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The objective of this study was to determine the effect of selected traits such as age, sex, body weight, body length and height, body condition score (BCS), coatscore (CS), skin thickness and average skin surface temperature on tick burdens in beef cattle. Bonsmara cattle (n= 143) were used to measure visible tick counts, body condition score, coat score, skin thickness, body height and length, body weight, body surface temperature, gender and inter calving period. Measurements were taken from April to December. All animals were managed extensively on natural and cultivated pastures near George in the Southern Cape. Female animals had significantly (p<0.05) greater tick infestation (37.98±2.7) compared to male animals (16.52±1.2). Age was a significant factor (p<0.001) with the younger animals below two years having (46.40±5.26) more ticks than those of two years and older (20.15±2.44). A significant negative correlation (p<0.001; -0.29) was reported between the infestation of ticks on the animals and the age of the animal. Animals with an average body weight below 250kg had 42% (p<0.05) more ticks compared to animals with a body weight above 250kg. Age of the animal and weight were highly correlated (r= 0.70); p<0.001), while the correlation between the number of ticks per cow and the mean weight was negatively correlated (r= -0.37; p<0.001). Skin surface temperature significantly influenced tick infestation on the animals (p<0.001). The degree of infestation increased as body surface temperature exceeded 30º C. Coat score, skin thickness, body condition score and inter calving period did not significantly influence tick infestation on the animals. The infestation of ticks on the animals were significantly influenced by body height (p<0.019) and body length (p<0.001). Animals smaller than a 130cm in height had a significantly (p<0.05) greater tick infestation (36.5±5) compared to animals taller than 130cm (21.2±1.5). This trend was also observed for body length. Animals with a body length shorter than 145cm had a greater (p<0.05) average tick infestation of 41.3±4.5 compared to 23.2±1.3 to animals longer than 145cm, indicating a 44% greater tick infestation in favour of the shorter animals. For increased production and tick resistance animals should have smoother coats and be able to dissipate heat effectively.

The traditional practice on beef cow-calf ranches in the high desert region of Eastern Oregon has been to breed the cows to calve in the Spring months. Interest has been growing recently in the practice of Fall-calving; that is, breeding cows to calve in the months of October and November. The Squaw Butte Experiment Station at Burns, Oregon, began a Fall-calving program with part of their range beef herd several years ago. They found that climatic conditions are generally more favorable for calving in the Fall, resulting in higher weaned-calf percentages. Calves from both Spring and Fall-calving herds were weaned in late Summer, with Fall calves averaging around 500 pounds compared with 330 pounds for the Spring calves. There was little doubt about the biological feasibility of the Fall-calving practice in that area, but its economic feasibility was somewhat in question. The purpose of this research was to analyze the economic aspects of Fall-calving and determine what are the most important factors in deciding its economic feasibility. A linear programming model was developed for comparing Fall and Spring-calving systems under different conditions. The model was designed to maximize net returns to labor, management and fixed resources in the beef enterprise. This model took account of range forage utilization patterns. Solutions from the model indicated that Spring-calving systems may have slightly higher net returns than Fall-calving because of two main differences: (1) the lighter Spring-born calves bring a higher average price per cwt. , and (2) the Fall-calving herd requires about 1500 pounds more Winter hay than cows in the Spring-calving herd. An algebraic relationship was found between calf price differentials and the price of meadow hay, which would equate the net return values for Spring and Fall-calving systems. With an expected differential of $2. 95, between the average prices of calves sold from the Spring and Fall-calving herds, it was found that a price as low as $14.12 per ton of meadow hay would be needed to equate the net returns of a Fall-calving system with those of a Spring-calving system (with calf sales on September 1). Labor costs were not included in the model, but the ranch operator's labor situation may well be the most important element in his decision to go with Fall rather than Spring calving. The main difference is in the times of the year that labor is needed. The Fall-calving system needs more labor in the Fall, and the Spring-calving system needs even more in the Spring. / Graduation date: 1972

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Call number: LD2668 .T4 1978 O36 / Master of Science

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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

Call number: LD2668 .T4 1985 M52 / Master of Science