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Automated measurements of the ratio of concentrations of methane and carbon dioxide, [CH 4 ]:[CO 2 ], in breath from individual animals (the so-called "sniffer technique") and estimated CO 2 production can be used to estimate CH 4 production, provided that CO 2 production can be reliably calculated. This would allow CH 4 production from individual cows to be estimated in large cohorts of cows, whereby ranking of cows according to their CH 4 production might become possible and their values could be used for breeding of low CH 4 -emitting animals. Estimates of CO 2 production are typically based on predictions of heat production, which can be calculated from body weight (BW), energy-corrected milk yield, and days of pregnancy. The objectives of the present study were to develop predictions of CO 2 production directly from milk production, dietary, and animal variables, and furthermore to develop different models to be used for different scenarios, depending on available data. An international dataset with 2,244 records from individual lactating cows including CO 2 production and associated traits, as dry matter intake (DMI), diet composition, BW, milk production and composition, days in milk, and days pregnant, was compiled to constitute the training dataset. Research location and experiment nested within research location were included as random intercepts. The method of CO 2 production measurement (respiration chamber [RC] or GreenFeed [GF]) was confounded with research location, and therefore excluded from the model. In total, 3 models were developed based on the current training dataset: model 1 ("best model"), where all significant traits were included; model 2 ("on-farm model"), where DMI was excluded; and model 3 ("reduced on-farm model"), where both DMI and BW were excluded. Evaluation on test dat sets with either RC data (n = 103), GF data without additives (n = 478), or GF data only including observations where nitrate, 3-nitrooxypropanol (3-NOP), or a combination of nitrate and 3-NOP were fed to the cows (GF+: n = 295), showed good precision of the 3 models, illustrated by low slope bias both in absolute values (-0.22 to 0.097) and in percentage (0.049 to 4.89) of mean square error (MSE). However, the mean bias (MB) indicated systematic overprediction and underprediction of CO 2 production when the models were evaluated on the GF and the RC test datasets, respectively. To address this bias, the 3 models were evaluated on a modified test dataset, where the CO 2 production (g/d) was adjusted by subtracting (where measurements were obtained by RC) or adding absolute MB (where measurements were obtained by GF) from evaluation of the specific model on RC, GF, and GF+ test datasets. With this modification, the absolute values of MB and MB as percentage of MSE became negligible. In conclusion, the 3 models were precise in predicting CO 2 production from lactating dairy cows., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Wheat is the most common concentrate fed to grazing dairy cows in Australia, but no studies have examined the effects of wheat proportion in a pasture-based diet on milk production and methane emissions. In this 47-d experiment, 32 Holstein dairy cows were offered 1 of 4 diets during d 1 to 36. Cows in each of the dietary treatment groups were individually offered no wheat (W0) or wheat at 3 kg of dry matter (DM)/d (W3), 6 kg of DM/d (W6), or 9 kg of DM/d (W9). The remainder of the diet was 2.2 kg of DM of concentrate mix and freshly harvested perennial ryegrass (Lolium perenne) such that all individual cows were offered a total diet of approximately 20.2 kg of DM/d. From d 37 to 47 the diets of cows receiving treatments W0 and W3 remained unchanged, but cows in treatments W6 and W9 received the W3 diet. Individual cow feed intakes, milk yields, milk compositions, and methane emissions were measured for d 31 to 35 (period 1) and d 45 to 47 (period 2). During period 1, the mean intakes of cows offered the W0, W3, W6, and W9 diets were 19.2, 20.4, 20.2, and 19.8 kg of DM/d. Diet caused differences in energy-corrected milk, and means for W0, W3, W6, and W9 were 29.5, 32.4, 33.0, and 32.9 kg/d, respectively. Milk fat percentage differed with respective means of 3.93, 3.94, 3.69, and 3.17. Diets also caused differences in methane emissions, with means for W0, W3, W6, and W9 of 440, 431, 414, and 319 g/d. During period 1, the cows fed the W9 diet produced less methane and had lower methane yields (g/kg of DMI) and intensities (g/kg of energy-corrected milk) than cows fed the W3 diet. However, in period 2 when the wheat intake of cows in the W9 treatment was reduced to the same level as in the W3 treatment, their methane emissions, yields, and intensities were similar to those offered the W3 treatment, yet protozoa numbers in ruminal fluid were still much lower than those in cows offered the W3 treatment. Our research shows that for diets based on perennial ryegrass and crushed wheat, only the diet containing more than 30% crushed wheat resulted in substantially depressed milk fat concentration and reduced methane emissions, methane yield, and methane intensity. Thus, although feeding a diet with a high proportion of wheat can cause substantial methane mitigation, it can come at the cost of depression in milk fat concentration., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

There is a need to quantify methane (CH 4 ) emissions with alternative methods. For the past decade, milk fatty acids (MFA) could be used as proxies to predict CH 4 emissions from dairy cows because of potential common rumen biochemical pathways. However, equations have been developed based on a narrow range of diets and with limited data. The objectives of this study were to (1) construct a set of empirical models based on individual data of CH 4 emissions and MFA from a large number of lactating dairy cows fed a wide range of diets; (2) further increase the models' level of complexity (from farm to research level) with additional independent variables such as dietary chemical composition (organic matter, neutral detergent fiber, crude protein, starch, and ether extract), dairy performance (milk yield and composition), and animal characteristics (days in milk or body weight); and (3) evaluate the performance of the developed models on independent data sets including measurements from individual animals or average measurements of groups of animals. Prediction equations based only on MFA [C10:0, iso C17:0 + trans-9 C16:1,cis-11 C18:1, and trans-11,cis-15 C18:2 for CH 4 production (g/d); iso C16:0, cis-11 C18:1, trans-10 C18:1, and cis-9,cis-12 C18:2 for CH 4 yield (g/kg of dry matter intake, DMI); and iso C16:0, cis-15 C18:1, and trans-10 + trans-11 C18:1 for CH 4 intensity (g/kg of milk)] had a root mean squared error of 65.1 g/d, 2.8 g/kg of DMI, and 2.9 g/kg of milk, respectively, whereas complex equations that additionally used DMI, dietary neutral detergent fiber, ether extract, days in milk, and body weight had a lower root mean squared error of 46.6 g/d, 2.6 g/kg of DMI, and 2.7 g/kg of milk, respectively). External evaluation with individual or mean data not used for equation development led to variable results. When evaluations were performed using individual cow data from an external data set, accurate predictions of CH 4 production (g/d) were obtained using simple equations based on MFA. Better performance was observed on external evaluation with individual data for the simple equation of CH 4 production (g/d, based on MFA), whereas better performance was observed on external evaluation mean data for the simple equation of CH 4 yield (g/kg of DMI). The performance of evaluation of the models is dependent on the domain of validity of the evaluation data sets used (individual or mean)., (The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).)

The fortification of milk with phytosterols is an increasingly common practice to enhance the sterol profile and offer consumers potential health benefits. This study investigated whether cattle feed can influence the profile of phytosterols and cholesterol in the milk produced as an alternative to direct fortification of milk. Five experiments were performed using feeds commonly used by Australian dairy farmers and selected formulated rumen-protected feeds. Statistical significances were observed for some individual plant sterols and cholesterol in milk under these differing feeding regimens compared with the respective controls. In the case of the phytosterols, where the daily recommended consumption is typically 2 g per day, the total phytosterols were <0.12 mg/100 mL of milk. An experiment using a rumen-protected feed with high phytosterol levels suggested a decreased transfer of cholesterol to the milk by as much as 20%, although further work is required to confirm these preliminary results. Overall, the study suggests that different feeding practices have minimal effect on the resulting sterol profile of the milk., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Enteric methane (CH 4 ) production from cattle contributes to global greenhouse gas emissions. Measurement of enteric CH 4 is complex, expensive, and impractical at large scales; therefore, models are commonly used to predict CH 4 production. However, building robust prediction models requires extensive data from animals under different management systems worldwide. The objectives of this study were to (1) collate a global database of enteric CH 4 production from individual lactating dairy cattle; (2) determine the availability of key variables for predicting enteric CH 4 production (g/day per cow), yield [g/kg dry matter intake (DMI)], and intensity (g/kg energy corrected milk) and their respective relationships; (3) develop intercontinental and regional models and cross-validate their performance; and (4) assess the trade-off between availability of on-farm inputs and CH 4 prediction accuracy. The intercontinental database covered Europe (EU), the United States (US), and Australia (AU). A sequential approach was taken by incrementally adding key variables to develop models with increasing complexity. Methane emissions were predicted by fitting linear mixed models. Within model categories, an intercontinental model with the most available independent variables performed best with root mean square prediction error (RMSPE) as a percentage of mean observed value of 16.6%, 14.7%, and 19.8% for intercontinental, EU, and United States regions, respectively. Less complex models requiring only DMI had predictive ability comparable to complex models. Enteric CH 4 production, yield, and intensity prediction models developed on an intercontinental basis had similar performance across regions, however, intercepts and slopes were different with implications for prediction. Revised CH 4 emission conversion factors for specific regions are required to improve CH 4 production estimates in national inventories. In conclusion, information on DMI is required for good prediction, and other factors such as dietary neutral detergent fiber (NDF) concentration, improve the prediction. For enteric CH 4 yield and intensity prediction, information on milk yield and composition is required for better estimation., (© 2018 John Wiley & Sons Ltd.)

Short-term studies have shown that feeding dairy cows diets containing a high proportion (>40%) of wheat may result in reduced milk fat concentration and reduced CH 4 emissions (g of CH 4 /cow per d), but no long-term studies have been done on these responses. This study compared the milk production and CH 4 responses when 24 dairy cows were fed diets containing high proportions of either wheat or corn over 16 wk. Cows were assigned to 2 groups and offered a diet (CRN) containing 10.0 kg of dry matter/d of crushed corn grain, 1.8 kg of dry matter/d of canola meal, 0.2 kg of dry matter/d of minerals, and 11.0 kg of dry matter/d of chopped alfalfa hay or a similar diet (WHT) in which wheat replaced the corn. Dry matter intake and milk yields of individual cows were measured daily. Methane emissions from individual cows were measured using controlled climate respiration chambers over 2 consecutive days during each of wk 4, 10, and 16. Milk composition was measured on the 2 d when cows were in chambers during wk 4, 10, and 16. Over the 16-wk experimental period, total dry matter intake remained relatively constant and similar for the 2 dietary treatment groups. At wk 4, CH 4 emission, CH 4 yield (g of CH 4 /kg of dry matter intake), milk fat yield, and milk fat concentration were substantially less in cows fed the WHT diet compared with the same metrics in cows fed the CRN diet; but these differences were not apparent at wk 10 and 16. The responses over time in these metrics were not similar in all cows. In 4 cows fed the WHT diet, CH 4 yield, milk fat concentration, and milk fat yield remained relatively constant from wk 4 to 16, whereas for 5 fed the WHT diet, their CH 4 emissions, milk fat yields, and milk fat concentrations almost doubled between wk 4 and 16. In the short term (4 wk), the inclusion of approximately 45% wheat instead of corn in the diet of cows resulted in reductions of 39% in CH 4 yield, 35% in milk fat concentration, and 40% in milk fat yield. However, these reductions did not persist to wk 10 or beyond. Our data indicate that cows do not all respond in the same way with some "adaptive" cows showing a marked increase in CH 4 yield, milk fat concentration, and milk fat yield after wk 4, whereas in other "nonadaptive" cows, these metrics were persistently inhibited to 16 wk. This research shows that short-term studies on dietary interventions to mitigate enteric CH 4 emissions may not always predict the long-term effects of such interventions., (Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Almond hulls and citrus pulp have been fed to dairy cows with variable responses for milk production, but no information exists on their effect on enteric methane emissions. This experiment examined the effects of dietary supplementation with either almond hulls or ensiled citrus pulp on the milk yield, milk composition, and enteric methane emissions of dairy cows. Thirty-two Holstein dairy cows in mid lactation were offered 1 of 3 diets over a 28-d experiment. Twelve cows received a control (CON) diet, 10 cows a diet containing almond hulls (ALH), and 10 cows a diet containing ensiled citrus pulp (CIT). All cows were offered 6.0 kg of dry matter (DM)/d of crushed corn, 2.0 kg of DM/d of cold-pressed canola, and 0.2 kg of DM/d of a mineral mix. In addition, cows fed the CON diet were offered 14.5 kg of DM/d of alfalfa cubes; cows fed the ALH diet were offered 10.5 kg of DM/d of alfalfa cubes and 4.0 kg of DM/d of almond hulls; and cows on the CIT diet were offered 11.5 kg of DM/d of alfalfa cubes and 3.0 kg of DM/d of ensiled citrus pulp. Milk yield was measured daily and milk composition was measured on 4 d of each week. Individual cow methane emissions were measured by a sulfur hexafluoride tracer technique on d 24 to 28 of the experiment. The mean milk yield of cows fed the CON diet (27.4 kg/d) was greater than the mean milk yield of cows fed the ALH diet (24.6 kg/cow per day), whereas the mean milk yield of cows fed the CIT diet (26.2 kg/cow per day) was not different from the mean milk yield from cows fed the other 2 diets. Dietary treatment did not influence the concentrations of milk fat, protein, and lactose or fat yields, but the mean protein yield from cows fed the CON diet (0.87 kg/d) was greater than that from cows fed the ALH diet (0.78 kg/d) but not different to those fed the CIT diet (0.85 kg/d). In general, we found no differences in the proportion of individual fatty acids in milk. The mean pH of ruminal fluid from cows offered the CON diet was not different to the pH in the ruminal fluids of cows offered the ALH or the CIT diets. The mean methane emissions (g/d) and yields (g/kg of DM intake) were not influenced by dietary treatment. These findings indicate that, although almond hulls and ensiled citrus pulp can be used as a low-cost feed supplement, almond hulls did negatively affect milk production and neither inhibited enteric methane emissions., (Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Effects of different strategies for feeding supplements to grazing dairy cows on the composition and coagulation properties of milk and the subsequent yield and quality of Cheddar cheese were measured. The experiment used milk from 72 Holstein-Friesian cows, averaging 45d in milk, fed according to 1 of 3 feeding strategies: (1) cows grazed a restricted allowance of perennial ryegrass pasture [approximately 14kg of dry matter (DM)/cow per day, to ground level] supplemented with milled wheat grain fed in the milking parlor and alfalfa hay offered in the paddock (control); (2) same pasture and allowance as control, supplemented with a formulated grain mix containing wheat grain, corn grain, and canola meal fed in the parlor and alfalfa hay fed in the paddock (FGM); or (3) same pasture and allowance as control, supplemented with a partial mixed ration comprising the same formulated grain mix but mixed with alfalfa hay and presented on a feed pad after each milking (PMR). For all strategies, supplements provided the same metabolizable energy and grain:forage ratio (78:22, DM basis). Within each feeding strategy, milk was sampled from cows receiving either 8 or 16kg (DM) of supplement/cow per day. There were 2 replicated groups of 6 cows per supplement amount per dietary strategy; approximately 250L of milk was sampled from each for analyses of composition and coagulation properties and the manufacture of Cheddar cheese. The experiment had a 14-d adaptation period and a 14-d measurement period. For cows fed according to the control strategy, those fed 16kg/cow per day produced milk with lower concentrations of milk fat than cows fed 8kg/cow per day. This effect was not observed for cows fed according to the FGM and PMR strategies. Milk from cows fed 16kg of DM/cow per day according to the control strategy yielded less Cheddar cheese than milk from cows fed according to the PMR strategy, with cheese yields from FGM cows being intermediate. Amount of supplement offered had minor effects on percentages of some fatty acids. We observed few other effects of feeding strategy on milk composition, types of milk protein, milk coagulation properties, or the composition and quality of the resultant Cheddar cheese. These data show that, compared with the traditional control strategy, feeding PMR or FGM may increase milk fat concentration and the subsequent yield of Cheddar cheese without compromising cheese composition or quality., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This experiment investigated the metabolic response of dairy cows undergoing an extended lactation to a frequently sampled intravenous glucose tolerance test. The experiment used 12 multiparous Holstein cows that calved in late winter in a seasonally calving pasture-based system and were managed for a 670-d lactation by delaying rebreeding. In each of four 5-wk experimental periods commencing at approximately 73, 217, 422, and 520 (±9.1) days in milk (DIM), cows were offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and silage (217 and 520 DIM) supplemented with 1kg of DM grain (control; CON) or 6kg of DM grain (GRN) as a ration. Daily energy intake was approximately 160 and 215 MJ of metabolizable energy/cow for the CON and GRN treatments, respectively. At all other times, cows were managed as a single herd and grazed pasture supplemented with grain to an estimated minimum daily total intake of 180 MJ of metabolizable energy/cow. Cows were fitted with an indwelling jugular catheter during the final week of each experimental period. The standard intravenous glucose tolerance test using 0.3g of glucose per kilogram of body weight was performed on each cow at approximately 100, 250, 460, and 560 DIM. Plasma concentrations of glucose, insulin, and nonesterified fatty acids (NEFA) responses were measured. Milk yield, milk solids yield, body weight, and basal plasma glucose were greater in the GRN compared with the CON treatment. The area under the plasma response curve relative to baseline (AUC) for glucose, insulin, and NEFA and their apparent fractional clearance rates indicated varied whole body responsiveness to insulin in terms of glucose metabolism throughout the 670-d lactation. The glucose AUC 0 to 20 min postinfusion was increased at 560 DIM, indicating reduced utilization of glucose by the mammary gland at this stage of lactation. The NEFA clearance rate, 6 to 30 min postinfusion, was greater at 460 and 560 DIM. These data indicated an increase in lipogenic activity or a decrease in lipolysis as lactation progressed, suggestive of an overall increase in responsiveness to insulin in terms of whole body lipid metabolism as lactation progressed. These observations are consistent with decreased priority of lactation beyond 300 DIM. Cows in the GRN treatment had decreased whole body responsiveness to hyperglycemia compared with CON cows in terms of glucose clearance and AUC for the glucose response. Variation in the response curves of plasma glucose, NEFA, and insulin was predominantly a result of stage of lactation and not diet. This may be due to changes in mammary gland uptake of glucose that is independent of insulin and the responsiveness of peripheral tissues to the actions of insulin at different stages of the lactation that are independent of diet., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This experiment was conducted to determine the effects of diets supplemented with cottonseed oil, Acacia mearnsii-condensed tannin extract, and a combination of both on composition of bovine milk. Treatment diets included addition of cottonseed oil (800 g/d; CSO), condensed tannin from Acacia mearnsii (400 g/d; TAN) or a combination of cottonseed oil (800 g/d) and condensed tannin (400 g/d; CPT) with a diet consisting of 6·0 kg dry matter (DM) of concentrates and alfalfa hay ad libitum, which also served as the control diet (CON). Relative to the CON diet, feeding CSO and CPT diets had a minor impact on feed intake and yield of lactose in milk. These diets increased yields of milk and protein in milk. In contrast to the TAN diet, the CSO and CPT diets significantly decreased milk fat concentration and altered milk fatty acid composition by decreasing the proportion of saturated fatty acids but increasing proportions of monounsaturated and polyunsaturated fatty acids. The CPT diet had a similar effect to the CSO diet in modifying fatty acid profile. Overall, reduction in milk fat concentration and changes in milk fatty acid profile were probably due to supplementation of linoleic acid-rich cottonseed oil. The TAN diet had no effect on feed intake, milk yield and milk protein concentration. However, a reduction in the yields of protein and lactose occurred when cows were fed this diet. Supplemented tannin had no significant effect on fat concentration and changes in fatty acid profile in milk. All supplemented diets did not affect protein concentration or composition, nitrogen concentration, or casein to total protein ratio of the resulting milk.

Grape marc (the skins, seeds, stalk, and stems remaining after grapes have been pressed to make wine) is currently a by-product used as a feed supplement by the dairy and beef industries. Grape marc contains condensed tannins and has high concentrations of crude fat; both these substances can reduce enteric methane (CH4) production when fed to ruminants. This experiment examined the effects of dietary supplementation with either dried, pelleted grape marc or ensiled grape marc on yield and composition of milk, enteric CH4 emissions, and ruminal microbiota in dairy cows. Thirty-two Holstein dairy cows in late lactation were offered 1 of 3 diets: a control (CON) diet; a diet containing dried, pelleted grape marc (DGM); and a diet containing ensiled grape marc (EGM). The diet offered to cows in the CON group contained 14.0kg of alfalfa hay dry matter (DM)/d and 4.3kg of concentrate mix DM/d. Diets offered to cows in the DGM and EGM groups contained 9.0kg of alfalfa hay DM/d, 4.3kg of concentrate mix DM/d, and 5.0kg of dried or ensiled grape marc DM/d, respectively. These diets were offered individually to cows for 18d. Individual cow feed intake and milk yield were measured daily and milk composition measured on 4d/wk. Individual cow CH4 emissions were measured by the SF6 tracer technique on 2d at the end of the experiment. Ruminal bacterial, archaeal, fungal, and protozoan communities were quantified on the last day of the experiment. Cows offered the CON, DGM, and EGM diets, ate 95, 98, and 96%, respectively, of the DM offered. The mean milk yield of cows fed the EGM diet was 12.8kg/cow per day and was less than that of cows fed either the CON diet (14.6kg/cow per day) or the DGM diet (15.4kg/cow per day). Feeding DGM and EGM diets was associated with decreased milk fat yields, lower concentrations of saturated fatty acids, and enhanced concentrations of mono- and polyunsaturated fatty acids, in particular cis-9,trans-11 linoleic acid. The mean CH4 emissions were 470, 375, and 389g of CH4/cow per day for cows fed the CON, DGM, and EGM diets, respectively. Methane yields were 26.1, 20.2, and 21.5g of CH4/kg of DMI for cows fed the CON, DGM, and EGM diets, respectively. The ruminal bacterial and archaeal communities were altered by dietary supplementation with grape marc, but ruminal fungal and protozoan communities were not. Decreases of approximately 20% in CH4 emissions and CH4 yield indicate that feeding DGM and EGM could play a role in CH4 abatement., (Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Previously observed relationships between dietary composition and production of a small number of individual milk fatty acids were the motivation to examine whether equations could be developed to predict production of all the major individual milk fatty acids. Such equations could be incorporated into ration formulation programs and used to examine factors that influence milk fat composition. Data from 29 published experiments on Holstein cows that provided 120 dietary treatments were entered into CPM-Dairy to obtain estimates of amounts of individual long-chain fatty acids (LCFA) absorbed from the intestines. These derived data and other dietary and animal data including the reported fatty acid composition of milk fat were entered into a spreadsheet. Descriptors of diet included daily intake of dry matter, total fermentable carbohydrate, total fatty acids, and profile of dietary fatty acids, intake of neutral detergent fiber, supplemental fish-oil, buffer, and magnesium oxide. Cow data included body weight and days in milk (DIM). Multiple linear regression was used to develop equations to predict the production (g/d) of each of 26 major LCFA. The equations developed generally had R(2) values in excess of 0.5. Production (g/d) of total de novo fatty acids (C4:0 to C15:0) (PTdenovo) was found to be positively related to the intake of fermentable carbohydrate, and negatively related to the intake of fish oil fatty acids and the estimated total amount of unsaturated fatty acids absorbed from the intestines. The PTdenovo was greater in pasture-fed cows than total mixed ration-fed cows and was negatively related to the square root of DIM. Production of each individual de novo fatty acid was described by a fixed proportion of PTdenovo. These proportions were 0.12 +/- 0.006 (C4:0), 0.083 +/- 0.0039 (C6:0), 0.0516 +/- 0.0025 (C8:0), 0.111 +/- 0.003 (C10:0), 0.134 +/- 0.0037 (C12:0), 0.441 +/- 0.007 (C14:0), 0.046 +/- 0.0024 (C14:1), and 0.0432 +/- 0.0017 (C15:0). Separate independent equations were developed to describe the daily production of C16:0, C16:1, and the main individual preformed fatty acids (>C16). The productions of each of the main individual pre-formed fatty acids were generally strongly related to the corresponding estimated amount (g/d) of specific fatty acids absorbed from the intestines. Percentage estimates for the direct transfer of the major absorbed LCFA to their corresponding LCFA in milk were 42% (C16:0); 9.5% (C18:0); 47.5% (cis-9 C18:1); 16.1% (all isomers of trans-C18:1), 38% (cis-9, cis-12 C18:2); and 31% (cis-9, cis-12, cis15 C18:3). High dietary intake of fish oil fatty acids was negatively associated with the production of all of the major individual preformed fatty acids with the exception of C20:5 and C22:6. In some instances, particular dietary factors were found to have positive influences on production of one fatty acid and negative influences on another. For example, high levels of dietary magnesium oxide were positively associated with production of C17 fatty acids but negatively associated with production of C18:0 and cis-9, trans-11 C18:2 (conjugated linoleic acid). This analysis quantified effects of major dietary and cow factors on production of individual fatty acids in milk.

Data from 29 published experiments on Holstein cows, providing 120 dietary treatments, were collated to obtain means, standard deviations, and ranges for the concentrations (mg/g) of 26 major individual fatty acids in bovine milk fat. The influence of diet type (total mixed ration- vs. pasture-based diet) on concentrations of individual fatty acids was examined. Pairwise correlations for concentrations (g/kg) of individual fatty acids in milk showed that almost all of the individual de novo fatty acids were significantly correlated with each other and with the total concentration of de novo fatty acids. Concentrations of individual unsaturated preformed fatty acids were generally positively correlated with each other but were negatively correlated with concentrations of total de novo fatty acids. Substantial variation was found in the concentrations of individual milk fatty acids and, apart from those synthesized de novo, concentrations of individual fatty acids did not vary in concert. The adequacy of literature data for the development of a model to predict the production of the major individual fatty acids in milk is discussed. The limitations associated with the currently available studies that may be used in a predictive model are 1) failure of many publications to adequately describe dietary details, 2) reporting poorly defined milk fatty acids, 3) aggregating a number of closely related fatty acids under a single category, and 4) the selective reporting of only those fatty acids that are present in milk fat in appreciable quantities. Despite these limitations, the data are sufficient to enable development of a model to predict the concentrations and production of major individual fatty acids in milk fat. The extreme variability in concentrations of individual milk fatty acids and the complex matrix of positive and negative correlations among the concentrations of many individual fatty acids suggest that separate equations will be needed to predict the production of each individual milk fatty acid.

The Dairy Herd Improvement Fund of Victoria recently identified a requirement for a simple and inexpensive in-line sampler to enable dairy farmers to collect representative milk samples for counting somatic cells. We found that the currently available simple in-line milk samplers, when connected to standard 35 ml collection vessels, terminate sampling early in a milking, and thus provide samples that are unrepresentative of the whole milking. We showed that cell count during a milking varies greatly, tending to be high for the first 1-21. Analyses of resulting samples will thus tend to overestimate cell counts if samplers are used in their traditional way. We found greater sampling rates in high-line compared with low-line milking systems, and consequently developed modified samplers suitable for both situations. Our samplers utilize low sampling rates (approximately 1-3%) and large collection vessels (450 ml). Compared with currently available simple in-line samplers, our type of sampler provided milk samples considerably more representative of the entire milking for the majority of cows. In conjunction with subsampling, they provided samples of appropriate size (12.5 ml minimum to 25 ml maximum) for testing fat, protein, lactose and cell count. Cell count results indicated that errors associated with the use of currently available simple in-line samplers could frequently be > 200%. In contrast, we found that use of our samplers gave an estimate for cell count that was only slightly higher (mean 20%) than that from samples collected by an approved Tru-Test sampler.

The requirement for accuracy in the counting of somatic cells in milk has been increased by the use of this measurement as a basis of payment for milk. This paper reports on several factors that can substantially affect efficiency of staining and cell detection in various types of fluorescent cell counters. These mordant factors include sample age, chemical preservative, other sample preservation treatments and reagent properties. Experiments were conducted in several laboratories with Fossomatic 215 and 360 cell counting instruments to measure the effect of these mordant factors on both cell fluorescence and cell count. Counting efficiency was as low as 20% for some instruments counting some particular samples, depending upon the combination of adverse mordant factors. The problem of poor counting efficiency was also not detected by calibration samples that had more favourable mordant treatments applied. The adverse mordant factors were shown to reduce the intensity of fluorescence of cells for all instruments. We suggest that a significant reduction in counting efficiency due to these adverse mordant factors is most likely to occur when the particular instrument already has an intrinsic inability to separate cell fluorescence properly from background noise. This paper also discusses quality control samples, the impact of various factors on discriminator curves and the use of appropriate measures to maintain good calibration adjustment.

Slow-release bST was given to dairy cows as a single injection prior to calving to determine whether such treatment prevented parturient hypocalcemia or modified the concentrations of Ca and parathyroid hormone-related protein in milk during the periparturient period. Cows were treated about 1 wk prepartum, and serial blood and milk samples were taken from these and similar prepartum control cows over a 3-wk period. Plasma growth hormone concentrations in the bST-treated group reached a peak 2 d after administration and then declined linearly to control concentrations over a 14-d period. Plasma Ca was unaffected by bST treatment 1 d prior to parturition, on the day of parturition, and at 1 and 6 to 9 d postpartum. Plasma P was higher, and plasma Mg was lower, in the bST-treated group on the day of parturition and 1 d postpartum. Concentrations of Ca, P, Mg, and protein in milk were lower in bST-treated cows than in controls at parturition. Milk production of the bST-treated and control groups was similar when measured at d 6 to 9 postpartum. Concentrations of parathyroid hormone-related protein in milk were substantial at parturition and remained high thereafter, although at parturition the concentration in the milk of the bST-treated group was lower than that of the control group.

Parathyroid hormone-related protein (PTHrP) has been shown to be present in milk of various mammals. We have assayed PTHrP in milk of various species by radioimmunoassay and estimated the molecular weights by Western blot analysis. PTHrP concentrations in bovine, ovine and human milk were 59.2 +/- 18.5, 74.1 +/- 35.0 and 36.6 +/- 20.7 micrograms/l (mean +/- S.D.) respectively, in pooled samples collected at various stages of lactation. PTHrP in mammalian milk was found to exist in two forms with molecular weights of 17.5 kDa and 21.5 kDa approximating those of PTHrP(1-108) and (1-141) respectively. In comparison, marsupial milk PTHrP appeared as a single low molecular weight form of 14.4 kDa which approximated to that of PTHrP(1-84). We performed a longitudinal study measuring the concentration of PTHrP in milk throughout lactation in cows, and found it to increase with the duration of lactation (r = 0.669, n = 91). We further examined the relationship between the concentration of PTHrP and total calcium in bovine milk, and the differences between these constituents in milk from Friesian and Jersey cows. PTHrP concentrations correlated positively with total milk calcium (r = 0.346, n = 105). The mean milk concentration of PTHrP of the Jerseys was significantly higher than that of the Friesians (52.6 +/- 5.4 micrograms/l compared with 41.0 +/- 4.8 micrograms/l, P less than 0.01), as was the mean milk calcium concentration (30.5 +/- 3.0 mmol/l compared with 26.7 +/- 2.7 mmol/l, P less than 0.01). We therefore postulate that production of PTHrP by the mammary gland may be associated with calcium transport from blood to milk. Also PTHrP may play a role in the development of milk fever in Jerseys which are predisposed to this condition.