D In Milk Research Articles

Preference of Dairy Cows for Free-Stalls Bedded with Sand or Granite Fines and Changes in Bacterial Counts in Those Materials

Sand and granite fines were compared as bedding in free stalls for lactating cows. Eighteen stalls were randomly bedded with sand or granite fines. Lactating cows [100 to 160; 31 to 90 d in milk (DIM)] had access to these stalls plus 142 other stalls bedded with sand. Experimental stalls were observed on 6 d (4 times/d) during the 27-d study. Using a logistic procedure, experimental stalls bedded with sand were 2.8 times more likely to be used than those bedded with granite fines (P<0.01). Stall usage was analyzed using a frequency procedure (P<0.001); cows were observed lying on sand 90% of the time and on granite fines 73% of the time. On d 24, hardness of the surface, measured at a pressure of 2 kg/cm2, was greater for granite fines (P<0.01). On d 0 and 1, Streptococci spp. counts in granite fines and sand did not differ; however, on d 7 and 11 after adding new materials, Streptococci spp. counts in granite fines were greater than in sand (bedding material × time of sampling interaction, P<0.05). Cows preferred sand to granite fines in free stalls, possibly because sand was the softer bedding surface. Streptococci spp. counts were less in stalls bedded with sand on d 7 and 11 after cows had used the bedding. Costs (without shipping) of sand were $0.096/d compared with $0.049/d for granite fines.

Statistical Evaluation of Factors and Interactions Affecting Dairy Herd Improvement Milk Urea Nitrogen in Commercial Midwest Dairy Herds

In this study, 400,729 Dairy Herd Improvement (DHI) records collected on 77,178 cows in 692 Midwest herds over 29 mo (January 1999 to May 2001) were used to analyze milk urea nitrogen (MUN) as collected the day of the test in 6 breeds. Records of Holsteins, Jerseys, and Brown Swiss were subjected to stepwise backward elimination analysis with a model including parity (primiparous vs. multiparous cows), sample type (morning vs. evening), milking frequency (2× vs. 3× [Holstein only]), season (winter, spring, summer, and fall), yield of fat-corrected milk (FCM) classified into 1 of 3 FCM categories (FCMc) and all possible higher-order interactions. Results indicated that FCMc contributed to test-day MUN variation in multiparous, but not primiparous, Holsteins. Sample type and season were significant in both parity groups; milking frequency was not significant, but milking frequency×season and milking frequency×FCMc were significant in both parity groups. The nature of these interactions differed for each parity group. For Jersey and Brown Swiss data analyzed by sample type separately, parity was not significant but tended to interact with FCMc, whereas season, FCMc, and season×FCMc were generally significant. Mean test-day MUN was 12.7, 14.6, and 14.4mg/dL, with 24, 45, and 42% of records above 14.5mg/dL in Holsteins, Jerseys, and Brown Swiss in single-breed herds, respectively. In Holsteins, MUN peaked at 7 to 10 d in milk (DIM), declined until 28 to 35 DIM, and rose again thereafter. In primiparous Holsteins, MUN did not change with FCM ≤42kg/d, but for higher FCM yield, MUN declined linearly by 0.05mg/dL per kilogram of FCM. In multiparous Holsteins, MUN increased by 0.06 and 0.03mg/dL per kilogram of FCM as FCM yield increased from 5 to 29 and from 30 to 59kg/d, respectively, but decreased by 0.06mg/dL as FCM yield increased from 60 to 85kg/d. The use of adjustment coefficients may facilitate interpretation of test-day MUN on commercial herds. Research should focus on the biological significance of the pattern of change in MUN the first few weeks postpartum and the drop in MUN in unusually high-producing cows.

Impact of Early Lactation Somatic Cell Count in Heifers on Milk Yield Over the First Lactation

The objective of this study was to estimate the impact of somatic cell count (SCC) in early lactation (SCCel) [measured between 5 to 14 d in milk (DIM)] of dairy heifers on test-day milk yield (MY) during the first lactation.In total, 117,496 four-weekly test-day records of 14,243 heifers were used. A multilevel regression analysis, which included test-day SCC among the explanatory variables, revealed that an increase by one unit of the natural log-transformed SCCel (LnSCCel) was on average associated with a decrease in MY of 0.13kg/d later in lactation. As an example, a heifer with an SCCel of 50,000cells/mL measured at 10 DIM was estimated to produce 119 and 155kg more milk during its first lactation than heifers with a SCCel of 500,000 and 1,000,000cells/mL, respectively. When not accounting for test-day SCC, the effect of LnSCCel on MY was larger, indicating that part of the negative impact of elevated SCCel was associated with elevated test-day SCC later in lactation.Furthermore, an elevated SCCel at 14 DIM had a larger impact than an equally elevated SCCel measured at an earlier DIM. In addition, the negative effect of an elevated SCCel remained present during almost the entire first lactation in a subgroup of heifers with a second test-day SCC ≤50,000cells/mL, suggesting that prevention rather than cure of an elevated SCCel should be preferred.This study stresses the importance of heifers having low SCCel, as an elevated SCCel will negatively affect milk production during the first lactation, probably via impairment of mammary function and, to a smaller extent, via elevated test-day SCC later in lactation.

Pregnancy Rates in Lactating Dairy Cows After Presynchronization of Estrous Cycles and Variations of the Ovsynch Protocol

Our objectives were to determine pregnancy rates after altering times of the second GnRH injection, insemination, or both in a combined Presynch + Ovsynch protocol, to accommodate once-daily lockup of dairy cows. Lactating dairy cows (n=665) from 2 dairy herds in northeastern Kansas were studied. Cows ranged from 24 to 44 d in milk (DIM) at the start of the Pre-synch protocol, which consisted of 2 injections of PGF2α 14 d apart, with the second injection given 12 d before initiating the Ovsynch protocol. Cows were blocked by lactation number and assigned randomly to 3 treatments consisting of variations of the Ovsynch protocol. Cows in 2 treatments received injections of GnRH 7 d before and 48h (G48) after the PGF2α injection. Timed AI (TAI) was conducted at the time of the second GnRH injection (G48 + TAI48) or 24h later (G48 + TAI72). Cows in the third treatment received the injections of GnRH 7 d before and at 72h after PGF2α and were inseminated at the time of the second GnRH injection (G72 + TAI72). Pregnancy was diagnosed weekly by palpation per rectum of uterine contents on d 40 or 41 after TAI. Pregnancy rates differed between herds, but they were consistently greater for G72 + TAI72 than for G48 + TAI48 and G72 + TAI72. Subsequent calving rates were consistent with differences in initial TAI pregnancy rates. Pregnancy loss was least for cows on the G72 + TAI72 treatment. Body condition scores (BCS) ranged from 1.0 to 4.0 when assessed on Monday of the breeding week. An interaction of BCS and herd was detected in which cows in herd 1 having poorer BCS (<2.25) had greater pregnancy rates than cows of greater BCS (≥2.25), whereas the reverse was true in herd 2 in which overall pregnancy rates were greater. We concluded that inseminating at 48 or 72h after PGF2α, when GnRH was administered at 48h after PGF2α, produced fewer pregnancies than inseminating and injecting GnRH at 72h after PGF2α for cows whose estrous cycles were synchronized before initiating this variant of the Ovsynch protocol.

Association Between Somatic Cell Count in Early Lactation and Culling of Dairy Heifers Using Cox Frailty Models

The association between somatic cell count (SCC) of dairy heifers in early lactation [SCCel; measured between 5 and 14 d in milk (DIM)] and the culling hazard during the first lactation was studied using Cox frailty models. Udder health problems were the culling reason for 10% of the culled heifers in this study. For each unit increase in the log-transformed SCCel (LnSCCel), the culling hazard increased by 11% [Hazard ratio (HR) = 1.11]. The strength of the association depended on 5 factors. Firstly, the association was stronger when SCCel was recorded after 10 DIM than at an earlier DIM. Secondly, the association was stronger if only culling events for udder disorders were considered (HR = 1.32) instead of all culling events (HR = 1.11). Furthermore, for each unit increase of test-day LnSCC after 14 DIM, modeled as a time-varying covariate, the culling hazard in the first lactation increased by 26% (HR = 1.26). Including LnSCC in the model already containing LnSCCel, reduced the estimate of LnSCCel slightly. Fourth, a higher test-day milk yield, modeled as a time-varying covariate, protected against culling and reduced the magnitude of the effect of LnSCCel as well when taken into account. Finally, the association between LnSCCel and culling was still present, although smaller, in the group of heifers with a second test-day SCC ≤50,000 cells/mL.

Cow-Related Risk Factors for Milk Leakage

Milk leakage in dairy cows is a symptom of impaired teat sphincter function. Milk leakage is related to an increased risk of mastitis in heifers and cows, and causes hygiene problems. The aim of our study was to assess whether teat shape, condition of teat orifice, and peak milk flow rate are risk factors for milk leakage. We conducted a longitudinal observational study in 15 German dairy farms in which cows were maintained in loose housing. The farms were visited monthly at 2 consecutive milkings. During the evening milking, milk flow curves were measured with the LactoCorder. Milk leakage was recorded during the subsequent morning milking, when cows entered the milking parlor. Immediately after detachment of the milking cluster, teat shape, teat end shape, and condition of the teat orifice of cows were assessed between 9 and 100 d in milk (DIM) and during late lactation (>250 DIM). Data from 1600 cows were analyzed. Milk leakage was treated as the binary response variable in a logistic regression model with herd as a random effect. Primiparous cows with high peak milk flow and teat canal protrusion were at greater risk of milk leakage. High peak milk flow rate, short teats, teat canal protrusion, inverted teat ends, and early lactation increased the risk of milk leakage in multiparous cows. Random herd effects accounted for only 10% of the total variation, indicating that the impact of management or other herd-level factors on the occurrence of milk leakage is virtually negligible for practical purposes.

Feeding Glycerol to Transition Dairy Cows: Effects on Blood Metabolites and Lactation Performance

Glycerol can alleviate the symptoms of ketosis when delivered as an oral drench. The addition of glycerol to the diet would eliminate the need for restraining cows for drenching yet deliver a glucogenic substrate, alleviate the fatty liver-ketosis complex, and improve lactational performance. For this study, 21 multiparous and 9 primiparous Holstein cows blocked by parity and expected calving date were used in a randomized block design to evaluate the effects of feeding glycerol from 14 d prepartum to 21 d in milk (DIM). Treatments (kg/d dry matter basis) were 0.86 of cornstarch (control), 0.43 cornstarch+0.43 glycerol (LG), or 0.86 glycerol (HG), topdressed and hand-mixed into the upper one-third of the daily ration. All cows were fed a common diet from 22 to 70 DIM. Prepartum dry matter intake (DMI) was greater for cows fed the control diet compared with LG or HG (13.3, 10.8, and 11.3±0.50kg/d, respectively). Prepartum plasma glucose, insulin, β-hydroxybutyrate, nonesterified fatty acids, and ruminal profiles were not affected by treatments. Rumen fluid collected postpartum from cows fed LG and HG had greater total volatile fatty acids, greater molar proportions of propionate, and a decreased ratio of acetate to propionate. Furthermore, concentrations of butyrate tended to be greater in rumens of cows fed LG and HG. Postpartum concentrations of glucose in plasma were greatest for cows fed the control diet relative to LG and HG (66.0 vs. 63.1 and 58.4mg/dL, respectively) and decreased sharply at 21 DIM, after treatments ended, for cows fed HG (diet × day interaction). Body weight and condition loss, plasma nonesterified fatty acids, and liver lipids during the first 21 DIM were similar among treatments. Postpartum DMI was not affected by treatments; however, a tendency was observed for a diet × day interaction for body weight, as cows fed LG gained more body weight from 21 to 70 DIM relative to cows fed HG. Yield of energy-corrected milk during the first 70 DIM tended to be greatest for cows fed the control diet. The LG and HG diets decreased urea nitrogen concentrations in milk relative to controls. Based upon prepartum DMI and concentrations of glucose and β-hydroxybutyrate in blood postpartum, feeding glycerol to dairy cows at the levels used in this experiment increased indicators used to gauge the degree of ketosis in dairy cattle.

Impact of Early Lactation Somatic Cell Count in Heifers on Somatic Cell Counts Over the First Lactation

The objective of this study was to estimate the impact of somatic cell count in early lactation (SCCel) from Belgian dairy heifers on test-day somatic cell count (SCC) in first lactation. Geometric mean SCCel [5 to 14 d in milk (DIM)] of the 14,766 available samples was 104,000 cells/mL, and decreased from 178,000 at 5 DIM to 74,000 cells/mL at 14 DIM. Proportion of SCCel >200,000 cells/mL was 27.5. Heifers calving in the period April–June had highest SCCel.In total, 117,496 monthly SCC were measured. A multilevel regression analysis revealed that an increase of the natural log-transformed SCCel (LnSCCel) by one unit on average resulted in an increase of test-day natural log-transformed SCC (LnSCC) by 0.22 unit. The impact of LnSCCel on LnSCC depended on when LnSCCel was measured; an elevated LnSCCel at 14 DIM was more consequential than an equally elevated LnSCCel at 5 DIM. The probability of having a test-day SCC >200,000 cells/mL during the first lactation, also increased with an increasing LnSCCel. The negative effect of an elevated LnSCCel was still present, although to a lesser extent, in heifers with a second test-day SCC ≤50,000 cells/mL.This study indicates that udder health problems in heifers in early lactation have a high prevalence and stresses that heifers should have a low SCCel, because an elevated SCCel will negatively influence test-day SCC during the whole first lactation.

Timed Artificial Insemination with Estradiol Cypionate or Insemination at Estrus in High-Producing Dairy Cows

A total of 799 Holstein cows from 3 herds were randomly assigned at 37±3 d in milk (DIM) to timed artificial insemination (AI) or insemination at detected estrus. Cows were presynchronized with injections of PGF2α at 37 and 51 DIM. At 65 DIM, cows received an injection of GnRH, followed 7 d later by PGF2α. Cows in the estrus-detected group were inseminated after being observed in estrus during the 7 d after the last PGF2α. Cows in the timed AI group received an injection of 1mg of estradiol cypionate (ECP) 24h after the last PGF2α. If detected in estrus≤24h after ECP, cows were inseminated then or at a fixed time 48h after ECP. Pregnancy was diagnosed by ultrasonography at 30 d and by palpation at 44 and 58 d after AI. Plasma progesterone was measured in 4 samples per cow collected on days of 1) second PGF2α, 2) GnRH, 3) third PGF2α, and 4) 48h after third PGF2α. Cows were classified as cyclic or anovulatory based on progesterone concentrations in samples 1 and 2. Similarly, cows were classified according to progesterone concentrations in samples 2, 3, and 4 (H = ≥1 ng/mL; L = <1 ng/mL), resulting in 8 combinations (LLL, LHL, LLH, LHH, HHH, HHL, HLH, and HLL). Conception rates and pregnancy rates were higher for cows in the timed AI group than in the estrus-detected group at 30, 44, and 58 d (e.g., at 58 d, pregnancy rates were 42.2% for multiparous cows or 34.4% for primiparous cows in the group receiving ECP and timed AI compared with only 20.8 or 18.8% for respective parity subgroups for the treatment group inseminated only at detected estrus). Pregnancy losses were 11.5% from 30 to 58 d and did not differ between treatments. Cyclic cows within both treatments had higher estrous responses, conception rates, and pregnancy rates. Cows that responded to presynchronization and to luteolysis (HHL) had the highest conception and pregnancy rates, followed by cows classified as LHL. Use of 1mg of ECP to induce ovulation as part of a synchrony regimen improved reproduction at first postpartum insemination in dairy cows.

Body Condition Scores and Dairy Form Evaluations as Indicators of Days Open in US Holsteins

The objectives of this study were to estimate genetic correlations among body condition score (BCS), dairy form, milk yield, and days open in US Holsteins and investigate the potential of using BCS or dairy form evaluations as early indicators of days open. Dairy form and BCS obtained from the Holstein Association USA, Inc., were merged with mature equivalents (ME) for milk yields and days open data from AIPL-USDA. Cows were required to be classified between 24 and 60 mo of age, before 335 d in milk (DIM) and have ME milk of at least 4537kg. A minimum of 20 daughters per sire and 10 cows per herd-classification visit (HV) or herd-year-season of calving (HYS) were required. The final data set included 159,700 records. Heritabilities and correlations among dairy form, BCS, milk yield, and days open were estimated with multiple trait sire models. Fixed effects included age at classification for dairy form and BCS, age at calving for milk yield, HV for dairy form and BCS, HYS for milk yield and days open, DIM within lactation group for dairy form and BCS and lactation group for milk yield and days open. Correlations among dairy form, BCS, and days open were generated with and without a ME milk covariable. Correlations between ME milk and days open were generated with and without covariables for dairy form or BCS. Random effects included sire and error. The genetic correlation estimates of days open with dairy form, BCS, and ME milk were 0.48, −0.30, and 0.38, respectively. The genetic correlation estimate between days open and dairy form was 0.38 after adjustment for ME milk, whereas the genetic correlation between days open and BCS was −0.24 after adjustment for ME milk. Combining dairy form evaluations with days open evaluations for 19 recently proven bulls resulted in an average increase of 0.06 for reliability of days open evaluations. The addition of BCS evaluations did not increase reliability when dairy form observations were available.

Use of early lactation days open records for genetic evaluation of cow fertility.

National genetic evaluations for cow fertility were introduced by the USDA in February, 2003. These evaluations, reported as daughter pregnancy rate, are based on days open. One requirement of the evaluation system is that lactations be at least 250 d in milk (DIM) to be included for analysis. The objective of this research was to develop a predictor of days open, usable in genetic evaluation, to allow for earlier predicted transmitting abilities (PTA), especially for young bulls. The final prediction equation included an overall intercept, the effects of lactation and calving ease score, the linear and quadratic effects of age at calving, and a regression on days open based on last breeding. Data used for estimation were breeding records from 4 dairy records processing centers for the years 1995 through 1998. Genetic correlations were > or =0.91 by d 130, and phenotypic means of predicted days open were in agreement with means for final days open, indicating that the predictions were phenotypically unbiased. Comparison of mean PTA based on actual and predicted days open indicated no bias in PTA, and correlations between PTA were > or =0.92 by d 130. The earlier use of data increased reliability by about 5% for sires between the ages of 4 and 5 yr. The USDA began using predicted days open for records that are at least 130 DIM in national evaluations starting November, 2003.

Short commuunication: Effect of dietary protein depletion and repletion on skeletal muscle calpastatin during early lactation.

Sixteen multiparous Jersey cows were assigned at calving to one of 4 dietary treatments. An 18% crude protein (CP) diet was fed as a total mixed ration through 30 d in milk (DIM), and beginning at 31 DIM a 9, 12, 15, or 18% CP diet was fed through 58 DIM (depletion). All cows were then fed the 18% CP diet until 84 DIM (repletion). Muscle biopsies were taken under local anesthesia at 49 and 84 DIM from the semitendinosus muscle. Milk production, DMI, and milk component contents were measured. Calpain and calpastatin contents of muscle taken at biopsy were evaluated using Western blotting techniques. Milk production and milk protein content were reduced during the depletion period by decreasing dietary protein. Diet had no effect on milk fat content or DMI. During repletion, DMI was affected by dietary treatment. Western blots of muscle extracts indicated no differences in calpain content at any stage of the experiment or in calpastatin content of muscle at 49 DIM. However, at 84 DIM, calpastatin (135 kDa) was lower or undetectable in cows fed either the 9 or 12% CP diets from 31 to 59 DIM. Bands for a 110-kDa degradation product of calpastatin were present in some cows fed the 9, 12, and 15% CP diets during the depletion period. Results indicate a change in skeletal muscle calpain/calpastatin proteolytic system during protein repletion following depletion with diets of less than 15% CP during early to peak lactation in dairy cows.

Effect of bST and reproductive management on reproductive performance of Holstein dairy cows.

The objective was to determine the effects of bovine somatotropin (bST) and two artificial insemination (AI) protocols on reproductive performance of Holstein cows. Lactating cows (n = 840) were assigned at 37 d in milk (DIM) to one of four treatments in a 2 x 2 factorial arrangement. Treatments consisted of either bST (500 mg/14 d) starting at 63 +/- 3 DIM or no bST (control), with cows either submitted for timed AI following a synchronized ovulation (Ovsynch) protocol or assigned to receive AI based on estrus detection (ED). Two injections of PGF2, at 37 +/- 3 and 51 +/- 3 DIM were used to presynchronize estrous cycles. Cows then received an injection of GnRH at 63 +/- 3 DIM, followed 7.5 d later by PGF2. Cows assigned to ED treatments were inseminated after observed estrus during a 7-d period. Cows in Ovsynch treatments received a second GnRH injection 48 h after the last PGF2alpha and received timed AI 16 to 18 h later. Pregnancy was diagnosed by ultrasound at 31 d after AI and confirmed 14 d later. Frequency of anovulation (18.5%) at 63 DIM was similar across treatments, but proportions of anovulatory cows decreased quadratically as body condition at 70 DIM increased from 2.25 to 3.75. Estrus detection rate after PGF2alpha tended to be lower in multiparous cows receiving bST, and bST reduced returns to estrus in nonpregnant cows. Conception rates were higher in cows receiving AI after ED and bST improved conception rates to first AI in cyclic cows by reducing embryonic mortality. Pregnancy loss was similar for cows inseminated following ED or the Ovsynch protocol. There was a positive impact of bST on fertility of cyclic cows inseminated at fixed time or at detected estrus, but effective resynchronization protocols are needed to optimize reinsemination of non-pregnant bST-treated cows.

Heritability and correlations for body condition score and dairy form within and across lactation and age.

The objectives of the current study were to investigate the relationship between body condition score (BCS) and dairy form and changes in genetic parameters for BCS and dairy form within and across lactations and age. Body condition score and dairy form were obtained from the Holstein Association USA, Inc. Records were edited to include those cows classified between 24 and 60 mo of age and between 0 and 335 d in milk (DIM). A minimum of 20 daughters per sire and 15 cows per herd-classification visit were required. The dataset consisted of 135,178 records from 119,215 cows. Repeatability, multiple trait, and random regression models were used to analyze the data. All models included fixed effects for herd-classification visit, age within lactations 1, 2, and 3 or higher, and 5th-order polynomials for DIM. Random effects included sire and permanent environment for all models. Random regression models included age at classification nested within sire or DIM and lactation number nested within sire. Genetic variance for both BCS and dairy form was lowest in early lactation and highest in midlactation. Genetic correlations within and across lactations were high. The genetic correlation between DIM 0 in lactation 1 and DIM 305 in lactation 3 was estimated to be 0.77 for BCS and 0.60 for dairy form. The genetic correlation estimate between 30 mo of age at classification and 50 mo of age at classification was 0.94 for both dairy form and BCS. The repeatability models appeared to generate accurate evaluations for BCS or dairy form at all ages and stages of lactation.

Inorganic Versus Complexed Trace Mineral Supplements on Performance of Dairy Cows

To determine the effects of chemical form of trace mineral supplements on performance of dairy cows, Holstein cows (n = 36) were assigned to dietary treatments of inorganic trace minerals or a combination of inorganic and complexed trace minerals (CTM). Starting at 21 d prepartum, dry cows were fed hay and a grain supplement that contained one of the trace mineral supplements. Cows continued to receive their respective trace mineral treatment from parturition until 150 d in milk (DIM). Cows fed the CTM lost less BW prepartum (P<0.05); however, there was no difference between treatments in postpartum BW change or body condition score (BCS). The DMI of lactating cows were similar between treatments. Actual milk yield (42.2 vs 41.7 kg/d), 3.5% fat-corrected milk (FCM) (42.3 vs 42.3 kg/d), and measures of production efficiency also were similar between treatments. There was a week × treatment interaction (P<0.05) for yield of milk, energy-corrected milk, and 3.5% FCM; the response to CTM was greatest from wk 5 through wk 10 postpartum. Colostrum of cows fed the CTM prepartum had greater IgG (P<0.05) and lesser Zn concentrations. There was no difference between treatments in concentrations of IgM, Co, Mn, or Cu in colostrum. Although there were period effects on serum concentrations of IgG, IgM, nonesterified fatty acids (NEFA), Zn, Co, and Ca, there were no treatment effects. These results indicate that CTM may benefit cows at peak production.

Influence of Transition Diets on Occurrence of Subclinical Laminitis in Holstein Dairy Cows

Pre- and postpartum diets varying in energy and fiber were studied for effects on subclinical laminitis in Holstein cows. Also, ruminal acidosis was examined relative to sole hemorrhages and ulcers. Cows (n = 98) were assigned to a 2 x 2 factorial arrangement of treatments in a randomized complete block. Diets high in net energy of lactation (NE(L)) and low fiber were classified as high NE(L), whereas low NE(L) and higher fiber were defined as low NE(L). Two diets were fed for 3 wk before calving and 2 others fed for 3 wk postpartum resulting in 4 treatment combinations: high NE(L), low NE(L); high NE(L), high NE(L); low NE(L), low NE(L); and low NE(L), high NE(L). Levels of NE(L) (Mcal/kg DM), percentage of acid detergent fiber, and percentage of neutral detergent fiber for low NE(L) vs. high NE(L) prepartum diets, were 1.51, 30.2, 47.2 vs. 1.65, 23.4, 39.8, respectively, and 1.70, 22.4, 36.8 vs. 1.77, 17.5, 31.4 for low NE(L) vs. high NE(L) lactating diets, respectively. A single diet was fed after 21 d in milk (DIM). Measures of hoof discoloration, hemorrhage, and/or ulcer formation were done at about 45 d before calving, and near 28 and 70 DIM. Rumenocentesis was performed 14 d before calving and at 8, 22, and 70 DIM. Hoof scores among treatments were similar at 28 DIM. The low NE(L), high NE(L) group had less desirable hoof scores than high NE(L), high NE(L), or low NE(L), low NE(L) groups from 55 to 75 DIM. Rumen pH did not differ by treatment before calving. The lowest postpartum rumen pH was significantly lower and rates of ruminal acidosis (pH < or = 5.8) at 8 and 22 DIM were higher for groups fed high NE(L) after calving. No direct relationship between low postpartum rumen pH and hoof scores on individual cows was found. Low NE(L) before calving and high NE(L) right after calving may increase risk of subclinical laminitis if not carefully managed.

Splanchnic Metabolism of Dairy Cows During the Transition From Late Gestation Through Early Lactation

Blood flow and net nutrient fluxes for portal-drained viscera (PDV) and liver (total splanchnic tissues) were measured at 19 and 9 d prepartum and at 11, 21, 33, and 83 d in milk (DIM) in 5 multiparous Holstein-Friesian cows. Cows were fed a grass silage-based gestation ration initially and a corn silage-based lactation ration peripartum and postpartum. Meals were fed at 8-h intervals and hourly (n = 8) measures of splanchnic metabolism were started before (0730h and 0830h) feeding at 0830h. Dry matter intakes (DMI) at 19 and 9 d prepartum were not different. Metabolism changes measured from 19 to 9 d prepartum were lower arterial insulin and acetate, higher arterial nonesterified fatty acids and increased net liver removal of glycerol. After calving, PDV and liver blood flow and oxygen consumption more than doubled as DMI and milk yield increased, but 85 and 93% of the respective increases in PDV and liver blood flow at 83 DIM had occurred by 11 DIM. Therefore, factors additional to DMI must also contribute to increased blood flow in early lactation. Most postpartum changes in net PDV and liver metabolism could be attributed to increases in DMI and digestion or increased milk yield and tissue energy loss. Glucose release was increasingly greater than calculated requirements as DIM increased, presumably as tissue energy balance increased. Potential contributions of lactate, alanine, and glycerol to liver glucose synthesis were greatest at 11 DIM but decreased by 83 DIM. Excluding alanine, there was no evidence of an increased contribution of amino acids to liver glucose synthesis is required in early lactation. Increased net liver removal of propionate (69%), lactate (20%), alanine (8%), and glycerol (4%) can account for increased liver glucose release in transition cows from 9 d before to 11 d after calving.

Performance of Lactating Holstein Cows as Influenced by Forage Species, Maturity, and Level of Inclusion

Three trials were conducted with the objective of evaluating the influence of fiber and indigestible NDF as affected by forage species, maturity, and level of inclusion on intake and milk production parameters. In the first trial, 60 multipa-rous Holstein cows [109 ± 49 d in milk (DIM)]were fed alfalfa- or orchardgrass-based total mixed ration(s)(TMR)for 70 d. Diets did not differ in NDF, ADF, CP, or non-fibrous carbohydrate(NFC) content. Cows fed these diets did not differ in DMI or milk production, even though the alfalfa had greater lignin and indigestible NDF than the orchardgrass-based TMR. Similar ADF and indigestible fiber in alfalfa and late-cut orchardgrass forages might have contributed to the similar performance of cows fed these diets. In the second trial, 50 multiparous cows (57 ± 28 DIM) were fed early- or late-cut orchardgrass-based TMR for 50 d. Diets did not differ in NDF, ADF, CP, NFC, or indigestible NDF, but early-cut orchardgrass had less (P<0.05) ADF, NDF, lignin, and indigestible NDF and greater (P<0.05) NFC and soluble CP than late-cut orchardgrass. Cows fed the early-cut orchardgrass-based TMR had greater (P<0.05) DMI, milk production, and milk protein than those fed late-cut orchardgrass-based TMR. Fiber digestibility of early-cut orchardgrass was much greater than late-cut orchardgrass, contributing to the improved DMI of cows on the early-cut orchardgrass TMR. In Trial 3, 20 Holstein cows (183 ± 22 DIM) were assigned to a repeated 4 × 4 Latin square design with 5 cows per treatment and 21-d periods to evaluate the influence of level of orchardgrass inclusion (50 to 80%) on DMI and milk production parameters. Dry matter intake and milk production decreased linearly as forage included in the diet increased (P<0.05). Amount of NDF consumed per day did not vary among diets in this study, suggesting that when a single forage source is used, diet NDF content is highly correlated with DMI. Variations in fiber digestibility and indigestibility of fiber may account for differences in intake and milk production of cows fed diets similar in chemical composition but varying in ingredient composition.

Milk Production from Cows Fed Corn, Alfalfa, or Ryegrass Silage Ensiled in Conventional, Vacuum, or Packed Systems

Temperature of alfalfa silage was monitored for 28 d at three depths following ensiling in a vacuum bag system. For this silo system, silage was piled on one sheet of plastic and covered by another; the plastic sheets were connected on all sides by rolling and clamping around a polyvinylchloride pipe. The silo was evacuated with a vacuum pump attached to a perforated pipe placed on the bottom sheet of plastic prior to filling. Temperatures increased linearly as depths increased (0.3 to 0.6 and 0.9 m), but temperature measurements were <35.9oC at all depths. Storage cost per ton of silage ensiled was very sensitive to the quantity ensiled and marginally sensitive to DM losses. For a vacuum silo with 40 metric ton (mT)(DM) capacity, storage cost estimates per mT (DM) were $8.90, $9.50, $9.95, and $10.44 for 5, 11, 15 or 19% DM losses, respectively. Temperature differences attributable to post-ensiling days were detected. The performance of 48 midlactation (187+ 45 din milk) cows fed diets based on forages (45.8 to 61.4% DM) of corn(CS),alfalfa, or ryegrass silages(RS)with or without 7.0% cottonseed hulls(CSH) was compared in a 75-d lactation trial. Corn silage was ensiled in an upright silo; alfalfa silage was ensiled in both an Ag-Bag® (Ag-Bag International, Warrenton, OR) and vacuum bag system (BALandVAL,respectively); RS was ensiled in an Ag-Bag® system. Cows fed CS without CSH produced more milk (21.1 kg/d) than did cows fed the other three silages (17.1 to 19.1 kg/d). No differences in milk production were detected for cows consuming silage from the different ensiling systems, indicating that the vacuum ensiling process can be a satisfactory method of making silage. Cows fed RS consumed less DM (11.0 to 12.1 kg/d) than did cows fed the other three silages (14.4 to 20.4 kg/d). Inclusion of CSH in the alfalfa silage-based diet increased DMI, milk production, and BW gain but had no effect on milk fat or protein percentage. A vacuum silo system may be a satisfactory method of ensiling crops, especially during emergency situations, for short-term ensiling, and for small herds. Systems, Silage, Dairy Cows, Milk Production.)

Effect of Heat Stress on Nonreturn Rate in Holsteins: Fixed-Model Analyses

The objective of this study was to examine the relationship between reproductive traits and heat stress. Nonreturn rate at 45 d (NR45) was analyzed in a fixed-effect model that included the temperature-humidity index (THI) from a nearby weather station as a measurement of heat stress. Data consisted of 150,200 first inseminations at first and later parities of 110,860 Holstein cows from 550 herds in Georgia, Tennessee, and Florida with weather information from 16 weather stations. THI on the day of the insemination, 2 d prior, 5 d prior, 5, 10, 20, and 30 d after insemination were studied as independent variables. The THI on the day of insemination showed the highest effect on NR45, followed by 2 d prior, 5 d prior, and 5 d after insemination, but no relationship was found with THI at 10, 20, and 30 d after insemination. NR45 showed a decrease of 0.005 per unit increase in THI on the day of insemination for THI >68. First and later parities presented similar thresholds but responded differently to an increase in THI, with NR45 being significantly lower and more susceptible to increases of THI in cows in their first parity than in later parities (0.008 vs. 0.005 decrease). Threshold for sensitivity to heat stress changed with the states, with Florida, Georgia, and Tennessee having thresholds of 70, 70, and 66, respectively. The decrease in NR45 per unit increase of THI was 0.007, 0.005, and 0.006 for Florida, Georgia, and Tennessee, respectively. With respect to only the Florida data, the final fixed-effect model used was NR45 = herd(year) + month(year) + month(year) + age(parity) + days in milk + 100d milk + THI + error. Animals with more than 150 d in milk (DIM) had a 0.16 lower NR45 than animals with less than 60 DIM at insemination. Lower milk-producing animals showed 0.08 higher NR45 than higher-producing animals. A difference of 0.10 in NR45 was observed between THI lower than 70 and THI 84. This variation in NR45 caused by THI changes is sufficient to merit further studies to examine genetic components of heat tolerance for this trait.