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Purified brush border and basolateral membranes were isolated from homogenized intestinal enterocytes of Holstein steers by divalent cation precipitation followed by differential and sucrose density gradient centrifugation. Membrane marker enzymes were used to determine the effectiveness of the fractionation procedure. Alkaline phosphatase and sodium-potassium adenosine triphosphatase served as the marker enzymes for the brush border and basolateral membranes, respectively. The brush border fraction was enriched 5.1-fold over the cellular homogenate. Purification of 10.1-fold over cellular homogenate was obtained for the basolateral membrane fraction. Electronmicrographs and osmotic response data were used to confirm the vesicular nature of the membrane preparations. Brush border membrane vesicles from bovine jejunal and ileal tissue were used to evaluate lysine (LYS) and methionine (MET) transport. Total transport of LYS and MET was divided into mediated and diffusion components. Mediated uptake was further divided into sodium-dependent (Na⁺) and sodium independent (Na⁻) systems. Total LYS and MET uptake by ileal tissue tended to be higher than jejunal tissue at all concentrations evaluated but differences were significant (P<.O5) at 2.5 and 7.5 mM for LYS and 5, 12.5 and 15 mM for MET. The greater capacity of ileal tissue appeared to be due to the Na⁺ component of LYS uptake and the diffusion component of MET uptake. Methionine transporters had lower affinities and higher capacities than the corresponding LYS transporters in both ileal and jejunal tissue. Methionine transport was greater (P<.O5) than LYS transport in both ileal and jejunal tissue when initial amino acid concentration was 7.5 mM. When initial amino acid concentration was 1.25 mM, MET uptake was greater (P<.13) than LYS uptake in jejunal but not ileal tissue. The relative contribution of mediated and diffusion uptake systems to total MET and LYS uptake was found to be dependent of substrate concentration. / Ph. D.

Two groups of cows were fed a ration in which three pounds of a grain mixture was used to every four pounds of hay. Two cows (Test Tube and Deborah) were fed Timothy hay with a grain mixture containing yellow corn. The other three cows (Dolly, Connie and Dot) were fed Alfalfa hay with a grain mixture containing white corn. The grain was also modified for protein balance. Relationships of carotene and Vitamin A concentrations in the blood, milk and feed were then studied. An attempt was made to correlate the various factors involved, the variables being: period of gestation; time after calving; intake of the vitamin and its precursor in the feed; milk produced; percent of the concentration of Vitamin A activity of blood and milk represented by carotene; total Vitamin A activity of the same; and, the efficiency of the secretion in the milk of the Vitamin A activity of the feed ration. The methods of determination of the carotene and Vitamin A (together constituting the Vitamin A activity) are given with details of the calculations. Milk was collected on the first, third and fifth day after calving and at approximately monthly intervals thereafter. Having begun the experiment with the cows in various stages of gestation, it was possible to obtain only six samples from Dot while ten were collected from others. The blood samples also were taken monthly. The feeds were analyzed at three monthly intervals and the rate of loss of Vitamin A activity observed. Minimum values were used in all calculations. / M.S.

Mammary tissue from nine Holstein cows was collected within one week of parturition, at 60 and 180 days postpartum. Blood samples were collected at 6-hr intervals from two days prior to . until two days after surgery. A membrane-enriched fraction of tissue homogenates was prepared by differential centrifugation. Displacement curve data was analyzed by a microcomputer program. Mean prolactin (Prl) during the periparturient period was greater than either postpartum period, but not prior to biopsy. Dissociation constants (Kd) estimated with NIH-bPRL-6 as competitor were not different among stages of lactation, and averaged 8.97 x 10⁻⁸M. Receptor concentrations were less during _the periparturient period than later lactation. The Kd was 100-fold greater when estimated with human growth hormone as competitor. It is concluded that lactogenic hormone receptor concentrations in bovine mammary tissue increase with the onset of lactation, following a pattern similar to that observed in non-ruminants. Three experiments were conducted to investigate endocrine metabolic hormone profiles in Holstein cattle of differing genetic merit at several ages. Control animals were randomly bred to non-AI sires originating in the Virginia Tech Dairy herd. Selected animals were offspring of commercially available AI sires. In one experiment, mean plasma Prl was greater in control animals after feeding and insulin injection, while growth hormone (GH) was greater in selected animals at all ages. Free fatty acids were greater in selected animals at 6 and 24 months of age, while glucose (Glc) and urea were unaffected by genetic merit. In a second experiment, Holstein bull calves were administered Glc and thyrotropin releasing hormone (TRH) on different days. Plasma GH was greater in selected animals. Plasma Prl was greater in control animals after TRH. In the third experiment, Holstein cows received TRH at 30, 90 and 200 days postpartum (DPP). Net energy balance was negative at 30, while positive at 90 and 200 DPP. Plasma GH before and after TRH was greater in selected animals, and greater during early than later lactation. Thus, the results of the three experiments indicate that increased plasma GH may be associated with selection for increased milk yield. / Ph. D.

Data for this study was collected over a six-year period (1970 through 1975) on 217 bulls and 211 steers at the Bland Correctional Center, Bland, Virginia. Animals of this study were primarily cross-breds of Angus, Charolais, Hereford, Holstein and Simmental breeds. The objective of this study was to compare bulls and steers for growth and carcass traits. Bulls (220, 310, 449 kg) weighed more than did steers (204, 273, 381 kg) at weaning, 12 and 18 months of age, respectively, (P < .05), and scored higher on condition at weaning and 18 months of age (P< .05). Bulls (501, 281, 0.48 kg) were also heavier than steers (414, 219, 0.39 kg) for live slaughter weight, carcass weight, and carcass weight per day of age, respectively, (P< .05). Bulls and steers did not differ in ribeye area per 100 kg of carcass weight, backfat thickness, and marbling scores. Percent kidney and kidney fat per carcass weight was less in bulls (1.59%) than steers (2.58%) (P < .05). Bull carcasses graded low good whereas steer carcasses graded low to middle good. Armour tenderometer measurements were 8.25 kg and 7.09 kg for bulls and steers, respectively, (P < .05) , with any reading below 8.2 kg being of acceptable tenderness. Carcass yield grades were 1.29 and 1.90 for bulls and steers, respectively, (P < .05). The superior growth rate of bulls and the minimal sex differences in carcass quality renders the present market bias against bull beef questionable. / Master of Science

Bovine morulae (day 6: n=257) were obtained to evaluate the [effect of immunoglobulins (Ig) on early bovine embryo development in vitro. Fifty-four cows superovulations were conducted in 36 cows with follicle stimulating hormone. Embryos were collected by non-surgical procedures and morphologically evaluated and randomly assigned to culture. Embryos were cultured in Ham's F-10 containing 10% (6.4 mg/ml) steer serum (SS), 1% (.64 mg/ml) bovine gamma . globulins (GG), 1% (.64 mg/ml) bovine IgG, 1% (.64 mg/ml) bovine 1gM, 10% SS plus 1% GG, 10% SS plus 1% 1gG, or 10% SS plus 1% 1gM. Embryos were cultured to the hatched blastocyst stage or degeneration and evaluated at 12 h intervals. / Master of Science

The ability of mammary tissue from prepubertal bulls and heifers of beef and dairy breeds to respond to hormonal stimuli through synthesis and secretion of milk proteins was studied. Experimental animals were six to eight month old Angus and Holstein cattle. All subjects were injected with estradiol and progesterone for seven days and slaughtered on day 15. Mammary tissue was explanted and cultured for 96 h in basal medium (B) which contained hormones necessary for maintenance, or stimulatory medium (P), further supplemented with prolactin. Selected cultures were incubated for 24 h in B or P medium containing 3H-amino acids. Concentrations of non-labeled alpha-lactalbumin (Alac), 3H-Alac, and 3H-total protein (TP) were determined in media and in explant homogenates. Among cultures of bull mammary tissue, Angus explants secreted greater overall quantities of 3 H-TP and 3H-Alac than Holstein explants (p<.05). Secretion of Alac was also greater in Angus cultures at two of eight treatment periods (p<.01). Concentrations of all three protein fractions were likewise enhanced in homogenates of Angus explants for at least three of four treatment periods (p≤.05). Presence of prolactin in medium stimulated secretion of Alac (p<.005), and accumulation of all three fractions in explants (p<.10). Holstein heifer explants secreted more Alac at three of eight treatment periods than Angus explants (p<.0005). Overall secretion of ³H-TP and ³H-Alac also was elevated in Holstein over Angus females (p<.10), as were concentrations of all three fractions in homogenates (p≤.01). Presence of prolactin had no direct effect on any protein parameters in female tissue. I conclude that mammary tissue of immature bulls and heifers can be hormonally induced to express it's genetic merit for milk production (based on breed differences), through synthesis and secretion of milk proteins. Prolactin stimulated protein production in bulls but not in heifers. These findings indicate that similar methods of stimulating mammary tissue to produce milk proteins may be adaptable for commercial evaluation of genetic potential for milk production, especially in young bulls. / M.S.

Forty-two high producing Holstein cows were paired by body condition and mature equivalent milk production and fed either a high or low energy complete ration ad libitum during the last 16-20 weeks of lactation. Cows fed the high energy ration ate more feed, produced more milk and gained more body condition than cows fed the low energy ration. Cows were fed to maintain condition during the dry period. During weeks 3-15 of the next lactation, half the cows in each condition group (fat or thin) were fed a mixed ration with soybean meal (SBM) as the major protein source. The remaining cows were fed a ration with dried brewers grains (DBG) as the main protein source. / Master of Science