Sheep breed evaluation : grazing behavior, condition scores and lamb production Public Deposited

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  • 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 selected. 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, respectively. 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.
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