Milk, fat and protein first lactation records of 27,137 British Columbia Dairy Herd Improvement cows were analysed for gross genetic and environmental influences. The average production was 5,663 kg of milk containing 3.59% fat and 3.23% protein. Age at freshening accounted for 3.0, .3.7, 3.7, .0.28 and 0.15% of the variance in milk, fat, protein, percent fat and percent protein respectively. Cows freshening in the winter had higher average milk, fat and protein yields than those freshening in summer; however, the percentage constituents of both fat and protein were higher for the summer cows than for the winter cows. Heritability of each characteristic and the phenotypic and genetic correlations between different characteristics were derived from paternal half-sib analyses with 100 sire groups. Heritability values were: milk 0.18; fat 0.24; protein 0.21; % fat 0.38, and % protein 0.47. Within herd-year-season phenotypic correlations between milk yield and the percentages were both negative, whereas the correlation between the constituent percentages was positive. Genetic trends in the cow population averaged 51.5 kg, 2.77 kg, 1.87 kg, 0.015% and -0.049% for milk, fat and protein yields and fat and protein percentages respectively. The dollar returns from incorporating milk, fat and protein yields and/or the constituent fractions in various selection indices were estimated for different levels of protein payment. Higher dollar returns will be expected from selection based on total yields than from selection based on either fat or protein percentage. Measuring protein for a genetic program will be feasible only when unrealistically high prices are paid for protein. / Land and Food Systems, Faculty of / Graduate

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Thesis (MSc (Agric)(Production Management)) -- University of Pretoria, 2007. / Includes bibliographical references.

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No description available.

This study was conducted to determine the relationships among the linear type traits of rump angle, rump width, rump length, rear legs side view, rear legs position, rear legs rear view, tailhead, vulva angle, mobility, pasterns, foot angle, and toes with reproductive performance (days open and times bred) in Holstein cows and to develop indices to predict reproductive performance from mathematical functions of the anatomical traits. Two trials were conducted. The first trial involved 7630 registered Holstein cows from Oregon and California. The regression analysis (R²) showed only 1.1% of the variability of times bred and 1.3% of the variability of days open was accounted for by the rump and rear leg type traits. In the second trial, 8155 Holstein cows, both registered and grade, were analyzed using the linear type traits of rump angle, rump width, rear legs side view, rear legs position, rear legs rear view and foot angle.. Grade and registered cows were analyzed separately to determine if differences in management between them would be reflected in the statistical analysis. Evaluator, lactation number (parity), season, geographic location, and the interaction of evaluator and lactation number had a significant effect on most of the type traits and the scorecard category (General Appearance, Mammary System, Dairy Character and Body Capacity) scores examined. The effects of these variables were statistically removed and the residuals of the type traits were used in the final regression analysis. Using stepwise regression analysis, several non-significant traits were omitted from the final model. The analysis used days open and times bred as dependent variables. Lactation number, mature equivalent milk, foot angle, rump width and their respective quadratics were independent variables, as were season calved and geographic location. The regression analysis (R²) indicated that 5.3% of the variability in days open and 4.7% of the variability in times bred in registered cows was accounted for by the type traits, foot angle and rump width, respectively, when the effects of season calved, geographic location, lactation number and mature equivalent milk were included in the model. For the grade cows the regression analysis (R²) indicated that 3.5% of the variability in days open was accounted for by foot angle. None of the type traits examined had a significant effect on times bred. This study detected no significant influence of rump angle or rear leg position, as described by the HFA linear classification program, on reproductive performance. However, our analysis indicated that fertility decreased as rear foot angles became more steep in grade and registered cows and as rump width increased in registered cows. / Graduation date: 1991

In order to establish a method of assessing the degree of inbreeding within herds of cattle, we constructed a calibration index relating kinship and the degree of DNA band sharing in DNA fingerprints. Firstly, chickens were used as a model system to test the possibility of using microsatellite DNA as a probe for DNA fingerprinting in inbreeding analysis. Six genetic groups of chickens with estimated coefficients of inbreeding ranging from 0.026 to $>$ 0.98 (pedigree analysis) were fingerprinted using the minisatellite probe derived from M13 and the microsatellite probe (CAC)$ sb5$. The degree of band sharing using either probe increased in concert with the known amount of inbreeding and was described by the equation Y = 0.56X ($ pm$0.06) + 0.42 ($ pm$0.03); r = 0.998. Since in-gel hybridization using the microsatellite probes was faster and less labour intensive than using the minisatellite probe, it was used in the subsequent studies. Pedigree analysis in Holstein dairy cattle allowed for the empirical calibration of the association of band sharing with the coefficient of relatedness, (r), defined as the expected proportion of genes in 2 individuals that are identical by descent (i.e. for monozygous twins r = 1; for first order relatives r = 0.5; for half sibs r = 0.25 etc.). The average band sharing between pairs (6 pairs at each r value) of individuals within each class formed the basis for calibration. DNA was digested using RsaI. The relationship between band sharing and relatedness was well represented by a linear approximation Y = 0.51X ($ pm$0.09) + 0.50 ($ pm$0.04); r = 0.992. Using this calibration curve, random samples of animals within herds can be tested to establish the herd variability and to minimize inbreeding.

The effect of composite and descriptive linear type traits on Functional Herd Life in Holstein cows was studied by means of Survival Analysis (Ducrocq and Solkner, 1998a). The original data set contained 331,105 lifetime records from the Programme d'Analyse des Troupeaux Laitiers du Quebec, from January 1980 to March 1995. Only 191,167 records (or cows) had type information. Mixed Weibull models were fitted to analyse the data; the probability of being culled (hazard) was defined as a product of a baseline Weibull hazard function and explanatory variables. The heritability estimates for Functional Herd Life were 0.07 in the log scale and 0.15 in the original scale. Sire Estimated Transmitting Ability for FHL, expressed as relative culling rate, ranged from 0.6 to 1.4 for all models. Solutions for fixed effects (all significant) indicated a higher probability of being culled for primiparous cows calving at older ages, for cows producing below herd average, for first lactation cows in the first and last stage of lactation and for older cows at the end of lactation. The risk of being culled did not change for cows in herds decreasing or increasing in size. Cows classified with a high score for Final Score were less likely to be culled; Final Score seems to be an important selection criteria among Quebec producers. Feet and Legs, Rump and Mammary System are traits that producers consider in their culling policies; cows classified with a high score had more chance of surviving. Among the linear type traits, the 5 traits with the highest impact on productive life, were Rear Attachment Height, Fore Attachment, Bone Quality, Stature and Fore Teat Placement; Quebec producers seem to consider these traits when they make their culling decisions.

Methodologies have been devised to genotype the $ kappa$-casein ($ kappa$-CN) and $ beta$-lactoglobulin ($ beta$-LG) loci using the polymerase chain reaction (PCR) and restriction fragment length polymorphisms (RFLPs) analysis. A fragment of 432 base pair from the $ kappa$-CN gene which contains the nucleotide substitutions diagnostic of the A- and B-alleles of $ kappa$-CN was amplified. DNA amplified from the A-variant contained a unique HinfI restriction site, whereas DNA amplified from the B-variant contained a unique TaqI site. Thus, the genotype of the animal could be determined by restriction enzyme analysis. A region extending from exon IV to V of the $ beta$-LG gene was also amplified using PCR. In this region, the B-allele contains 2 HaeIII restriction sites which are not present in DNA amplified from the A-allele. The digestion of the PCR product with HaeIII thus allowed discrimination between the A- and B-alleles. Analysis of bulls (n = 68) used by artificial insemination (AI) centres after 1980, bulls (n = 27) used before 1960, a random sample of male calves (n = 102) and cows (n = 123) revealed a frequency of the B allele of $ kappa$-CN as 0.13, 0.37, 0.22 and 0.19 in these populations, respectively. In the populations of bulls (n = 69) used by AI centres after 1980, bulls (n = 27) used before 1960, a random sample of male calves (n = 99), and cows (n = 129), the B-allele of $ beta$-LG was present at frequencies of 0.60, 0.52, 0.67, and 0.65, respectively. Statistical analysis of these data shows the frequency of the B-allele of $ kappa$-CN was significantly higher in sires (n = 27) which were used by the AI centre before 1960 compared to more modern proven sires (n = 68) (P $<$ 0.01).