A meta-analysis of the effects of high ambient temperature on growth
performance of growing-finishing pigs
ABSTRACT: High ambient temperature (T) is one
of the most important climatic factors influencing pig
performance. Increased T occurs sporadically during
summer heat waves in temperate climates and year
round in tropical climates. Results of published experiments
assessing the effects of high T on pig performance
are surprisingly variable. Thus, a meta-analysis
was performed to aggregate our knowledge and attempt
to explain differences in the results across studies on
the effect of increased T on ADFI and ADG in growingfinishing
pigs. Data for ADFI and ADG were extracted
from 86 and 80 trials, respectively, from articles published
in scientific journals indexed in PubMed, Science
Direct, and from proceedings of scientific meetings
through November 2009. Data on ADFI and ADG were
analyzed using a linear mixed model that included the
linear and the quadratic effects of T and BW, and their
interactions as continuous, fixed effects variables, and
the trial as a random effect factor (i.e., block). In addition,
the effects of housing type (2 levels: individual
and group housing) and the year of publication (3 levels:
1970 to 1989, 1990 to 1999, and 2000 to 2009) on
the intercept and the linear regression term for T (i.e.,
the slope) were also tested. Results showed that high
T had a curvilinear effect on ADFI and ADG and that
this effect was more pronounced in heavier pigs. Across
T, ADFI was less when pigs were group-housed. The
intercept and the regression coefficient (slope) for T
were significantly affected by the year of publication.
The effect of increased T was greater in more contemporary
works, suggesting that modern genotypes could
be more sensitive to heat stress than older genotypes of
lesser growth potential. In conclusion, pig performance
decreases at an accelerating rate as T is increased. The
large between-study variability on the effects of high T
on pig performance is partially explained by differences
in pig BW and to a lesser extent by the year the study
was published.
Key words: feed intake, growing pig, growth, meta-analysis, temperature