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Slowly Fermentable Grains May
Reduce Metabolic Heat and
Ameliorate Heat Stress in Grain-Fed
Sheep
P.A. Gonzalez-Rivas, K. DiGiacomo, V. M .Russo*,
B.J. Leury, J.J. Cottrell, and F.R. Dunshea
Faculty of Veterinary and Agricultural Sciences, The University
of Melbourne, Parkville, Victoria, Australia.
*Department of Economic Development, Jobs, Transport and
Resources, Ellinbank, Victoria, Australia.
INTRODUCTION
• Ruminants can be more susceptible to Heat stress
(Coppock, 1985; Goetsch and Johnson, 1999; Roy and Collier, 2012).
• Rapidly fermentable grains (wheat); digestive
disorders, laminitis and higher metabolic heat
production (Nocek, 1997; Oetzel and Smith, 2000; Stone, 2004, Grant
and Albright, 1995; Brosh et al., 1998; Mader et al., 1999).
• Slowly fermentable grains (corn); better utilization of
ME and reduction of the heat from fermentation
(Ørskov, 1986; Owens et al., 1986).
Objectives
• To characterise the in vitro gas production kinetic
parameters of wheat and corn grains.
• To compare physiological parameters of sheep fed
either slowly or rapidly fermentable grain-based diets
under heat stress conditions.
Hypotheses
• Wheat has a faster rate of in vitro fermentation than
corn.
• Feeding slowly fermentable grains can reduce
the impact of heat stress in grain-fed sheep.
MATERIAL AND METHODS
In Vitro Experiment
• 28 replicates of 1g of 1mm-
ground wheat ASW 10% (70%
starch) and corn (74% starch).
• Buffered rumen fluid (Kansas-
State buffer pH 6.8) ratio 1:3
• Gas recording modules
ANKOMRF Wireless system
every 5 minutes
• Incubated for 24 h at 39⁰C
www.ankom.com
MATERIAL AND METHODS
In Vivo experiment
Experimental Design
Randomized Control Trial
Animals
– 22 Merino X Poll Dorset crossbred wether lambs.
– 11-12 mo
– 41.2±2.4 Kg BW
– Fleece cover 3 cm
Diets
• Control - rapidly fermentable diet “Wheat Diet”
50% crushed wheat grain + 50% of oaten/lucerne
chaff
• Intervention - slowly fermentable diet “Corn Diet”
50% crushed corn grain + 50% of oaten/lucerne
chaff
Both: 4% DM Balanced Supplement
12.7 % CP, 11.9 MJ ME/Kg DM,
23.8% NDF and 37.9% starch
Fed three times a day (0900, 1300,1700h)
MATERIAL AND METHODS
Accl.
(15 d)
• Acclimation feeding (1.5 x Maintenance requirements)
Period 1
(P1,7d)
• Thermoneutral (18 to 21⁰C and 40-50% RH, 24 h)
• Restrictive feeding (1.3 x Maintenance requirements)
Period 2
(P2, 7d)
• Heat stress (38⁰C/ 30% RH; 0900 to 1700 h, 28⁰C/50% RH;1700 to 0900 h)
• Restrictive feeding (1.3 x Maintenance requirements)
Period 3
(P3,7d)
• Heat stress (38⁰C/ 30% RH; 0900 to 1700 h, 28⁰C/ 50% RH;1700 to 0900 h)
• Acclimation feeding (1.5 x Maintenance requirements)
MATERIAL AND METHODS
• Respiration rate (RR)
• Rectal temperature (RT)
• Left and right flank skin temperature (LST and
RST)
• 0900, 1300, 1700 and 2100h during the experiment.
• Feed /water intake
PHYSIOLOGICAL
MEASUREMENTS
STATISTICAL ANALYSIS
In vitro gas production
• Gas production curve was fitted to the Gompertz
model. REML using the statistical package GenStat
(GenStat release 14; VSN International Ltd., Hemel
Hempstead, UK)
Y = A + C exp (-exp (-B(X-M)))
Where:
• B = Rate of gas production (mL h-1)
• M = Time at which the maximum rate of gas production is
reached (h)
• C = Maximum gas produced (Max gas mL/g DM)
• A = Y-intercept
STATISTICAL ANALYSIS
In vivo experiment
• Restricted Maximum Likelihood (REML) analysis
procedure for GenStat
• True differences between left and right flank skin
temperature were estimated by conducting a t-Test.
Corn had slower rate of gas production (ml gas h-1)
than wheat (P<0.001). Wheat reached the maximum
rate of gas production earlier than corn (P<0.001)
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14 16 18 20 22 24
Ga
s P
rod
uct
ion
(m
L/g
DM
)
Time (h)
Corn (74% Starch)
Wheat (70% Starch)
Max Rate 8.7 h
Max Rate 6.8 h
• Protein Matrix
• Amylose content
• Resistance to bacterial enzymatic
attack
Heat stress increased RR (P<0.001) and
corn-fed sheep had lower RR across periods
(P<0.001)
20
40
60
80
100
120
140
160
180
200
9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00
Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)
Res
pir
ati
on
Ra
te, b
rea
ths
per
min
ute
Corn
Wheat
Max Heat Max Heat
Corn -fed sheep showing lower RR at 38 C⁰/30% RH
Corn-fed sheep Wheat- fed sheep
Heat stress increased RT (P<0.001),
Corn-fed sheep had lower RT at high ambient
temperature (P<0.001).
39.0
39.1
39.2
39.3
39.4
39.5
39.6
39.7
39.8
39.9
40.0
9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00
Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)
Rec
tal T
emp
era
ture
, ⁰C
Corn
Wheat
Max Heat Max Heat
Skin temperature increased with heat stress (P< 0.001)
Corn- fed sheep had lower skin flank temperature (P<0.001)
LST was higher than RST (P<0.001)
38.2
38.4
38.6
38.8
39.0
39.2
39.4
39.6
9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00
Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)
Sk
in T
emp
era
ture
, ⁰C
LST Corn
RST Corn
LST Wheat
RST Wheat
Max Heat Max Heat
Wheat-fed sheep had larger difference between left
and right flank skin temperature (P<0.001)
Left Flank Right Flank
http://bvetmed1.blogspot.c
om.au/2013/03/ruminant-
abdomen-lecture-157.html
(Laue and Petersen, 1991;
Montanholi et al., 2008)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
Corn Wheat
Tem
per
atu
re, ⁰C
Difference left -right flank skin
temperature
CONCLUSION
• Corn grain had slower fermentation rate than wheat
grain
• Feeding a corn-based diet reduced the total heat
increment.
• Corn grain diet ameliorated the physiological
responses negatively affected by HS in grain-fed
sheep compared to dietary wheat.
• Higher feed intake increased the thermal load of the
animals under HS.
ACKNOWLEDGMENTS
• Faculty of Veterinary and Agricultural Sciences,
The University of Melbourne
• Animal Science group, animal house Parkville
and Dookie campus staff
Dr. Surinder Chauhan, Ms Maree Cox, Mr Evan Bittner, Ms
Shannon Holbrook, Dr. Michelle Henry, Ms Paula Giraldo, Mr
Ashley Gabler, Mr Frank O’Connor.
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