Crossbreeding parameters (additive (a), dominance (d) and additive x additive (aa) epistatic effects for individual $ sp{ rm (I)}$ and for maternal $ sp{ rm (M)}$ performance) on body weight growth and first lactation performance traits of females from a crossbreeding experiment between Holstein (H) and Ayrshire (A) based lines were estimated by individual animal models, incorporating all known additive genetic relationships amongst animals, through restricted maximum likelihood and mixed-model methodologies. / The growth traits (asymptotic weight (A), rate parameter (k), inflection parameter (m), average lifetime absolute growth rate (AGR), average lifetime absolute maturing rate (AMR) and average lifetime relative growth rate (RGR)) were estimated by fitting the nonlinear equation, W$ sb1$ = A(1 $ pm$ be$ sp{ rm -kt}) sp{ rm M}$, to the observed weight-age data of 3076 individual females. / Results from the analyses of growth traits indicated that the H line exceeded the A line in addition genetic effects for individual performance (a$ sp{ rm I}$) for both A and AGR. The H line also exceeded the A line in additive effects for maternal performance (a$ sp{ rm M}$) in trait A. Both dominance (d) and additive x additive (aa) epistatic effects were statistically important in most cases. Individual heterosis (h$ sp{ rm I}$ = d$ sp{ rm I}$ $-$ 0.5aa$ sp{ rm I}$) was positive for traits A and AGR, whereas maternal heterosis (h$ sp{ rm M}$ = d$ sp{ rm M}$ $-$ 0.5aa$ sp{ rm M}$) was negative for A and positive for AMR. Total heterosis (TH = h$ sp{ rm I}$ + h$ sp{ rm M}$) had positive effects on AGR and AMR. For all growth traits, heterosis retained in advanced crossbred generations was statistically irrelevant. The overall conclusion was that crossbreeding systems designed to capitalize on TH would produce faster growing and earlier maturing animals. / The analyses of production traits found the additive effect of the H line for individual performance to be a major factor to increase yields of milk, protein and fat. On the other hand, line maternal and cytoplasmic source tended to favour the A line, but none reached statistical significance in any of the traits. Results indicate that two-line specific crosses or synthetic development would be sound breeding strategies for taking advantage of first cross heterosis or of line additive differences, respectively. / Estimates of crossbreeding parameters from mixed-model analyses, were found to be more reliable than those from ordinary least squares analyses. (Abstract shortened by UMI.)

Tierärztliche Hochsch., Diss., 2005--Hannover.

Freie Universiẗat, Diss., 2005--Berlin. / Dateiformat: zip, Dateien im PDF-Format. Erscheinungsjahr an der Haupttitelstelle: 2004.

The influence of the nutritive plane on the early growth of the Holstein calf has been investigated. Particular attention has been given to near-maximal growth rates, and to the ability of calves to exhibit compensatory growth after nutrient restriction is removed. A whole milk feeding standard, intended to allow maximum consumption, was established and used as the plane of nutrition for a group of high-plane calves. A second group of calves was fed milk at a lower plane for a period, before being realimentated to the same high plane that their contemporaries had received. Metabolic rate measurements were made on all calves at regular intervals. The animals of both groups were slaughtered at a body weight of 113 kgm (250 lb) and various measurements were taken from the dissected carcasses. The high-plane feeding standard proved to be quite satisfactory and permitted weight gains from 1.09 to 1.34 kgm/ day for the calves reared continuously on this plane. Highly reproducible rates of gain were displayed by the low-plane calves, both during the periods of restriction and realimentation. The growth rates of the low-plane calves in the latter period exceeded those of the high-plane animals, being from 1.45 to 1.6l kgm/day. The possible reasons for this increased growth capability are discussed in relation to the studies of other workers on compensatory growth. Nutrient restriction depressed the metabolic rates of low-plane calves below those exhibited by their high-plane partners of equal weight. Upon realimentation, the metabolic rates of the previously-restricted calves rose quite rapidly to levels commensurate with the heat losses of the high-plane animals. The carcass dissection studies did not reveal extensive modifications in body composition that could be attributed to the treatments. The growth of certain visceral organs was retarded or accelerated by the nutritive planes imposed, but the musculature and skeleton were apparently unaffected by the pattern of growth. The yield of edible meat was essentially the same for both groups of animals, despite a lower consumption of milk by the calves whose growth had been interrupted. A model, for comparison of the relative efficiencies of restricted and unrestricted meat-producing animals, is suggested. / Land and Food Systems, Faculty of / Graduate

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