One hundred and eight Holstein dairy heifers were divided into two weight blocks based on beginning body weight (E = < 182 kg, light, > 270 kg, heavy). Heifers within weight blocks were randomly assigned to one of five treatments. Treatments consisted of three levels of NDF (35%, 45%, 55%) at 100% ofNRC TDN recommendation, and three levels of TDN (85%, 100%, 115 of NRC) at 45% NDF for light heifers. For heavy heifers, treatments consisted of three levels of NDF (40%, 50%, 60%) at 100% NRC TDN, and three treatments with similar levels of TDN at 50% NDF. Heifers were fed total mixed rations of corn silage, alfalfa haylage, ground orchardgrass hay, soybean meal, high moisture corn and a mineral mix formulated for 0.68 kg ADG. Mean gains (kg/d) were 1.07 and .96 for the light and heavy blocks, respectively. DMI as a percent of BWT differed across NDF levels for light heifers (3r'= 2.96, 2.56, 2.57, 2.57, and 2.87 % of BWT for the low, med., high NDF, and low, high TDN treatments, respectively). Heavy heifer DMI% did not differ (.Â¥= 2.45, 2.40, 2.24, 2.15, and 2.42 % ofBWT for low, med., and high NDF, and low, high TDN treatments, respectively). Equations to predict DMI were developed using intake information from this and a previous study. Backward stepwise regression was utilized to generate a simplified model. Model selected was: DMI (kg/d) = -5.9781 + (2.2120E-05 * BWTSQ) - (5.5527 * GAIN) + (2.7837 * GAINSQ) + (0.4668 * NDF) + (5.3930 * NDFSQ) + (0.03285 * DM) + 1 (7.7859E-03 * BWT * GAIN);11 = 514, rz = .67. / Master of Science

M.S.

Three experiments were conducted to determine the relationship of milk fat secretion to concentration and ratio of rumen fermentation products, blood metabolic parameters, ration characteristics, and certain enzymic activity involved in fatty acid synthesis. In Experiment I, 21 cows in mid-lactation were randomized according to milk production to (1) roughage ration (~22% CF) restricted to NRC; (2) concentrate ration (~12% CF) ad libitum; or (3) concentrate ration (~12% CF) restricted to NRC and fed for 30 days. Ad libitum concentrate showed higher dry matter intake (DMI), body weight (BW), milk production than restricted concentrate. The opposite was true for fat test. Concentrate rations (ad libitum and restricted) when compared to roughage showed higher values for DMI, BW, milk production, serum glucose, molar proportion propionate and valerate and lower values for fat test and molar proportion acetate. In Experiment II, 24 cows 180 d. post parturition, were assigned to four rations based on anticipated parturition. Rations were: (1) roughage ad libitum (~20% CF); (2) concentrate ad libitum (~10% CF); (3) concentrate restricted (~10% CF) to NRC; and (4) normal ration (~14% CF) ad libitum. Cows on ad libitum and restricted concentrate consumed less dry matter, acid detergent fiber, neutral detergent fiber and crude protein than control cows (roughage and normal). Cows fed control rations gained more weight than concentrate fed cows. No difference was found for milk production. Milk protein was higher for control cows. Concentrate cows had lower fat test than control cows. Cows on all rations decreased fat test up to week three or four but by week eight or nine, concentrate fed cows had decreased to their lowest fat test. Energy restriction improved milk fat secretion compared to ad libitum intake after the eighth week. Molar proportion VFA favored propionate for concentrate cows and was similar for restricted and ad libitum concentrate. Total ruminal VFA concentration was higher for ad libitum concentrate cows and those cows showed slightly higher glucose and smaller blood acetate compared to control. Twelve cows in mid-lactation were fed the rations of Experiment II to determine the effect of available energy intake on activity of key enzymes of fatty acid synthesis. Activity of 6-phosphogluconate dehydrogenase was not different among rations. Mammary tissue showed from five to six times higher activity than adipose tissue. Fat tissue activity tended to be higher for concentrate rations compared to roughage. No differences among rations were found for glucose 6-phosphate dehydrogenase nor isocitrate dehydrogenase. Mammary tissue was 21 to 28 times more active than adipose tissue for latter enzyme. Fatty acid synthetase showed no difference in activity due to rations, but mammary tissue was seven to ten times more active than adipose tissue. / Ph. D.

no abstract provided by author / Master of Science

At least five million heifers are raised annually in the United States to maintain the dairy cattle population and provide for our future needs. These animals are in reality the very foundation of the dairy business and the prosperity of everyone connected with it are dependent, at least to a certain extent, upon how well and how economically these animals are produced. Any practice that might possibly increase the efficiency with which these animals are raised is certainly worthy of thorough study and consideration. In the past the livestockman has paid little attention to the effect that frequency of feeding may have on the efficiency with which his animals convert feed to milk, meat, and. eggs. This is surprising when one considers the feeding behavior of the animal in its native or unconfined state. In its wild state the animal took in food throughout the day and also undoubtedly at night. The quantity eaten and the frequency of intake was entirely dependent upon the desire of the animal and the availability of feed. This condition still exists to a very large extent in the case of the free-grazing animal. However, with the closely confined or hand-fed animal both the quantity of feed eaten and the frequency of intake are regulated according to the judgment of the husbandman. Since this is a definite change from the feeding habits of the animal in its native state, it is conceivable that some change in the efficiency of feed utilization, if not the overall physiology, of the animal has occurred as a result of domestication. Like the livestockman the research worker has considered frequency of feeding to have little or no influence on his research results. A limited amount of work (15, 70, 27) has demonstrated that frequency of feeding is important in livestock production. If additional work confirms these results, it will become necessary to interpret past feeding experiments in the light of these new findings and to give more attention to frequency of feeding in future nutritional research. Such information would be of considerable practical importance since it would be a comparatively simple matter to design automatic feeders which would feed animals at periodic intervals. The present study was initiated to obtain data on the differences in body weight gain, digestion coefficients, heart rate, rectal temperature, rumination time, and rate of passage of food of dairy heifers fed equalized intakes of feed two and ten times daily. / Master of Science

Master of Science

Master of Science

When corn and corn silage were fed in equal quantities to all lots of steers, the animals receiving four pounds of cotton seed meal per head per day made a greater average gain than those receiving either three, two, or one pound. The animals receiving one pound cottonseed meal per head per day made cheaper gains, however, than did those receiving either two, three, or four pounds. In other words, the average gains made by the various lots varied directly in proportion to the count of cottonseed meal fed, whereas the economy of gains varied inversely in proportion to the amount of cottonseed meal. The greatest gains and quickest gains are not always the cheapest gains. In the handling of feed lot cattle during the winter season under Virginia conditions, where cheap gains are sought, just enough high protein feed should be given to supply the actual need of the animal body. / Master of Science

A 130-d study was conducted with 24 363kg steers allotted to four diets containing .3 (basal), 1.4, 2.5 and 3.7% Mg, dry basis. An attempt was made to feed cattle on all treatments equal amounts of the basal diet, but steers fed the two high levels refused some feed. Grab fecal samples were collected during nine 10-d periods. Chromic oxide was used as a digesta marker. Jugular blood samples were taken on d 1, 5, 10, 20 and every 10 d thereafter. Steers were sacrificed at the end of the study for gross pathological and histological observations and tissue samples were taken for mineral analysis. Severe diarrhea was observed in steers fed the two higher Mg levels. Tubular strands of mucosal tissue were consistently voided in the feces of cattle fed these levels of Mg. Steers fed the two higher Mg levels became more lethargic as the study progressed. Fecal dry matter content and apparent dry matter digestibility decreased linearly (P<.01) with increasing dietary Mg. Weight losses for steers fed 1.4, 2.5, or 4.7% Mg were 5, 27 and 29 kg, respectively, during the study, compared to a weight gain of 9 kg for cattle fed .3% Mg (quadratic effect, P<.01). Apparent absorption of Mg generally increased with dietary Mg (P<.01), except between d 20 and 70 when it decreased (P<.01). Apparent absorption of Ca and P generally decreased with dietary Mg but effects on P absorption were not always significant. Increasing dietary Mg resulted in a linear elevation of serum and erythrocyte Mg (P<.01) and inorganic P (P<.05) and a linear decrease in serum Ca (P<.01). Plasma osmolality tended to be lowest in steers fed the highest dietary Mg. Serum parathyroid hormone was suppressed at the higher Mg intakes at 3 h but not at 9 h after feeding. Ruminal fluid pH increased as dietary Mg increased from .3 to 2.5%, then decreased (quadratic effect, P<.05). A linear increase in pH (P<.05) was recorded with increasing dietary Mg in digesta samples taken at slaughter from the lower ileum and large intestine. The Mg concentration in the liver, kidney, skeletal muscle and rib-bone and the P concentration in the skeletal muscle increased linearly (P<.05) with dietary Mg. Histologically, amorphous crystals were seen in the kidney tubules of all animals. Increasing dietary Mg in the steers caused a progressive degeneration of the rumen papillae epithelium. / Ph. D.

Six lactating Holstein cows fitted with rumen cannulae and T-type cannulae in the proximal duodenum were used to measure digesta and nitrogen compounds flow to the small intestine during early and midlactation. Fish meal and soybean meal provided 54 and 56% of the protein in the diets composed of corn grain, corn silage and orchardgrass hay, and which contained 15.4 and 15.5% crude protein and 20.9 and 20.5 acid detergent fiber. Spot samples of digesta were collected from the rumen, duodenum and rectum over a period of 72 hours. Co-EDTA and ytterbium were used as liquid and particulate digesta markers to estimate flow and digestibility of nutrients. Cytosine was used as microbial marker. True organic matter digestibility in the stomachs was 48.4, 49.8, 44.9, and 53.2% for fish meal and soybean meal diets and early and midlactation respectively. Protein degradability in the stomachs were 47.2, 65.8, 56.7, and 56.2% for fish meal and soybean meal diets and early and midlactation respectively. Amino acids intake was greater for soybean meal diet but total amino acids reaching the the duodenum were similar for both diets. Valine, methionine, lysine and histidine were less degraded for fish meal but were extensively degraded in soybean meal diet. Least degraded for both diets were glycine, valine, serine, proline and histidine. The advantage of greater quantity of protein escaping ruminal degradation with fish meal supplementation was counterbalanced by less microbial synthesis in the rumen partly explaining the similar response obtained with diets especially in early lactation. / Ph. D.