Article by Dr Carel Muller
Directorate: Animal Sciences, Research & Technology Development Services,
Elsenburg
I
ntroduction
The nutritional requirements of dairy cows have
been established in different feeding trials under
controlled conditions. The chemical composition
of feeds has been determined in laboratory analyses using standard methods and is described in a
number of reference manuals. Additional components
are estimated from basic nutrient components. Therefore, in practice, the feeding of dairy cattle rests on
these two principles, i.e. the nutritional requirements
of cows and the chemical composition of feeds. However, feeding dairy cattle practically, it is difficult to use
the science of these two components to their full extent. Farmers and their advisors must try to satisfy the
“estimated” nutrient requirements of the “average”
cow based on its “expected” daily feed intake using the
chemical values of feeds as recorded in a number of
reference manuals. The problem is that the actual nutrient requirements of dairy cows differ from estimated
values because the average cow does not exist as each
cow has its own nutrient requirements as determined
by its live weight, feed intake, body condition, milk
yield and milk composition. Therefore, while using all
this information it is possible that not all cows are fed
correctly all the time. Fortunately dairy cows have the
ability to buffer the negative effect of over- and underfeeding during their production cycle by using their
own body reserves stored away as adipose tissue (fat).
By monitoring the breaking-down and recovery of the
body reserves of cows, feeding management could be
improved bringing it closer to feeding cows in a more
scientific way. The response to feeding changes can be
done by monitoring the live weight and body condition
as indicators of the body reserves of dairy cows.
The live weight and body condition score of dairy
cows
Lactating dairy cows show a specific trend with regards
to their live weights which is affected by their body
condition as indicated by a body condition score. At
Elsenburg Holsteins cows are weighed and their body
condition, as an indicator of the amount of body reserve, is scored using the Mulvany body condition scoring system. This system scores the amount of fatty tissue under the skin of cows at the tail head and loin
areas as an indication of the cows’ body reserves. The
change in live weight and body condition score for Holstein cows in different lactations is shown in Figure 1.
The live weight of cows is affected by age (lactation
number) with cows showing an increase in live weight
within each lactation period and up to third lactation.
On average the live weight of cows in first, second and
third-plus lactation was about 500, 560 and 600 kg
respectively. On the other hand, the lactation curve for
body condition score was the same for cows in all lactation periods, i.e. cows losing body condition during
the early part of the lactation reaching nadir at about
60 days after calving after which the condition of cows
increases as each lactation period progresses. The decrease in live weight is the result of the loss in body
condition during the early part of the lactation.
The lactation curve for milk production follows a trend
that is opposite to that of the live weight and body
condition curves. Milk yield increases after calving
reaching a peak production at about 60 days after calving after which the daily milk yield starts to decline towards the end of the lactation period. The reason for
the reduction in the live weight and body condition is
because feed intake of cows early in the lactation is not
sufficient to satisfy the nutritional requirements for
cows just after calving and into the early lactation period because of a rapid increase in milk yield. Often, just
before calving, cows lose their appetite and eat very
little at or around the time of calving down. The initial
low voluntary feed intake and increasing energy requirements for the production of milk results in cows
going into a negative energy balance with regards to
milk production. For this reason the breakdown of
body reserves aids in the production of milk during ear-