E. Zerbini et al., EFFECT OF DRAFT FORCE AND DIET ON DRY-MATTER INTAKE, MILK-PRODUCTION AND LIVE-WEIGHT CHANGE IN NONPREGNANT AND PREGNANT COWS, Animal Science, 62, 1996, pp. 225-231
Eighteen F-1 crossbred dairy cows (Friesian x Boran and Simmental x Bo
ran) were allocated to one of three diet groups (H: natural pasture ha
y; H + 3: natural pasture hay + 3 kg concentrate; and H + 5: natural p
asture hay + 5 kg concentrate) using a stratified random sampling proc
edure, with parity, milk production genotype, body weight and body con
dition score as blocking variables. Cows on each diet were then alloca
ted to three draught forces (7, 11 and 15 kg draught force per 100 kg
live weight) in a cross-over design to investigate relationships betwe
en work output, live-weight changes, dry-matter intake (DMI) and milk
yield. Each cow worked for 36 days in early lactation (from calving to
90 days) and for a further 36 days in late lactation (from 250 to 340
days post partum). Work output was similar for cows on each of the th
ree diets. Cows on the H diet consumed more hay than cows on H + 3 and
H + 5 diets. Hay and total DMI, milk yield and milk fat were similar
across draught forces and during working and resting days when the cow
s were not pregnant. Similar results were obtained when cows were from
82 to 172 days pregnant. Pregnancy did not affect the ability of cows
to perform work at different intensities. During working days cows lo
st live weight both when pregnant and when non-pregnant. During rest d
ays, non-pregnant cows on diets H, H + 3 and H + 5 compensated proport
ionately 0.12, 0.59 and 0.59, respectively, of the live weight lost du
ring working days. Pregnant cows on diet H + 3 and H + 5 compensated p
roportionately 0.95 and 1.77 live weight, respectively. Lower total li
ve-weight losses during the pregnant period could be attributed partly
to relatively greater DMIs and lover mild production, but also to ges
tation. Prediction of live-weight change from total DMI above maintena
nce, milk yield and work output during periods of 6 working days was p
oor (R(2) = 0.18). However, the same parameters explained adequately c
hanges in live weight for supplemented and nonsupplemented working cow
s (R(2) = 0.38 and 0.79, respectively) during a period of 90 days.