Browsing by Author "Burger, Marelee"

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    Studies on the genetics of ovine behaviour in a Western Cape resource flock aimed at improving animal welfare
    (Stellenbosch : Stellenbosch University, 2019-04) Burger, Marelee; Cloete, Schalk W. P.; Dzama, Kennedy; Cloete, J. J. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Data were collected on a Merino resource flock on the behaviour of ewes and lambs from 1993 to 2002. This flock was divergently selected from the same base population since 1986 for the number of lambs weaned per mating (NLW). Selection resulted in two selection lines, namely the High line (H line, upward selection for NLW) and the Low line (L line, downward selection for NLW). Additionally, the effect of these behaviours and selection lines were reported for NLW and lamb survival, as a key welfare indicator trait. Data from arena behaviour on Merino weaners were also collected over a 15-year period using the same resource population divergently selected for NLW. Ram lambs, progeny of mature ewes and singles were heavier at birth than ewe lambs, progeny of young and old ewes and multiples respectively. H line lambs had shorter lengths of parturition than L line lambs, where this difference was also found in H line and L line ewes. The effects of dam age were significant for the latency from birth to suckling as it improved with ewe age, and in both ewe and lamb studies H line ewes had better maternal cooperation scores than L line ewes. Maternal cooperation also had a significant effect on the latency for the lamb to progress from birth to suckling and maternal cooperation score improved with age in ewes. H line ewes had an improved NLW compared to L line ewes while H line lambs had a better survival. For production traits, H line lambs derived from embryo transplants were heavier at yearling age, had a lower fibre diameter, less wrinkles at the neck, body, breech and overall when compared to L line lambs. Survival of lambs reared by surrogate dams was higher in the H line than in the L line. Single-trait direct heritability estimates (h²) in lambs were 0.15 for birth weight, 0.07 for lamb survival, 0.06 for length of parturition, 0.12 for latency from birth to suckling and 0.00 for maternal cooperation score. Direct heritability estimates, assessed as trait of the ewe, were 0.04 for NLW, 0.17 for length of parturition, 0.07 for maternal cooperation score and 0.20 for the interval ewes remained on or near their lambing sites. Genetic trends suggested divergence between the lines for breeding values for length of parturition, suggesting that parturitions became shorter in the H line and longer in the L line. The results and parameter estimates obtained, suggested that selection for improved NLW would yield desirable outcomes for ewe behavioural traits. Maternal permanent environment variance ratios (c²) were 0.07 for lamb survival and 0.17 for maternal cooperation score. Survival of the lamb was favourably correlated to the length of parturition and maternal behaviour score on the genetic level. It was evident that neonatal behaviour was, to an extent, under genetic control in paddock-reared sheep. In the arena test, animals from the H line approached closer to stationary human seated between the test animal and its flock mates and had fewer urination and defecation events than their L line contemporaries but travelled longer distances in the arena. The distance the lambs maintained from the human operator (0.08), urinating events (0.13), and defecating events (0.04) were all lowly heritable. However, the number of lines crossed (0.22) and the number of bleats (0.35) were moderately to highly heritable. Selection for NLW and certain neonatal and perinatal ewe behaviours would benefit the welfare of ewes and lambs. From the arena test it was also evident as H line lambs experienced lower levels of stress in the contrived area environment.