Production Of Milk Components Research Articles

Growth, Reproduction, and Lactation in Somatic Cell Cloned Cows with Short Telomeres

We previously showed that telomere lengths of 10 somatic cell cloned cows were significantly shorter than normal. In this study, we investigated growth, reproduction, and lactation in these animals to determine if shortened telomeres have any effect on these characteristics. Six Holstein and 4 Jersey cloned cows, derived from oviduct cells, were reared under general group feeding. Body weights were recorded from birth to 48 mo of age. A number of reproductive characteristics were screened during the prepubertal, postpubertal, and postpartum periods. After parturition, milk yields were recorded daily and percentages of milk fat, proteins, and solids-not-fat were measured at monthly intervals. These data were used to estimate production of milk components over a 305-d period. Overall, the cloned heifers exceeded standard growth rates for each breed. The cows were inseminated at the first estrus after they reached 450 d of age, and delivered normal calves except for one stillbirth in the Holstein group. They were inseminated at postpartum estrus to provide second and third parturitions and, again, these pregnancies were normal. Gestational periods and birth weights of the calves were both within the normal range. The average total milk yield per cow in Holstein group clones was less than that of the original cow, whereas Jersey group clones showed a higher average milk yield than the original cow. In both groups of cloned cows, inter-individual variation in milk production was relatively large; however, the coefficient of variation was less than 10%. Our results suggest that the cloned cows have normal growth, reproductive, and lactation characteristics, and thus normal productivity, despite having reduced telomere lengths.

Response to Increased Rumen Undegradable Protein Intake by Lactating Dairy Cows

A dataset was constructed from literature published between 1988 and 2000 to determine whether increased intake of rumen undegradable protein (RUP) was related to increased milk and milk component production. The dataset represented 436 treatment means from 77 published reports. Nutrient intakes were calculated using tabular values for nutrient contents of individual feeds. There was no relationship between RUP content of diets and milk production, unless RUP content of feeds was adjusted to reflect differences in DMI. Increased intake of RUP was associated with increased yield of milk, 4% fat-corrected milk (FCM), and energy-corrected milk (ECM). Using new systems to adjust intake of rumen undegradable intake protein for diet and DMI effects resulted in marginal improvement to the relationships when compared with the use of tabular values for the RUP content of feeds. Within the dataset, a 526-g increase in RUP intake at constant DMI was required to produce a 1-kg increase in milk. Further improvement in predicting milk production response to undegradable protein intake will require investigation of other factors such as amino acid flow, specific attributes of feeds, and/or stage of lactation.

Dietary Supplements of Two Doses of Calcium Salts of Conjugated Linoleic Acid During the Transition Period and Early Lactation

Reduction of milk fat secretion by the use of conjugated linoleic acid (CLA) supplements may alleviate energy demands during early lactation. The objective of the present study was to evaluate lactational performance, net energy balance, and reproductive response of dairy cows supplemented with 2 doses of CLA from 2 wk before predicted calving until 9 wk postpartum. Holstein cows (n = 48) were divided into 3 treatment groups: 1) control, 2) low dose CLA treatment (CLA-1), and 3) high dose CLA treatment (CLA-2). Supplements for all treatments provided 230 g/d of fat; the control group received Ca salts of palm fatty acid distillate and the CLA groups received a mixture of Ca salts of CLA isomers and Ca salts of palm fatty acid distillate (31.6 and 63.2 g/d of CLA isomers for CLA-1 and CLA-2, respectively). Supplementation with CLA resulted in an 11 and 21% decrease in milk fat yield for CLA-1 and CLA-2, respectively. Milk production and secretion of other milk components did not differ among treatments. Milk energy output was significantly reduced with CLA-2, but net energy balance, body weight, and body condition scores were unaffected. Treatment had no effect on hepatic triglyceride concentration or plasma glucose and insulin, but nonesterified fatty acids tended to be lower for CLA-1. There were no consistent dose-related effects on reproduction variables, and no adverse effects were observed during the treatment or posttreatment period. Supplemental CLA was effective in reducing milk fat content, but it did not have a significant effect on milk yield or net energy balance.

Deconstructing Milk Yield and Composition During Lactation Using Biologically Based Lactation Models

A recently developed biological model of lactation described changes in daily milk yield throughout lactation as the result of 3 processes, secretory cell differentiation, cell death, and secretion rate per cell. This paper extends the model to describe the production of milk components (fat, protein, lactose, and water) throughout lactation by replacing milk secretion rate of the original model with the secretion rates of the four components. The milk component model approach was used to examine the relationship between milk yield and the major determinants of its production, using the secretion of milk components throughout lactation. Newly derived models were tested on 461 lactations from a single Holstein herd and used to estimate variability of secretion rates throughout lactation. Because the pattern of cell numbers throughout lactation is not precisely known, an alternative pattern of cell numbers was modeled and the concomitant change in secretion rates outlined. Fat secretion rate was the most variable, as measured by its weekly coefficient of variation throughout lactation. Secretion rates of lactose and water were nearly constant throughout lactation and highly correlated (0.94). Fat and protein secretion rates also were well correlated (0.53). The known biochemistry of milk component production related well to the secretion rate observations derived from the model. Lactose secretion rate and numbers of active secretory cells primarily determined daily milk yield.

Maximizing the value of milk through separation technologies.

Milk is the source of a wide range of proteins that deliver nutrition to the most promising new food products today. Isolated milk proteins are natural, trusted food ingredients with excellent functionality. Separation technologies provide the basis for adding value to milk through the production of proteins that provide the food industry with ingredients to meet specific needs, not possible with milk itself or with other ingredients. The major milk proteins, casein and whey protein, can be isolated by manipulating their compositional and physical properties and then by using various separation technologies to recover the proteins. Additionally, they can be processed in various ways to create a wide range of ingredients with diverse functional characteristics. These ingredients include milk protein concentrate, milk protein isolate, casein, caseinate, whey protein concentrate, whey protein isolate, hydrolysates, and various milk fractions. Within each of these ingredient categories, there is further differentiation according to the functional and nutritional requirements of the finished food. Adding value to milk by expanding from consumer products to ingredients often requires different technologies, marketing structure and distribution channels. The worldwide market for both consumer products and ingredients from milk continues to grow. Technology often precedes market demand. Methods for the commercial production of individual milk components now exist, and in the future as clinical evidence develops, the opportunity for adding value to dairy products as functional foods with health benefits may be achieved. The research and development of today will be the basis of those value-added milk products for tomorrow.

Effect of additional cobalt, copper, manganese, and zinc on reproduction and milk yield of lactating dairy cows receiving bovine somatotropin.

The objective of this study was to determine whether organically complexed Co, Cu, Mn, and Zn would improve the reproductive performance and milk and milk component production in lactating dairy cows that began receiving bovine somatotropin in the ninth week of lactation. Holstein (n = 50) and Jersey (n = 10) cows were blocked by breed, lactation number, and incidence of retained fetal membranes. Two diets assigned within blocks and fed from parturition until 154 d of lactation were control or control supplemented daily with 26 mg of Co as Co glucoheptonate, 125 mg of Cu as Cu-Lys, 199 mg of Mn as Mn-Met, and 359 mg of Zn as Zn-Met. Cows were fitted with electronic pressure-sensing devices in the second week of lactation for detection of estrus. Ovarian structures were determined via transrectal ultrasonography at 7-d intervals from parturition until observation of the first corpus luteum. Blood samples were taken at 7-d intervals and analyzed for plasma concentrations of progesterone, insulin, and urea nitrogen. Onset of luteal activity was identified by progesterone concentrations > or = 1 ng/ml. Retained fetal membranes increased days to first estrus (detected via electronic estrous detection), first luteal activity, and first corpus luteum in control cows but not in supplemented cows. Days to first observed estrus were greater for control cows than for supplemented cows. Days to first service, days open, days from first service to conception, services per conception, milk yield, milk components, and somatic cell counts were similar for control and supplemented cows. Supplementation with complexed trace minerals effectively reduced days to first estrus.

Effect of yeast culture (Saccharomyces cerevisiae) on adaptation of cows to postpartum diets and on lactational performance.

Multiparous (n = 26) and primiparous (n = 18) Holstein cows were fed prepartum and postpartum total mixed diets that were, or were not, supplemented with a yeast culture (YC) for approximately 23 d prepartum and 56 d postpartum. Multiparous cows supplemented with YC selected a prepartum diet higher in CP than did unsupplemented cows, although prepartum performance of cows of both parities, as assessed by DMI and measures of body status, was not influenced by YC. The extent of the prepartum DMI depression was not influenced by YC supplementation in cows of either parity. An intake behavior study with six multiparous cows suggested that cows supplemented with YC exhibited repeated diurnal feed intake patterns until approximately 7 d prepartum, vs 10 d prepartum for unsupplemented cows. Cows of both parities supplemented with YC had numerically higher DMI and production of milk and milk components, although only DMI for multiparous cows and milk production for primiparous cows approached statistical significance. Intake behavior results suggested that cows supplemented with YC achieved repeated diurnal feed intake patterns by approximately 14 d postpartum, vs 20 d postpartum for unsupplemented cows. Concentrations of ruminal metabolites and pH did not differ between treatments, although ruminal fluid collection occurred while diurnal feed intake patterns were repeated (regular). Overall, our results can be interpreted to support a trend toward a modest postpartum improvement in performance of primiparous and multiparous cows supplemented with this YC for 23 d prepartum and 56 d postpartum. However, primiparous cows seemed to achieve this modest overall improvement primarily through enhanced postpartum DMI, whereas in multiparous cows it was due almost equally to enhanced postpartum DMI and higher energy density of the diet.

Influence of postruminal supplementation of methionine and lysine, isoleucine, or all three amino acids on intake and chewing behavior, ruminal fermentation, and milk and milk component production.

Four multiparous Holstein cows were fed a basal diet balanced with the Cornell Net Protein and Carbohydrate System (CNCPS). Diets were formulated to be co-limiting in intestinally absorbable supplies of methionine, lysine, and isoleucine. Cows were supplemented with no amino acids (control); lysine and methionine in a ruminally protected form; isoleucine by abomasal infusion; or lysine, methionine, and isoleucine in a 4x4 Latin square arrangement of treatments with 28-d periods. Performance of cows on all treatments was lower than expected due to low intake of DM that could have been caused by the high fiber level of the basal diet. This high fiber level was likely responsible for the high daily chewing times for cows fed all diets, which was consistent with the high ruminal pH values. Intake of DM and its components were not influenced by any treatment. Milk protein percentage tended to be higher when cows were fed diets supplemented with ruminally protected lysine and methionine; however, production of milk, milk fat, and milk lactose were not affected by any treatment. Cows tended to have a higher milk lactose proportion and tended to produce more milk and milk lactose when they were abomasally infused with isoleucine alone. However, when cows were supplemented with all three amino acids, milk production and composition did not differ from that of cows fed the unsupplemented diet. Use of the CNCPS to evaluate the performance of the cows fed the unsupplemented diet suggested that these cows may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and methionine in addition to metabolizable protein. Evaluation of the unsupplemented diet with an alternate model, Shield, suggested that cows fed the unsupplemented diet may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and arginine. Results suggest that enhanced delivery of intestinally absorbable isoleucine may stimulate milk lactose synthesis.

Investigating potential risk factors for seasonal variation: an example using graphical and spectral analysis methods based on the production of milk components in dairy cattle

The objective of this study was to illustrate methods for investigating factors associated with seasonality, using milk-component production as an example. Milk-protein and fat percentages showed a seasonal pattern; percentages were lowest during June and July and highest in October and November. Graphical methods were used to compare herd calving patterns to seasonal production patterns and spectral analysis were used to compare seasonal production patterns between farm groups with different management practices. For the comparison of seasonality of production and herd calving patterns, data was obtained from archival records for all cows enrolled in Dairy Herd Improvement (DHI) milk recording in Ontario, Canada from 1990 to 1994. For comparisons of seasonality and management practices, monthly protein and fat percentages were obtained from the Dairy Farmers of Ontario from March 1985 to July 1994. Management information was obtained from responses to questionnaires completed by 364 dairy producers in Ontario. Graphical analyses provided a visualization of the relationship between herd calving patterns and seasonality of production – however, graphical methods alone did not allow statistical inferences to be made. Spectral analyses provided a formal statistical test of the null hypothesis of no association between an independent variable (farm management type) and seasonal production pattern in the data over time, provided that the outcome followed the same seasonal pattern regardless of covariate levels under the null hypothesis.

Trends in milk component production in dairy herds in Ontario: 1985–1994

The objectives of this study were to investigate the dynamics of milk component production in dairy herds in Ontario, Canada, over time and to assess the impact of changes to the allocation of milk quota and payment systems on component production. The data consisted of monthly production records from all of the approximately 11 000 farms that shipped milk in Ontario between March 1985 and July 1994.Farm mean yields of milk and milk components have increased over the past decade. The mean fat percentage among the farms increased from 3.85% in 1985 to 3.99% in 1994; protein percentage remained relatively constant at 3.30% in 1985 to 3.32% in 1994. The percentages of protein and fat showed a seasonal pattern. Relatively high component percentages were observed during the fall of each year, and low component percentages were observed during the summer months. Mean fat and protein percentages did not appear to change in response to changes in the allocation of quota or pricing systems. Farms with high (or low) relative protein percentage in one year tended to maintain high (or low) relative protein percentage in the subsequent year, suggesting that herd level factors are related to protein percentage. Key words: Milk components, time trends, dairy

Ruminally Protected Lysine or Lysine and Methionine for Lactating Dairy Cows Fed a Ration Designed to Meet Requirements for Microbial and Postruminal Protein

The purpose of this study was to separate the effects of ruminally protected Lys from effects of ruminally protected Met on the performance of lactating dairy cows fed a ration calculated to be first-limiting in intestinally delivered Lys and second-limiting in intestinally delivered Met. Thirty multiparous Holstein cows were examined in a 20-wk study that started on wk 5 postpartum. Rations contained timothy silage, corn silage, barley, corn, corn gluten meal, and soybean meal. Treatments were 1) no supplemental amino acids, 2) 21g/d of intestinally available Lys, and 3) 22 g/d of intestinally available Lys and 6 g/d of intestinally available Met. Post-experimental calculations suggested that, in contrast to the objective, the unsupplemented ration was colimiting in intestinally available His (0.96 of requirement), followed by Lys (1.00), digestible ruminally undegraded protein (1.01), Ile (1.03), Arg (1.04), Val (1.10), and Met (1.14). In this context, the virtually identical performance of cows fed the unsupplemented ration and cows fed the ration supplemented with ruminally protected Lys demonstrated that dairy cows did not respond to enhanced intestinal supplies of Lys when Lys was not calculated to be the first-limiting nutrient. In contrast, for cows fed rations supplemented with both ruminally protected Lys and ruminally protected Met, the production of both milk protein (40g/d) and fat (40g/d) was numerically increased to an extent that was consistent with earlier reported studies, although calculations did not indicate that performance was limited by intestinal supplies of Lys or Met. This result, which may be disputed because of a lack of statistical significance, suggests that Met, apparently unlike Lys, may enhance the production of milk components beyond an enhancement expected because of its role as a limiting amino acid.

Milk Production of Holstein Heifers Fed Either Alfalfa or Corn Silage Diets at Two Rates of Daily Gain

Seventy-five prepubertal heifers were fed diets based on either alfalfa silage or corn silage plus soybean meal for daily gains of either 725 or 950 g/d in a 2 × 2 factorial. Heifers were fed from 175 to 325kg of body weight (BW). The alfalfa diet contained more digestible protein and less digestible energy than did the diet containing corn silage plus soybean meal. Actual gains were preexperimental BW gain, 633 g/d; lowest experimental BW gain, 785 g/d; highest experimental BW gain, 994 g/d; lowest postexperimental BW gain, 494 g/d; and highest postexperimental BW gain, 546 g/d. Compensatory postexperimental BW gains of heifers fed a common diet allowed the heifers to calve at 732 d of age. The postcalving BW was 508kg, and precalving height at withers was 134cm. A total mixed diet containing 17.1% CP and digestible energy at 3.12 Mcal/kg of dry matter was fed during lactation. Feed intake, milk and milk component production, and milk composition were not affected by either experimental diet or growth rate. As covariates, milk production was related to age at calving and was more strongly related to BW after calving, but no differences were observed among growth diets. Differences in protein and energy concentrations in experimental growth diets did not affect lactation performance. About 75% of total BW gains during the treatment period occurred before puberty, but rate of gain did not affect milk production. This lack of an effect of prepubertal growth rates on the milk production of primiparous heifers is consistent with six other similar studies that were conducted recently.

Diurnal Variation in Milk and Plasma Urea Nitrogen in Holstein and Jersey Cows in Response to Degradable Dietary Protein and Added Fat

Four Holstein and four Jersey cows fitted with ruminal and duodenal cannulas were used in two 4×4 Latin squares to investigate the effects of varying protein degradability and supplemental fat on diurnal changes in plasma and milk urea N. Dietary dry matter contained 16.2% crude protein with two concentrations of ruminally undegradable protein (RUP) that were obtained by substituting blood meal for a portion of soybean meal. Treatments were 1) 29% RUP and 0% added fat, 2) 29% RUP and 2.7% added fat (Ca soaps of fatty acids), 3) 41% RUP and 0% added fat, and 4) 41% RUP and 2.7% added fat. Dry matter of the total mixed diet fed at 1000 and 1400h consisted of 30% corn silage, 29% alfalfa haylage, and 41% concentrate. Ruminal ammonia, plasma urea N, and milk urea N were measured every 4h over a 24-h period. Dry matter intake was depressed 6.7% by added fat. Ruminal ammonia was 25 to 45% lower when the 41% RUP diets were fed. Overall, the concentration of plasma urea N and milk components were not influenced by diet. However, milk urea N was higher in Holsteins than in Jerseys. Both plasma and milk urea N increased within 2h after the 1000-h feeding followed by a decline at 6h after the 1400-h feeding. In this short-term study, fat supplementation had no effect on milk production or yields of milk components. The inclusion of blood meal, however, increased the yields of milk components. Plasma and milk urea N did not differ among dietary treatments but varied throughout the day in relation to the time of feeding.

Effects of Amount and Ruminal Degradability of Protein on Nutrient Digestibility and Production by Cows Fed Tallow

Five cows with ruminal cannulas were used in a 5 × 5 Latin square design to determine the effects of fat and amount and ruminal degradability of dietary crude protein (CP) on nutrient digestibility and production of milk and milk components. Treatments were 1) control; 2) 15% CP, soybean meal; 3) 15% CP, by-product proteins; 4) 18% CP, soybean meal; and 5) 18% CP, soybean meal and by-product proteins. Diets 2 through 5 contained 3.5% tallow. Diets consisted of 28% alfalfa haylage, 22% corn silage, and 50% concentrate on a dry matter (DM) basis. Fat did not affect dry matter intake or percentages and yields of fat and CP in milk but increased milk yield 2.5 kg/d. Fat did not affect N fractions in milk but decreased the percentages of short- and medium-chain fatty acids (C6:0 to C16:0) and increased the percentages of long-chain fatty acids (C18:0 and C18:1) in milk fat. Fat did not affect ruminal fermentation characteristics or the percentages of dietary DM, organic matter, CP, acid detergent fiber, neutral detergent fiber, starch, ether extract, and energy that were digested. An increase in dietary CP from 15 to 18% increased dry matter intake 1.7 kg/d; increased intake of gross energy 8 Mcal/d; increased the percentages and quantities of DM, organic matter, CP, and energy digested; increased the quantities of acid detergent fiber and neutral detergent fiber digested; decreased ruminal pH; increased concentrations of total volatile fatty acids; and increased NH3 N in ruminal fluid. However, the difference in dietary CP did not affect milk yield or composition. Replacement of soybean meal in the diet with a mixture of by-product proteins decreased NH3 N in ruminal fluid, tended to decrease concentrations of total volatile fatty acids and increase pH of ruminal fluid, but did not affect milk yield or percentages and yields of milk components.

Producing milk with 2.5% fat — the biology and health implications for dairy cows

Consumer demand for the major components of milk has changed considerably over the past 10 years. The trend in recent years is for reduced consumption of milk fat as a component of fluid milk and in dairy products such as butter, cheese and yoghurt. Matching production of milk components to demand improves biological efficiency and ultimately enhances the overall profitability of the dairy industry. Genetic selection of dairy cattle allows the dairy industry to respond to consumer demand in the long-term. However, it is not a satisfactory means of manipulating milk composition in the short- or medium-term. The potential of nutrition as a tool to alter the composition of milk — especially milk fat percentage — has not been fully exploited. Changes in the composition of the diet, in particular the forage to concentrate ratio, can result in changes in milk fat percentage in the range of 2.0 to 4.0%. The largest reduction in milk fat is achieved in mid- to late-lactation and this is also a time when cows are less susceptible to metabolic disorders. Although experiments designed to evaluate the long-term effects of feeding extreme fat-depressing diets have not been conducted there are sufficient examples of apparently healthy herds which produce milk with a fat content in the range of 2.5 to 3.0% to allow cautious optimism that low milk fat is not necessarily incompatible with ‘healthy’ cows.

Utilization of Supplemental Fat by Dairy Cows Fed Diets Varying in Content of Nonstructural Carbohydrates

Sixteen Jersey cows were used in a Latin square design to determine milk production and composition when the cows were fed supplemental fat in diets varying in nonstructural carbohydrate content. Eight cows were used in a second experiment to assess ruminal fermentation and nutrient digestibilities. Diets were 1) high nonstructural carbohydrates, no added fat; 2) high nonstructural carbohydrates, 2.5% added fat; 3) low nonstructural carbohydrates, no added fat; and 4) low nonstructural carbohydrates, 2.5% added fat. Diets consisted of alfalfa haylage, corn silage, and concentrate (22:22:56, DM basis). Soyhulls replaced corn grain in diets 3 and 4; high and low diets contained 37.3 and 27.2% nonstructural carbohydrate. The DMI, milk production, and milk fat content were not affected by fat or nonstructural carbohydrates, although milk production tended to be higher when cows were fed fat. Fatty acid composition and N distribution of milk were unchanged by nonstructural carbohydrates. Supplemental fat decreased contents of CP, casein N, and true protein N in milk. Low nonstructural carbohydrates increased total VFA concentration and percentage of acetate and decreased percentages of propionate and butyrate in ruminal fluid. Total fatty acid digestibility decreased when cows were fed fat. Digestibilities of fiber components and total fatty acids were higher for diets low in nonstructural carbohydrates. Dietary content of nonstructural carbohydrates did not affect production of milk or milk components by Jersey cows fed supplemental fat.

Increased Milk Production of Cows in Early Lactation Fed Chemically Treated Soybean Meal

Holstein cows in early lactation and producing about 35 kg/d of milk were fed TMR for ad libitum intake and 1 kg/d of long alfalfa hay. Soybean meal and soybean meal treated by a novel technique were compared in diets of 15 and 17% CP in a 2 x 2 factorial design. Digestibilities of DM, CP, and ADF were significantly lower for treated soybean meal diets. Mean DMI was about 21 kg/d and was unaffected by treatment. Milk production was significantly increased during wk 7 to 16 of lactation for cows fed treated soybean meal diets. The production of SCM and milk components was greater for cows fed treated soybean meal than for cows fed soybean meal, but the differences were not significant. By wk 16, compared with wk 3 of lactation, the persistency of production of milk and lactose was markedly increased by treated soybean meal. The persistency of milk protein production was 100.5% for cows fed the diet containing treated soybean meal at 17% CP and about 97% for the other diets. The hypothesis that Met supply was limiting secretion of milk protein in cows fed treated soybean meal is discussed.

Effects of Amount of Protein and Ruminally Protected Amino Acids in the Diet of Dairy Cows Fed Supplemental Fat

The objectives of this experiment were to investigate the effects of amount of dietary CP and ruminally protected AA supplementation on production of milk and milk components, ruminal fermentation, and nutrient digestibilities by cows fed diets containing high oil corn and tallow. Holstein cows in midlactation producing 22 to 25 kg/d of milk were used in a 5 × 5 Latin square design. Treatments were 1) control (16.8% CP, no added fat); 2) 14.2% CP, no AA; 3) 14.2% CP, with AA; 4) 17.5% CP, no AA; and 5) 17.5% CP, with AA. Diets 2 to 5 contained supplemental fat from high oil corn and tallow. Diets consisted of 33% alfalfa haylage, 17% corn silage, and 50% concentrate DM. Intake of DM was not different among treatments. Dietary fat increased yields of milk, fat, SNF, and total solids and percentages of fat and total solids. Increasing CP from 14.2 to 17.5% did not alter production or composition of milk. Supplemental AA increased yields of 4% FCM, milk fat, milk CP, true protein, and casein protein and percentages of CP, true protein, and casein protein in milk when either 14.2 or 17.5% CP was in the diet. Supplemental fat did not alter ruminal fermentation, but increases in dietary CP increased total VFA concentration in the rumen without affecting proportions of individual VFA. Apparent digestibilities of DM, OM, CP, starch, and energy in the total tract were greater for cows fed the 17.5% CP diets. Addition of AA to the 14.2% CP diet increased apparent digestibilities of DM, OM, ADF, NDF, and energy in the total tract but decreased digestibilities for cows fed the 17.5% CP diets. Feeding AA to midlactation cows in diets containing supplemental fat may alleviate the decrease in milk protein percentage associated with fat supplementation; this response was similar for cows fed diets that contained either 14.2 or 17.5% CP.

The economic performance of dairy cows of different predicted genetic merit for milk solids production

AbstractThe aim of this study was to examine the relationship between pedigree index for kg fat plus protein and the financial margins between milk returns and food, health and reproduction costs in individual lactations. Records of milk and milk component production, food intake, health and reproduction were obtained for individual Holstein-Friesian cows over 38 weeks of lactation over a 7-year period, at the University of Edinburgh/Scottish Agricultural College Langhill dairy cattle research centre. Records for a total of 302 lactations were collected. Milk prices, input costs and margins were calculated for individual animals, using 1989/90 values. Regressions of margin over food costs (MF) and margin over food, health and reproduction costs (MFHR) on pedigree index (PI) for kg fat plus protein were all positive and ranged from £2·50± 3·00 per kg PI for MFHR for heifers, to £6·50 ± 2·10 per kg PI for MFHR for all animals. The lower regression for heifers was attributed to higher reproduction costs in animals of higher genetic merit, though the standard error for the regression estimated in this smaller data set was high. Sensitivity analyses showed that the regression coefficients remained very similar, even with ±50% changes in food, health or reproduction costs. It was concluded that selection on PI for kg fat plus protein is likely to lead to increased margin over food, health and reproduction costs.

Nutrient Requirements and Feed Costs Associated with Genetic Improvement in Production of Milk Components

Dietary requirements for NEL and absorbed true protein were summarized for marginal production of milk components because of genetic improvement through selection. Shelled corn and soybean meal were used to meet marginal nutrient requirements and were assigned variable concentrations of absorbed true protein, depending on rumen-available energy and protein. Mean ratios among national averages for shelled corn to milk prices and soybean meal to milk prices (DM: standardized milk, dollars per kilogram) over a recent 25-yr period were .52 and 1.20, respectively. Stability of these relationships over time permits estimation of feed costs from milk price as prices inflate. Feed costs per kilogram of component, expressed as kilograms of standardized milk with equivalent value, were 1.00 for lactose, 1.89 for fat, and 3.49 for protein. Costs of milk protein were higher if production of absorbed true protein was limited by rumen-available energy, suggesting that selection for fat or lactose, in addition to protein, may be beneficial. High feed costs for milk protein indicate a need for adequate compensation to producers for milk protein and consideration of feed costs during selection. A net value index is proposed that considers feed costs associated with marginal production of individual milk components.