In dairy cattle, treatment with exogenous growth hormone (GH) affects growth and function of mammary gland. The actions of GH are mediated via interaction with GH receptors (GHR). The first step in signal transduction is homodimerization of two GHR molecules by GH. This step is critical since mutation in either GH or GHR can block dimerization and thus target cell activation. However, association between milk related traits and combination of GH and GHR variations are not known. Accordingly, DNA genotypes in the GH and GHR genes were investigated for association with milk, fat and protein lactation yields in Holsteins. The marker data were obtained on 873 progeny tested bulls by using PCR-RFLP and PCR-SSCP analysis. There were five markers in GH and three in GHR. Estimated breeding values (EBVs) were obtained from Canadian Dairy Network for milk, fat, and protein lactation yields for the 873 genotyped bulls. / There was significant difference among GH6.1 alleles (C-to-G transversion at position 2141) for the milk yield (P < 0.05) and protein yield (p < 0.05). There were significant differences in GHR AluI (A-to-T transversion at -1182) for milk (p < 0.05) and fat (p < 0.05), and GHR StuI (C-to-T transversion at -232) for fat (p < 0.0001) and protein (p < 0.05). Allele frequencies for GH6.1 (C), GHR AluI (A) and GHR StuI (C) alleles in bulls genotyped were 0.95, 0.63 and 0.95, respectively. Bulls with GH6.1 (C/G) genotype had higher milk EBV (p < 0.05) compared to C/C bulls. Bulls with GHR AluI (A/A) genotype had higher milk EBV (p < 0.01) and fat EBVs (p < 0.05). Bulls with StuI (C/C) genotype had higher fat EBV (p < 0.0001) and protein EBV (p < 0.05) compared to StuI (C/T). This study indicates that the combination of GH and GHR markers could serve as a tool to aid in selection for improving milk, fat, and protein production.

Increase in profits corresponding to a one unit increase in Estimated Breeding Value (EBV) for 3 production traits and for 21 type traits were estimated from 31,123 merged "Official" first lactation records, type records and Estimated Breeding Value (EBVs) records of Canadian Holstein cows using multivariate REML and a mixed model accounting for herd and year of calving effects. The same regression model was used to estimate the same profit increases corresponding to a one unit change in EBVs from 336 merged "Non-Official" first lactation records, type records and EBV records of Canadian Holstein Cows to investigate whether purebred breeders are selecting their animals according to type and production performances while commercial producers are selecting animals that maximize their milk profits. Finally, the usefulness of DHAS cow records for increasing milk profits was investigated by comparing the average profit level of cows with "Official" milk records and their time of registration under the DHAS scheme. / Size had the largest negative impact on profits, with estimates ranging from $-$41.70 $ pm$ 6.60 to $-$26.62 $ pm$ 5.91. Chest width and fore attachment had the largest positive impact on profits, with estimates ranging from 4.30 $ pm$ 5.94 to 16.82 $ pm$ 6.00 and from 4.71 $ pm$ 3.52 to 14.57 $ pm$ 3.97 respectively. Grade cows were found to have on average lower EBVs for most type and production traits than purebred cows. However, grade and purebred cows generated similar milk profits. Finally, the efficiency of using information provided by DHAS to increase profits did not increase with the number of years of participation with DHAS.

This trial was carried out in order to elucidate factors affecting milk urea nitrogen (MUN). Twenty-five herds were selected for MUN testing. Three sampling periods were chosen. The first occurred during the months of March and April, the second during July and August, and the third during November and December 1997. A total of 2,686 samples were collected and analyzed. Two different methods were employed for MUN analysis and were referred to as the Macdonald Campus method (MUN-MAC) and the Programme d'Analyse des Troupeaux Laitiers du Quebec method (MUN-P.A.T.L.Q.). The MUN-MAC consists of an enzymatic method while the P.A.T.L.Q. method is an infra-red method. Prior to initiation of the trial, the MUN-MAC method was validated and found suitable for use in this experiment. The results demonstrated that the factors which significantly contributed to the models were the ration's net energy of lactation, season, region, somatic cell count, total dry matter, neutral detergent fiber, non-structural carbohydrates, total fat, crude protein, protein to energy ratio, starch to protein ratio, parity and days in milk. (Abstract shortened by UMI.)

No description available.

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

No description available.

No description available.