Thesis (Magister Institutionis Agrariae (Animal Production))-University of Pretoria, 2005. / Abstract in English. Includes bibliography. Available on the Internet via the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 198-213). Available also in a digital version from Dissertation Abstracts.

A study to evaluate the effect of feeding a high energy diet on the productive and reproductive characteristics of young bulls was carried out at two different locations in the Free State Province. Two trials were conducted with the aim of evaluating the effect of level of dietary energy and age of the bulls on their productive performance and reproductive characteristics. In the first trial, two levels of energy were fed to two groups of young (343 ± days) Bonsmara bulls. The high energy group HE (n=36) bulls were Phase-C performance tested in an official performance testing center and received a high energy diet for 112 days (28 days adaptation and 84 days testing). The medium energy group ME (n=18) bulls were phase-D performance tested and received a medium-energy diet for 140 days (28 days adaptation and 112 days testing). At the end of both performance testing periods, the productive performances and reproductive characteristics of the two groups were compared. The productive parameters compared included final live body weight (FLW), average daily gain (ADG), average daily gain per day of age (ADA) and body condition score (BCS). The reproductive parameters compared between groups included scrotal circumference (SC), semen volume (Vol) and concentration (SConO), mass movement (MV), linear motility (LM), percentage live sperm (LS), as well as percentage of total abnormalities: major (MD) and minor (MinD). The results of this trial indicated that in general, bulls from the HE group showed a significant (p<0.01) higher FLW, BCS, ADG and ADA, but a significant (p<0.01) lower volume and concentration of the ejaculate, lower mass movement and linear motility, lower percentage of live sperm and higher percentage of major defects and significantly (p<0.05) higher percentage of minor defects than the bulls from the ME group. In the second trial, 36 young Bonsmara bulls were divided into two groups according to their age at the arrival at an official Phase-C performance testing center. Older bulls (OB) (n=19) and younger bulls (YB) (n=17) all received a high energy diet for 112 days (28 days adaptation and 84 days testing). At the end of the Phase-C test the productive performances and reproductive characteristics of the two groups were compared. The animals from both groups that did not pass the Phase-C test, either due to poor performance or not meeting the breed standards, were slaughtered at an official abattoir and their scrotums and carcass characteristics were also compared. The productive parameters compared between the two groups included final live body weight (FLW), average daily gain (ADG), average daily gain per day of age (ADA), body condition score (BCS), feed conversion ratio (FCR), carcass weight both warm (CWW) and cold (CWC), as well as dressing percentage (CDP) and fat grade (CFG). The reproductive parameters compared between the two groups included scrotal circumference (SC), total scrotal weight (TSW), scrotal fat (SF), scrotal skin weight (SSW), paired testes weight (PTW), scrotal skin thickness (SST), total testes circumference (TTC), total testicle volume (TTV), weight of epididimis / spermatic cord (WESC), volume of epididymis / spermatic cord (VESC) and the percentage of bulls with depressed spermatogenesis (PBDS), semen concentration (SConO), mass movement (MV), linear motility (LM), percentage live sperm (LS), percentage of total abnormalities: major (MD) and minor(MinD) as well as the percentage of bulls with depressed spermatogenesis (PBDS). The results of this trial indicated that in general, the younger bulls showed a significant (p<0.05) higher ADG, but a significant (p<0.05) lower ADA than the older bulls. Regarding the reproductive organs compared, the younger bulls showed a significantly (p<0.01) higher total scrotal weight, scrotal fat and scrotal skin weight and thickness. No significant differences were observed on the testicular parameters measured between the two groups. In addition, both weight (WECS) and volume (VECS) of the epididymis / spermatic cord were significantly (P<0.05) higher in the older bulls. In general, the younger group showed poorer semen characteristics. A significantly (p<0.01) lower sperm concentration and linear movement and a significantly (p<0.05) higher percentage of major defects were recorded on the younger bulls, when compared to the older bulls. About half of the bulls in each group showed clear signs of depressed spermatogenesis in their seminiferous tubules, during the histological examination of testicular tissue. The results of this study indicates that high energy diets are beneficial for the productive performance of young bulls (growth rate, BCS and carcass characteristics), but have a detrimental effect on the reproductive characteristics of young bulls. The effect of high energy diets on both the productive and reproductive performances of young beef bulls are more pronounced at a younger age. High energy diets resulted in heavier scrotums in the younger bulls when compared to the older bulls, as a direct result of a higher fat deposition in this region without any relevant effect on testicular size. No intra-testicular fat deposition was observed. The scrotal fat observed in high energy fed young bulls accumulated mainly in the neck of the scrotum, although subcutaneously. These fat deposits may impair testicular thermoregulation and negatively affect the spermatogenesis in the seminiferous tubules, reducing both sperm quantity and quality. Further studies on the effect of high energy diets on bull fertility (as well as on rams and buck) are recommended, to evaluate the extension and duration of its detrimental effects on subsequent fertility.

Introduction : Indigenous cattle are mostly reared where the traditional farming is practiced including Northern Region of South Africa. The majority of farmers own Nguni type of cattle although other breeds are found in the region. They perform well under harsh conditions and they seem to produce better under intensive management. However, communal farmers are becoming aware and interested in indigenous breeds especially Nguni cattle type because of their adaptability. Beef cattle production and research require constant movement and handling of livestock (Erf et al., 1992 & Grandin, 1993). Dipping, castration, branding, ear-tagging and counting is commonly practiced as beef cattle management norms hence dehorning are partly practiced as some of the animals had horns which were disturbing them to pass through crushpens and as a result they increased bruising to other animals. At Matatani and Muledzhi areas animals including calves are packed in the crushpens, counted, weighed and temperament traits were also measured on the scale and this is done in order to document the information for this research and future use. Temperament is a behavioural response of animals as handled by man. It is important to be measured in beef cattle farmers under communal grazing conditions as it reduces farmer’s profit and it makes the stock man’s work unpleasant. Therefore, it is also needs to be improved for the improvement of beef cattle schemes. Management system of communal farmers was not conducive to better quality meat due to horns in some animals which ultimately cause bruising in other animals. However, exotic bulls were bought at random for the improvement of other breed types found in these two areas. The focus of this study is almost in Nguni cattle type managed under communal grazing system. Lastly, the purpose of this study is to determine behavioral response of beef cattle under communal management system at their dipping tanks.

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[No abstract available] / Land and Food Systems, Faculty of / Graduate

Nine purebred Hereford bulls which had been tested for rate and efficiency of gain at the University of British Columbia, were bred to 99 heifers, 11 heifers to each bull, obtained from commercial breeders. Bach of the offspring, a total of 84, was weaned at 400 pounds and then placed on an individual feeding test, using the same feeding schedule and the same concentrate ration as that used for the bulls. At 800 pounds, the animals were slaughtered, rail graded and several carcass measurements were collected. Daily rate of gain and feed efficiency were computed over three periods. The following correlations were calculated: birth weight and daily gain during pre-weaning period; birth weight and daily gain during post-weaning period; daily gain during pre-weaning and post-weaning period; daily gain during post-weaning period and percentage lean in ribcut; daily gain during post-weaning period and carcass grade. The "r" value of each of the above calculations was found to be "low". There was a very high correlation between rate and efficiency of gain for each of the three periods: 400 - 800 pounds, r = -0.98 400 - 600 pounds, r = -0.97 600 - 800 pounds, r = -0.98 A simple plan for home testing was outlined. This plan calls for selection on the basis of rate of gain during a test period of approximately 5 months. Animals enter the test period in groups with equal body weight and are full fed. / Land and Food Systems, Faculty of / Graduate

This dissertation investigates the process of genetic-based technical change in the Canadian beef cattle industry. Specifically, I analyze the effect of market forces on three processes necessary for genetic-based technological change: expansion of the genetic pool, inbreeding of divergent genetic strains to increase the probability of desired heritable properties in a pure breeding strain, and crossing of pure breeding strains to take advantage of hybrid vigour. This is accomplished through two studies. The first study, examines the expansion of the genetic pool through the establishment of purebred breeders of cattle breeds imported since 1965. A model is developed to explain the location of breeders within a time framework. The model was tested across breeds and over time. The process of breeder location appears consistent for the various breeds and can help explain the dates of availability of new breeds of cattle in different areas of the country. The second study examines the ongoing process of genetic technical change through the improvement and sale of breeding stock. A model is developed explicitly using the "characteristics" approach to production with the phenotypic characteristics of breeding bulls as arguments in a production function. Prices of individual bulls and values for the characteristics were collected at bull sales and shadow values for the characteristics estimated. These shadow values were used to predict characteristics which should be emphasized in herd improvement, and the prediction was compared to observed practices. The use of the characteristic: approach led to the identification of a different production function for the traditional straightbred technology and the new crossbred technology. Market forces seem to regulate the process of technological change and promote breed improvement. The major constraint to availability appears to be the limitation on imports and the biological limits to increasing the stock of purebred females. / Arts, Faculty of / Vancouver School of Economics / Graduate

The body weight of beef cows (cow weights) on nine ranches and farms located in the province of British Columbia were recorded each fall and spring for three years. Cow weights were also recorded on two additional occasions during the winter in the largest of these herds. The cows in these herds were all straightbred Hereford or Angus cows, or crossbreds of one or other of these breeds. During the summer five of the herds used rangeland, and four used pasture. Each herd calved in the spring after overwintering on conserved forage. The influence of breedtype, year, age, season and herd on the spring and fall weight records were determined by a least-squares analysis as outlined by Harvey (1975). Season was found to have a major influence on cow weight. Each weight change (considered as a percentage of the mean weight during the period) was included as a dependent variable in separate analyses. In addition to the parameters already mentioned, calf sex, calf age, calf weaning weight, previous weight change and the interval from calving to weighing in the spring were included where appropriate in the models for these analyses. The two mid-winter weights were included in a similar statistical analysis to determine the influence of pregnancy per se on cow weight in this herd. The parameters fitted in this model were age, year, age x year, days pregnant (DP), DP² and DP³. Age, season and herd were found to be significant sources of variation in the cow weight records; bat, within each herd, genetically different breedtypes normally had similar weights. The cows on summer rangeland were on average 119.0 lb. lighter than those on summer pasture. The increase in weight over age and the seasonal fluctuations around this mean growth curve also varied significantly between herds. However, in all but one of the herds there was a weight loss each winter and a weight gain each summer. The mean spring/fall weight difference was 114.2 lb. The mean mature age of the cows was six, and the mean mature weight was 1083.9 lb. The summer change in weight of a cow depended on age and herd, but not on breedtype. Younger cows gained more weight through the summer than older cows; the influence of herd on cow weight was not correlated with any single factor. Summer weight change was not influenced by the calf the cow suckled during the summer, but cows which lost the most weight during the previous winter gained the most the following summer. The winter weight change of a cow was not the same for all ages and breedtypes, but differed from herd to herd according to the level of winter feeding in each herd. Again there was a close correlation between this weight change and that in the previous period. The winter weight loss was found to continue through the interval from calving to weighing. The average weight loss during this period was around 0.7 lb. per day. A mean weight increase of 101.4 lb. was recorded between the 90th and 260th days of pregnancy. There was then a 6.8 lb. weight loss in the remaining 25 days through to parturition. The weight loss at parturition was 80.0 lb. or 7.3% of the cow's pre-partum weight. / Land and Food Systems, Faculty of / Graduate

No description available.