Effects of brown midrib corn silage on the energy balance of dairy cattle

Effects of genotype and level of intake on net energy for lactation values of corn silage were evaluated by indirect calorimetry in two experiments using lactating and dry, nonpregnant dairy cows. In experiment 1, six multiparous Holstein cows in early lactation were fed experimental diets containing either brown midrib (bm3) or isogenic normal corn silage. Dietary treatments were isogenic and bm3 diets fed ad libitum, and the bm3 diets restricted-fed. Dry matter (DM) intake was 2.4 kg/d greater for cows fed the bm3 diet ad libitum compared with cows fed the isogenic diet. Apparent digestibilities of DM, organic matter, neutral detergent fiber, and acid detergent fiber were greater for cows restricted-fed bm3 than the isogenic diet. In experiment 2, six dry, nonpregnant Holstein cows were fed maintenance diets containing either bm3 or isogenic corn silage. Apparent digestibilities of DM, organic matter, neutral detergent fiber, and acid detergent fiber were greater for cows fed bm3 compared with isogenic corn silage. Digestible energy and metabolizable energy were greater for maintenance diets containing bm3 compared with isogenic corn silage, respectively. These data indicate increased milk production seen in other studies is a result of increased DMI rather than an increase in energy efficiency. Increased organic matter digestibility of bm3 corn silage resulted in greater digestible energy and metabolizable energy values in cows fed at maintenance energy intake. However, calculated net energy for lactation values of bm3 and isogenic corn silages were similar at both productive and maintenance levels of feeding.     

The effects of gradual replacement of barley with oats on enteric methane emissions,rumen fermentation,milk production,and energy utilization in dairy cows

This study evaluated the effects of gradual replacement of barley with oats on enteric CH₄ emissions, rumen fermentation, diet digestibility, milk production, and energy utilization in dairy cows fed a grass silage-based diet. Sixteen lactating Nordic Red dairy cows received a total mixed ration [58:42 forage:concentrate on dry matter (DM) basis]. Grass silage (Phleum pratense) was the sole forage with canola meal (10% of diet DM) as a protein supplement. The effects of gradual replacement of barley with oats on DM basis were evaluated using a replicated 4 × 4 Latin square design with 21 d periods. The grain supplements (30% of diet DM) consisted of 100% barley, 67% barley and 33% oats, 33% barley and 67% oats, and 100% oats. In addition to intake, milk production, and digestibility measurements, CH₄ emissions were measured by the GreenFeed system (C-Lock Inc.). The energy metabolism was estimated from the gas exchange measurements recorded by the GreenFeed unit. The last 10 d of each period were used for recordings of gas exchanges, feed intake and milk production. Dry matter intake, body weight, milk yield, and energy-corrected milk yield were not affected by gradual replacement of barley with oats in the diet. Increased inclusion of oats linearly decreased CH₄ emissions from 467 to 445 g/d, and CH₄ intensity from 14.7 to 14.0 g/kg energy-corrected milk. In addition, the ratio of CH₄ to CO₂ decreased with increasing inclusion of oats in the diet. Digestibility of organic matter, neutral detergent fiber, and potentially digestible neutral detergent fiber decreased linearly with increasing inclusion of oats. Increased inclusion of oats linearly increased fecal energy from 121 to 133 MJ/d, whereas urinary energy and heat production were not affected by dietary treatment. This resulted in a linear decrease in metabolizable energy intake. However, increased levels of oat in the diet did not significantly affect energy balance or efficiency of metabolizable energy utilization for lactation. This study concludes that barley could be replaced with oats in the diet of dairy cows fed a grass silage-based diet to mitigate CH₄ emissions without having any adverse effects on productivity or energy balance. However, the effect of replacing barley with oats on CH₄ emissions is dependent on the differences between barley and oats in the concentrations of indigestible neutral detergent fiber and fat.     

Responses of primiparous and multiparous Holstein cows to additional energy from fat or concentrate during summer

Supplemental fat has been advocated for use during hot weather and often increases milk yield of cows past peak production when energy intake should not be limiting. Relative responses of primiparous and multiparous cows to supplemental fat or isocaloric addition of concentrates under hot weather conditions have not been determined. Nine multiparous and nine primiparous Holstein cows (154 and 167 d in milk, respectively) were used in a replicated 3 x 3 Latin square design with 28-d periods. Diets were 1) control (35% alfalfa silage, 25% corn silage, and 40% concentrate, dry matter [DM] basis); 2) control plus 3% fat (HF); and 3) high concentrate ([HC] 15% alfalfa silage, 25% corn silage, and 60% concentrate). Diets were isonitrogenous; diets HF and HC were isocaloric (1.60 Mcal of net energy for lactation [NE(L)] per kilogram DM) and higher energy than the control (1.52 Mcal/kg). No parity x diet interactions approached significance. DM intake (DMI) was greater when cows were fed HC than when they were fed HF (21.0, 20.1, and 21.3 kg/d for control, HF, and HC, respectively); intake of NE(L) tended to be increased only for HC. Milk yield was increased by higher-energy diets, but milk fat content was decreased. Milk total protein content was decreased by HF and increased by HC. Yield of solids-corrected milk (SCM) was not different among diets. Efficiency of milk production, expressed either as total milk solids yield per kilogram of DMI or as kilograms of SCM per megacalorie of NE(L) intake, was greater for HF than for HC. Plasma glucose was higher after feeding for cows fed HC; plasma nonesterified fatty acids were greater for HF. Respiration rate and rectal temperature were greater for HC than for HF. Regardless of parity, increased energy density from either fat or concentrate increased milk yield in midlactation cows, but diets caused energy to be partitioned differently among milk components and body storage. Supplemental rumen-active fat had modest advantages over additional starch-based concentrate during summer heat conditions.     

Responses of plasma glucose and nonesterified fatty acids to intravenous insulin tolerance tests in dairy cows during a 670-day lactation

The metabolic response of dairy cows undergoing an extended lactation to an insulin tolerance test (ITT) was investigated. Twelve multiparous Holstein-Friesian cows that calved in late winter in a pasture-based system were managed for a 670-d lactation by delaying rebreeding. Four 5-wk experimental periods commenced at approximately 73, 217, 422, and 520 d 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 1 kg dry matter (DM) of grain (control; CON) or 6 kg DM of grain (GRN). Daily energy intake was approximately 160 and 215 MJ of metabolizable energy/cow for CON and GRN, respectively. At all other times, cows were managed as a single herd and grazed pasture supplemented with grain to an estimated daily intake of 180 MJ of metabolizable energy/cow. Cows were fitted with a jugular catheter during the final week of each experimental period. An ITT using 0.12 IU of insulin/kg of body weight (BW) was conducted on each cow at approximately 100, 250, 460, and 560 DIM. Cows in the GRN treatment had greater milk yield, milk solids yield, and BW than cows in the CON treatment. Within treatment, individual cow responses to the ITT were highly variable. Plasma glucose and nonesterified fatty acid (NEFA) concentrations declined at all stages of lactation. The clearance rate of plasma glucose was slower before 300 DIM than after 300 DIM, which indicates greater inhibition of hepatic glucose synthesis and uptake of glucose by insulin-dependent tissues later in the lactation. The clearance rate, area under the curve, and recovery of plasma NEFA were greatest at 100 DIM, indicating greater responsiveness to the antilipolytic effect of insulin in early lactation, but also greater lipolytic responsiveness. The variation in response to the ITT was mostly a result of DIM rather than diet. However, the plasma NEFA response showed interactions between diet and DIM, indicating that energy intake may affect tissue responses to insulin. The responsiveness of peripheral tissues to insulin, primarily adipose tissue, changed throughout a 670-d lactation and contributed to a greater proportion of nutrients being partitioned to body reserves at the expense of milk yield as lactation progressed. Both stage of lactation and dietary intake have a role in the determination of whole-body and peripheral tissue responses to insulin; however, the exact mechanisms in control of this are unclear.     

The effects of milk yield and stage of lactation on the partitioning of nutrients in lactating dairy cows

The objective of the experiment was to examine, using indirect calorimetry, the effects of milk yield and stage of lactation on the response in milk and body tissue energy, and heat production, to a reduction (decrement) in nutrient intake (assessed as metabolizable energy intake). Eight lactating dairy cows, four representing each of two stages of lactation [either mean initial days in milk (DIM) 158 (SD 6.1) or 414 (SD 51.1)] were used. Each cow underwent four 17-d periods incorporating two physiological states [number of mammary glands milked: either four (periods 1 and 2), or two (periods 3 and 4)], and two levels of metabolizable energy intake within each physiological state [either sufficient to meet requirements for zero tissue balance plus 10 MJ/d (periods 1 and 3)] or these allowances reduced by 20 MJ/d in the subsequent period (periods 2 and 4, respectively). Partitioning was calculated from the changes in metabolizable energy intake, milk energy, tissue energy, and heat production between DIM groups and between four and two gland milking (milk yield) components of the study. Partitioning of the changes in metabolizable energy intake was not influenced by DIM, but milk yield response was greater in the early lactation cows compared with the late group. Cows milked in four glands (higher milk yield) partitioned a significantly greater proportion of decremental changes in metabolizable energy intake to milk energy and less to tissue energy, than when milked in only two glands (lower milk yield).     

Genetic background in partitioning of metabolizable energy efficiency in dairy cows

The main objective of this study was to assess the genetic differences in metabolizable energy efficiency and efficiency in partitioning metabolizable energy in different pathways: maintenance, milk production, and growth in primiparous dairy cows. Repeatability models for residual energy intake (REI) and metabolizable energy intake (MEI) were compared and the genetic and permanent environmental variations in MEI were partitioned into its energy sinks using random regression models. We proposed 2 new feed efficiency traits: metabolizable energy efficiency (MEE), which is formed by modeling MEI fitting regressions on energy sinks [metabolic body weight (BW^0.75), energy-corrected milk, body weight gain, and body weight loss] directly; and partial MEE (pMEE), where the model for MEE is extended with regressions on energy sinks nested within additive genetic and permanent environmental effects. The data used were collected from Luke's experimental farms Rehtijärvi and Minkiö between 1998 and 2014. There were altogether 12,350 weekly MEI records on 495 primiparous Nordic Red dairy cows from wk 2 to 40 of lactation. Heritability estimates for REI and MEE were moderate, 0.33 and 0.26, respectively. The estimate of the residual variance was smaller for MEE than for REI, indicating that analyzing weekly MEI observations simultaneously with energy sinks is preferable. Model validation based on Akaike's information criterion showed that pMEE models fitted the data even better and also resulted in smaller residual variance estimates. However, models that included random regression on BW^0.75 converged slowly. The resulting genetic standard deviation estimate from the pMEE coefficient for milk production was 0.75 MJ of MEI/kg of energy-corrected milk. The derived partial heritabilities for energy efficiency in maintenance, milk production, and growth were 0.02, 0.06, and 0.04, respectively, indicating that some genetic variation may exist in the efficiency of using metabolizable energy for different pathways in dairy cows.     

Milk production and energy efficiency of Holstein and Jersey-Holstein crossbred dairy cows offered diets containing grass silage

Eight Holstein and 8 Jersey-Holstein crossbred dairy cows (all primiparous) were used in a repeated 2 (genotype) × 2 (concentrate level) factorial design study involving a total of 4 periods (each of 6-wk duration), designed to examine the effect of cross-breeding on the efficiency of milk production and energy use. The 4 periods began at 5, 11, 27, and 33 wk of lactation, respectively. Animals were offered a completely mixed diet containing grass silage and concentrates, with the level of concentrate in the diet either 30 or 70% of dry matter (DM). During the final 10 d of each period, ration digestibility and energy use was measured, the latter in indirect open-circuit respiration calorimeters. No significant interaction existed between cow genotype and dietary concentrate level for feed intake, milk production, or any of the energy use parameters measured. Across the 2 genotypes, total DM intake, milk yield, and milk protein and lactose concentrations increased with increasing dietary concentrate level. Thus, cows offered the high-concentrate diet had a higher gross energy (GE) intake, and a higher energy output in feces, urine, milk as heat, and a higher metabolizable energy (ME) intake as a proportion of GE intake and as a proportion of digestible energy intake. Across the 2 levels of concentrates, the Jersey-Holstein cows had a significantly higher total DM intake and body condition score, and produced milk with higher fat, protein, and energy concentrations, compared with those of the Holstein cows. In addition, the Jersey-Holstein cows had a significantly higher GE intake and energy output in urine, methane, and milk. However, crossbreeding had no significant effect on energy digestibility or metabolizability, energy partitioning between milk and body tissue, or the efficiency of ME use for lactation. Relating ME intake to milk energy output and heat production indicated that crossbreeding did not influence ME requirement for maintenance or energy efficiencies. The energy metabolism data were also used to compare energy efficiencies between “early” (data pooled for the first 2 periods) and “late” (data pooled for the second 2 periods) stages of lactation. Stage of lactation had no effect on energy digestibility or metabolizability, whereas increasing stage of lactation increased the rate of energy partitioning into body tissue and reduced the rate of energy partitioning into milk, irrespective of cow genotype. In conclusion, crossbreeding of Holstein dams with Jersey sires had no adverse effects on the overall production efficiency of Holstein dairy cows in terms of milk production, efficiency of ME use for lactation, and energy partitioning between milk and body tissue.     

The influence of body condition on the fasting energy metabolism of nonpregnant, nonlactating dairy cows

The objective of this experiment was to investigate the effect of cow body condition score on fasting heat production. Twelve nonpregnant, nonlactating Holstein-Friesian cows were selected from within the dairy herd at the Agricultural Research Institute of Northern Ireland. Six of these animals (group A) had condition scores > or = 4.5, and the remainder (group B) had condition scores <2. All cows were offered dried grass pellets at estimated maintenance energy level (0.58 MJ of metabolizable energy/kg(0.75)) for a minimum of 21 d. The diet also supplied 2.5 times the metabolizable protein requirement for maintenance. Following this, each cow underwent a 5-d fast in open circuit respiration calorimeters during which fasting heat production (FHP) was measured. On completion of measurement, group A was fed to reduce condition score (CS) below 2, while group B was fed to raise each individual condition score above 4.5. When the appropriate condition scores were achieved, dried grass pellets were again offered at maintenance for a minimum of 21 d, and fasting heat production was measured. It was observed that fasting heat production (MJ/kg(0.75)) was significantly higher for cows with low body condition (<2; ultrasonic fat depth < or = 2.9 mm) compared with cows displaying high body condition (> or = 4.5; ultrasonic fat depth > or = 8.2 mm). A linear relationship between condition score and fasting heat production (MJ/kg(0.75)) was defined by regression analysis as; FHP (MJ/kg(0.75)) = 0.501(SE 0.0121) - 0.030CS (SE 0.0035).     

Optimizing the level of wet corn gluten feed in the diet of lactating dairy cows

Twenty-four multiparous Holstein cows averaging 566 +/- 43 kg of body weight and 83 +/- 49 d in lactation were assigned to treatments stratified by age, days in milk, and milk yield to evaluate the effects of feeding increasing levels of wet corn gluten feed (WCGF) on lactational performance and milk composition. Complete diets containing 0, 15, 30, or 45% of the total ration dry matter (DM) as WCGF were formulated to be 17.2% crude protein and 1.72 Mcal of NE(L) per kilogram of DM, and fed twice daily to individual cows in Calan gates for 15 wk. All diets had a positive metabolizable protein balance. WCGF did not alter DM intake, but feed intake variance tended to be more consistent among cows fed 15 and 30% WCGF (DM basis). Weight gain was numerically greatest for those cows receiving 45% WCGF. Efficiency of energy and protein utilization was not different among treatments. Milk components of fat, protein, and casein were not different among treatments. Milk urea nitrogen was greater for cows on WCGF. Serum urea nitrogen was greatest in cows fed diets containing 15 and 45% WCGF. Serum insulin was lowest in the groups receiving 30 and 45% WCGF, but serum glucose and total protein were unaffected. The concentration of the ruminal volatile fatty acid, valerate, was greater in cows on the WCGF diet and highest in cows fed 30% WCGF. Ruminal ammonia was greatest in cows receiving 30% WCGF. It was estimated that 18.6% of the dietary DM fed as WCGF as a replacement for both portions of the concentrate and the forage in similar diets would have maximized milk yield without negatively affecting milk composition or feed efficiency.     

Methane prediction in dry and lactating Holstein cows.

Data from six experiments (two with dry cows) were used to predict partitioning of gross energy to CH4 in Holstein cows using selected independent variables, some of which were intercorrelated, and a stepwise backward elimination regression procedure. Methane outputs ranged from 3.1 to 8.3% (mean 5.5) of gross energy intake for 134 dry cow balance trials and from 1.7 to 14.9% (mean 5.2) of gross energy intake for 358 lactating cow energy balance trials. This is equivalent to 176 and 300 g/d or 245 and 419 L/d of CH4 for dry and lactating Holstein cows, respectively. Digestibilites of hemicellulose and neutral detergent solubles were positive predictors, and cellulose digestibility was a negative predictor of CH4 output in dry cows fed all forage diets, but hemicellulose digestibility was not a significant variable for predicting CH4 production by lactating cows fed diets with concentrate and forages. Fiber digestibility generally remained in models to predict CH4 output. Except for one data set, regression equations accounted for 50 to 72% of the variation in percentage of gross energy partitioned to CH4 by Holstein cows. Results confirm that increased concentrate feeding reduces CH4 production. Supplementation of lactation diets with fat generally increases fat digestibility, and this trait was associated with reduced CH4 output. Results enable 1) estimation of CH4 output for calculation of metabolizable energy and 2) computation of the contribution from dairy cows to global warming.     

Nitrogen supplementation of corn silages. 1. Effects on feed intake and milk production of dairy cows

Feed intake and milk production responses to N supplementation of corn silage-based diets were measured in three 3 x 3 Latin square experiments. In each experiment, 9 Holstein cows received total mixed rations (TMR), based on corn silage. In Exp. 1, midlactation cows were used to study effects of diets with different ratios of effective rumen-degradable protein (ERDP; g) to fermentable metabolizable energy (FME; MJ), providing a large deficiency (RL), a slight deficiency (RM), and a slight excess (RH) in relation to the target level of 11 g of ERDP/MJ of FME, respectively, for lactating cows. Diets were formulated to be isoenergetic, and to satisfy the metabolizable protein requirements. In Exp. 2, early-lactation cows were used to evaluate effects of different proportions of quickly and slowly rumen-degradable protein (RDP), achieved by replacing soybean meal with urea in the concentrates (0, 0.5, and 1% urea). Experiment 3 investigated effects of synchronizing the availability of FME and ERDP in the rumen. Midlactation cows received a diet containing, on a dry matter (DM) basis, 45% corn silage, 5% ryegrass hay, 35% energy-rich concentrate, and 15% protein-rich concentrate (crude protein: 38% of DM; urea: 2% of DM). The protein-rich concentrate was fed either once (D1) or twice (D2) per day before the meal, or included in the TMR (DU). Treatment RL led to lower DM intake and milk yield, but higher milk production efficiency; there were no significant differences between treatments RM and RH. There were no significant treatment effects on DM intake, milk yield, or milk composition in Exp. 2. Manipulating rumen synchrony by altering the timing of feeding affected milk yields, with D1 cows producing significantly less than D2 and DU cows, which were similar. The amount of ERDP in the diet should be matched to the amount of fermentable energy available to maximize intake, milk yields, and the conversion of feed N into milk protein. However, this study showed only small benefits to altering the diurnal pattern of supply of RDP and FME, and only with extreme feeding strategies that would not be used in practice. Urine volume increased in response to increased or unbalanced protein supply. Analysis of the allantoin:creatinine ratio in spot samples of urine was not useful in identifying predicted differences in microbial protein yield from the rumen.     

A meta-analysis on the relationship between intake of nutrients and body weight with milk volume and milk protein yield in dairy cows

Previously observed strong relationships between dry matter (DM) intake and milk yield in dairy cows were the basis for this meta-analysis aimed to determine the influence of intake of specific dietary nutrients on milk yield and milk protein yield in Holstein dairy cows. Diets (563) from feeding trials published in the Journal of Dairy Science were evaluated for nutrient composition using 2 diet evaluation programs. Intake of nutrients was estimated based on DM intake and program-derived diet composition. Data were analyzed with and without the effect of stage of lactation. Models based on intake of nutrients improved prediction of milk yield and milk protein yield compared with DM intake alone. Intake of net energy of lactation was the dominant variable in milk yield prediction models derived from both diet evaluation models. Milk protein yield models also improved prediction over the DM intake model. These models were dominated by ruminally undegradable protein intake and included a number of energy-related intake variables. In most models, incorporating stage of lactation improved the model fit.     

Effect of prepartum maternal energy density on the growth performance, immunity, and antioxidation capability of neonatal calves

This study investigated the effect of prepartum diets differing in energy density on growth performance, immunity, and antioxidation capability of neonatal calves. Thirty Holstein dairy cows were allocated at random into 3 groups: low energy group [L; net energy of lactation (NE(L))=5.25 MJ/kg of dry matter (DM)]; medium energy group (M; NE(L)=5.88 MJ/kg of DM); and high energy group (H; NE(L)=6.48 MJ/kg of DM) at d 21 prepartum. Plasma was sampled for analysis of glucose, total protein, β-hydroxybutyrate, and nonesterified fatty acids at 21, 14, and 7 d before parturition. After calving, birth weight and measurements of the calves in each group were recorded, and blood samples were collected for analysis of CD4, CD8, CD21, IL-2, IL-4, IL-6, total antioxidant capacity, superoxide dismutase, glutathione peroxidase, and maleic dialdehyde. The results indicated that although maternal weight did not differ among L, M, and H groups at 21, 14, and 7 d before parturition, the concentrations of glucose and β-hydroxybutyrate at 14 and 7 d in the L group were decreased compared with that in the H group. In addition, nonesterified fatty acids concentrations increased significantly in the L group at 14 and 7 d before parturition compared with that in the M and H groups. Birth weight, body height, body length, abdominal circumference, thoracic girth, umbilical girth, and levels of CD4, CD4:CD8, IL-2, IL-4, total antioxidant capacity, and superoxide dismutase were decreased in calves of the L group compared with those of the H group. For the M group, CD4, CD4:CD8, and superoxide dismutase were decreased; and in the L group glutathione peroxidase and maleic dialdehyde levels were significantly increased compared with those of the H group. Reducing the maternal energy density during the last 21 d before parturition had a negative effect on growth and development, immunity, and antioxidation capability of neonatal calves.     

Improved energy prediction equations for dairy cattle rations

The objective was to develop equations that would accurately predict energy contents of rations commonly fed to milking cows and that were simple to apply. Six published equations that predicted TDN from ration content of crude fiber or ADF or predicted digestible energy, metabolize energy, or NE(1) from ration ADF content were modified to remove bias caused by dietary fiber contents. The modified equation that predicted metabolizable energy from ADF was tested for accuracy using data from several feeding trials in which DM intakes and dietary ADF contents were known. Dietary metabolizable energy content calculated by the equation was multiplied by DM consumed to obtain metabolizable energy intake. Requirement of dietary metabolizable energy was calculated using factors for maintenance, milk produced, and BW changes from 1988 NRC feeding standard. Concurrence values (energy intake/energy required) from feeding trials were calculated and served as the criterion of equation accuracy. Several trials resulted in concurrence values approximating 1.0, indicating that the equation to predict dietary metabolizable content was accurate. However, values for individual trials ranged from .84 to 1.21. Concurrence values that deviated considerably from 1.0 occurred most frequently in trials in which animals experienced negative or large changes in BW. It appeared that errors may have occurred in calculating energy requirements when BW changes were negative or large. It was concluded that the modification improved the original equation and it probably was accurate. The other modified equations would be expected to be equally accurate.     

Evaluation of different energy feeding systems with production data from lactating dairy cows offered grass silage-based diets

A set of data from 838 lactating dairy cows, drawn from 12 long-term feeding studies (at least 8 wk/period), was used to evaluate the energy feeding systems for dairy cows currently adopted in Australia, France, The Netherlands, the United Kingdom, and the United States. The animals were offered mixed diets of concentrates, forage [grass silages (n = 33) and corn silages (n = 5)] ad libitum. Data used in the present evaluation were either measured [dry matter (DM) intake, milk production and live weight], measured/estimated [dietary metabolizable energy (ME) concentration] or estimated [milk energy output and live weight change (LWC)]. The mean-square prediction error (MSPE) was used for the evaluation. Total ME intake, milk yields, and LWC varied from 91 to 338 MJ/d, 7.7 to 48.9, and -1.23 to 1.73 kg/d, respectively. Australian and French systems predicted total energy requirement and milk yield relatively well, while British, Dutch and American systems underpredicted total energy requirement by proportionately 0.06, 0.04, and 0.03, respectively; and overpredicted milk yield by 0.09, 0.06, and 0.04. The Agricultural and Food Research Council (AFRC) each produced a relatively larger error of the bias (predicted - actual data) over the total MSPE for ME requirement and milk yield and a relatively smaller error of random than other systems. However, an addition of proportionately 0.05 to the total predicted ME requirement of AFRC, as suggested in this system and currently used in the UK, indicated the prediction accuracy of ME requirement and milk yield is similar to Australian and French systems. Nevertheless, all the systems had a poor prediction of LWC. For each system, the total prediction error (total MSPE) was mainly derived from the line (slope; 0.49 to 0.64 of total MSPE), while less derived from the random (0.20 to 0.48 of total MSPE), indicating a large variation between the predicted and actual LWC existed among individual cows. The residual plots of the residual differences in LWC against predicted LWC revealed that the prediction error was greater with increasing LWC. It is concluded that Australian and French systems have a better prediction of total energy requirement and milk yield than other systems, and LWC is an inappropriate indicator of energy balance in lactating dairy cows.     

Effect of forage to concentrate ratio and intake level on utilization of early vegetative alfalfa silage by dairy cows.

Two experiments were conducted to measure the effects of intake and forage: grain ratio on utilization of early maturity alfalfa silage in dairy cows. In Experiment 1, diets with three forage: concentrate ratios (percentage of silage, percentage NDF): low (56, 28.3), medium (71, 31.0), or high (86, 33.4) were fed ad libitum to six lactating, ruminally cannulated cows in a replicated 3 x 3 Latin square. The same diets were then fed at 1.3 x maintenance intake to six gestating dry cows. Dairy milk yield and percentage and yield of milk protein and casein were higher for cows fed the low silage diet than for cows receiving other treatments. Fat percentage and yield were not different among diets. Lactating cows consumed more DM on low silage (23.0 kg/d) than on medium or high silage diets (21.4 kg), but NDF intake as percentage of BW was higher for the high silage diet. Digestibility of DM in the lactating (70.7, 69.9, and 67.5% for low, medium, and high) and dry cows (76.7, 73.5, and 69.0%, respectively) decreased as the level of silage increased. Depression in digestibility was greater as dietary concentrate increased. Cows fed the high silage diet had a faster fractional passage rate of solids and higher rumen fill. Digestion of concentrate cell walls appeared to be depressed more than alfalfa cell walls as intake increased.     

Carbohydrate supplements and their effects on pasture dry matter intake,feeding behavior,and blood factors associated with intake regulation

Supplementary feeds are offered to grazing dairy cows to increase dry matter (DM) and metabolizable energy (ME) intakes; however, offering feed supplements reduces pasture DM intake, a phenomenon known as substitution. The objective of the study was to investigate changes in blood factors associated with intake regulation in monogastric species in pasture-fed dairy cows supplemented with either a starch- or nonforage fiber-based concentrate. Fifteen multiparous Friesian × Jersey cross cows were assigned to 1 of 3 treatments at calving. Measurements were undertaken in wk 8 of lactation. Treatments were pasture only, pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day). Pelleted concentrates were fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings. Measurements were undertaken to investigate differences in pasture DM intake, feeding behavior, and profiles of blood factors for 4 h after a.m. and p.m. milkings, the periods of intensive feeding in grazing cows. Supplementing cows with STA concentrate reduced pasture DM intake to a greater extent than the fiber concentrate, although time spent eating did not differ between treatments. The blood factor response to feeding differed between the a.m. and p.m. feeding events. Blood factors associated with a preprandial or fasted state were elevated prefeeding in the a.m. and declined following feeding, whereas satiety factors increased. In comparison, the blood factor response to feeding in the p.m. differed, with responses to feeding delayed for most factors. Plasma ghrelin concentration increased during the p.m. feeding event, despite the consumption of feed and the positive energy state remaining from the previous a.m. feeding, indicating that environmental factors (e.g., sunset) supersede physiological cues in regulating feeding behavior. The greater reduction in pasture DM intake for the STA treatment in the p.m. may be related to the level of hunger or satiety before the feeding event and not solely to the consumption of supplement. Data indicate that neuroendocrine factors are, at least in part, responsible for the substitution of pasture for supplementary feeds.     

Effects of nutrition on the fertility of lactating dairy cattle

This meta-analysis of 39 experiments containing 118 treatments explored the effects of diet interventions in early lactation on the proportion of dairy cows pregnant to artificial insemination (AI; pregnancy to AI) and on calving to pregnancy interval. It also identified factors that may explain variation in these responses. The objectives were to identify effects of diet on reproduction, rather than differences between specific dietary interventions. The examination of calving to pregnancy interval used the more traditional method of analyzing differences between a treatment and the reference treatment used for comparison within a given experiment. The systematic review identified fewer experiments (n = 39) than had been expected. Four different multivariable models including the random effect of experiment were used to examine the effects of CPM-Dairy (version 3.08) estimated diet and production variables on proportion pregnant to AI. These models examined (1) output of products, (2) balance or duodenal availability of nutrients, (3) intake of nutrients, or (4) percentage of nutrients in the diet. The multivariable models identified positive associations between estimated increased fatty acid intake [incidence rate ratio (IRR) = 1.0003 ± 0.0001g/d; ±standard error], starch intake (IRR = 1.061 ± 0.029 kg/d), metabolizable energy balance (IRR = 1.004 ± 0.002 MJ/d), and duodenal C14:0 (IRR = 1.008 ± 0.004 g/d) availability with the proportion of cows pregnant to AI, whereas rapidly fermentable sugar intake (IRR = 0.813 ± 0.054 kg/d), percentage of sugar in the diet (IRR = 0.960 ± 0.015%), and milk protein yield (IRR 0.922 ± 0.022 g/100 g per day) were associated with a reduced proportion of cows pregnant to AI. There was no multivariable model developed to assess variables associated with calving to pregnancy interval but, univariably, increased metabolizable energy balance was associated with a shorter calving to pregnancy interval whereas increased milk production was associated with longer time to pregnancy. Increased intake of some AA, particularly threonine and lysine, were associated with a longer calving to pregnancy interval. It is clear nutritional management around calving can influence reproductive success. The importance of dietary fats and increased energy and protein balances in early lactation for improved fertility outcomes is supported and suggests that starch and sugars may have different effects on the proportion of cows that are pregnant to AI. This work also highlighted a need for further focused field studies exploring the roles of specific fatty acids, AA, phosphorus, and carbohydrates on reproduction.     

Effect of dried oregano (Origanum vulgare L.) plant material in feed on methane production,rumen fermentation,nutrient digestibility,and milk fatty acid composition in dairy cows

Essential oils (EO) from oregano may have antimicrobial properties, potentially representing a methane mitigation strategy suitable for organic production. This study aimed to (1) examine the potential of oregano in lowering enteric methane production of dairy cows fed differing levels of dried oregano (Origanum vulgare ssp. hirtum) plant material containing high levels of EO; (2) determine whether differing levels of dried oregano plant material of another subspecies (Origanum vulgare ssp. vulgare) with naturally low levels of EO in feed affected enteric methane production; and (3) evaluate the effect of various levels of the 2 oregano subspecies (containing high or low levels of EO) in feed on rumen fermentation, nutrient digestibility, and milk fatty acids. Each experiment had a 4 × 4 Latin square design using 4 lactating Danish Holstein dairy cows that had rumen, duodenal, and ileal cannulas and were fed 4 different levels of oregano. Experiment 1 used low EO oregano [0.12% EO of oregano dry matter (DM)] and evaluated a control (C) diet with no oregano and 3 oregano diets with 18 (low; L), 36 (medium; M), and 53 g of oregano DM/kg of dietary DM (high; H). Experiment 2 used high EO oregano (4.21% EO of oregano DM) with 0, 7, 14, and 21 g of oregano DM/kg of dietary DM for C, L, M, and H, respectively. Oregano was added to the diets by substituting grass/clover silage on a DM basis. Low or high EO oregano in feed did not affect dry matter intake (DMI) or methane production (grams per day, grams per kilogram of DMI, grams per kilogram of energy-corrected milk, and percentage of gross energy intake). Rumen fermentation was slightly affected by diet in experiment 1, but was not affected by diet in experiment 2. In both experiments, the apparent total-tract digestibility of DM, organic matter, and neutral detergent fiber decreased linearly and cubically (a cubic response was not observed for neutral detergent fiber) with increasing dietary oregano content, while milk fatty acids were slightly affected. In conclusion, dried oregano plant material with either high or low levels of EO did not lower the methane production of dairy cows over 4 consecutive days, and no substantial effects were observed on rumen fermentation or nutrient digestibility. This conclusion regarding methane production is in contrast with literature and requires further study.     

Nitrogen efficiency of eastern Canadian dairy herds: Effect on production performance and farm profitability

Nitrogen efficiency (milk N/dietary N; NE) can be used as a tool for the nutritional, economic, and environmental management of dairy farms. The aim of this study was to identify the characteristics of herds with varying NE and assess the effect on farm profitability. One hundred dairy herds located in Québec, Canada, comprising on average 42 ± 18 cows in lactation were visited from October 2014 to June 2015. Feed intake was measured over 24 h. Samples of each feedstuff were taken and sent to a commercial laboratory for analysis of chemical composition. Feeding management and feed prices were recorded. Milk yield was recorded and milk samples were collected over 2 consecutive milkings. Fat, protein, and milk urea N were analyzed. Balances of metabolizable protein (MP; MP supply ? MP requirements) and rumen degradable protein (RDP; RDP supply ? RDP requirement) were calculated. A hierarchical cluster analysis was conducted and allowed grouping the farms by their NE. Four clusters were identified with an average NE of 22.1 (NE22), 26.9 (NE27), 30.0 (NE30), and 35.8% (NE36). Herds in clusters NE30 and NE36 were fed diets with greater concentrations of starch, net energy for lactation, and nonfiber carbohydrates than those in the other 2 clusters. Moreover, the average proportion of corn silage was lower for herds in cluster NE22 compared with NE30 and NE36 (8.23 vs. 31.8 and 31.3% of total forages, respectively). In addition, crude protein of the diets declined from an average of 16.0 to 14.9% with increasing NE among clusters. Average dry matter intake declined from 26.1 to 22.5 kg/d as NE of clusters increased. Herds in cluster NE22 had lower yields of milk (28.7 vs. 31.8 kg/d), fat (1.15 vs. 1.29 kg/d), and protein (0.94 vs. 1.05 kg/d) than the other clusters. Also, milk urea N was greater for farms in cluster NE22 (13.2 mg/dL) than for farms in the other clusters (11.4 mg/dL). Furthermore, MP and RDP balances decreased from 263.2 to ?153.7 g/d and from 594.7 to 486.9 g/d, respectively, with increasing NE among clusters. Income over feed cost increased from $14.3 to $17.3/cow per day (Can$) as NE among clusters augmented. Results from this study showed that some farms were able to achieve high NE by using lower levels of dietary N and having cows with lower DMI while maintaining milk performance. These farms had a potentially lower environmental impact, and they were more profitable.