Graduate Thesis Or Dissertation
 

Estimation of general and specific combining abilities from a diallel cross of three inbred lines of Suffolk sheep

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  • The investigations were based on a complete diallel cross among three inbred lines of Suffolk sheep. Line of sire effects were assumed to be an estimate of general combining ability effects while sire x dam interaction was assumed to be an estimate of specific combining ability. The line of dam effects were also a measure of general combining ability plus any maternal effects that were present. General and specific combining ability effects were observed for birth weight, 120-day adjusted weaning weight, and conformation and condition scores at weaning. The linecross individuals were generally superior to the inbred lambs for all six traits studied on the lambs produced by the diallel matings. Among the linecrosses, considering all six traits, 3 x 1 and 1 x 3 appeared to be the superior crosses implying that lines 1 and 3 combined more effectively than either lines 1 and 2 or lines 2 and 3. Significant general combining ability effects were not observed for any of the traits studied on the lambs born from diallel matings. Significant specific combining ability effects were observed only for yearling wool weight. Significant line of dam effects were observed for birth weight and yearling wool weight indicating a possibility of maternal effects for these two traits. The linecross ewe lambs produced by the diallel matings were bred as yearlings and two-year-olds to a common sire to obtain two lamb crops for evaluation of the lamb producing ability of the linecross ewes. No straight line ewe lambs were included. Estimates of general combining ability and reciprocal effects were obtained on the lambs produced by these linecross ewes. Year effects were removed before estimates of general combining ability and reciprocal effects were obtained. Observations were made of birth weight, 120-day adjusted weaning weight, conformation and condition scores at weaning, endocrine gland weights, detailed carcass information, and organoleptic and cooking evaluations. The endocrine glands weighed were right and left adrenals, pituitary, and thyroid. Carcass characteristics observed were cold carcass weight, carcass grade and length, fat thickness, and rib eye area as well as brisket-flank-and-shank, shoulder and neck, rack, trimmed loin, trimmed legs, fat trim, and kidney knob percentages. A seven rib rack was used to determine percent total loss in cooking, percent drip, tenderness, juiciness, flavor of lean, flavor of fat, and overall score. Significant general combining ability effects were observed for carcass grade, fat thickness over the 12th rib, percent fat trim, percent kidney knob, and percent trimmed legs. All other traits exhibited a lack of either general combining ability or reciprocal effects. Line 1 was the highest in general combining ability for carcass grade and percent kidney knob while line 3 was the greatest in general combining ability for fat thickness and percent fat trim, which was considered an undesirable trait. Line 2 was the most effective in general combining ability for percent trimmed legs. Considering the entire study, line 1 was the most effective combiner followed by lines 3 and 2, respectively. The 1 x 3 and 3 x 1 linecross lambs of the diallel matings appeared superior. Linecross 1 x 3 and 3 x 1 ewes produced crossbred lambs of outstanding quality when compared to the lambs from the other linecross ewes.
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file details SchillingPrentissE1967.pdf 2017-08-14 Pubblico Scaricare