Sixty healthy Rasa Aragonesa entire male lambs (65 days old) with
an average live weight of 17.13 (±0.18) kg were allocated into two
treatments (weights were balanced across treatments) according to
their pen environment during the finishing phase, which lasted five
weeks. Lambs were housed indoors in six pens with 10 lambs each
(2.9 × 3.3 m, animal density of 0.95 m2 per lamb) and three replicates
per treatment. Lambs from the enriched group (EG) were maintained
in 3 pens with a wooden platform with ramps that provided access to
a concentrate hopper (Fig. 1). The platform dimensions were 2.35 m
long, 1.55 m wide and 0.35 m high (surface area of platform, 1.67 m2).
The ramp slopewas approximately 20°. The platformin the pen was attached
to the solid fence that separated each pen, allowing the lambs to
feed, explore and exercise or to rest lying down. The EG lambswere providedwith
cereal straw as bedding (on the floor) and as forage (in a fodder
rake). Additionally, a small ramp (0.90min length, 0.50minwidth,
0.30mhigh and 0.08m2 of surface of platform)was placed near the opposite
solid fence, but away from the food hopper and fodder rake, to
allow lambs to play. Lambs from the control group (CG) were maintained
in barren pens of similar dimensions to that used commercially
at the CC, without cereal straw as bedding or forage. For hygienic reasons
a thin layer of sawdust was added at the beginning of the experiment.
All lambs were fed with commercial ground (4–6 mm sieve)
concentrate (Ovirum Alta Energía®) containing barley, wheat, calcium
carbonate, sodium chloride and a vitamin supplement corrector (18%
crude protein and 11.5 MJ metabolisable energy/kg DM). Feeding and
water consumptionwere ad libitum. In both treatments the concentrate
hopper was wide enough to allow all lambs to eat simultaneously.
Water was provided using a float drinker installed in a corner of each
pen. Animals were weighed individually at the beginning (W1) of the
experimental period (35 days) and just before slaughter (W2). Feed intake
was recorded to calculate the conversion index.