Graduate Thesis Or Dissertation
 

Sheep selection in retrospect

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  • A total of 399 crossbred ewes from two birth years were raised under two management systems, irrigated vs. dryland hill pastures. The crossbred ewes were sired by North Country Cheviot, Dorset, Finnsheep and Romney rams that were mated to Suffolk and Columbia-type ewes. Hampshire rams were the terminal sire breed used to mate the crossbred ewes throughout the experiment. Total feed cost and gross income from feeder and orphan lambs were estimated per ewe for either 4 or 5 potential years of production. Efficiency was defined as estimated dollars net revenue per ewe, the difference between estimated gross income and estimated feed and ewe ownership cost. Crossbred group and crossbred group x management system interaction significantly affected net revenue. The relative merit of crossbred groups was strongly dependent upon the environment in which the comparison was made. Ten ewe lamb traits were then used (individually and in combinations) in regression analyses to determine their relationships with lifetime production efficiency (LPE). The ewe's within-year birthdate, postweaning average daily gain, age at first estrus and lambing date during her first production year were not predictive of subsequent LPE. Ewes born as triplets had better future LPE than those born as either twins or singles (P < .05), but single-born ewes surpassed twins in LPE. Actual weaning weight (WWt), weaning weight adjusted for age of dam, date of birth and type of birth and rearing (AWWt), postweaning weight (PWWt) and lamb production and net revenue of ewes mated to lamb at 12 months of age were correlated to the ewe's LPE (P < .05). Results of "paper selection" involving single traits, independent culling level based upon birth type and postweaning weight and backward selection showed that either of the three ewe lamb weights (WWt, AWWt, PWWt) was a good predictor of future cumulative and subsequent ewe productivity (excluding first year contribution). None of the ewe lamb early life traits was predictive of ewe longevity, i.e., the ability to survive the entire duration of the experiment. It is suggested that a selection scheme, perhaps an index, including type of birth and either of the three weights could be most efficient in predicting the maximum LPE per ewe.
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  • File scanned at 300 ppi (Monochrome) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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file details SaoudNabeelB1983.pdf 2017-08-23 Pubblico Scaricare