Abstract :
Most livestock production systems, animals are classified by sex, age or weight at different
times in their productive life. In recent years, the pre-slaughter logistics for lamb
production has been modified to include an intermediate step between the farm and the
abattoir at classification centres (CC), where animals are classified by weight upon arrival
and finished to the appropriate slaughter weight. In this study we describe the changes
in social behaviour and stereotype profiles of lambs during one month after exposure to
novel environment (CC) and social mixing as well as changes in key physiological variables
associated with stress. We used a total of 36 male lambs (live weight of 17 ± 0.9 kg, approximately
60 days old and weaned at 45 days). Lambs were allocated to three different pens
with 12 lambs each (0.75 m2 per lamb) and took behavioural and physiological measurements
at 1, 7, 14 and 28 days after classification and mixing. Behaviour was video recorded
continuously for 8 h on each sampling day (08:00–17:00 h) to note aggressive, affiliation
and stereotypic behaviours. Blood samples were taken by jugular venipuncture after the
behavioural observations to measure plasma cortisol, lactate, glucose, creatine kinase (CK),
non-esterified fatty acid (NEFA) and haematological counts. The number of interactions
with physical contact and stereotypes decreased with time (P < 0.01), while aggressive and
affiliative interactions without physical contact remained the same throughout the trial. The
average number of aggressions and affiliative interactions with contact were significantly
higher on day 1. Total aggressions peaked on day 1, but decreased to a similar frequency as
total stereotypes later on, while total affiliative interactions also peaked on day 1 but were
much less frequent. Oral stereotypes peaked on day 1 as did body-rubbing. Plasma cortisol
was significantly higher (P < 0.01) in lambs sampled on days 1 and 7, compared with days 14
and 28. Plasma CK (P < 0.05) was higher on day 1 but then decreased. In conclusion, exposure
to novel environment (CC) and social mixing can be considered an important stress
for lambs, and increased levels of aggression, stereotypes and plasma cortisol levels can be
used reliably to indicate welfare problems at the CC.
