Université Abdelhamid Ibnbadis Mostaganem
Faculté de la sciences de la nature et vie
Filiè re : Sciè nes alimentaires
Spé cialité : Technologie agroalimentaire et contrô le de qualité
Effects of stocking rate and physiological state of
meat goats grazing grass/forb pastures on forage
intake, selection, and digestion, grazing behavior, and
performance
Presented by:
• SOUFI Salima.
• TOUTA Asmae.
1. Introduction:
The study investigated the effects of forage conditions with
different stocking rates on the performance and grazing behavior of
Boer goats at different physiological states. The experiment
involved Boer goat does nursing two kids, growing wethers, and
yearling wethers grazing on grass/forb pastures for a period of 114
days.
The forage mass and botanical composition of the diet were
similar among animal types, while the digestibility of organic
matter was highest for growing wethers. Intake of
metabolizable energy was greater for animals at a low stocking
rate compared to a high stocking rate. There was an interaction
between animal type and period in average daily gain and time
spent grazing , with differences in metabolizable energy intake
among the different physiological states and periods.
The study concluded that forage mass above 1400 kg/ha
would not benefit the performance of meat goats regardless of
their physiological state and nutrient requirements.
II. Problematic:
What are the effects of stocking rate and
physiological state of meat goats grazing
grass/forb pastures on forage intake, selection,
and digestion, grazing behavior, and
performance?
Hypothesis:
Matching stocking rates with the physiological state of meat goats
grazing grass/pastures is expected to impact forage intake,
selection, digestion, grazing behavior, and ultimately, overall
performance.
III. The main stages of the experiment:
Materials and methods
•Animals and treatements:
-The experiment was conducted ethically
with approval from the Langston
University Animal Care Committee.
-Boer goats of different physiological
states were used in the experiment.
-The goats were divided into high and
low stocking rate groups and placed in
pastures with bermudagrass and ragweed.
-The animals were treated with Cydectins
before the experiment, with the assumption
that internal parasite burden was similar among
physiological states.
•Measurments:
-Goetsch et al. conducted a 114-day experiment using IceTag
activity monitors and GPS collars to study grazing behavior in
goats.
-Animal measures such as weight and forage mass were taken
at the beginning and middle of each period, with temperature
and humidity monitored regularly.
-GPS collars were used to estimate distance traveled and time
the head was in a 'down' position, with data being post-
differentially corrected.
- Despite some data collection issues, the study aimed to
develop prediction equations for estimating grazing/eating
times and behaviors of animals, finding no discernible
differences in forage selection among animal types.
•Calculations and statistical analyses:
-n-alkanes were used to estimate botanical composition
of forage selected in a grazing experiment with goats.
-Least squares optimization procedure with Excel
Solver was used to determine botanical composition.
-Recovery of n-alkanes was determined after the
grazing experiment.
- Digestibility of dry matter and other nutrients was
calculated based on forage and fecal concentrations of
n-alkanes.
Results:
•Temprature and humidity:
-Temperature and THI were highest in period 3 and lowest in period 4.
-Forage mass was not affected by stocking rate, period, or their interaction.
-The IVDMD of simulated grazed forage samples was higher for low
stocking rate compared to high stocking rate.
-IVDMD was highest in period 2 and greater in period 1 compared to period
•Intake and digestion:
- Differences in botanical composition of the diet were observed,
with high intake of johnsongrass in period 1 and ragweed in period
3.
-The crude protein (CP) level was highest in period 3, while the
neutral detergent fiber (NDF) concentration was lower in period 3
compared to periods 2 and 4.
-Digestibility of dry matter (DM) and organic matter (OM) was
highest among growing wethers, leading to similar intake of
digestible OM and energy between growing and yearling wethers.
- Rate of metabolizable energy intake (MEI) was highest for does,
and similar between growing and yearling wethers. NDF
digestibility was unexpectedly low in period 3.
•BW and ADG:
-Stocking rate did not affect animal performance or behavior variables.
-Body weight rankings differed among lactating does, yearling wethers,
and growing wethers.
-Differences in average daily gain (ADG) varied among periods for each
animal type.
-ADG was lowest for does in period 3, and values for growing and
yearling wethers were also low in that period.
-Kid BW and ADG were not impacted by stocking rate.
-Kid ADG was significantly higher in periods 142 and 443.
-There were interactions between animal type and period in predicted ME
intake.
- Predicted ME intake was lowest in period 3 and greater for does
compared to wethers.
•Grazing behavior:
-Grazing time varied between animal types and periods, with
yearling wethers spending less time grazing in period 1.
-The percentage of time spent grazing during daytime hours
was higher in period 4 compared to other periods.
-Resting behavior while lying was influenced by specific time
periods and stocking rates, but not by animal type.
- Time spent walking was similar among animal types, with
some differences in periods, and distance traveled was not
affected by animal type or period.
Discussion:
•Stocking rate:
-High stocking rates led to higher average total animal body weight
compared to low stocking rates.
-Forage intake in period 1 was correlated with the highest average
daily gain.
-Stocking rate did not significantly impact average daily gain in
period 1 despite differences in forage intake.
- Forage mass levels above 1400 kg/ha did not limit performance of
meat goats, indicating their ability to select forage of sufficient
nutritive value.
•Animal type:
-Diet composition for different animal types was similar despite
differences in energy needs.
-Greater digestibility for growing wethers did not involve dietary
selection.
-Grazing goats of different physiological states together influenced
forage selectivity and behavior.
- Lactating does had a constant rate of ME intake and spent less time
grazing compared to other animal types.
•Period:
-There was a general agreement between period differences in average
daily gain (ADG) and estimates of forage intake and digestion, but not
a very close one.
-Factors such as cool conditions and lower nutritive value of available
forage may have influenced variations in grazing behavior among
periods.
-Differences in time spent grazing among animal types were
inconsistent across the four periods.
- The rate of metabolizable energy intake (MEI) can vary significantly
during a summer grazing season, with changes not related to forage
mass but to the changing nutritive value of the forage.
IV. Conclusion:
The study found that higher levels of forage mass above 1400 kg/ha
did not significantly benefit the performance of meat goats,
regardless of their varying nutrient requirements. Differences were
observed among animal types during grazing periods, with lactating
does and growing yearling wethers spending similar amounts of
time grazing.
The pattern of grazing time varied across periods due to changing
climatic conditions and forage nutritive value, with factors such as
forage intake rate and physiological states impacting meat goats'
grazing behavior. The study also emphasized the importance of
considering potential differences in pasture infective larvae levels of
internal parasites like Haemonchus contortus when evaluating
grazing performance.
Our opinion on the whole study:
Optimal stocking rates tailored to the physiological state of
meat goats are crucial for maximizing forage intake, digestion,
and overall performance. Matching stocking rates with forage
availability promotes natural grazing behavior and ensures
goats can select high-quality forage, leading to better digestion
and improved performance outcomes.
