Corpus luteum (CL) dysfunction has been implicated among various factors predisposing early embryonic mortality in cattle. Two experiments were conducted to evaluate the efficacy of using human chorionic gonadotropin (hCG) given either at the time of breeding (day 0) , day 7 or 14 post breeding, in reducing that component of early embryonic mortality caused by CL dysfunction. The aims of experiment 1 were to investigate the effectiveness of using hCG, in inducing the development of accessory CL, their formation and growth, and the effect of such treatments on the function of both the induced and spontaneous CL. Thirty-four lactating Holstein cows were randomly assigned to one of four treatments. A single intramuscular injection of 1000 IU of hCG was given either at the time of breeding (day 0, n=8), day 7 (n=9) or 14 (n=9) post breeding or no hCG given (control, n=8). A real-time ultrasound machine was used to study follicular dynamics and CL growth. The CL and antral follicle diameter was determined using a built-in system of calibrated callipers. Ultrasound scanning was carried out on days 7, 9, 11, 14, 16, 18, 21, 28, 35 and 42 post breeding. Blood and milk samples, for progesterone (P₄) determination using radioimmunoassay, were collected on days coincident with ultrasonography. Diameter of the CL is presented as the sum of the diameter of all luteal tissue in each animal. Differences in CL diameter, milk and plasma P₄ were analyzed using the General Linear Models Procedures while pregnancy data were analyzed using Chi-Square analysis in Statistical Analysis Systems (SAS, version 6.3). Based on the day 7 ultrasound scanning, the incidence of twin ovulations was higher among cows treated on day 0 (3/8) compared to control cows (1/8) and day 7 (1/9). Accessory CL were detected in 7/9 of the day 7-treated cows compared to 4/9 among the day-14 treated cows. Least squares means (LSMeans) for CL diameter were significantly higher (P<0.001) among cows treated with hCG compared to control cows starting at day 7 continually until day 42. Plasma P₄ profiles were significantly higher (P<0.05), at days 18, 35 and 42, in cows treated on day 7 or 14 compared to control cows. The first detectable differences (P<0.05) between hCG treated and control cows, in milk P₄ occurred at day 21 and persisted until day 42. Pregnancy rates were highest among cows treated with hCG on day 7 where 6 of the 9 cows were diagnosed pregnant. Corresponding pregnancy rates for day 0, 14 or control cows, were 4/8, 5/9 and 3/8, respectively. In the second experiment, two trials were conducted at two different farms to investigate the efficacy of using hCG to increase milk P₄ and pregnancy rates. In trial one, 79 lactating Holstein cows were exposed to the treatment protocol described in experiment 1. In addition to the milk sample collection schedule given in experiment 1, a sample was collected on day 0. Milk samples were stored at 4°C and later transported to the UBC laboratories for P₄ analysis. LSMeans for milk P₄ concentrations were different only at days 16 and 18 post breeding. Pregnancy rates were improved (P<0.01) by hCG treatments. The respective pregnancy rates for cows receiving hCG on day 0 (n=20), 7 (n=20), 14 (n=20) or control (n=19) were 25, 35, 35 and 21 %. In the second trial, 121 lactating Holstein cows were randomly assigned to treatments as described earlier. Weekly milk samples were collected from each animal and assayed for P₄ as described above. LSMeans for milk P₄ were significantly different (P<0.05) among groups starting at day 14 until day 42 post breeding. hCG increased pregnancy rates over control cows. The pregnancy rates for cows treated on day 0, 7, 14 and control were 31, 50, 41 and 26 %, respectively. In conclusion, this study revealed that treatment with hCG induced accessory CL development, increased P₄ production and improved pregnancy rates. It is evident, too, that treatment with hCG on day 7 post breeding may have greater potential for improving pregnancy rates not only in dairy and beef cattle but equally beneficial to the embryo transfer programmes. Increased pregnancy rates confirm the hypothesis that CL dysfunction does cost the livestock industry appreciable losses in embryos. / Land and Food Systems, Faculty of / Graduate

In a Holstein herd (125 cows) the influence of early and late breeding post partum on reproduction and production was investigated. At calving the cows were randomly assigned to two groups. The early bred group was scheduled to be bred at the first visible heat following 50 days post partum which resulted in an average interval of 73 ± 18 days from parturition to the first service. The average interval from parturition to conception was 88 ± 33 days. The cows in the early bred group conceived after an average of 1.50 (range: 1 to 3) services per conception. The late bred group was scheduled to be bred at the first visible heat following 80 days post partum which resulted in an average interval of 93 ± 17 days from parturition to the first service. The average interval from parturition to conception was 120 ± 40 days. The cows in the late bred group conceived after an average of 1.96 (range: 1 to 5) services per conception. The number of services per conception was significantly (P£.05) higher for the late bred group. The early post partum reproductive activity was monitored with milk progesterone analyses. A sample of milk strippings was analysed by a radioimmunoassay technique every second day from 6 days post partum until conception occurred or the animal was removed from the herd. Cows which did not conceive were excluded from the statistical analyses. The average length of the first estrous cycle was 17 ± 7.5 days. The first progesterone detected heat occurred 33 ± 10 days post partum compared to the first visible heat which occurred 48 ± 26 days post partum. Calving associated problems and the calving during the pasture season delayed conception in the late bred group but not in the early bred group. The late bred group produced more fat corrected milk (FCM) in the 305 day lactation and in the first 150 days of the subsequent lactation and also gained more (P≤.05) weight between calvings. Cows calving during the pasture season produced more FCM in the 305 day lactation but gained significantly (P≤.01) less weight between calvings than cows calving in the non-pasture season. There was no difference between early and late bred group, health status groups or groups according to the calving season in terms of average daily milk and FCM yield calculated over the entire period of this experiment (beginning of current lactation to day 150 of the subsequent lactation, including the dry period). Calving difficulties and early post partum reproductive problems were not related to production traits. / Land and Food Systems, Faculty of / Graduate

Recent studies show polymorphisms in the leptin gene significantly impact milk production in dairy cattle. If the leptin gene were to have a similar impact on beef cattle, calf weaning weights would be expected to increase from the increased milk production in the cows. Since weaning weight is a key component of profitability in a cow-calf operation, leptin genotyping may prove to have an economic impact in breeding cattle. However, no research has been done to link the economic impact of increased milk production to breeding cattle. Using 595 observations from genotyped cows spanning 11 years (1995-2005), calf weaning weight by genotype is estimated as a function of calf and dam characteristics and environmental effects. A MIXED procedure, utilizing data from 89 culled cows, is used to determine statistical differences in average cull age by genotype. A simulation model calculates mean annualized equivalent return by genotype and breed using the regression coefficients and residuals and 16 years of price data. results show that at least one T-allele in breeding cows increases calf weaning weight, average cull age, and annualized equivalent return compared to cows with homozygous C-alleles. These results indicate that there may be future premiums and discounts for breeding cattle based on genotype. Seedstock producers could potentially begin to segregate herds based upon genotype so that they could sell genotypic registered products. Cow-calf producers may also benefit from this knowledge by increasing the amount of TT genotype breeding cattle in their herd to maximize profits.

The primary objective of this research was to study the effects of breed, age, season, and their interactions on semen morphological characteristics. The study was done on 329 bulls (271 Friesland and 58 Jersey) aged 12, 24, 36,48, 60, 72, 84, 96 and> 96 months. The collection of semen was carried out using the artificial vagina method in all four seasons of the year. Spermatozoa were screened for the percentages normal sperm, percentage and total major defects such as knobbed acrosome, pyriform, abnormal lose head, dag defects, nuclear vacuole, degenerative heads, mid-piece reflexes, percentages and total minor defects such as normal lose heads, distal droplets, curled end-piece, lose acrosome. Statistical analyses of the data were done using the general linear model (GLM) procedure of the Statistical Analyses System (SAS, 1999). The results of the study indicate that breed did not significantly affected the percentage normal sperm and percentage major sperm defects, but significantly affected the percentage minor defects (P = 0.01). The Least square means (LSM±SE) for the percentage normal sperm, major defects and minor defects in Friesland and Jersey bulls were 80.6 ±1.06%; versus 78.9±2.31 %; 14.8±0.90% versus 15.0± 2.62%, 5.1±0.43% versus 7.6±0.94%, respectively. The results obtained show that the prevalence of sperm defects that differed significantly between breeds was higher in Jersey bulls compared to Friesland bulls. The results of the study indicated the percentage of normal sperm to differ (P = 0.01) with season. The percentage of normal sperm during the summer, autumn, winter and spring, were 72.8±1.6%, 79.4±2.2%, 82.5±2.4% and 84.4±2.4% respectively. Season also affected the percentage of major defects (P = 0.01) and percentage of minor defects (P = 0.03). The results demonstrate that even though there was a higher variation in sperm morphology with season, better sperm morphology was recorded in spring and winter than summer and autumn. Results also indicate the percentage of normal sperm (P = 0.05) and major defects (P = 0.01) to be affected significantly by age. On the other hand, the percentage of minor defects did not differ significantly with age. Bulls of 36-48 months of age showed better semen quality than bulls older than 72 months and bulls younger than 36 months. The percentage of major defects, particularly the incidence of major defects such as knobbed acrosomes, pyriforms, dag defects and broken flagella were significantly affected by the interaction between age and breed (P = 0.05) and age and season (P = 0.05). There was an increase in the susceptibility to these sperm defects in Jersey bulls with an increase in age, while no variation was observed in Friesland bulls. With age and season combined, young bulls recorded poor semen morphology during winter, while old bulls showed poor morphology during summer. In conclusion, the study suggested that breed, age and season and their interactions are important sources of variation in sperm morphology. For a successful AI programme, semen collection should be done at the age of 36-48 months for both breeds. It is therefore recommended that age, breed and season should be given urgent attention in any bull management system employed in South Africa in order to obtain the best semen quality. / Dissertation (M Inst Agrar (Animal Production))--University of Pretoria, 2003. / Animal and Wildlife Sciences / unrestricted

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First available appraisals for 67644 Jersey cows were used to estimate relative magnitudes of additive and selected sources of nonadditive genetic variation, and evaluate corrective mating programs for 13 linear type traits scored linearly from 50 to 99 points. Estimates of additive genetic variances were 11 to 36 percent of within herd-classifier variance, with largest values for stature, strength, rump angle, rump width and udder depth. Dominance components ranged from 2 to 4 times as great as additive components for dairy character, rump width, and the udder traits; fore udder, rear udder height, rear udder width, and suspensory ligament, but were small for the other 7 traits. Maternal effects and the direct additive - additive maternal genetic covariance were unimportant. Sire predicted differences and four measures of dam's merit (dam's phenotypic score, this score relative to herd average, dam's cow index, and half the maternal grandsire predicted difference) were used to predict offspring scores, deviated from herd average. Sire regression coefficients were much larger than those for dam's measures, suggesting that sire evaluations should receive more weight than dam measures in a corrective mating context. Mean squares for effects on offspring scores of interactions between categorical levels of sire predicted differences and dam measures generally were nonsignificant, indicating that additively combining measures is appropriate for predicting offspring performance. Dam's cow index was found to be superior to dam's score for predicting mean performance of offspring groups (e.g., for large groups of offspring or over time) and is therefore preferred for corrective mating decisions. / Master of Science

The growth performance of Angus-Polled Hereford F₁ calves was compared to the expected progeny differences (EPD) estimated by the American Polled Hereford Association to evaluate the usefulness of EPD estimates for improving commercial beef production. Polled Hereford sires were selected from the high accuracy sires listed in the American Polled Hereford Association's sire summary. Four types of sires were used: 1) Sires with high yearling weight and high maternal EPD's; 2) Sires with high yearling weight and low maternal EPDâ s; 3) Sires with low yearling weight and high maternal EPD's; and 4) Sires with low yearling weight and low maternal EPD's. The resulting progeny were weighed at birth, approximately 135 d, weaning and approximately 1 yr. Hip heights were also measured at weaning. Linear regressions of progeny performance on EPD indicated that birth and yearling weights were accurately predicted by their respective EPD estimates. Weight and height at weaning were not accurately predicted by weaning weight EPD. Partial regressions of progeny performance on yearling weight and maternal EPD's were also calculated. Regression of progeny performance on yearling weight EPD resulted in .16 ±.09 kg/kg for 135-d weight, .28 ± .09 kg/kg for weaning weight, .073 ± .020 cm/kg for weaning hip height and .93 ±.19 kg/kg for yearling weight. Comparable regression values for maternal EPD were .44 ± .18 kg/kg, .31 ± .17 kg/kg, .100 ± .040 cm/kg and .22 ± .36 kg/kg for 135-d, weaning weight, weaning hip height and yearling weight, respectively. These results indicate that maternal EPD values predicted some differences in preweaning growth that were not predicted by yearling weight EPD. The progeny performance data was also used to calculate independent EPD estimates for birthweight, weaning weight, and yearling weight. Correlations between these EPD estimates and those made by the American Polled Hereford Association were .49 for birthweight, .26 for weaning weight and .66 for yearling weight. The low correlation between weaning weight EPD estimates was significantly below expectation and indicates that the American Polled Hereford Association estimates were inadequate for predicting preweaning growth differences in these crossbred calves. / Master of Science

This study assessed the effects of prenatal androgen exposure during three periods, of gestation on the external genitalia, estrous cyclicity, postnatal growth, social dominance and sexual behavior of female beef cattle. Pregnant cows received 17a methyl-testosterone (250 mg/d, sq) on d 40 to 100 (group 1), 70 to 130 (group 2) or 100 to 160 (group 3) of gestation. Control cows (group 0) received no treatment. Group 1 females exhibited completely masculinized external. genitalia. No vulval opening was present and the ano-genital distance (A-g) was similar to that of control male calves. Group 2 females exhibited small vulval openings and enlarged clitoral structures while group 3 females exhibited normally appearing female external genitalia. Anogenital distances for the heifers in groups 2 and 3 were similar to those of the control heifers. Androgen exposure during the three periods of gestation did not affect age at puberty (P<.80), estrous cycle length (P<.63) or postnatal growth (P<.60) of the heifers. At 9, 16 and 21 mo of age, social dominance values (SDV) were determined for each heifer by 3 min random pair contests for a restricted feed source. The animal with the greatest feed source control time was awarded a win. Social dominance value was calculated as 10 times the number of wins divided by the number of competitions for each animal. Group 3 heifers had significantly greater SDV values than group 1 and 2 females (P<.03). SDV did not differ among groups at 16 mo of age (P<.59). Group 1 females had greater SDV than group 2 females at 21 mo of age (P<:.04). At 9, 16 and 21, mo of age, sexual behavior of the heifers was characterized by exposure of the heifers to a teaser female in estrus. Sexual behavior, as indicated by the number of mounts, head placements and interest time, was lower for group 3 females compared to females in groups 1 and 2 at 9 mo of age (P<.04). There were no treatment differences for any sexual behavior variable at 16 or 21 mo of age. These results indicate that there is little potential for increasing postnatal growth or altering the estrous cyclicity of female cattle by exposure of the fetus to testosterone during the periods of gestation selected in this study. External genitalia of females were masculinized by androgen exposure during d-40 to 100 of gestation. Social dominance values were increased and sexual behavior was reduced in females by exposure to androgen during d 100 to 160 of gestation. / Master of Science

De Kol 2d, Pietertje Hengerveld and Belle Koendyke each have two daughters. For each daughter the following number of grand daughters are found. For Belle Korndyke 93.5, De Kol 2d 81.5 , and Pietertje Hengerveld 60.5. The following number of great-grand-daughters may be attributed to each grand-daughter: De Kol 2d 5.29, Belle Korndyke 3.11 and Pietertje Hengerveld 2.96. This shows De Kol 2d was more prepotent over her great-grand-daughters or her daughters were bred to better sires. The percent of the progeny found in each class clearly shows the prepotency of the progenitor. The most noticeable influence over the grand daughters of the first class was that of Belle Korndyke, having 16.52% of progeny in first class. De Kol ranked second and Pietertje Hengerveld third. In class two Belle Korndyke ranks first, De Kol 2d second, and Pietertje Hengerveld third. In classes three and four some change is order is noticeable; Pietertje Hengerveld ranks first, De Kol 2d second, and Belle Korndyke third. / Master of Science