Dairy farmers feed their cows to aim to produce 1.4 to 1.6 L of milk per kg of dry matter intake. In early lactation ( less than 100 days in milk), cows will produce an average of 40 L of milk per day and eat 50 kg of feed per day, which averages 50% water and 50% dry matter.

Early lactation cows need 1.25 kg of feed per L of milk, which results in 1.6 L of milk per kg of dry matter intake. In late lactation (over 200 days milking), cows will only produce an average of 25 L of milk and eat 36 kg of feed per day. So, late lactation cows need 1.44 kg of feed per L of milk, which results in 1.4 L of milk per kg of dry matter intake.

In general, dairy cows are fed a total mixed ration, which should contain all the nutrients a cow needs in every bite. A total mixed ration will contain roughly 50 to 60% forage (hay and silage) and 40 to 50% concentrates (grain, protein meal, fat, vitamin/mineral) and each kg of dry matter should break down to 70% carbohydrate, 18% protein, 6% fat and 6% vitamins and minerals.

Effects Of Lactation

During peak lactation, a high-yielding cow may produce as much as 60 litres per day and up to 12,000 litres over her whole lactation. Be subject to intensive. A cow weighing 550 kg giving 30 kg milk can eat 3.7% of her body weight in DM daily or about 20.4 kg. A bigger cow (650 kg) at the same milk yield can eat.. Cows are normally milked twice a day: early morning and late afternoon. Milk obtained at the morning milking is much lower in fat (e.g. 3 percent) than at the afternoon milking (e.g. 5 percent). 

This is not because fat secretion is reduced in the longer night interval but because there is a net carryover of residual milk rich in fat from the night to the day interval. Time of Milking. Cows are normally milked twice a day: early morning and late afternoon. Milk obtained at the morning milking is much lower in fat (e.g. 3 . Cows must calve to produce milk and the lactation cycle is the period between one calving and the next.

The cycle is split into four phases, the early, mid and late lactation (each of about 120 days, or d) and the dry period (which should last as long as 65 d). In an ideal world, cows calve every 12 months.

A number of changes occur in cows as they progress through different stages of lactation.

As well as variations in milk production, there are changes in feed intake and body condition, and stage of pregnancy. Figure 1 presents the interrelationships between feed intake, milk yield and live weight for a Friesian cow with a 14 month inter-calving interval, hence a 360 d lactation.

Following calving, a cow may start producing 10 kg/d of milk, rise to a peak of 20 kg/d by about 7 weeks into lactation then gradually fall to 5 kg/d by the end of lactation.

Although her maintenance requirements will not vary, she will need more dietary energy and protein as milk production increases then less when production declines. However to regain body condition in late lactation, she will require additional energy.

Cows usually use their own body condition for about 12 weeks after calving, to provide energy in addition to that consumed. The energy released is used to produce milk, allowing them to achieve higher peak production than would be possible from their diet alone.

To do this, cows must have sufficient body condition available to lose, and therefore they must have put it on late in the previous lactation or during the dry period.

From Calving To Peak Lactation

Milk yield at the peak of lactation sets up the potential milk production for the year; one extra kg per day at the peak can produce an extra 200 kg/cow over the entire lactation.

There are a number of obstacles to feeding the herd well in early lactation to maximise the peak. The foremost of these is voluntary food intake.

At calving, appetite is only about 50 to 70 per cent of the maximum at peak intake. This is because during the dry period, the growing calf takes up space, reducing rumen volume and the density and size of rumen papillae is reduced.

After calving, it takes time for the rumen to “stretch” and the papillae to regrow. It is not until weeks 10-12 that appetite reaches its full potential.

Peak Lactation To Peak Intake

Following peak lactation, cows’ appetites gradually increase until they can consume all the nutrients required for production, provided the diet is of high quality. From Figure 1, cows tend to maintain weight during this stage of their lactation.

Mid and Late Lactation

Although energy required for milk production is less demanding during this period because milk production is declining, energy is still important because of pregnancy and the need to build up body condition as an energy reserve for the next lactation. It is generally more efficient to improve the condition of the herd in late lactation rather than in the dry period.

The two major factors determining total lactation yield are peak lactation and the rate of decline from this peak. In temperate dairy systems, total milk yield for 300 day lactation can be estimated by multiplying peak yield by 200.

Hence a cow peaking at 20 litres per day (L/d) should produce 4000 L/lactation, while a peak of 30 L/d equates to a 6000 L full lactation milk yield. This is based on a rate of decline of 7 to 8 per cent per month from peak yield, that is every month the cow produces, on average, 7 to 8 per cent of peak yield less than in the previous month.

This level of persistency is the target for well managed, pasture-based herds in temperate regions.

Actual values can vary from 3 to 4 per cent per month in fully fed, lot fed cows to 12 per cent or more per month in very poorly fed cows, for example during a severe dry season following a good wet season in the tropics.

The rate of decline from peak, or persistency, depends on:
• peak milk yield
• nutrient intake following peak yield
• body condition at calving
• other factors such as disease status and climatic stress

Generally speaking, the higher the milk yield at peak, the lower its persistency in percentage terms.

Underfeeding of cows immediately post-calving reduces peak yield but also has adverse effects on persistency and fertility. Dairy cows have been bred to utilise body reserves for additional milk production, but high rates of live weight loss will delay the onset of oestrus.

Underfeeding of high genetic merit cows in early lactation is one of the biggest nutritionally induced problems facing many small holder farmers in the humid tropics, because they often do not have the necessary improvements in feeding systems to utilise high genetic potential.

If imported high genetic quality cows are not well fed, milk production is compromised, but of more importance, they will not cycle until many months post-calving.

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