The ability of mammary tissue from mature Holstein bulls to respond to hormonal stimuli in organ culture to synthesize and secrete milk proteins was studied. Sixteen bulls from the genetic selection and control lines developed at Virginia Polyteclmic Institute were randomly assigned to either a non-treated or steroid pretreated group. The steroid pretreated group received estradiol 17-B and progesterone at 0.1 and 0.25 mg/kg/day, respectively, for 7 d starting 15 d before slaughter. Mammary tissue was explanted and cultured for up to 96 h in basal medium (B) which consisted of Media 199 supplemented with fetal calf serum and bovine insulin, or stimulatory medium (St), which was further supplemented with triiodothyronine, estradiol 17-B, hydrocortisone, and bovine prolactin (PRL). Explants in duplicate multi-well culture dishes were incubated in the presence of 3H-Iabeled amino acids or 3H-Iabeled thymidine. Measurements made included: casein in media and homogenized tissue, alpha-lactalbumin in homogenized tissue, tri-chloro-acetic acid precipitable 3H-protein in media and homogenized tissue, and DNA content of cultured tissue. A subset of cultured explants from each bull was fixed and embedded for histological evaluation and auto radiographic localization of incorporated 3H-labeled thymidine. Synthesis and secretion data, as well as growth responses of the epithelium were compared between selection and control bulls. / Master of Science

Increasing feeding costs has led many dairy farmers to use pasture for lactating cows to reduce their production cost. Little is known about the efficiency of nutrient utilization by lactating cows under grazing conditions. The objective of this study, therefore, was to investigate ruminal turnover, intake and site and extent of nutrient digestion in grazing lactating cows. Four dual cannulated (rumen and proximal duodenum) cows were randomly assigned to two groups to graze permanent pasture with no supplement or with 6.4 kg/d corn-mineral mix in a switchback design with three periods of two wk each. Solid and liquid markers (chromic oxide and CoEDTA), used to estimate duodenal flow, fecal output, and ruminal turnover, were administered through the rumen cannula twice daily at 1100 and 2300 h. The supplemented cows had greater milk production (23.7 kg/d) than those on pasture only (19.5 kg/d) with an increase of .66 kg of milk production per kg of concentrate. Corn, however, depressed milk fat percentage resulting in a similar milk fat yield between the two diets. Supplemental corn reduced rumen ammonia-N (22 vs 17 mg/dl) and increased N recovery at the duodenum (86 vs 75% of N intake). True Nitrogen digestibility averaged 72% and microbial N flowing to the duodenum was 67% of the total N flow. This results indicated that grazing cows may benefit from concentrates containing undegradable protein. Daily OM intake was not different, but when cows were fed the supplemented diet, pasture OM was lower than when fed pasture only. Organic matter, NDF and ADF digestibility in the rumen and whole digestive tract were greater when cows were fed. Cellulolytic activity may have been reduced by grain supplementation due to decreased ruminal pH (6.4 vs 6.2). The reduction in fiber digestibility may explain the decrease in forage intake when cows were fed supplemental grain. Ruminal rates of passage (kp) for solid (7.3 %/h) and liquid (18.2 %/h) markers were similar for both diets. The kp values observed for solid and liquid indicate that grazing cows may have a faster ruminal turnover than cows fed diets containing primarily hay or silage. / Master of Science

Monthly milk production data collected by DHI supervisors in 28 Virginia dairy herds over a three year period were analyzed. Relationships between somatic cell count and milk production were determined. A curvilinear relationship between somatic cell count and daily milk yield was shown to exist. The relationship indicated daily milk yield declined more rapidly as somatic cell counts increased from 50 X 10³ through 300 X 10³ cells per ml compared to daily milk decline as somatic cell counts rose from 400 X 10³ through 1,200 X 10³ cells per ml. Daily milk yield declined at a slower rate at somatic cell levels above 400 X 10³ cells per ml. There was an apparent cumulative or continual relationship between somatic cell count and daily milk yield. Losses and declines in test day milk production were greater when cumulative somatic cell count was considered. Complete lactation records of 305-day, mature equivalent milk production were compared to weighted, lactational somatic cell counts. Lactational milk production losses were not as great as daily milk production losses, extended to full lactation, indicated. Design difficulties and inadequacies of models used in complete lactation evaluation may explain the discrepancies. A maximum somatic cell count of 150 X 10³ to 200 X 10³ cells per ml was indicated as an optimum level for somatic cell count. Above this level milk losses were excessive. / Master of Science

I. Introduction. II. Production of Sanitary Milk. III. Milk as a Disease Distributor. IV. Pasteurization of Milk. V. Methods of Bacterial Count. VI. Intensive Study of Desirable and Undesirable Bacteriain Milk. VII. Conclusion. VIII. References / 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.

Responses to daily abomasal infusions of 400 g sodium caseinate, 400 g hydrolyzed casein or 11.3 g L-methionine-30.1 g L-lysine and rumen degradability of dietary protein were studied in eight Holstein cows during mid-lactation. Basal diets contained com silage, com and either soybean meal or 60:40 soybean meal:corn gluten meal, and had estimated rumen degradabilities of 70 and 60.5%. Duodenal cannulas were installed in four of the cows to allow measurement of digesta composition and flow. Methionine-lysine infusion increased milk protein percentage on both diets and milk fat percentage and yield on the soybean meal diet. Sodium caseinate increased milk and milk protein production, body weight gain, and decreased milk fat percentage, but not yield. Hydrolyzed casein did not produce the same responses, suggesting differences in amino acid absorption and utilization between the sources. Basal diet affected the responses to abomasal infusions demonstrating that amino acid nutrition of the cow was affected by dietary protein degradability. Concentration of total essential amino acids, branched-chain amino acids, and urea cycle amino acids were increased by the infusion of the caseins. There were differences between the caseins in their effects on individual plasma free amino acids. Methionine-lysine infusion increased plasma lysine and taurine, a metabolite of methionine, suggesting that infused methionine was extensively metabolized. Total duodenal nitrogen flow and non-microbial nitrogen flow tended to be increased by inclusion of corn gluten meal in the diet. Rumen degradation of crude protein was greater for the soybean meal diet. Both diets had lower rumen degradability than predicted from previous experiments. / Ph. D. / incomplete_metadata

Two trials were conducted to determine the effect of protein degradability (low (LD) vs high (HD)) and evaporative cooling (shade cooling vs shade) on performance of 60 lactating Holstein cows in mid-lactation. Cooling and the LD diet increased milk production, 3.5% FCM and feed efficiency in trial 1 (24 cows) while in trial 2 (36 cows) LD diet increased milk production and feed efficiency and cooling did not exert a significant effect. Differences between trials were probably due to higher environmental temperature humidity indexes (77.0 vs 72.0), and a higher quality of the rumen bypass protein in the LD diet in trial 2 than trial 1. Cooling reduced respiration rates in trial 1 and respiration rates, rectal and inner ear temperatures in trial 2. Eating patterns were unaffected by protein degradability or cooling.

Thesis (MScAgric (Animal Sciences)--University of Stellenbosch, 2007. / The objective of this investigation was to determine the effect of supplemented conjugated linoleic acid (CLA) on milk production and milk composition of lactating dairy cows in production systems commonly used in South Africa. In the first of three trials, samples of 24 bulk tanks were collected to get an impression of the CLA status of milk in the Western Cape Province, South Africa. Six samples were each collected from Jersey and Holstein herds in total mixed ration (TMR)-based systems. Another six samples were each collected from Jersey and Holstein herds on pasture-based systems. An additional three samples were also collected from co-op silos. One of these came from a mixed herd on TMR, one from a Jersey herd on TMR and the third sample from a mixed herd on pasture. The CLA levels of the milk were within the range reported in literature, albeit on the low side. The mean CLA level in milk fat of cows from pasture and TMR-based systems were 10.5 and 5.45 mg/g of fatty acids, respectively. This is in agreement with trends reported in the literature with cows on pasture having higher levels of CLA in their milk than cows on TMR’s. In this study, breed had no effect on the CLA level in milk fat.

Thesis (MScAgric)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Statistical analysis was conducted on data from two Elsenburg herds, containing 105 Jersey and 232 Holstein cows. The data was examined for external factors which may affect milk yield and milk composition. The data consisted of 337 first lactation records, taken over a 20 year time period. Breed of cow had an effect on milk yield, butterfat and protein production, as did the year in which the cows were born and the age of the heifer at first calving. There was a significant interaction between the breed and year of birth. There are other external factors, which are difficult to quantify, which may have an effect on production. In the following trials, eight ruminally cannulated dairy cows (four Jerseys and four Holsteins) were used to determine the effect of breed on forage digestibility in the rumen. All cows received a high concentrate mixed ration, with supplementary wheat straw. An in situ rumen degradability trial was conducted with three different forages, viz. lucerne, wheat straw and NaOH-treated wheat straw. The bags were incubated in the rumen for time intervals of 2,4, 8, 12, 16,20,24, 36,48, 72 and 96 hours and samples were analysed for dry matter (DM) and neutral-detergent fibre (NDF). Higher rumen degradability values (P<0.01) ofDM and NDF were observed in Jerseys for all three forages. Differences were more apparent for wheat straw and treated wheat straw than for lucerne. The rate of passage of digesta from the rumen was measured in both breeds by a chromium mordanted wheat straw marker. The Holsteins manifested a higher rate of passage (P<0.05) than the Jerseys, while daily feed intakes were also higher (P<O.Ol) for the Holsteins than for the Jerseys. Daily feed intake, expressed as percentage of body weight was, however, slightly higher for the Jerseys than for the Holsteins. The pH value of the rumen fluid was measured at 0, 4, 8, 10 and 12 hours postfeeding. The only significant difference (P<O.OI)in pH between the breeds was at 4 hours post-feeding, when the ruminal pH dropped more rapidly in the Holsteins than in the Jerseys. The pH in the Holsteins dropped below 6.2, which may have inhibited fibrolytic microbe activity in the rumen, resulting in a lower effective degradability of forages. Total volatile fatty acids were higher in Holsteins from four to 10 hours after feeding, but no differences were observed in acetic acid:propionic acid ratios. It was concluded that Jerseys appear to utilize forages more efficiently than Holsteins and that the differences are more apparent in low quality forages than in high quality forages. / AFRIKAANSE OPSOMMING: Statistiese analises is op data van twee kuddes te Elsenburg uitgevoer, bestaande uit 105 Jersey- en 232 Holsteinkoeie. Die data is ondersoek vir eksterne faktore wat melkproduksie en melksamestelling kan beinvloed. Die data het uit 337 eerste-laktasierekords bestaan, wat oor 'n periode van 20 jaar ingesamel is. Ras van die koei, sowel as die jaar van geboorte en ouderdom met eerste kalwing het 'n invloed op melkproduksie, bottervet- en proteienopbrengs gehad. 'n Betekenisvolle interaksie is tussen ras en jaar van geboorte waargeneem. Ander moeilik kwantifiseerbare faktore mag ook 'n invloed op melkproduksie he. In daaropvolgende proewe is agt rumen-gekannuleerde melkkoeie (vier Jerseys en vier Holsteins) gebruik om die invloed van ras op ruvoerverteerbaarheid in die rumen te bepaal. Al die koeie het 'n hoe-kragvoerdieet ontvang, aangevul met koringstrooi. 'n In situ rumendegradeerbaarheidstudie is met drie verskillende ruvoere, naamlik lusernhooi, koringstrooi en NaOH-behandelde koringstrooi uitgevoer. Die ruvoere is vir tye van 2, 4, 8, 12, 16, 20, 24, 36, 48, 72 en 96 ure in die rumen geinkubeer en monsters is ontleed vir droemateriaal (DM) en neutraal-bestande vesel (NDF). Hoer rumen-degradeerbaarheidswaardes (P<O.Ol) van DM en NDF is in Jerseys waargeneem as in Holsteins vir al drie ruvoere. Verskille was meer opvallend vir koringstrooi en NaOH-behandelde koringstrooi as vir lusem. Uitvloeitempo van digesta uit die rumen is in beide rasse met behulp van chroomgemerkte koringstrooi bepaal. Hoer uitvloeitempo's is in die Holsteins waargeneem as in die Jerseys, terwyl daaglikse voerinnames ook hoer was (P<O.05) by die Holsteins as by die Jerseys. Daaglikse voerinname, uitgedruk as persentasie van liggaamsmassa, was egter effens hoer (P<O.OI)by die Jerseys as by die Holsteins. Die pH van die rumenvloeistof is op 0, 4, 8, 10 en 12 ure na voeding gemeet. Die enigste betekenisvolle verskil (P<O.OI)in pH tussen die rasse het op 4 ure na voeding voorgekom toe die pH van die rumeninhoud vinniger in die Holsteins as in die Jerseys gedaal het. Die pH in die Holsteins het onder 6.2 gedaal, wat moontlik fibrolitiese mikrobe-aktiwiteit in die rumen kon inhibeer, met 'n gevolglike daling in effektiewe degradeerbaarheid van die ruvoere. Vanaf 10 ure na voeding was die totale vlugtige vetsuurkonsentrasies hoer in die Holsteins, maar geen verskille in asynsuur:propionsuurverhoudings is waargeneem nie. Die gevolgtrekking is gemaak dat Jerseys skynbaar meer doeltreffend is om ruvoere te benut as Holsteins en dat die verskil tussen rasse meer opvallend is vir lae kwaliteit ruvoere as vir hoe kwaliteit ruvoere.

In experiment 1, fourteen cows were blocked for milk yields and balanced for days in lactation. Treatments were: (1) Air conditioning (AC), five cows; (2) Evaporative cooling (EC), four cows; and (3) Conventional shade (S), five cows. Sequential samples were taken for 8 h at 12 min intervals starting at 2200 and then at hourly intervals for 13 h. Serum was assayed for insulin, thyroxine (T4), triiodothyronine (T3) and cortisol using a double-antibody radioimmunoassay procedure. Free fatty acids (FFA) were determined in serum by an enzymatic method. In experiment 2, ten cows were blocked for milk yields and days in lactation. Treatments were: (1) Evaporative cooling (EC), five cows; and (2) conventional shade (S), five cows. Blood was drawn at 60 and 90 d of lactation. Blood sampling, hormone and FFA assays were carried out as in experiment 1. Sequential samples were taken for 8 h at 12 min intervals starting at 2300 and then at hourly intervals from 1030 to 1830. In experiment 1, insulin was depressed (P <.05) treatment effects for T3 in either experiment. There were significant treatment differences (P <.05) in respiration rates and body temperatures in experiment 1. Shade were higher than AC or EC cows. These studies demonstrated that summer heat stress depressed insulin and increased FFA with variable effects on T4 and cortisol but no effect on T3.