Biomedical Engineering Reference
In-Depth Information
Control
Experimental
Max. temp.
Relative humidity
14
100
90
12
80
10
70
60
8
50
6
40
30
4
20
2
10
0
0
Days of experiment
Fig. 2
Milk yield of cows of control group and experimental group (provided with mist and fan system) during hot-
humid season
cows and buffaloes during heat stress have been
discussed in Chap.
7
.
in order to increase dietary proteins in relation to
requirements, but there is an energetic cost asso-
ciated with feeding excess proteins. Excess nitro-
gen above requirements reduces metabolisable
energy by 7.2 kcal/g of nitrogen (Tyrrell et al.
1970
). Feeding 19 and 23% crude protein diets
reduced milk yield by over 1.4 kg (Danfaer et al.
1980
), and the energy cost associated with syn-
thesising and excreting urea accounted for the
reduced milk yield (Oldham
1984
) . Dietary
protein degradability is critical under heat stress
conditions. As diets with low (31.2% of CP) and
high (39.2% of CP) rumen undegradable protein
fed during hot weather had no effect on DMI,
however, milk yield increased (Belibasakis et al.
1995
). Cooling the cow may affect the response
of the cow to protein supplementation. Although
the interaction of protein quality and environment
is not significant, the greater response to high
quality protein for cows in the cooled environ-
ment was attributed to the reduced amount of
protein metabolised for energy reduced, and less
energy was used in converting NH
3
to urea. When
12.1
Nutritional Management
to Reduce Heat Stress
There are several key areas related to nutritional
management which should be considered while
feeding in hot weather.
12.1.1 Water Intake
Water is the most important nutrient for the live-
stock species. Water intake is closely related to
DMI and milk yield of cows, but minimum tem-
perature was the second variable to enter a step-
wise regression equation after DMI, indicating
the influence of ambient temperature on water
consumption (Murphy et al.
1983
) . Water intake
has been observed to increase by 1.2 kg/°C
increase in minimum ambient temperature. Intake
of dry matter declines during heat stress; there-
fore, nutrient density of the diet must be increased
