Our objectives were to determine the effects of reducing dietary crude protein (CP) concentration on nutrient digestibility, rumen function, N balance, and serum AA concentration for dairy cows in late lactation. At the initiation of the experimental period, we stratified Holstein cows (n = 128; mean ± standard deviation 224 ± 54 d in milk) by parity and days pregnant (86 ± 25 d) and assigned them to 1 of 16 pens. For 3 wk, all cows received a covariate diet containing 16.9% CP [dry matter (DM) basis]. For the subsequent 12 wk, we assigned pens to 1 of 4 treatments containing 16.2, 14.4, 13.4, or 11.9% CP (DM basis) in a randomized complete block design. Diets were fed as a total mixed ration once daily. To reduce dietary CP, we replaced soybean meal with soybean hulls in the concentrate mix (DM basis). Diet evaluations suggested that several EAA, especially His, limited productivity as dietary CP declined. Digestibility of DM and CP decreased linearly with dietary CP reduction. Digestibility of neutral detergent fiber and potentially digestible neutral detergent fiber tended to respond in a quadratic pattern with the greatest digestibility at intermediate treatments. The reduction in dietary CP did not affect ruminal pH, but ruminal ammonia-N and branched-chain VFA concentrations declined linearly. The concentration of milk urea-N and plasma urea-N, secretion of milk N, and excretions of fecal N, urinary N, urinary urea-N, and unaccounted N decreased linearly with the reduction in dietary CP concentration. Urinary N expressed as a percentage of N intake was unaffected by dietary CP. Serum concentrations of total essential AA and non-essential AA were unaffected by dietary CP concentration. However, the ratio of essential to non-essential AA decreased with decreasing dietary CP. Serum 3-methylhistidine concentration increased linearly with decreasing dietary CP concentration, indicating greater skeletal muscle breakdown. Although our trial confirmed that reducing dietary CP decreased absolute excretion of urinary N, diet evaluations suggested that milk protein production decreased as certain essential AA became increasingly limited. Thus, reduced-CP diets have the potential to lessen reactive-N outputs of late lactation cows, but more research is needed to design diets that minimize deleterious effects on productivity.

Predicting dry matter intake (DMI) and feed efficiency by leveraging the use of data streams available on farm could aid efforts to improve the feed efficiency of dairy cattle. Residual feed intake (RFI) is the difference between predicted and observed feed intake after accounting for body size, body weight change, and milk production, making it a valuable metric for feed efficiency research. Our objective was to develop and evaluate DMI and RFI prediction models using multiple linear regression (MLR), partial least squares regression, artificial neural networks, and stacked ensembles using different combinations of cow descriptive, performance, sensor-derived behavioral (SMARTBOW; Zoetis), and blood metabolite data. Data were collected from mid-lactation Holstein cows (n = 124; 102 multiparous, 22 primiparous) split equally between 2 replicates of 45-d duration with ad libitum access to feed. Within each predictive approach, 4 data streams were added in sequence: dataset M (week of lactation, parity, milk yield, and milk components), dataset MB (dataset M plus body condition score and metabolic body weight), dataset MBS (dataset MB plus sensor-derived behavioral variables), and dataset MBSP (dataset MBS plus physiological blood metabolites). The combination of 4 datasets and 4 analytical approaches resulted in 16 analyses of DMI and RFI, using variables averaged within cow across the study period. Additional models using weekly averaged data within cow and study were built using all predictive approaches for datasets M, MB, and MBS. Model performance was assessed using the coefficient of determination, concordance correlation coefficient, and root mean square error of prediction. Predictive models of DMI performed similarly across all approaches, and models using dataset MBS had the greatest model performance. The best approach-dataset combination was MLR-dataset MBS, although several models performed similarly. Weekly DMI models had the greatest performance with MLR and partial least squares regression approaches. Dataset MBS models had incrementally better performance than datasets MB and M. Within each approach-dataset combination, models with DMI averaged over the study period had slightly greater model performance than DMI averaged weekly. Predictive performance of all RFI models was poor, but slight improvements when using MLR applied to dataset MBS suggest that rumination and activity behaviors may explain some of the variation in RFI. Overall, similar performance of MLR, compared with machine learning techniques, indicates MLR may be sufficient to predict DMI. The improvement in model performance with each additional data stream supports the idea of integrating data streams to improve model predictions and farm management decisions.

Fatty acids (FA) provide an energy source to the liver during negative energy balance; however, when FA influx is excessive, FA can be stored as liver lipids or incompletely oxidized to β-hydroxybutyrate (BHB). The objectives of this study were to quantify plasma and liver FA profiles and hepatic gene expression in cows diagnosed with hyperketonemia (HYK; BHB ≥ 1.2 mM) or not (nonHYK; BHB < 1.2 mM) to determine a relationship between FA profile and expression of hepatic genes related to oxidation and gluconeogenesis. Production parameters, blood samples (-28, -3, 1, 3, 5, 7, 9, 11, and 14 d relative to parturition; n = 28 cows), and liver biopsies (1, 14, and 28 d postpartum; n = 22 cows) were collected from Holstein cows. Cows were retrospectively grouped as HYK or nonHYK based on BHB concentrations in postpartum blood samples. Average first positive test (BHB ≥ 1.2 mM) was 9 ± 5 d (± SD). Cows diagnosed with HYK had greater C18:1 and lower C18:2 plasma proportions. Liver FA proportions of C16:0 and C18:1 were related to proportions in plasma, but C18:0 and C18:2 were not. Some interactions between plasma FA and HYK on liver FA proportion suggests that there may be preferential use depending upon metabolic state. Cows diagnosed with HYK had decreased pyruvate carboxylase (PC) expression, but no difference at 1 d postpartum in either cytosolic or mitochondrial isoforms of phosphoenolpyruvate carboxykinase (PCK). The increased PC to PCK ratios in nonHYK cows suggests the potential for greater hepatic oxidative capacity, coinciding with decreased circulating BHB. Interestingly, FA, known regulators of PC expression, were not correlated with PC expression at 1 d postpartum. Taken together, these data demonstrate that HYK cows experience a decrease in the ratio of hepatic PC to PCK at 1 day postpartum prior to HYK diagnosis which, on average, manifested a week later. The differential regulation of PC involved in HYK diagnosis may not be completely due to shifts in FA profiles and warrants further investigation.

The objectives of this study were to measure performance responses and to evaluate indictors of N utilization in late-lactation cows fed diets with incremental reductions in crude protein (CP) concentration. Holstein cows (n = 128; 224 ± 54 d in milk) were stratified by parity and days pregnant (86 ± 25 d) and randomly assigned to 1 of 16 pens in a randomized complete block design. For 3 wk, all cows received a covariate diet containing 16.9% CP [dry matter (DM) basis]. For the subsequent 12 wk, pens were randomly assigned to 1 of 4 treatments that contained 16.2, 14.4, 13.1, or 11.8% CP (DM basis). Diets were offered once daily and contained 32.5% corn silage, 32.5% alfalfa silage, 13.5% high-moisture corn, and 21.5% concentrate mix. A reduction in dietary CP was achieved by replacing soybean meal with soy hulls in the concentrate mix (DM basis). Dry matter intake, milk urea N (MUN; mg/dL), and the yield of milk urea N (g/d) decreased linearly with dietary CP. Compared with a 16.2% CP diet, a 14.4% CP diet did not alter milk yield throughout the study, but the 13.1 and 11.8% CP diets reduced milk yield after 4 and 1 wk, respectively. Furthermore, milk protein percentage was reduced for all dietary CP less than 16.2%, but this negative effect was temporary and disappeared after 7 wk for the 14.4% CP diet. In contrast, MUN adjusted to a new steady state within 1 wk for all dietary treatments. Modeling quadratic responses with a plateau led to predictions of no reduction in fat- and protein-corrected milk (32.6 kg/d) and yields of fat (1.31 kg/d), lactose (1.49 kg/d), and true protein (1.12 kg/d) until dietary CP decreased below 15.5, 15.3, 15.9, and 16.2%, respectively. In this study, MUN and the yield of MUN were highly correlated with N intake, milk protein yield, and fat- and protein-corrected milk. Surprisingly, N use efficiency (milk protein N/intake N) was not correlated with any variables related to N utilization and reached an apparent upper limit of approximately 30%. Although this observation may be associated with feeding diets deficient in metabolizable protein, late-lactation cows in this study adjusted to low dietary CP concentration better than anticipated as milk production was 2.6, 3.6, 6.4, and 8.0 kg/d higher than National Research Council (2001)-predicted metabolizable protein-allowable milk for dietary CP of 16.2, 14.4, 13.1, and 11.8%, respectively.

Extensive efforts have been made to identify more feed-efficient dairy cows, yet it is unclear how selection for feed efficiency will influence metabolic health. The objectives of this research were to determine the relationships between residual feed intake (RFI), a measure of feed efficiency, body condition score (BCS) change, and hyperketonemia (HYK) incidence. Blood and milk samples were collected twice weekly from cows 5 to 18 d postcalving for a total of 4 samples. Hyperketonemia was diagnosed at a blood β-hydroxybutyrate (BHB) ≥1.2 mmol/L and cows were treated upon diagnosis. Dry period, calving, and final blood sampling BCS was recorded. Prior mid-lactation production, body weight, body weight change, and dry matter intake (DMI) data were used to determine RFI phenotype, calculated as the difference between observed DMI and predicted DMI. The maximum BHB concentration (BHBmax) for each cow was used to group cows into HYK or not hyperketonemic. Lactation number, BCS, and RFI data were analyzed with linear and quadratic orthogonal contrasts. Of the 570 cows sampled, 19.7% were diagnosed with HYK. The first positive HYK test occurred at 9 ± 0.9 d postpartum and the average BHB concentration at the first positive HYK test was 1.53 ± 0.14 mmol/L. In the first 30 d postpartum, HYK-positive cows had increased milk yield and fat concentration, decreased milk protein concentration, and decreased somatic cell count. Cows with a dry BCS ≥4.0, or that lost 1 or more BCS unit across the transition to lactation period, had greater BHBmax than cows with lower BCS. Prior-lactation RFI did not alter BHBmax. Avoiding over conditioning of dry cows and subsequent excessive fat mobilization during the transition period may decrease HYK incidence; however, RFI during a prior lactation does not appear to be associated with HYK onset.

The objective of this study was to evaluate 3 milk replacer (MR) feeding programs on calf performance up to 4 mo of age. Neonatal Holstein male calves (n = 48; 44 ± 1.5 kg BW) were randomly assigned to either a moderate rate of MR (MOD; 0.66 kg/d for 39 d then 0.33 kg/d for 3 d), an ad libitum rate of MR (ADLIB; offered twice daily between 0630 and 0830 h and between 1430 and 1630 h for 35 d, 0.66 kg/d for 4 d, and 0.33 kg/d for 3 d), or a step-up rate of MR (STEPUP; increased from 0.32 to 0.62 kg/d in first 12 d, 0.66 kg/d for 27 d, and 0.33 kg/d for 3 d). The MR (25% CP, 18% fat) was fed 2× daily up to d 39 and 1× daily thereafter. Texturized starter (40% starch, 21% CP) and water were offered ad libitum. Calves were housed in individual pens through d 56. Calf BW was measured initially and weekly thereafter. Hip widths (HW) were measured initially and every 2 wk thereafter. Feces were scored and feed intake recorded daily. From 56 to 112 d, calves were grouped by the 3 MR programs and moved to group pens (4 calves/ pen). The same starter blended with 5% chopped grass hay was offered ad libitum. BW and HW were measured on d 56, 84, and 112. Data, within period, were analyzed as a completely randomized design with repeated measures when appropriate. Experimental units were calf in first period and pen in second. Total MR intake per calf averaged 27, 51, and 25 kg for MOD, ADLIB, and STEPUP programs, respectively, with a range of 42 to 63 kg for ADLIB. In the first 56 d, starter intake and feed efficiency were less for ADLIB vs. MOD (P < 0.05), while fecal scores and abnormal fecal score days were greater for calves fed ADLIB vs. MOD (P < 0.05). Calves fed STEPUP had lesser ADG than calves fed MOD (P < 0.05). In the second 56 d, initial BW was greater for ADLIB vs. MOD (P < 0.05), though final BW was not different between MOD and ADLIB or STEPUP (P > 0.05). Calves previously fed MOD had greater ADG, feed efficiency, and HW change than calves fed ADLIB (P < 0.05). Though BW were greater at weaning when MR was fed ad libitum, calves were less efficient and growth advantages were lost by 4 mo of age.

Metabolizable methionine (Met) concentrations can be increased by feeding rumen-protected dl-Met or the isopropyl ester of 2-hydroxy-4-(methylthio) butanoic acid (HMBi). Hepatic responses to increasing concentrations of metabolizable Met as a result of supplementation of different Met sources have not been comparatively examined. The objective of this experiment was to examine the regulation of key genes for Met metabolism, gluconeogenesis, and fatty acid oxidation in response to increasing concentrations of dl-Met or 2-hydroxy-4-(methylthio) butanoic acid (HMB) in bovine primary hepatocytes. Hepatocytes isolated from 4 Holstein calves less than 7d old were maintained as monolayer cultures for 24h before addition of treatments. Cells were then exposed to treatments of dl-Met or HMB (0, 10, 20, 40, or 60 µM) in Met-free medium for 24h and collected for RNA isolation and quantification of gene expression by quantitative PCR. Expression of betaine-homocysteine methyltransferase (BHMT), 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR), and 5,10 methylenetetrahydrofolate reductase (MTHFR) genes, which catalyze regeneration of Met from betaine and homocysteine, decreased linearly with increasing dl-Met concentration. We observed similar effects with increasing HMB concentration, except expression of MTHFR, which was not altered. Expression of Met adenosyltransferase 1A (MAT1A), which catalyzes the first step of Met metabolism to generate S-adenosylmethionine (SAM), a primary methyl donor, was decreased with increasing dl-Met or HMB concentration. Expression of S-adenosylhomocysteine hydrolase (SAHH) was decreased linearly with increasing HMB concentration, but not altered by dl-Met. Increasing concentrations of dl-Met and HMB decreased cytosolic phosphoenolpyruvate carboxykinase (PCK1) expression, but did not alter the expression of mitochondrial phosphoenolpyruvate carboxykinase (PCK2) or pyruvate carboxylase (PC). Expression of glucose-6-phosphatase(G6PC) decreased linearly with increasing HMB concentration, but not altered by dl-Met. Neither dl-Met nor HMB altered the expression of carnitine palmitoyltransferase 1A(CPT1a). These findings demonstrate reduced necessity for Met regeneration with increased Met concentrations in the medium, regardless of the Met source. The lack of upregulation of gluconeogenesis indicates that increased dl-Met or HMB is not prioritized for glucose synthesis in primary bovine hepatocytes.

The transition period in dairy cows is associated with the onset of negative energy balance and body fat mobilization. Mobilized lipids can lead to excessive ketone production. The objective of this trial was to characterize the relationship between hyperketonemia (HYK) and milk production, BCS, and residual feed intake (RFI). Blood and milk samples were collected twice weekly from cows 5 to 18 d in milk (DIM) for a total of 4 samples. Hyperketonemia was diagnosed using the Precision Xtra Meter and defined as blood β-hydroxybutyrate (BHBA) ≥ 1.2 mmol/L. Cows were treated on diagnosis. Dry period (−28 DBCS), calving, and final blood sampling BCS was recorded. Previous midlactation production and DMI were used to calculate RFI by subtracting predicted energy intake from the observed energy intake. Effect of milk composition, milk yield, lactation number, BCS, and previous RFI on the observed maximum BHBA concentration (MAXBHBA) was determined using PROC MIXED of SAS 9.4. Least squares means ± SE are reported. Of the 570 cows sampled, 19.7% were diagnosed with HYK. Mean DIM at the first positive HYK test was 9 ± 0.9 d and the average BHBA concentration at the first positive HYK test was 1.53 ± 0.14 mmol/L. MAXBHBA was greater (P ≤ 0.05) for multiparous cows compared with primiparous cows. Milk fat content was increased (4.33 vs. 4.69 ± 0.05%; P < 0.0001), milk protein content was decreased (3.60 vs. 3.40 ± 0.02%; P < 0.0001), somatic cell count was decreased, and milk yield was increased (44.02 vs. 47.47 ± 1.46 kg/d; P < 0.0001) in the first 30 DIM for cows positive for HYK compared with negative cows. Cows with a DBCS ≥ 4.0 had greater MAXBHBA (0.88 vs. 1.28 ± 0.08 mmol/L; P ≤ 0.05) than cows with lower BCS. Cows that lost >0.75 BCS units after calving had greater (P ≤ 0.05) MAXBHBA than cows that lost ≤0.75 BCS units. MAXBHBA was not significantly correlated to RFI. Prompt diagnosis and treatment of HYK appears to prevent HYK-associated decreases in milk production. Avoiding overconditioning of dry cows and excessive fat mobilization during the transition period may decrease HYK incidence; however, previous lactation RFI does not appear to be correlated to developing HYK.

Tricarboxylic acid cycle (TCA) and gluconeogenic carbon flux are controlled by balances of pyruvate carboxylase (PC) and phosphoenolpyruvate carboxykinase (PEPCK). The lipotropic action of choline and methionine may alter fatty acid (FA) oxidation and gluoneogenic carbon availability. The objective of this experiment was to examine regulation of genes controlling gluconeogenesis in response to increasing concentrations of choline chloride (CC), DL-methionine (DLM), and added FA. Primary hepatocytes isolated from 4 Holstein calves were maintained as monolayer cultures for 24 h in media containing optimal concentrations of essential amino acids and 1.25 mM pyruvic acid. Treatments of physiologically relevant concentrations of CC (33, 100, 2000, 4500 μM) and DLM (16, 30, 100, 300 μM), with or without a 1 mM FA cocktail, were added to a methionine-free media in a factorial design. After 24 h of treatment, cells were harvested for RNA isolation, cDNA generation, and quantification of gene expression by quantitative PCR. Abundance of mRNA was normalized to the geometric mean of three reference genes. Data were analyzed using PROC MIXED of SAS 9.4 with linear and quadratic contrasts in a model accounting for fixed effect of treatment and random effect of calf and reported as least squares means ± SE. Expression of PC tended to be linearly increased (P = 0.06) by CC (1.28, 1.42, 1.43, 1.50 ± 0.21 arbitrary units (AU)) and was unaffected (P > 0.15) by DLM (1.39, 1.51, 1.38, 1.35 ± 0.21 AU). Although, mitochondrial PEPCK (PEPCKm) expression was unaffected (P ≥ 0.15) by CC (1.64, 1.58, 1.60, 1.59 ± 0.5 AU) or DLM (1.49, 1.57, 1.65, 1.69 ± AU), cytosolic PEPCK (PEPCKc) tended to be linearly increased (P = 0.11) by CC (1.03, 1.19, 1.30, 1.57 ± 0.32 AU) and decreased (P = 0.08) by DLM (1.60, 1.31, 1.21, 0.97 ± 0.32). Expression of glucose 6-phosphatase (G6P) was quadratically affected (P = 0.009) by CC (1.14, 1.42, 0.99, 1.13 ± 0.30) and unaffected (P > 0.15) by DLM (1.14, 1.17, 1.19, 1.17 ± 0.30). Treatment with FA increased (P < 0.001) expression of PC (1.11 vs. 1.70 ± 0.20 AU), PEPCKc (0.55 vs. 2.0 ± 0.27 AU), PEPCKm (1.36 vs. 1.84 ± 0.48 AU), and G6P (0.93 vs. 1.41 ± 0.29 AU). Coordinated increases in PC and PEPCKc with increasing CC suggests increased capacity for gluconeogenesis. Conversely, decreased PEPCKc without altered PC may indicate that DLM may increase TCA capacity but not gluconeogenic capacity. Choline and methionine appear to differentially regulate TCA cycle and gluconeogenesis.

Prior to genomic selection on a trait, a reference population needs to be established to link marker genotypes with phenotypes. For costly and difficult-to-measure traits, international collaboration and sharing of data between disciplines may be necessary. Our aim was to characterize the combining of data from nutrition studies carried out under similar climate and management conditions to estimate genetic parameters for feed efficiency. Furthermore, we postulated that data from the experimental cohorts within these studies can be used to estimate the net energy of lactation (NEL) densities of diets, which can provide estimates of energy intakes for use in the calculation of the feed efficiency metric, residual feed intake (RFI), and potentially reduce the effect of variation in energy density of diets. Individual feed intakes and corresponding production and body measurements were obtained from 13 Mid-western nutrition experiments. Two measures of RFI were considered, RFIMcal and RFIkg, which involved the regression of NEL intake (Mcal/d) or dry matter intake (DMI; kg/d) on 3 expenditures: milk energy, energy gained or lost in body weight change, and energy for maintenance. In total, 677 records from 600 lactating cows between 50 and 275 d in milk were used. Cows were divided into 46 cohorts based on dietary or non-dietary treatments as dictated by the nutrition experiments. The realized NEL densities of the diets (Mcal/kg of DMI) were estimated for each cohort by totaling the average daily energy used in the 3 expenditures for cohort members and dividing by the cohort's total average daily DMI. The NEL intake for each cow was then calculated by multiplying her DMI by her cohort's realized energy density. Mean energy density was 1.58 Mcal/kg. Heritability estimates for RFIkg, and RFIMcal in a single-trait animal model did not differ at 0.04 for both measures. Information about realized energy density could be useful in standardizing intake data from different climate conditions or management systems, as well as investigating potential genotype by diet interactions.

LB1 Fertility may depend on conceptus-derived signals in lactating dairy cows. Bethany E. Liebig*1, Milton G. Thomas2, Kevin D. McSweeney3, Hana Van Campen1, Jeanette Bishop1, and Thomas R. Hansen1, 1Department of Biomedical Sciences, Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, CO, 2Department of Animal Sciences, Colorado State University, Fort Collins, CO, 3Department of Clinical Sciences, Colorado State University, Fort Collins, CO.

An experiment was conducted to determine the effects of dietary starch content in corn-based diets and corn particle size on lactation performance, nutrient digestibility, and bacterial protein flow in dairy cows using the omasal and reticular sampling technique. Eight ruminally cannulated lactating multiparous Holstein cows were used in a replicated 4×4 Latin square design with a 2×2 factorial arrangement of treatments. Treatments were fine (FG; mean particle size=552µm) and coarse (CG; 1,270µm) ground dry shelled corn in normal- (NS) and reduced- (RS) starch diets fed as total mixed rations. The NS and RS rations contained 27 and 18% starch (dry matter basis), respectively, and were formulated by partially replacing corn with soy hull pellets. Mean dry matter intake was unaffected by treatment (23.2kg/d). Cows fed NS diets produced 1.9kg/d more milk and 0.06kg/d more milk protein compared with cows fed RS diets. Cows fed NSFG and RSCG diets produced more fat-corrected milk than did cows fed NSCG and RSFG diets. Milk urea concentration was decreased for cows fed NS diets (12.4mg/dL) compared with RS diets (13.5mg/dL). Ruminal digestibility of neutral detergent fiber (NDF; % of NDF intake) determined by the omasal sampling technique was increased in cows fed RS diets compared with NS diets (43.4 vs. 34.9%), and total-tract digestibility of NDF (% of NDF intake) was increased in cows fed RS diets compared with those fed NS diets (50.1 vs. 43.1%). Ruminal digestibility of starch (% of starch intake) determined by the omasal sampling technique was greater in cows fed NS diets compared with those fed RS diets (85.6 vs. 81.6%). Total-tract starch digestion was increased in cows fed RS diets compared with those fed NS diets (96.9 vs. 94.6%) and in cows fed FG diets compared with those fed CG diets (98.0 vs. 93.5%). Bacterial protein flow was unaffected by treatment. The omasal and reticular sampling techniques resulted in similar treatment effects for nutrient flow and digestibility, although nutrient flow was lower and nutrient digestibility was greater in cows when sampled by the omasal technique compared with the reticular technique. Cows fed FG diets had greater ruminal propionate, lower acetate:propionate ratio, and lower pH. Feeding NS diets increased milk and protein yields and feeding finely ground corn increased ruminal propionate concentration.

The objective of this study was to determine the effects of monensin (M) supplementation on lactation performance of dairy cows fed diets of either reduced (RS) or normal (NS) starch concentrations as total mixed rations. One hundred twenty-eight Holstein and Holstein × Jersey cows (90 ± 33 d in milk) were stratified by breed and parity and randomly assigned to 16 pens of 8 cows each in a randomized controlled trial. Pens were then randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement of treatments. A 4-wk covariate adjustment period preceded the treatment period, with all pens receiving NS supplemented with 18 g of monensin/t of dry matter (DM). Following the 4-wk covariate adjustment period, cows were fed their assigned treatment diets of NS with M (18 g of monensin/t), NS with 0 g of monensin/t (C), RS with M, or RS with C for 12 wk. Actual starch concentrations for the RS and NS diets were 20.4 and 26.9% (DM basis), respectively. Mean dry matter intake (DMI; 27.0 kg/d) was unaffected by the treatments. Feeding M compared with C and NS compared with RS increased milk yield by 1.3 and 1.5 kg/d per cow, respectively. Milk protein percentage and yield and lactose yield were increased and milk urea nitrogen was decreased for NS compared with RS. Feeding M increased actual and component-corrected milk feed efficiencies (component-corrected milk yield/DMI) and lactose yield and tended to increase milk urea nitrogen compared with C. Milk protein percentage was decreased for M compared with C, but milk fat percentage and yield, protein yield, and lactose percentage were unaffected by M. We observed a tendency for a starch × monensin interaction for milk feed efficiency (actual milk yield/DMI); M tended to increase efficiency more for NS than for RS. Starch and monensin had minimal effects on milk fatty acid composition and yields. Feeding RS decreased milk and protein yields, but component-corrected milk yields and feed efficiencies were similar for RS and NS. Monensin increased feed efficiency and lactation performance for both dietary starch concentrations.

The objective of this study was to determine lactation performance and metabolism of primiparous and multiparous dairy cows fed different levels and sources (inorganic and organic) of Co or given weekly vitamin B(12) injections. Forty-five primi- and multiparous cows at 60 d prepartum were blocked by expected calving date, and randomly assigned to 1 of 5 treatments in a randomized complete block design with treatments starting at 60 d prepartum. The 5 treatments were (1) no supplemental dietary Co (control, CON), (2) 25mg/d of supplemental dietary Co from Co carbonate (CoCarb), (3) 25mg/d of supplemental dietary Co from Co glucoheptonate (LCoGH), (4) 75 mg/d of supplemental dietary Co from Co glucoheptonate (HCoGH), and (5) CON diet plus weekly 10mg i.m. of vitamin B(12) injections (IB12). Cows remained on their respective treatment until 150 d after calving. Cobalt concentrations (mg/kg of dry matter) in the lactating diets were 1.0, 1.9, 2.3, and 5.1 for CON/IB12, CoCarb, LCoGH, and HCoGH, respectively. Dry matter intake, body weight, and body condition score were not affected by treatment. The LCoGH treatment tended to have greater milk yield than CoCarb, and CON had similar milk yields to the mean of LCoGH and HCoGH. Cobalt supplementation or the use of vitamin B(12) injections did not influence plasma or liver measures of energy metabolism. Injections of vitamin B(12) increased plasma, liver, and milk vitamin B(12) contents. Dietary Co addition did not affect plasma vitamin B(12) concentrations; however, it did increase milk vitamin B(12) concentrations throughout lactation and liver vitamin B(12) at calving with no effect of source or level of Co. Folate status of cows in the study was low and possibly limited the effect of improved vitamin B(12) status on lactation performance. Overall, Co supplementation (inorganic and organic) or vitamin B(12) injections improved measures of vitamin B(12) status, but not lactation performance compared with CON possibly due to Co being above requirements in the CON diet.

ABSTRACT Although opaque endosperm2 ( o2 ) gene that alters protein composition of maize ( Zea mays L.) endosperm improves dry matter degradability (DMD) in ruminants it is also associated with soft endosperm texture, low yield, and susceptibility to diseases and insects. To circumvent the undesirable traits, breeders developed high lysine modified endosperm genotypes called quality protein maize (QPM). The objectives of this study were to determine whether DMD is maintained in modified endosperm and to map major quantitative trait loci (QTLs) associated with ruminal in situ DMD (RDMD). Composited 1.5‐g ground grain samples of 140 recombinant inbred lines (RILs) derived from the cross between o2 (B73 o2 ) and QPM (CML161) lines were assayed for 14‐h RDMD in three rumen‐cannulated, mid‐lactation Holstein cows ( Bos taurus ) and 0‐h rapidly soluble dry matter (RSDM) in tepid water. The RILs were grown in Texas and were evaluated for RDMD at Madison, WI. Slowly degradable dry matter (SDDM = RDMD – RSDM) was estimated. Kernel opacity was positively correlated to 14‐h RDMD ( r = 0.68 and 0.71 in 2005 and 2006, respectively; P < 0.05). Quantitative trait loci for 14‐h RDMD were detected on chromosomes 4, 5, 7, 9, and 10; QTLs for RSDM were detected on chromosomes 3, 5, 7, and 10; and QTLs for SDDM were detected on chromosomes 5, 6, and 9. Quantitative trait loci for 14‐h RDMD and RSDM colocated on chromosomes 5, 7, and 10 might be genomic regions influencing 14‐h RDMD mainly through kernel modification. Quantitative trait loci for 14‐h RDMD and/or SDDM, on chromosomes 6 (SDDM) and 9 (colocated) where 14‐h RDMD appears to be mediated through SDDM and most likely enzymatic RDMD, may be good candidates for improvement of RDMD.

The experimental objective was to determine the effect of dietary supplementation with live-cell yeast (LCY; Procreatin-7, Lesaffre Feed Additives, Milwaukee, WI) at 2 dosages in high-starch (HS) diets [30% starch in dry matter (DM)] on lactation performance, ruminal fermentation, and total-tract nutrient digestibility in dairy cows compared with HS or low-starch (LS; 20% starch in DM) non-LCY diets. Sixty-four multiparous Holstein cows (114±37 d in milk and 726±74kg of body weight at trial initiation) were randomly assigned to 32 electronic gate feeders (2 cows per feeder), which were randomly assigned to 1 of 4 treatments in a completely randomized design. A 2-wk covariate adjustment period with cows fed a 50:50 mixture of the HS and LS diets was followed by a 12-wk treatment period with cows fed their assigned treatment diets. The HS diets were fed without (HS0) and with 2 (HS2) or 4 (HS4) g/cow per day of LCY. The LS diet did not contain LCY (LS0) and was formulated by partially replacing dry ground shelled corn with soy hulls. Cows fed LS0 consumed more DM than cows fed HS diets during wk 3, 10, 11, and 12. Yields of actual (44.5kg/d, on average), fat-, energy-, and solids-corrected milk were unaffected by treatment. Milk fat content tended to be greater for LS0 than for HS0 and HS2 but not different from HS4. Milk urea nitrogen contents were greater for cows fed LS0 than for cows fed the HS diets. Feed conversion (kg of milk/kg of DM intake) was numerically greater for HS diets than for LS0. Ruminal pH was unaffected by treatment. Ruminal molar proportion of acetate was greater, whereas that of propionate was lower, for LS0 compared with HS diets. Dry matter and organic matter digestibilities were greater for HS2 and HS4 than for HS0. Digestibility of neutral detergent fiber was greater for HS4 than for HS0 and HS2. Dry matter, organic matter, and neutral detergent fiber digestibilities were greater for LS0 than for HS diets; starch digestibility was greater for LS0 than for HS0 and HS4. Feeding LS0 increased DM intake and milk fat content, but reduced feed conversions. The addition of 4g/cow per day of LCY to HS diets tended to increase milk fat content and increased total-tract fiber digestibility in dairy cows.

The objective of this study was to evaluate the effect of a rumen-protected niacin product (RPN; 65% nicotinic acid; NiaShure, Balchem Corp., New Hampton, NY) on lipid metabolism, oxidative stress, and performance of transition dairy cows. Thirty nonlactating multiparous Holstein cows in late gestation were paired according to expected calving date and randomly assigned to 12 g/cow per day of RPN product or to an unsupplemented control (CON) diet. Treatment diets were fed from 21 d before expected calving through 21 d after parturition. Blood samples were taken on d -21, -14, -7, 1, 7, 14, and 21 relative to calving for plasma nonesterified fatty acid (NEFA), β-hydroxybutyrate (BHBA), glucose, and superoxide dismutase (SOD) analyses. Liver samples were taken by biopsy on d 1 and 21 relative to calving for triglyceride (TG) analysis. Data were analyzed for a randomized complete block design with repeated measures. Pre- and postpartum dry matter intake, milk yield, and protein were unaffected by treatment. Milk fat percentage (5.08 vs. 4.44%) and somatic cell score (3.93 vs. 2.48) were reduced for RPN. Treatment × time interactions were observed for energy-corrected milk (ECM) and fat-corrected milk (FCM) yields; RPN reduced ECM and FCM yields by 8.5 and 8.9 kg/cow per day, respectively, in the first week of lactation. Although body weight and condition score decreased during the experimental period, no differences due to treatment were observed. However, calculated postpartum energy balance tended to be improved for RPN because of the reduction in ECM yield. Time and treatment × time effects were observed for plasma NEFA. On d 1 postpartum, NEFA reached 1,138±80 μEq/L for CON compared with 698±80 μEq/L for RPN. Cows supplemented with RPN tended to have lower plasma NEFA concentrations than CON cows on d 7 and 14 postpartum. Plasma BHBA, glucose, and SOD and liver TG concentrations were unaffected by treatment. In conclusion, supplementation with 12 g/cow per day of the RPN product provided a bioavailable source of niacin that modified lipid metabolism but did not affect milk yield over the first 3 wk of lactation or oxidative stress of transition dairy cows.