Causes and effects of the most common
production diseases of high producing
dairy cows
Oorsig/Review
Dietmar Holm and Martin van der Leek
Department of Production Animal Studies,
Faculty of Veterinary Science, University of Pretoria
[email protected]
From Southern Cape Proceedings 2018
PART 01
COMMON PRODUCTION DISEASES:
CAUSES AND EFFECTS ON HIGH
PRODUCING DAIRY COWS
Production diseases are also known as metabolic
diseases, which is a bit of a misnomer. In human
and small animal medicine the term metabolic
disease implies some inherent defect in the
metabolic processes of a patient like a deficiency
in a vital enzyme. This may lead to failure of a
metabolic pathway and the accumulation of
certain metabolites.
Homeostasis is the preservation of an equilibrium
in the body through complicated endocrinological
systems. In production diseases this balance
is disturbed, usually not due to a failure of the
endocrinological control system, but due to an
imbalance between the rate of input of dietary
nutrients, the rate of metabolic processes and
the rate of output of production. Examples of
these are milk fever, where there is an imbalance
between calcium metabolism and output, and
ketosis, where there is an imbalance between
energy input and output.
High producing animals produce so much that
no naturally occurring diet can maintain a
positive nutritional balance. This situation was
brought about by the ongoing selection for higher
production, together with the relative neglect of
the improvement of management practices to
sustain such high production.
Production diseases are most important amongst
lactating dairy cows and pregnant ewes. The
reason in lactating dairy cows is that they will
continue to produce milk even when their
body reserves are depleted, because they have
been genetically selected to do so over many
18
generations, by physiologically separating the
control of milk production from the control of
homeostasis. Ewes on the other hand, become
affected during late gestation when the source
of increased output, the fast growing foetus(-es),
can not be ‘removed’ to correct the imbalance.
From the following table, it is clear that the
reason why certain metabolites are more likely to
lead to production diseases, is that the available
reserve pool of these metabolites is small relative
to the throughput. Take for instance Calcium,
where the throughput can be up to 10 times the
amount of the available (serum) reserve. This
leads to a very finely ‘tuned’ homeostasis that can
be disturbed easily.
The dry period should be regarded as a
preparatory period and as an investment for
optimal health and performance in the subsequent
lactation. Stress should be minimised as this
has been recognised as a common risk factor
for many production diseases. The rumen must
be adapted gradually to the higher energy diet
that will be fed in early lactation. Normal serum
calcium levels must be maintained to reduce the
risk of diseases associated with clinical and sub-
clinical hypocalcaemia. The maintenance of a
strong immune system and a positive energy
balance up to the time of calving is critical. The
close–up diet should be formulated as accurately
as possible to provide the required nutrients and
have an appropriate balance between anions and
cations.