Series of blood samples were taken from Holstein calves before, and at 2, 4, and 6 hours after feeding. The blood plasma levels of tryptophane and methionine were determined by microbiological assay. It was found that the blood plasma levels of tryptophane and methionine varied considerably at different time intervals after feeding milk. One calf was fed 50 grams dl-methionine with its regular feed of milk, and series of blood samples were taken and assayed as in previous work. The methionine level increased to approximately 4 times its initial value by 2 hours after feeding, continued to rise, and at 6 hours after feeding was more than 10 times the original level. At the same time the tryptophane level showed a consistent decline. Determinations for total amino nitrogen were made, using a modification of the Folin-Wu method. The values obtained at different time intervals after feeding ranged from 6.45 to 9.33 mg./100 ml. blood. It was found that feeding methionine increased the blood level for total amino nitrogen, reaching a peak four hours after feeding. A special electrometric titration apparatus was used for making titrations. Approximately 1750 assays, consisting of standards and test samples, were titrated in this experiment. / M.S.

Master of Science

Master of Science

Master of Science

Two feeding trials were conducted to study the effects of source of concentrate and level of concentrate and roughage on milk composition; changes in certain blood and rumen constituents; and efficiency of conversion of feed protein to milk protein. Trial A (63 days) employed two groups of six cows each. The following rations were fed: 1) Control consisting of 1 lb. concentrate per 3.5 lb. milk, 40 lb. corn silage. and orchardgrass hay, ad libitum; 2) Low-roughage composed of 5 lb. orchardgrass hay, 10 lb. corn silage, and concentrates ad libitum. Trial B (70 days) employed two groups (four each) of late and three of early lactation. A control ration similar to that fed in trial A, except 48 instead of 40 lb. of corn silage, and a low-roughage ration of only 2 lb. hay and concentrates ad libitum, were fed to two groups in each stage of lactation. The remaining early lactation group received a ration comparable to the control except the corn in the concentrate was replaced by lactose. The twelve early lactation cows were subjected to a balance study at the end of the feeding trial. Intake of concentrates and milk yields on the low-roughage rations were higher in trial A than trial B. Percent milk fat and the acetate/propionate ratio of rumen fluid were decreased by low-roughage; while rumen propionate was increased. No significant differences in milk protein were observed. Milk SNF and lactose-mineral were increased on low-roughage in trial B. Feeding only 2 lb. hay daily resulted in bloat and diarrhea; while blood glucose and gamma globulin were increased. Lactose increased rumen butyrate and tended to increase milk fat percentages above the controls. Digestibilities of all dry matter components, except crude fiber, were higher on low-roughage. Cows on low-roughage digested a larger proportion of the dietary protein, but were loss efficient in the conversion of digested protein to milk protein. / M.S.

Twenty-four cows in a production trial and 8 cows fitted with ruminal and duodenal cannulas were used in 4 x 4 Latin squares to investigate the effects of dietary protein degradability and supplemental fat on rumen, blood, and milk components. Diet dry matter contained 16% CP with two levels of rumen undegradable protein (RUP) obtained by substituting blood meal for soybean meal. Treatments were 29% RUP, 0% added fat; 29% RUP, 2.7% added fat (Calcium soaps of fatty acids); 41% RUP, 0% added fat; and 41% RUP, 2.7% added fat. Dry matter intake was depressed 6.2% by added fat. Plasma urea N (PUN) increased with added fat and 41% RUP, however greater changes were observed due to time of feeding. Milk production increased 7.1% in both breeds and 4% fat corrected milk increased by 8.4% in Jerseys fed added fat. Milk protein yield decreased in Holsteins fed 41% RUP. Milk protein content was reduced 7.1% by added fat and 3.9% by 41% RUP, and milk urea N (g/100g N) was increased by added fat and 41% RUP. Milk urea N followed PUN pattern throughout the day. Added fat reduced content, but not yield, of milk components. Blood meal substitution decreased content and yield of milk protein and casein N. / Master of Science

Data from the University of New Hampshire were used to analyze dry matter intake and milk production in Holstein dairy cows. Equations predicting 4% FCM and dry matter intake were derived from this data using ordinary least squares. Days in milk, available nutrients, calving date, and previous period 4% FCM accounted for 90% of the variation in 4% FCM for heifers and 93% of the variation in 4% FCM for cows with previous lactations. Days in milk, acid detergent fiber, calving date, and dry matter intake from the previous 28 day period accounted for 71% of the variation in heifer dry matter intake and 79% of the variation in dry matter intake for the older cows. First period dry matter intake was predicted from first period 4% FCM, cow body weight, and acid detergent fiber of the ration. The lower R² for the first period dry matter intake (41% for heifers and 43% for cows with previous lactations) indicated that dry matter intake for a cow within a lactation was much more predictable than dry matter intake between different cows. Rations were balanced for absolute amounts for simulated lactating cows using NRC requirements and 4% FCM and dry matter intake generated from the prediction equations. Relationships between 4% FCM and nutrient concentrations were determined for heifers and multiparous cows. These recommendations suggest maximum feeding of nutrients to groups producing at least 35 kg of 4% FCM daily. The effect of grouping and individual feeding on 4% FCM were analyzed. Independent variables included nutrient concentration, dry matter intake, groups, calving interval, variability of 305 day milk production within the herd, and level of feeding. Holding dry matter intake and nutrient concentrations constant, increasing the number of groups from one to two increased 4% FCM by 0%-3%, two groups to three groups by 0-2%, and three groups to four groups by 0-1%. Changing from one group to individual feeding increased 4% FCM by 2%-4% and two group to individual feeding increased 4% FCM by 0%-3%. The range of figures was influenced by herd production level, calving interval, and variability of within herd production. High variability of production favored additional groups, while high calving intervals favored individual feeding. To estimate expected change in profitability due to a change in grouping or feeding methods, multiply previous milk revenue by expected percentage change and subtract the increased cost of feeding. Feeding less than the group average for nutrients was not found conducive for increasing profitability. In fact, production response to protein suggested that the low producing groups in multiple group feeding systems should be increased in protein slightly. Individual feeding had the most potential for profitability, although group feeding compared favorably under some circumstances. If cows were grouped, a minimum of two groups was generally preferable. If the high producing group did not satisfy the needs of the high producing cows, or the drop in nutrients between groups was substantial, a three group system would appear more favorable. / Ph. D.

A computer modeling experiment showed that grouping dairy cattle based on requirements of crude protein and net energy per kilogram expected dry matter intake (Grouper) had unique characteristics relative to other grouping systems. The objective of this study was to adapt the computerized Grouper system for practical use by implementing a field trial in commercial dairy herds to determine its managerial benefits and economic merit. Ten cooperating dairy herds participated in the one year trial. Herds were grouped monthly using test day information obtained from the Dairy Records Processing Center, Raleigh, NC and reports mailed to the cooperators. Feed consumption data and a record of cows not placed according to Grouper recommendations were collected during monthly herd visits or by mail. One set of analyses examined trends in Dairy Herd Improvement (DHI) variables through trial duration while another set compared Grouper to a comparable milk production grouping program with all herd test day information grouped with both systems. No significant changes in DHI variables could be attributed to the Grouper system. Grouper retained younger, smaller cows and those with higher fat test in the high group longer and moved older, larger cows and cows with lower fat test into the low group sooner than grouping by milk production. Grouper produced higher intraclass correlations among cows in groups for percent Total Digestible Nutrients (0.59 versus 0.41) and percent crude protein (0.65 versus 0.57) than milk production grouping. Economically, Grouper was significantly more expensive when comparing systems based on average feed cost per cow per day. However, this did not consider increased income or decreased costs associated with the system or account for possible benefits such as better health and higher production resulting from feeding more precisely each individual's nutrient requirements. The Grouper program has been automated to be used through either a dairy records processing center or an individual microcomputer and can be considered a practical management tool to help the dairy manager group cows more efficiently and feed more accurately. / Master of Science

Equations to predict daily dry matter intake (DMI) of individual animals were developed with 118 Holstein heifers fed totally mixed rations (TMR). Animals grouped according to body weight (136, 227, 317 kg) were fed TMR (corn silage, ground hay, high moisture corn, soybean meal) once daily for 28 days. Rations were balanced to mean body weight according to National Research Council (NRC) recommendations for protein, vitamins and minerals, and to 85, 95, 105, and 115% of recommendation for energy. Independent variables were body weight (BWT, kg/day) daily body weight gain (GAIN, kg), environmental temperature (AMBT, °C), ration acid detergent fiber (ADF, percent of dry matter), neutral detergent fiber (NDF, percent of dry matter), net energy for maintenance and gain (NEM, NEG, megacalories), total digestible nutrients (TDN, percent of dry matter), and bulk density (BULK, g/ml as fed). Squared terms, appropriate interaction terms, and metabolic body weight (MBWT, kg^.75) were included in the model. Stepwise regression was utilized to generate two models, simplified and expanded. Simplified model was: DMI (kg/day) = -29.86 + (-.54E-05 * BWT²) + (.157 * MBWT) + (2.090 * GAIN) + (-.118 * GAIN²) + (.730 * TDN) + (-.005 * TDN²) + (-.001 * BWT * GAIN) + (-.019 * TDN * GAIN); n = 4797, r² = .59, s_y.x = 1.18. Expanded model was: DMI (kg/ day) = -1906.91 + (-0.04 * BWT) + (0.37 * MBWT) + (32.36 * ADF) + (2305.51 * NEM) + (-664.06 * NEG) + (-0.08 * AMBT) + (-0.13 * ADFSQ) + (-637.68 * NEMSQ) + (42.31 * NEGSQ) + (-5.35 * BULKSQ) + (0.001 * AMBTSQ) + (-1.56E-04 * BWT * ADF) + (8.873E-05 * BWT * AMBT) + (246.30 * NEM * NEG) + (-21.30 * NEM * ADF) + (7.83 * NEG * ADF) + (0.04 * NEG * AMBT) + (0.01 * GAIN * ADF) + (-0.01 * GAIN * AMBT); n = 4429, r² = .65, s_y.x = 1.09. Predicted intakes by simplified equation agree with those of NRC at TDN recommended by NRC and .7 kg/day. Computerized ration formulation systems were developed using simplified model. Expanded model requires further refinement prior to incorporation into a ration formulation system. / Ph. D.

Thesis (MscAgric (Animal Sciences))--University of Stellenbosch, 2006. / Six non-lactating, ruminally cannulated Holstein cows were used in a three part study to determine the effect of biotin supplementation to dairy cows on forage fermentation characteristics. Cows were randomly assigned to two groups in a 2 x 3 change-over experiment. All cows received oat hay ad libitum and one of two concentrate feeds, fed twice daily at 2 kg per feeding as a top dressing. The concentrates were identical in composition, except for a premix that was included to provide either 0 or 40 mg supplemental biotin/cow per day when the concentrate was fed at a rate of 4 kg/cow. Cows received the respective treatments for 28 days before being changed over to the other treatment. All cows therefore received both treatments. The first 21 days in each period were used for adaptation, while the last 7 days of the period were used for an in sacco trial, as well as for the collection of rumen liquor for two in vitro studies. The in vitro studies were a gas production trial and an in vitro digestibility trial. Forages differing in neutral detergent fibre (NDF) content were used as substrates in the study. Lucerne hay (440 g NDF/kg DM), oat hay (680 g NDF/kg DM), and wheat straw (798 g NDF/kg DM) were chosen to represent high, medium and low quality forages. In the gas production study, samples (0.5 g) of the three forages were incubated at 39ºC in buffered rumen liquor (obtained from cows in the different treatments) in glass vials. Pressure readings were taken after 12, 18, 24, 30 and 48 hours incubation using a digital pressure gauge fitted with a 21 gauge needle. Pressure readings were converted to gas volumes with the aid of a predetermined regression equation. In the in vitro digestibility trial, forage samples (0.25 g) were weighed into Ankom F57 filter bags and incubated at 39ºC in an Ankom Daisy II incubator in buffered rumen liquor. Three bags of each substrate were removed from the incubation jars after 18, 24 and 30 h incubation. Bag residues were analyzed for dry matter, organic matter and NDF. In the in sacco degradability trial, forage samples (5 g) were weighed into 100 x 200 mm Ankom Forage Bags and inserted into the rumina of the respective cow simultaneously. One bag per substrate was removed from each cow at after 4, 8, 18, 24, 30 and 48 h incubation, while two bags per substrate were removed after 72 and 96 h to ensure enough residue for subsequent chemical analysis. Samples of rumen liquor were taken at each of the mentioned incubation times for VFA analysis, while rumen pH was also measured at these times. All the data collected were subjected to a one-way ANOVA, least square means were determined and significance was declared at P<0.05. Biotin supplementation increased the rate of gas production (0-12 h) of all three substrates, as well as cumulative gas production at 48 h. No treatment effects were observed in the in vitro digestion study. Biotin supplementation increased the rate of in sacco NDF disappearance and calculated effective NDF degradability in oat hay and wheat straw, but not in lucerne hay. The rumen pH curve appeared higher for the biotin treatment than for the control and the value at the 72 h sampling time was significantly higher for the biotin treatment than for the control treatment (6.13 vs 5.94). Rumen pH tended to be higher (P<0.10) at 18 h (6.44 vs 6.23), 48 h (6.13 vs 6.00) and 96 h (6.14 vs 6.04). There was also a tendency (P<0.10) for the mean pH over the total 96 h period to be higher for the biotin treatment than for the control (6.09 vs 5.97), while the maximum and minimum pH values did not differ between treatments. Molar proportions of volatile fatty acids did not differ between treatments and the acetic acid proportion was relatively high (acetic:propionic = 74:15), which was probably because the cows were not on a very high concentrate diet. It was concluded that biotin supplementation to dairy cows may improve fermentation rates and NDF digestibility of certain forages.