*Feed cost: R2.60/kg, Milk price: R3.20/ℓ
Table 1 show that the daily feeding cost of a cow producing 15 kg/day is R36.66. Maintenance requirements constitute 44% of the total feeding costs and
the gross margin above feed cost is R11.34. Similarly,
the feeding cost of a cow producing 30 kg/day is
R50.44, while its maintenance requirements constitute
29% of the total feeding cost while the gross margin
above feed cost is R45.56. This means that although
the feeding cost of the higher-producing cow is 37%
higher than that of the lower-producing cow, the por-
tion of the feed used for maintenance is 34% less. The
milk income above feed costs is therefore four times
higher for the higher producing cow.
The lactation curve
The milk yield and milk composition of dairy cows follow a specific pattern (Figure 1). The greatest challenge in feeding dairy cows is to feed them according
to the lactation curve optimizing milk yield and profitability. Naturally this means that cows should not at
any stage during the lactation period either be overor underfed.
Figure 1. The change in feed intake (□), milk yield (■) and live weight (▲) of Holstein cows during the lactation
period
After calving, the daily milk yield of cows increases
reaching peak yield at about 30-60 days after calving.
After this peak in production, the daily milk yield of
cows gradually decreases at a rate of approximately 35% per month. When cows are about five months
pregnant (in calf), the decline in milk yield occurs at a
faster rate. Peak yield is not as high in first lactation
cows as for older cows while the decline in milk yield is
at a lower rate, i.e. approximately 1-3% per month.
Figure 1 further shows that the live weight of cows decreases after calving, reaching a minimum at about 60100 days after calving, after which it gradually increases once again at approximately 0.5 kg/day. In contrast
to this, the feed intake increases quickly after calving
until a maximum intake is reached at about 8-10 weeks
after calving. After approximately 150 days, the feed
intake of cows starts to decline gradually. The lactation
period of dairy cows could be divided into four main
phases, namely:
Early lactation
: from calving to 100 days
Mid-lactation
: 101-240 days
Late lactation
: from 241 days to drying off
Dry period
: from drying off to calving (50-60
days)