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The relationship of phenotype of Mexican steers to animal performance in two geographical locations
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The relationship between animal phenotype and the response variables average daily gain (ADG), final body weight (FW), final body condition (FC) and final body frame was studied for 352 Mexican steers backgrounded in a humid (n =1 10), or a semi-arid environment (n = 252). Following full feeding together for a constant number of days at another location, the relationship between animal phenotype and feedlot and carcass traits was studied. Initial body condition (IC), frame, weight, hair color, and estimated percent Brahman parentage were phenotypic variables of interest during the pasture phase of the experiment. At the humid environment (East Texas), steers were subdivided into four breed types based on Brahman breeding, and four different supplements were used during the pasture phase of the experiment. Two different forage systems were used in the semi-arid environment (South Texas). In the humid environment, all of the nutritional treatments had similar ADG (0.85 kg), and they were all different (p < 0.05) from the treatment which was pasture only (ADG = 0.78 kg). In the semi-arid environment, the oat-sorghum pasture produced significantly greater (p < 0.04) ADG than the native range (0.53 vs 0.5 kg ADG). IC (p < 0.003) and treatment (p < 0.009) were the most important factors affecting ADG on pasture in the humid environment. In the semi-arid environment, ADG was affected by IC (p < 0.0001) and treatment, but percent Brahman was also important (p < 0.03). The Mexican steers compensated during the pasture phase of the experiment in the humid environment. IC =3 (0.93 kg ADG) gained better than IC = 4 (0.84 kg ADG) and IC = 5 (0.79 kg ADG), p< 0.003 and p < 0.009 respectively. The ADG of IC = 4 and IC = 5 was also different, p < 0.02. For the Mexican steers pastured in the humid environment, linear contrasts were used to show a trend for the IC =3 to require more treatment for sickness than IC =4, and IC = 5 , p < 0.06. Compensation was completed during the pasture phase of the experiment for the Mexican steers grazed in the humid environment and IC was not related to ADG in the feedlot, p > 0. 1. The Mexican steers compensated during the pasture phase of the experiment in the semi-arid environment. IC = 3 (0.58 kg ADG) gained better than IC = 4 (0.50 kg ADG) and IC = 5 (0.46 kg ADG), p < 0.006 and p < 0.002 respectively. The Mexican steers pastured in the semi-arid environment continued to compensate in the feedlot. IC = 3 (2 kg ADG) gained better than IC 4, 5, or 6, 1.76, 1.74 and 1.67 kg ADG respectively, p < 0.003. The Mexican steers pastured in the humid environment with slight, moderate or high percent Brahman had higher ADG than the steers which had no obvious Brahman breeding (p < 0.004) Body frame score was important to Hot Carcass Weight (HCW), p < 0.04 and body condition score was related to USDA Quality Grade, p < 0.04, and USDA Yield Grade, p < 0.03. For steers previously pastured in a semi-arid environment, FC and FW off pasture was important to ADG p < 0. I and HCW p < 0. 00 I respectively. Phenotype by environment interactions were most prevalent during the stocker phase in the semi-arid environment. An initial frame by Brahman interaction p < 0.007 indicated that the high Brahman steers increased in FW at a greater rate than the none, slight or moderate Brahman steers with increasing frame size. An initial frame by treatment interaction (p < 0.06) showed a trend for FC to decrease at a greater rate for Mexican steers which grazed range relative to oat-sorghum pastures. In general, the environmental niches in the semi-arid environment were suited to a more narrow array of phenotypes than were the environmental niches in the humid environment or the feedlot.
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Chandler, Dan Thomas (1996). The relationship of phenotype of Mexican steers to animal performance in two geographical locations. Master's thesis, Texas A&M University. Available electronically from
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