| Sumario: | Knowledge of composition of fat, protein and water in the body is indicative for the
determination of effects of changes in nutrition in terms of body reserves. Deuterium
oxide dilution technique has been proposed as easy, reliable and non-destructive method
of determining body composition using the ratios of protein:water and mineral:water to
predict fat.
Twenty
Bos indicus
(Boran) and 21 Boran
×
Holstein have been exposed for 4 years
to calculated energy requirements for maintenance (M) (low) or M
+
20% (medium) and
M
+
40% (high). In the third lactation these treatments were sub-divided into either low
or high feeding level. Before deuterium application animals were weighed and a blood
sample was collected from the jugular vein. Deuterium was slowly administered at 0.3
g/kg fasted body weight, directly into the jugular vein and the syringe was rinsed with
refilled blood. Blood samples were taken at 5, 7, and 9 h post infusion and deuterium
concentrations in plasma were analysed using isotope mass spectroscopy (3960 nm against
water). The gastrointestinal tract (GIT) of the cows was assumed to amount to 0.20 of
body weight (BW), and empty body weight (EBW) was described as EBW = BW
−
GIT.
Body composition was estimated in the following equations:
Empty body water (kg) = 0.4717
×
BW (kg) + 0.1536
×
D
2
O-space (kg) – 25.046
Empty body ash (kg) = 0.0363
×
BW (kg) + 0.0231
×
D
2
O-space (kg) – 5.755
Empty body protein (kg) = 0.1624
×
BW (kg) + 0.0165
×
D
2
O-space (kg) – 11.488
Empty body fat (kg) = 0.3790
×
BW (kg) – 0.2955
×
D
2
O-space (kg) – 42.163
Previous feeding level and the genotype explained most of the differences between treat-
ment groups. Boran cows showed higher levels of fat, but the difference of 20% and 40%
of the previous medium and high treatment was still visible. Fat reserves from the cross-
bred cows were strongly influenced by milk production, however, crossbreds previously on
low plane of nutrition replenished their fat deposits instead of producing more milk when
receiving higher amounts of feed.
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