A rapid growth phase often occurs with the onset of spring in the young horse. This coincides with changes in day length, temperature, and progesterone concentrations. The change in growth, from slow to rapid in young horses has been associated with various forms of developmental orthopedic disease. The objective of this study was to distinguish associations between progesterone concentrations and other physiological and environmental measures from birth through 16 mo in young Thoroughbreds. Growth data and plasma samples were collected monthly from 3 annual crops of 20 foals. Plasma progesterone (P4) and insulin like growth factor one (IGF-I) concentrations were measured with previously validated radio immunoassay's (RIA). Progesterone concentrations were compared with day length, IGF-I and ADG using Spearman correlations. Concentrations of progesterone at birth (2.3 ± 0.4 ng/mL) decreased within the first week of life to basal values (0.11 ± 0.01 ng/mL) in colts and fillies. Progesterone in the geldings remained at baseline concentrations at all sample times. An abrupt increase in progesterone concentration was detected in fillies at a mean age of 385 ± 6.4 d, weight 381 ± 7.2 kg, and ADG 0.63 ± 0.04 kg/d. Elevations in progesterone concentrations coincided with a measured day length of 13 ± 0.1 hrs, and temperature of 15 ± 1.7 °C. Positive associations were established between progesterone concentration day length (r = 0.59; P<0.0001), IGF-I (r = 0.25; P<0.01) and ADG (r = 0.34; P<0.0001). Day length IGF-I and ADG began to increase for both geldings and fillies at approximately 340 d of age, while progesterone started to increase at 385 ± 6.4 d for the fillies only. From this it could be hypothesized that an increase in ADG combined with optimal environmental conditions, may be associated with the subsequent elevation in progesterone concentrations in fillies. The relationship between IGF-I, and various reproductive hormones has been studied in the adult horse, yet the associations between environmental factors, ADG, and progesterone concentrations demonstrated in growing yearlings further emphasizes the extensive changes occurring during this crucial developmental stage. / Master of Science

A radiographic examination forms part of the pre-purchase examination of Thoroughbred yearlings at national sales in many countries. This data enables the recording of the prevalence of radiographic changes in selected Thoroughbred populations around the world and assists veterinarians in advising clients on the purchase of yearlings. This has financial implications for the client as well as the racing industry as a whole. Radiographic examinations of the 269 Thoroughbred yearlings lodged at the 2008 National Yearling Sale in Germiston, South Africa were collected and individually evaluated. The prevalence of radiographic changes was recorded and percentages calculated. These changes were compared to studies of other yearling populations. Radiographic changes present in the studied Thoroughbred population are: pedal osteitis 1.26%, metatarsophalangeal joint dorsal osteochondral fragmentation 1.60%, sagittal ridge changes 5.7%, ulnar carpal bone lucencies 8.33%, carpal osteophytes 1.19%, distal intertarsal and tarsometatarsal joint radiographic changes 9.92%, tarsal osteochondrosis lesions 4.4% and stifle joint osteochondrosis lesions 0.4%. These changes were found to be of lower prevalence when compared to similar studies. The prevalence of dorsal osteochondral fragments in the metacarpophalangeal joint was 1.60% which was similar to other studies. A higher prevalence of vascular channels was visible in the proximal sesamoid bones as well as irregular borders and lucencies. Palmar metacarpophalangeal and plantar metatarsophalangeal osteochondral fragments had a recorded prevalence of 2% and 7.10%, respectively, this prevalence being generally higher when compared to similar studies. There was an absence of palmar metacarpal disease, supracondylar lysis, proximal sesamoid bone fractures and carpal osteochondral fragmentation in the current study. Additional findings recorded in the current study were: proximal interphalangeal joint hyperextension (left front 15.13%, right front 18.91%), the solar angle (right front 2.38°, left front 2.79°), the prevalence of carpal bone one (30.95%) and carpal bone five (1.59%). The study population was limited to the radiographs lodged at the sale repository. As radiographic changes may influence sale price of the yearling, radiographs of yearlings with severe radiographic changes may not have been lodged at the repository. For these reasons the prevalence of radiographic changes recorded in the current study may not be a true reflection of the entire 2006 Thoroughbred foal crop. Further work to correlate radiographic changes to differences in management, pre-sale exercise programmes and genetics needs to be done. The effect of radiographic changes on the future performance of the Thoroughbred yearling also warrants further investigation. Copyright / Dissertation (MSc)--University of Pretoria, 2009. / Companion Animal Clinical Studies / unrestricted

Master of Science / Department of Agricultural Economics / Glynn T. Tonsor / The purpose of this analysis is to examine two aspects of price analysis in the stocker industry in order to better assist producers making purchasing decisions. One analysis looks at forecasting value of gain, while the second looks at drivers of price differentials between calves and yearlings. When analyzing forecasts on value of gain, weekly data was collected to compare a naïve approach and futures market implied basis-adjusted approaches that include one to five years of historical average basis. This allowed for the assessment of five different models for nine scenarios. The conclusions from this were inconsistent with what was hypothesized and the naïve approach was either worse or no better when compared to using the futures market implied basis-adjusted approaches to forecast value of gain. The drawback to this analysis was that it was solely influenced by error on forecasting the selling price and in future work a forecasting horizon will be incorporated on the buying price. In order to analyze the price premiums and discounts between calves and yearlings, a confirmation, update and expansion were completed following monthly models by Marsh (1985). Three elements are considered when predicting price premiums and discounts between two weight classes; cost of gain (proxied by corn price), slaughter price, and seasonality. Estimated models in the confirmation for years 1972 to 1982 and the update for years 1973 to 2013, show that premiums and discounts are influenced by expected changes in corn price and/or slaughter price, but not highly affected by seasonality. However, in the expansion for years 1993 to 2013, corn price, slaughter price, and seasonality were all significant to the models and in higher magnitude when compared to those results in the confirmation and update. Understanding the relationships between all variables in these models allows producers in the cattle-feeding industry to make management decisions based on current marketing conditions and trends.