Research Results - (PDF, 101 mb) - USAID

expect, animal daily gains were influenced by
stocking rate despite the grazing behavior
compensations. The temporal data series on
grazing behavior and intake suggested that
seasonal changes in the vegetation were more
impoi rant than stocking rate in determining diet
and animal production, within the range of
stocking rates tested.
As with all stocking rate studies, conclusions
from only one year of data must be treated
with caution. The spring of 1989 was relatively
dry compared to that of 1990. Fortunately the
stocking rate trial was repeated in 1990 at the
same location with the same methodology, and
hopefully will be repeated again in 1991. The
three years of data, which include estimates of
forage available in each treatment over the
study season, will comprise a most valuable
data set. The third year of data should begin to
show whether the higher levels of stocking rate
affect vegetation composition and productivity,
a key question from a management point of
view.
The native vegetation has difficulty
maintaining livestock on a positive plain of
nutrition during the summer months. Many
sheep owners rely on access to post-harvest
cereal stubble, waste patches around irrigated
fields or supplementary feeds to bring small
ruminants up to market weight by the end of
summer. The stocking rate trial at Ain Beni
Mathar has a included a supplementary feed
treatment to address the problems of the summer
forage shortage.
The data from the first year of the study
(1989) were analyzed in the current reporting
period (1989-90), and data collected in 1990 were
prepared for analysis later in 1990. The timing
of data analysis is related to the schedules of
students working on the project who are using
the SR-CRSP research for their Memoires. The
results of the stocking rate trial will be published
after the three years of data have all been
analyzed. This paper will be largely a description
of the treatment effects, comparing seasons
and years, and looking at cumulative impacts on
the vegetation. A second paper will examine the
role of feed supplements during the summer.
This particular piece of research should
make a significant contribution to the literature.
There are few grazing trials that have employed
more than two or three stocking rates; many
studies last only one or two years; and such
trials as the SR-CRSP work reported here are not
often conducted in the semi-arid zone. Furthermore,
other grazing research by the Moroccan
scientist directing the study (Ahmed El Aich) in
the more humid Middle Atlas region with a
different breed of sheep provides an opportunity
to examine some theoretical questions on
the effects on stocking rate on livestock production.
Synthesis and Theory
A key aspect of the collaborative research
in 1989-90 was to develop a series of
analytical approaches to the treatment of the
data. Stocking rate experiments are confounded
by variability in forage on offer from year to
year, as well as from season to season. The
effect of a specific stocking rate on daily weight
gain will vary depending on that year's forage
cupply, or the forage available in a particular
month. That is why it is critical to conduct
stocking rate trials over several years, especially
in a semi-arid environment where rainfall is
highly variable. But the analysis and interpretation
of such variable data has often presented
problems For each curve relating stocking rate
to daily weight gain, however, there is always
one data point that represents the stocking rate
at maximum production per hectare. These data
points can be graphed in relation to season, or
for comparing years in terms of peak biomass,
or used to compare sheep breeds and contast
their ability to be productive under adverse
conditions. Another approach to minimizing
the influence of temporal variability in data
analysis is to employ grazing pressure instead of
stocking rate as the independent variable, where
grazing pressure is expressed as intake relative
to available forage. By this means we can
determine at what point in a situation of declining
forage the intake is affected, which should
be an attribute of the specific breed of sheep.
The SR-CRSP and Middle Atlas data sets also
allow us to examine different ways to quantify
how animals compensate for declining forage
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