The aim of this work was to investigate the effect of exercise
(walking a specified distance for a fixed number of days) on the
lactational performance of pregnant cows and to investigate the
effect of diet on the lactational response to exercise. The results
of the reseach are particularly applicable to the effects of
exercise on the lactational performance of cows which are used as
draught animals in tropical countries.
A literature review was carried out of the role of cows as
draught animals in tropical farming systems, of the metabolites
used for muscular activity and lactation, factors which affect the
supply of these metabolites and the effect of exercise on
lactational performance, body weight change and food intake.
Three experiments were done to investigate the effect of
exercise on milk yield, milk constituent yield (g/d), milk
constituent content <g/kg milk), body weight change, blood
metabolite concentrations and the voluntary intake of barley straw.
The effect of five different diets on the response of the above
variables to exercise was also investigated.
The experiments were carried out at the Easter Howgate Farm six
miles south west of Edinburgh using in each instance twelve
pregnant, lactating crossbred Hereford x Friesian cows in their
second or subsequent lactations. The animals were exercised in the
Peritland Hills for three five day periods each separated by two
non-walking days. They walked approximately 8.8 kilometres each
day and climbed a vertical distance of approximately 480 metres a
day. This exercise was calculated to be equivalent to an energy
expenditure of approximately 12MJ per day or a quarter of the
maintenance energy requirement of the animals.
It was found that the exercise carried out caused a milk yield
reduction of between 7 and 14 percent depending on diet. Milk
yields declined on walking days and recovered to almost non-walking
levels on the intervening non-walking days. Milk fat content
increased as milk yield declined, with the result that the daily
yield of milk fat was not affected by exercise. Milk protein
content and lactose content were not markedly affected by exercise,
with the result that the daily yields of these two milk
constituents declined approximately in proportion to the decline in
When animals walked, their rate of weight gain was not as great
as when they were not walking. Animals on some diets lost body
weight when they walked. After walking animals on all diets
increased weight faster than prior to the walking period and in
most cases achieved the expected weights (based on extrapolations
from the first non-walking period weight gains) by the end of the
experiment. It appeared that exercise may have caused changes in
gut-fill which influenced body weight.
Measurements of the concentrations of blood metabolites showed
increases in the concentrations of (3-OH butyrate and free fatty
acids and decreases in the concentrations of glucose, magnesium and
inorganic phosphorus. The response of blood metabolites to exercise
was influenced by diet and some adaptation to exercise was observed
over the three week walking period. These changes were indicative
of energy deficits when the animals exercised and in some cases
were similar to the changes in blood metabolites observed by other
authors in fasting animals
The intake of barley straw offered ad libitum and supplemented
with one of three diets was not affected by exercise.
No measurements were made of the products of digestion, but it
appeared that diets which might be expected to sustain high rates
of fermentation and high levels of propionate production supported
lactational performance during exercise better than diets which
were designed to supply larger quantities of rumen undegradable
protein and starch.
It was calculated that cows offered some diets were in energy
deficit when they walked and concurrent weight losses were
observed. In other groups however, although cows were in negative
energy balance, positive weight gains were measured. Gut-fill
changes, increased weight of concepta and changes in fat to lean
tissue ratio might explain these observations.
No adverse effects of exercise were observed in the animals and
all animals subsequently calved successfully.
It was concluded that the levels of energy expenditure
experienced by the cows in the present experiments would have no
long-term adverse effects on the lactational performance of the
animals and that while milk yields would suffer in the short term,
if working periods were separated by two or more non-working days,
milk yields would recover to near pre-work levels. The consequences
of heavier work, greater daily levels of energy expenditure, work
sustained for longer periods of time without intervening nonworking days, work carried out at different stages of lactation and
work carried out by animals fed tropical diets is worthy of further