- I. The Effects of Sire Breed, Forage Availability and Weather on the
Grazing Behavior of Crossbred Ewes.
Thirty nonpregnant, nonlactating crossbred ewes, six per sire
breed (Suffolk, Clun Forest, Dorset, Polypay and Border Leicester),
were observed grazing together in a 0.87 ha grass-clover pasture for
six days over a two-week period. Observations were taken every ten
minutes during the daylight hours (06.00-21.00 h Pacific daylight
time), when they were allowed to graze, and consisted of a location
and activity recording. Fecal samples were collected and analyzed for
crude protein content as an indicator of the quality of the diet
The daily grazing pattern consisted of heavy AM grazing until
about 10.00 h and heavy afternoon grazing after about 16.00 h. Cool,
cloudy days had less distinct grazing periods than warm, sunny days.
Average time spent grazing was 9.23 h (4.11 h AM and 5.12 h PM)
and the average times of AM stop and PM start were 10.23 h and 14.59
h, respectively. Average distance traveled was 1.39 km (0.76 km AM
and 0.63 km PM). Sire breed had no effect on either grazing time or
distance traveled. Weather had a greater effect on grazing time but
forage availability had a greater effect on distance traveled. Sire
breeds (averaged over days) differed in their grazing site preference,
and grazing site preference varied over the six observation days
(averaged over breeds). The average % fecal crude protein (% FCP) was
9.51%. Breed differences were not significant (P>.05), and the % FCP
declined as forage availability declined over time.
A ewe's AM and PM grazing times were not correlated but time of
AM stop and PM start were negatively correlated. Grazing time and
distance traveled were only moderately correlated, as were distance
traveled and % FCP. Change in body condition score from the beginning
to the end of the trial was positively correlated with distance and %
FCP, but body weight change was not correlated with any of the grazing
behavior components examined.
II. The Relationships Among Body Weights, Conditions Scores and Lamb
Production Traits in Crossbred Ewes.
Body weights, condition scores and lamb production traits were
measured periodically throughout two production years on 239 Panama
crossbred ewes born in 1980 and 1981 and sired by Suffolk, Clun
Forest, Dorset, Polypay and Border Leicester rams.
Maximum and minimum weights and condition scores occurred at
prelambing, weaning, prebreeding and early lactation, respectively.
Significant breed differences were found for nearly all seasonal
weights, some condition scores, none of the weight and condition score
changes, a few of the lamb production traits and average ewe weight.
Suffolk crossbred ewes were the heaviest, Dorset crossbreds were the
highest in condition and Clun Forest crossbreds weaned the most lambs.
The correlations between each ewe's mean weight and mean
condition score and regression coefficients of ewe's mean weight on
mean condition, for the 1980 and 1981 birthyear ewes were 0.55, 11.5
kg/unit; 0.66 and 9.9 kg/unit, respectively. Correlations between
lamb production traits and mean weight, coefficient of variation (CV)
for weight, mean condition score and CV for condition score were
positive, negative, nonsignificantly negative and near zero,
Numerous correlations between weight or condition score at key
periods and previous or subsequent lamb production were examined.
Prebreeding weight had a positive linear effect in both the 1980 and
1981 ewes (b= 0.029 and b= 0.025 lambs born/ewe/kg, respectively).
Also for 1980 ewes, prebreeding condition score had a negative
influence on number of lambs born (b= - 0.263 lambs/condition score
unit), while condition score change during flushing had a positive
impact (b= 0.466/unit change in condition score). Increase in
condition score during the prebreeding period had a positive effect on
the number of lambs born at lower levels of initial condition score.
All of the body weights and some of the condition scores at key
periods were repeatable between production years, while weight and
condition score changes were not. The number of lambs born per ewe
was repeatable (0.20) in the 1980 ewes and lambing date was repeatable
(0.26) in the 1981 ewes.