Direct and correlated responses to selection for weight gain were investigated after nine generations of within family selection. Four selection criteria were used: gain between 28 and 38 or 48 and 58 days of age, and under two feeding regimes, ad libitum consumption or restricted to 80% of control lines. Two lines consisting each of twenty pair matings were selected under each of these criteria. Two unselected control lines were kept. Carcass composition analyses were performed in generation nine at the beginning and end of each selection period and at 100 days of age. / Direct responses to selection in the first period were greater in the ad libitum lines while in the second period direct responses were greater in the restricted lines. Direct responses and realized heritability estimates were significantly different between the sexes; males had greater direct responses and higher heritabilities in all selected lines. Body weights before the selection periods decreased in all lines as a result of selection. Body weights after the selection period were not different from controls in the ad libitum lines while restricted lines remained smaller animals. Correlated responses in feed efficiency and feed consumption in the ad libitum lines were positive in the first period and negative in the second period. Restricted lines had a positive response in feed efficiency and negative response in consumption in both periods of selection. Changes in body composition in the first period reflected the changes in body weights through a lower crude protein percentage at the start of the period and a lower ash percentage at the end of the period. Body composition at the start of the second period was not altered by selection, while at the end of the selection period ad libitum lines had higher dry matter percentages and restricted lines had lower fat percentages. Body composition at 100 days of age was not affected by selection except for dry matter percent, that was lower in the restricted lines. / Correlated response in fitness was evaluated through litter size. In the first period lines selected under ad libitum feeding were not affected by selection for increased weight gain while selection for weight gain under restricted feeding caused a significant decrease in litter size.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 80-86). Also available via the Internet.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

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The effect of intracerebroventricular (ICV) injection of corticotrophin releasing hormone (CRH) and related compounds on appetite, behavior, and gastric motility in lines of chickens, one selected for low body weight (LWS) and the other high body weight (HWS), was determined. Nucleotide sequence and expression patterns of the CRHr2 receptor, involved in appetite regulation, were also determined. Some individuals of the LWS line are anorexics and many die simply from not eating while some individuals in the HWS line are compulsive eaters and exhibit obesity. CRH is a 41 residue peptide that initiates an organism's stress response and is a potent inhibitor of appetite. An ICV injection of CRH dose-dependently decreased feed intake in both lines but did not effect water intake. When CRH receptor antagonists were ICV injected an increase in feed intake in the LWS line but not in the HWS line was observed, however the appetite reducing effect of CRH was attenuated in the HWS line but not in the LWS line. The LWS line has higher concentration of corticosterone than does the HWS line. In both lines at all times treatment with CRH caused an increase in locomotion and no CRH-treated chicks from either line slept post injection. Chicks from the LWS line that were treated with CRH exhibited other anxiety related behaviors sooner than the HWS line. The LWS line showed a liner increase in crop emptying time as the dose of ICV CRH increased. The HWS line responded with a quadratic dose response to CRH treatment. Polymorphisms in the CRHr2 receptor were found in both lines in the same positions, thus we concluded these differences do not significantly contribute to body weight differences. However, differences detected in expression patterns between lines for the CRHr2 receptor may contribute to their different body weights. We conclude that differences in the CRH system, its concentrations and differential receptor action, of these two lines may be partly responsible for their altered body weight phenotype. / Ph. D.

Thesis (M. Agricultural Management (Animal Production)) -- University of Limpopo, 2022 / Modern analytical techniques such as data mining algorithms are used to create a model that accurately estimates continuous dependent variable from independent variables of a given set of data. The present study used different data mining algorithms to assess the association between body weight (BW) and morphological characteristics such as body length (BL), heart girth (HG), withers height (WH), rump height (RH), and rump length (RL) of South African non-descript indigenous goats. The research was carried out in the Lepelle-Nkumbi Local Municipality, Capricorn District in the Limpopo province of South Africa. The study used 700 non-descript indigenous goats which include 283 bucks and 417 does with age ranged from one to five years old. The morphological characteristics were taken with a tailor measuring tape and a wood ruler calibrated in centimetres (cm), while the BW was taken with a balanced animal scale calibrated in kilograms (kg). Before the goats were allowed to go for grazing, the following body measurements (BW, BL, HG, WH, RH and RL) was taken once in the morning. Data was analyzed using descriptive statistics, Pearson correlation, various data mining algorithms (Chi-square automatic interaction detector, Classification, and regression tree), analysis of variance and goodness of fit equations (Coefficient of determination (R2), adjusted coefficient of determination (Ajd.R2), root mean square error (RMSE), relative approximate error (RAE), standard deviation ratio (SD. ratio) and coefficient of variance (CV)). The result showed that, BW and HG had higher mean values in does than bucks, BL and WH had higher mean values in bucks than does, and RH and RL had equal mean values in bucks and does, according to descriptive statistics. Furthermore, our findings showed that the BW of does had positive significant correlation (P < 0.01) with BL (r = 0.65), and positive significant correlation (P < 0.05) with HG (r = 0.28), but non-significant correlation (P > 0.05) with WH (r = 0.21), RH (r = 0.23) and RL (r = 0.23). However, the result for bucks indicated that BW had positive significant correlation (P < 0.01) with BL (r = 0.65) but non-significant correlation with HG (r = 0.22), WH (r = 0.07), RH (r = 0.14) and RL (r = 0.12). The chi-square automatic interaction detector and classification and regression tree results indicated that BL in bucks and does had statistical significance (P < 0.01) on BW followed by age, HG, and villages where the animals were raised. Goodness of fit results indicated there was high R2 = 0.58, Adj. R2 = 0.58, and low SD. Ratio = 0.65, RAE = 0.02, RMSE = 5.53) and CV = 14.49 in CHAID model and low R2 = 0.51, Adj. R2 = 0.46 and high SD. Ratio = 0.70, RAE = 0.20, RMSE = 5.95 and CV = 15.49 in CART model. Analysis of variance results indicated that age had significant difference (P < 0.01) on BW and some morphological traits including BL, HG, WH and RH. Sex only revealed significant difference (P < 0.01) in RL. It was concluded that BL alone in both sexes can be used as a selection criterion when determining body weight of goats. Both CHAID and CART suggest that BL alone can be used as a predictor of body weight in goats. Goodness of fit calculations suggest that CHAID is the best model due to its high R2, Adj. R2 and low RAE and RMSE. Findings suggest that age can be used as deciding factor for the measured traits including BW, BL, HG, WH and RH in both does and bucks. Findings suggest that sex can only be used as a deciding for RL only in the current study. / National Research Foundation (NRF)

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