous group. Contrary to expectations, this negative effect could not be diminished by offering one ration (TMR or silage) ad libitum to the heifers.