Biomedical Engineering Reference
In-Depth Information
cows are subject to hot weather conditions, rumen
degradable protein (RDP) should not exceed 61%
of dietary CP, and total protein should not exceed
NRC recommendations by greater than 100 g N/
day (Huber et al.
1994
). One hundred grams N is
equivalent to about 3.1% CP in the diet, assuming
20 kg DMI/day. High dietary lysine (241 g/day,
1% of DM) increased milk yield by 3 kg over
diets containing 137 g/day lysine (0.6% of DM)
(Huber et al.
1994
) .
Metabolic heat production, though advanta-
geous during cold weather, is a liability during
hot weather due to the difficulty in maintaining
body heat balance. Heat production for a 600-kg
cow yielding 40 kg of 4% fat milk amounted to
31.1% of consumed energy, which was second to
faecal energy losses of 35.3% (Coppock
1985
) .
While maintenance was responsible for 23.5% of
the heat produced, greater milk yield also
increases heat production. Cows at high (31.6 kg/
day) and medium (18.5 kg/day) milk yield had
48.5 and 27.3% greater heat production than dry
cows (Purwanto et al.
1990
). Use of some dietary
ingredients may contribute less to heat increment
of the diet, thus reducing total heat production of
the cow. Lower efficiency for use of acetate may
account for the low net energy of high-fibre feeds
(Moe
1981
) and supports the feeding of low-fibre
diets during hot weather.
Particularly, chronic heat exposure of 6- and
12-month-old buffalo calves was accompanied
with highly significant (
P
< 0.01) increases in
total water intake (28.5 and 48.3%), total body
water (TBW) content (8. 5 and 9.6%), free water
intake (25.2 and 56.4%), urine excretion (24.8
and 108.0%) and evaporative water loss (51.2
and 69.4%). Significant respective decreases
were recorded in 6- and 12-month-old buffalo
calves in metabolic (which is derived from oxida-
tion of fats, carbohydrates and proteins) (20.8
and 16.8%) and faecal water excretion (36.4 and
8.5%). Dietary water intake decreased (16.3%)
due to chronic heat exposure in 12-month-old
calves (Nessim
2004
) .
The consumed water may replace the lost TBS
by heat stress, since it was found that a net total
body solids loss of 10 kg, in 3 days of elevated
heat exposure, was replaced by extra body water
retained during these 3 days without a significant
change in body weight, in cattle (Kamal and
Johnson
1971
) . Ambient relative humidity
showed no significant effect on water consump-
tion in cattle (Mullick
1964
) . However, Mishra
et al. (
1963
) showed that a drop in dietary water
intake occurred as ambient temperature increases
in buffalo cows. Particularly, a significant posi-
tive correlation between temperature and water
consumption and nonsignificant negative corre-
lation between relative humidity and water con-
sumption were found when temperature was held
constant in lactating and non-lactating dairy cows
(Harbin et al.
1958
) . Concerning the mechanisms
underlying water intake, water intake at low or
high ambient temperature was blocked when
urine excretion was inhibited by ADH adminis-
tration in cows. This indicates that water reten-
tion caused by ceasing urination might block
thirst (Kamal et al.
1959
) .
The drinking behaviour of the high-producing
cows increased compared to the low-producing
dairy cows, for which two factors were involved.
The first one is the higher milk yield, and the
other is hot environment since the high milk
yielding cows had faster dehydration rates by
increased sweating and respiratory water loss as
compared to low yielders (Berman et al.
1985
)
during summer. The higher drinking behaviour of
the high-producing cows is consistent with the
notion that high-producing cows try to overcome
effects of the high temperature of summer. Water
requirement by animal is highly influenced by
demands to maintain homeothermy during heat
stress (Beede and Collier
1986
) .
12.1.2 Rumen Health
The heat-stressed cows are prone to rumen acido-
sis, and many of the lasting effects of warm
weather (laminitis, low milk fats, etc.) are proba-
bly related to a low rumen pH during the summer.
Therefore, adequate care should be taken when
feeding
hot
rations during the summer months.
In addition, obviously fibre quality is important
all the time, but it is paramount during the summer
as it has some buffering capacity and stimulates
saliva production. Dietary HCO
3−
may be a valu-
able tool to maintain a healthy rumen pH.
