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Effect of thermal heat stress on energy utilization in two lines of pigs divergently
D. Renaudeau, G. Frances, S. Dubois, H. Gilbert and J. Noblet
selected for residual feed intake
doi: 10.2527/jas.2012-5689 originally published online January 7, 2013
2013, 91:1162-1175.J ANIM SCI
The online version of this article, along with updated information and services, is located on
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Effect of thermal heat stress on energy utilization
in two lines of pigs divergently selected for residual feed intake
D. Renaudeau,* G. Frances,†‡ S. Dubois,†‡ H. Gilbert,§# and J. Noblet†‡
*INRA, UR143, Unité de Recherches Zootechniques, F-97170 Petit Bourg, France; †INRA, UMR 1348, Physiologie,
Environnement et Génétique pour l’Animal et les Systèmes d’Elevage (PEGASE), F-35590 Rennes, France; ‡Agrocampus
Ouest, UMR1348 PEGASE, F-35000 Rennes, France; §INRA, UMR 444, Laboratoire de Génétique Cellulaire, F-31326
Toulouse, France; and #INRA, UMR 1313, Génétique Animale et Biologie Intégrative, F-78352 Jouy-en-Josas, France
ABSTRACT: Castrated males from 2 lines of purebred
French Large White obtained from a divergent selection
experiment for their residual feed intake (RFI) over
7
generations were measured for their energy
utilization
during thermal acclimation to increased ambient tempera-
ture. The RFI
+
line consumed more feed than predicted
from its performance, whereas the RFI− line consumed
less feed. Each pig was exposed to 24°C for 7 d (P0) and
thereafter to a constant temperature of 32°C for 3 consecutive
periods of 7 d (P1, P2, P3). Feed intake, feeding
behavior
parameters, digestibility,
components of heat
production
(HP; measured by indirect calorimetry in respiration
chambers), and energy,
nitrogen, fat, and water
balance
were measured in pigs offered
feed and water ad
libitum
and individually housed in respiratory chambers.
Two
identical respiratory chambers were simultaneously
used,
and 5 pigs of each line were measured successively.
Whatever
the trait, the interaction between line and period
was not signi
1162
1,2
3
Total HP tended to be greater in RFI+ than in RFI− lines
(1,279 vs. 1,137 kJ·kg BW-0.60·d−1; P = 0.065), which
tended to retain more energy (968 vs. 798 kJ·kg
BW-0.60·d
greater in RFI+ compared with the RFI− line (644 vs.
560 kJ·kg BW-0.60·d
Key words: energy use, growing pig, heat production, residual feed intake, thermal stress
©
1
The authors thank Y. Billon (INRA, GEPA) and F. Le Gouevec,
R. Janvier, Y. Jaguelin, and A. Pasquier (INRA, PEGASE) for their
skillful technical assistance and helpful collaboration.
2
This experiment was supported by the French National Research
Agency, program “PIG_FEED” (ANR-08-GENM-038).
3Corresponding author: jean.noblet@rennes.inra.fr
Received July 27, 2012.
Accepted November 26, 2012.
INTRODUCTION
Climatic environment is one of the main limiting
factors of production effi ciency in the swine industry,
especially when ambient temperature is above
the
zone of thermal comfort. Although
thermal
stress
is an occasional problem in temperate countries
during the 2 to 3 summer months and/or during
hot spells, it is a more permanent problem in many
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Energy utilization in heat stressed RFI pigs
1163
tropical countries where pig production has grown at
a high rate during the last 2 decades. Physiological
and metabolic adjustments resulting from the thermoregulatory
responses to thermal stress have negative
consequences
on pig performance. In ad libitum fed
pigs,
the reduction in heat production caused by the
lower
feed intake is an essential mechanism to maintain
body temperature within a physiological safe
range
(Renaudeau et al., 2011a).
The
related low energy
and nutrient intakes mainly explain the reduced
growth
rate in heat-stressed pigs. A
better understanding
of the physiological and metabolic responses during
thermal acclimation is a key factor for improving
thermotolerance,
especially if future solutions based
on
genetic selection require fi
ne
phenotyping of heattolerance-related
traits in commercial populations.
Feed accounts for 60% to 70% of the total production
cost in pig production. The
improvement
in feed effi ciency is therefore a main preoccupation
for maintaining or improving the competitiveness of
pig industry. In growing pigs, an important portion
of voluntary feed intake (i.e., 30% to 40%; Dekkers
and Gilbert, 2010) is not explained by maintenance
and production requirements. This unexplained variability,
referred to as residual feed intake (RFI
The purpose of this study was then to characterize
the effects
of acclimation at high ambient temperature
on pig energy
utilization and to determine
whether
the responses can change in 2 Large
White
lines
divergently
selected for high RFI (RFI
) or low
RFI (
–
). These 2 lines were obtained from a selection
experiment that was initiated at the Institut
National
de la Recherche Agronomique
(INRA)
in
2000
(Gilbert et al., 2007).
MATERIALS AND METHODS
This study was conducted in accordance with the
French legislation on animal experimentation and ethics,
and the senior researchers were authorized by the
French
Ministry of Agriculture
to conduct experiments
on
living animals at the INRA
facilities in Saint Gilles,
France.
+
Experimental Design and Animal Management
The aim of this study was to investigate the effect
of thermal acclimation at high ambient temperature on
energy use in Large White growing pigs from RFI
and
RFI
–
lines kept in respiration chambers. These animals
were obtained from a divergent selection experiment
for RFI conducted at INRA for 7 generations. More details
on the selection experiment are given by Gilbert
et
al. (2007, 2012). In generation 7, the line difference
amounted
to 3.1 genetic SD units of the selection criteria
recorded on male candidates at selection (H. Gilbert,
unpublished
data). Because only 2 respiration chambers
were
available, 2 pigs (1 RFI
+
and 1 RFI–) were measured
simultaneously for 28 consecutive d. A
total of 5
replicates
of 2 pigs was used. For this purpose, 2 to 3
castrated
male piglets per line were randomly chosen
at
weaning (28 d of age)for each replicate and transported
from the selection herd [INRA–Génétique et
Expérimentation en Productions Animales (GEPA
Magneraud, France] to the respiration chamber location
[INRA–Physiologie, Environnement et Génétique pour
l’Animal et les Systèmes d’Elevage (PEGASE), SaintGilles,
France]. From weaning to about 25 kg of BW,
the
animals were housed in metabolic crates designed
for
young pigs. From 25 kg until the beginning of the
experiment,
pigs were individually housed in metabolic
cages
similar to those used in the respiratory chambers.
The
average BW
at the beginning of the experiment was
approximately
47 (±2) kg. Genetic values of the pigs
selected
for the present experiment were calculated according
to the method described by Gilbert et al. (2007).
The
difference
(RFI+ vs. RFI–) in averaged genetic values
for the 10 pigs sampled in the present study was
close
to those estimated for pigs of generation 7 for the
selection
index (131 vs. 148 g for RFI in pigs of the
seventh
generation).
During the adaptation and the experimental periods,
pigs were given 1 daily meal; the feed was based on corn,
wheat, barley, and soybean meal and was formulated to
meet or exceed energy and AA requirements of pigs for
this BW range. This diet contained 9.2 MJ NE/kg and
8.1 g digestible lysine/kg. More details on the ingredients
and chemical composition of this experimental diet
are
given in Table
1. During the adaptation period, the
feeding
level was slightly below the ad libitum intake,
whereas
during the experimental period, feed and water
were
offered
ad libitum.
During the experimental period, pigs were kept at
24°C (thermoneutral zone) for 7 d (from d −7 to d
rate of 2°C/h beginning at 0900 h. The relative humidity
was kept at about 75% over the total experiment.
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+
Renaudeau et al.
1164
Two identical open-circuit respiration chambers
similar to those described by Vermorel et al. (1973)
were used. In the respiration chamber, the metabolic
cage was mounted on force sensors (Type 910A, Kistler,
Winterthur, Switzerland) that produced an electrical sig-
nal proportional to the physical activity of the animal.
The trough was placed on a load cell to allow a continu-
ous measure of feed intake and feeding behavior variables.
A
12-h lighting schedule (0800 to 2000 h) was
used.
Table 1.
Item Amount
Ingredients, g/kg
Corn 253.9
Wheat 230.0
Barley 230.0
Soybean meal 187.0
Molasses 20.0
Wheat bran 50.0
Dicalcium phosphate 11.0
Calcium carbonate 7.0
Salt 4.0
l-Lysine HCl 1.8
l-Threonine 0.30
Vitamins and mineral premix
1
5.0
Analyzed chemical composition
2
, %
CP 16.70
Ash 5.01
Ether extract 2.05
Crude
Nutritional values
2,3
ME, MJ/kg 12.47
NE, MJ/kg 9.22
Digestible AA, %
Lysine 0.81
Methionine + cystine 0.50
Threonine 0.52
Tryptophan 0.17
1
Supplied per kilogram (as-fed basis) of diet: vitamin A, 5,000 IU; vitamin
D
, 1,000 IU; vitamin E, 20 IU; menadione, 2 mg; thiamine, 2 mg; ribofl avin,
4 mg; niacin, 15 mg; pantothenic acid, 10 mg; pyridoxine, 1 mg; biotin, 0.2
mg; folic acid, 1 mg; cyanocobalamin, 0.02 mg; choline chloride, 500 mg; Fe,
80 mg as ferrous carbonate; Cu, 10 mg as copper sulfate; Zn, 100 mg as zinc
oxide; Mn, 37 mg as manganous oxide; I, 0.2 mg as calcium iodate; Se, 0.2
mg as sodium selenite; and Co, 0.1 mg as cobalt sulfate.
3
2
3
Adjusted for a 88% DM.
Values calculated according to Sauvant et al. (2002).
Measurements
Animals were weighed at the beginning (d −7), on
d 0, and on
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