W.K. Coblentz

Short-term foraging dynamics of cattle grazing swards with different canopy structures

The objective of the present experiment was to describe the sward canopy structures of 3 different wheat (Triticum aestivum L.) pastures and relate them to short-term herbage intake rate and foraging dynamics by steers. Pastures were sampled for leaf and stem fractions at the bottom, middle, and top canopy strata. Sward surface heights and tiller and bulk densities were measured. Herbage was separated into stem and leaf, and leaves were then ranked phenologically. Three steers grazed (grazing sessions) 3 different pastures in a Latin square design. Ruminal contents were emptied and weighed before and after grazing sessions to assess herbage intake rate and bite mass. All grazing sessions were video recorded and analyzed for feeding stations (eating steps demarking the potential area of herbage consumption), bites per feeding station, and feeding stations per minute. Bite depth, bite area, and area grazed per feeding station were calculated. Morphological components and tiller density did not differ (P > 0.05) between the pastures, but sward surface height (P < 0.05) and leaf proportions in the middle and top canopy strata did differ. The herbage intake rate, bite mass, and bite area differed between treatments (P < 0.05). Steers grazing the tallest pasture with the greatest leaf accessibility ate faster, navigated slower, and grazed more efficiently (P < 0.05). The area grazed per feeding station differed between treatments (P < 0.05), being 87% for the tallest pasture with the greatest leaf accessibility and the least, 31%, for the pasture with the least leaf accessibility. Pastures with greater leaf accessibility may lead grazing cattle to reach the same herbage intake amount in less time while grazing more efficiently per unit area. Therefore, it may be logical to reduce the area and time allocations in pastures with taller swards where a leafy upper canopy stratum is found.

Effect of herbage depletion on short-term foraging dynamics and diet quality of steers grazing wheat pastures.

Two complementary experiments were completed to assess short-term foraging dynamics, diet quality, and ruminal degradation kinetics of herbage consumed by steers with 3 levels of herbage depletion. Experiment 1 was a behavioral study in which 2 ruminally cannulated steers were allocated to grazing scenarios simulating 3 levels of herbage depletion. These treatments included an ungrazed sward (control), as well as medium and high levels of herbage depletion. Grazing scenarios were sampled for sward surface height and amount of green leaf and stem before being grazed. Foraging dynamics were determined through measurements of bite rate, bite depth, eating step rate, eating distance, potential area consumed while grazing, and bites and intake per eating step. Also, quality of potential herbage consumed was estimated from hand-plucked herbage. In Exp. 2, ruminal degradation kinetics of DM for samples of herbage consumed (masticate) by steers during Exp. 1 were assessed in situ using 5 ruminally cannulated steers. The immediately soluble, degraded, and undegraded DM fractions were determined. The DM disappearance rate and lag times were determined from a nonlinear regression model, and the effective degradability of DM was calculated. Herbage depletion resulted in increased eating steps/minute, as well as the potential area harvested while grazing (P < 0.05) and reduced herbage intake/eating step (P < 0.05). Neither the herbage potentially consumed nor the ruminal degradation kinetics was affected by extent of depletion (P > 0.05). Under these experimental conditions, steers adapted their foraging dynamic and were able to sustain diet quality in the short term. These results imply that behavioral adaptations would make diet quality less sensitive to certain levels of herbage depletion.

effects of spontaneous heating on fiber composition, fiber digestibility, and in situ disappearance kinetics of neutral detergent fiber for alfalfa-orchardgrass hays

During 2006 and 2007, forages from 3 individual hay harvests were utilized to assess the effects of spontaneous heating on concentrations of fiber components, 48-h neutral detergent fiber (NDF) digestibility (NDFD), and in situ disappearance kinetics of NDF for large-round bales of mixed alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.). Over the 3 harvests, 96 large-round bales were made at preset bale diameters of 0.9, 1.2, or 1.5 m, and at moisture concentrations ranging from 9.3 to 46.6%. Internal bale temperatures were monitored daily during an outdoor storage period, reaching maxima (MAX) of 77.2 degrees C and 1,997 heating degree days >30 degrees C (HDD) for one specific combination of bale moisture, bale diameter, and harvest. Concentrations of all fiber components (NDF, acid detergent fiber, hemicellulose, cellulose, and lignin) increased in response to spontaneous heating during storage. Changes in concentrations of NDF during storage (poststorage - prestorage; DeltaNDF) were regressed on HDD using a nonlinear regression model (R(2) = 0.848) that became asymptotic after DeltaNDF increased by 8.6 percentage units. Although the specific regression model varied, changes (poststorage - prestorage) in concentrations of acid detergent fiber, cellulose, and lignin also increased in nonlinear relationships with HDD that exhibited relatively high coefficients of determination (R(2) = 0.710 to 0.885). Fiber digestibility, as determined by NDFD, was largely unaffected by heating characteristics except within bales incurring the most extreme levels of HDD or MAX. In situ assessment of ruminal NDF disappearance kinetics indicated that disappearance rate (K(d)) declined by about 40% within the range of heating incurred over these hay harvests. The change in K(d) during storage (DeltaK(d)) was related closely to both HDD and MAX by nonlinear models exhibiting high R(2) statistics (0.907 and 0.883, respectively). However, there was no regression relationship between changes (poststorage - prestorage) in effective ruminal disappearance of NDF and spontaneous heating, regardless of which heating measure was used as the independent variable. The close regression relationship between DeltaK(d) and measures of spontaneous heating indicates clearly that ruminal NDF disappearance was altered negatively by some direct or indirect aspect of spontaneous heating. However, it was equally apparent that these effects were offset by an expanding pool of dry matter recovered as potentially degradable NDF.

Effects of bale moisture and bale diameter on spontaneous heating, dry matter recovery, in vitro true digestibility, and in situ disappearance kinetics of alfalfa-orchardgrass hays

Alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hay was made in 96 large-round bales over 3 harvests during 2006 and 2007 to assess the effects of spontaneous heating on dry matter (DM) recovery, in vitro true digestibility (IVTD), and in situ disappearance kinetics of DM. Throughout these harvests, bales were made at preset diameters of 0.9, 1.2, or 1.5 m and at moisture concentrations ranging from 9.3 to 46.6%. Internal bale temperatures were monitored daily during an outdoor storage period, reaching maxima of 77.2 degrees C (MAX) and 1,997 heating degree days >30 degrees C (HDD) for one specific combination of bale moisture, bale diameter, and harvest. Following storage, regressions of DM recovery on HDD and MAX indicated that DM recovery declined linearly in close association with measures of spontaneous heating. For HDD, slopes and intercepts differed across bale diameters, probably because the greater surface area per kilogram of DM for 0.9-m bales facilitated more rapid dissipation of heat than occurred from 1.2- or 1.5-m-diameter bales. Regardless of bale diameter, coefficients of determination were high (r(2) > or = 0.872) when HDD was used as the independent variable. Regressions of DM recovery on MAX also exhibited high r(2) statistics (> or = 0.833) and a common slope across bale diameters (-0.32 percentage units of DM/ degrees C). Changes in concentrations of IVTD during storage (poststorage - prestorage; DeltaIVTD) also were regressed on HDD and MAX. For HDD, the data were best fit with a nonlinear model in which DeltaIVTD became rapidly negative at <1,000 HDD, but was asymptotic thereafter. When MAX was used as the independent variable, a simple linear model (y = -0.23x + 9.5) provided the best fit. In both cases, coefficients of determination were comparable to those for DM recovery (R(2) or r(2) > or =0.820). Changes (poststorage - prestorage) in ruminal DM degradation rate (DeltaK(d)) and effective ruminal degradability of DM (DeltaDEG) were assessed similarly. Although the most appropriate statistical model varied, DeltaK(d) and DeltaDEG both became increasingly negative at low to moderate levels of heating, but generally stabilized thereafter. Both HDD and MAX were excellent predictor variables for both DeltaK(d) and DeltaDEG; r(2) or R(2) statistics ranged from 0.788 to 0.921. Measures of spontaneous heating are consistently effective indicators of DM recovery following storage, as well as good indicators of concurrent changes in IVTD or in situ disappearance of DM for heated alfalfa-orchardgrass hays.

The effect of dietary phosphorus on bone development in dairy heifers

Phosphorus requirements, as percent of dietary dry matter for heifers (0.20-0.35%) and endogenous levels of P in feeds (0.20-0.35% of dry matter) are similar, suggesting that supplementation of P in heifer diets may be infrequently required. Because long-term studies are unavailable, 183 Holstein heifers and 182 Holstein x Jersey crossbred heifers were fed diets with (0.39%) and without (0.29%) supplemental P from 4 to 21 mo of age in a replicated pen design. Two subpopulations of heifers were selected mid-trial for intensive measurement of bone development and metabolism. Thirty-two heifers at 628 d (+/-10.0 d) of age, balanced by breed and diet, were evaluated for bone development. External frame measurements included hip height, length, heart girth, hip width, cannon bone circumference, pelvic length, pelvic height, and pelvic width. Tails of heifers were surgically amputated with the 13 and 14th coccygeal vertebrae retained. After tissue removal, the 13th coccygeal vertebrae were scanned using peripheral quantitative computed tomography with cortical, trabecular, and total bone densities determined. A second subpopulation (n = 64) of heifers (375 d +/- 33 d), balanced for breed and diet, were evaluated for serum pyridinoline and osteocalcin to assess systemic bone metabolism. Data were analyzed as a completely randomized design with breed, treatment, and their interaction in the model. External skeletal measurements revealed significant differences in hip height, hip width, heart girth, cannon bone circumference, and pelvic length between Holstein and crossbred heifers. Supplementing P had no effect on external frame measurements, bone density, or bone metabolism markers. Bone P content was lower (18.1 vs. 18.6%) in heifers fed no supplemental P. Data suggest P supplementation to heifers modestly increased bone P content but increased bone P was not reflected in frame growth, bone density, or bone metabolism.

Effects of spontaneous heating on forage protein fractions and in situ disappearance kinetics of crude protein for alfalfa-orchardgrass hays packaged in large round bales.

During 2006 and 2007, forages from 3 individual hay harvests were used to assess the effects of spontaneous heating on concentrations of crude protein (CP), neutral detergent insoluble CP (NDICP), acid detergent insoluble CP (ADICP), and in situ disappearance kinetics of CP and NDICP for large round bales of mixed alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.). Over the 3 harvests, 96 large round bales were made at preset bale diameters of 0.9, 1.2, or 1.5m and at moisture concentrations ranging from 9.3 to 46.6%. Internal bale temperatures were monitored daily during an outdoor storage period. The change in concentrations of NDICP (poststorage - prestorage) increased with heating degree days (HDD) >30 degrees C in a relationship best explained with a nonlinear model {Y=24.9 - [22.7 x (e(-0.000010 x x x x))]; R(2)=0.892} that became asymptotic at +24.9 percentage units of CP, thereby indicating that NDICP increases rapidly within bales that heat spontaneously. When maximum internal bale temperature (MAX) was used as the independent variable, the best regression model was quadratic and the coefficient of determination was still relatively high (R(2)=0.716). The change in concentrations of ADICP (poststorage - prestorage; DeltaADICP) also increased with HDD and was best fitted to a nonlinear model {Y=14.9 - [15.7 x (e(-0.0000019 x x x x))]} with a very high coefficient of determination (R(2)=0.934). A similar quartic response was observed for the regression of DeltaADICP on MAX (R(2)=0.975). Increases in DeltaADICP as a result of heating (HDD or MAX) were paralleled by concurrent increases in hemicellulose at relatively low increments of heating, but the inverse relationship was observed as hemicelluloses likely became reactive and concentrations decreased in more severely heated hays. Changes in ruminal disappearance rate of CP were best fitted to cubic models for regressions on both HDD (R(2)=0.939) and MAX (R(2)=0.876); these changes represented an approximate 50% rate reduction in severely heated hays relative to prestorage controls. Within ranges of heating most commonly encountered under field conditions, changes in rumen-degradable protein decreased in a primarily linear relationship with HDD or MAX. However, the mean change in rumen-degradable protein for the 4 most severely heated hays was only -2.6 percentage units of CP, which represents a minimal reduction from prestorage controls and is far less than the maximum of -7.9 percentage units of CP observed with less-severe heating. Interpretation of these results was complicated by poor recovery of NDICP from our most severely heated hays following machine rinsing of 0-h Dacron bags; theoretically, and by definition, this unrecovered pool of NDICP is assumed to be entirely degradable in the rumen. It remains unclear whether these responses could be corroborated in vivo or by other analytical techniques, or whether the magnitude of HDD or MAX for our most severely heated hays exceeds the reliable limits for estimating RDP via in situ methodology.

Production, reproduction, health, and growth traits in backcross Holstein × Jersey cows and their Holstein contemporaries1

A total of 648 purebred Holstein and 319 backcross Holstein × Jersey dairy cattle were compared for production, reproduction, health, linear type, and growth traits. Animals were born between 2003 and 2009 and were housed in the University of Wisconsin-Madison Integrated Dairy Facility. All animals had Holstein dams; lactating dams were mated to unproven Holstein sires to produce purebred (control) Holsteins or to unproven F(1) Jersey × Holstein crossbred sires to produce backcross animals, whereas nulliparous dams were mated to proven Holstein sires to produce purebred (other) Holsteins. Traits were analyzed using mixed linear models with effects of season of birth, age of dam, sire, birth year of sire, days in milk, lactation, and linear type score evaluator. Control Holsteins had greater 305-d milk yield (12,645 vs. 11,456 kg), 305-d mature equivalent milk yield (13,420 vs. 12,180 kg), peak daily milk yield (49.5 vs. 46.4 kg), total lactation milk yield (11,556 vs. 10,796 kg), and daily fat-corrected milk yield (43 vs. 40 kg) compared with backcrosses. Days open and services per conception as a heifer or cow did not differ between control Holsteins, other Holsteins, or backcrosses. The proportion of first-parity births that required assistance was less in control Holsteins than in backcross cows (3.7 vs. 11.2%). The incidence of scours or respiratory problems in calves did not differ between control Holsteins, other Holsteins, and backcrosses, nor did the incidence of mastitis, injury, or feet problems. Control Holstein heifers were heavier (629 vs. 557 kg), with greater hip height (145 vs. 139 cm), body length (167 vs. 163 cm), heart girth (205 vs. 198 cm), and hip width (54 vs. 53 cm) at 22 mo of age. On a 50-point scale for linear type traits, Holsteins were larger in stature compared with backcrosses (41 vs. 28), had wider rumps (37 vs. 33), and wider rear udders (34 vs. 32). Results of this study suggest that backcross Holstein × Jersey cattle have decreased production but fail to demonstrate an advantage in health and reproduction compared with purebred Holsteins.

Evaluation of potential carryover effects associated with limit feeding of gravid Holstein heifers

Ninety-six Holstein heifers (400±6kg, 15.2±0.1 mo), including 9 with ruminal cannulas, were offered 1 of 3 diets for 180±8 d in a randomized replicated pen design. Dietary treatments included a control diet (C100) and 2 independent limit-fed (LF) diets. The LF diets included one offered at 85% of C100 intake (L85) without an ionophore, and a second containing an ionophore (325 mg/head per day of lasalocid) that was offered at 80% of C100 intake (L80+I). Heifers were evaluated for growth, rumen digesta volume, nutrient excretion, and subsequent lactation performance. Limit-fed heifers consumed less dry matter and neutral detergent fiber, and had greater respective average daily gains (0.96 or 0.89 vs. 0.81 kg/d), and lower feed:gain ratios (9.1 or 9.3 vs. 13.0 kg/kg) compared with heifers offered the C100 diet. No differences in rumen pH, NH(3)-N, or volatile fatty acid concentrations were observed between C100 and LF heifers. Rumen digesta volume, density, and weight were unaffected by LF, and feeding L85 or L80+I did not result in carryover effects for rumen digesta volume when these heifers were offered a common high-fiber diet immediately after the 180-d growth trial. At parturition, no differences were observed for dystocia index, calf body weight, or 7-d postpartum body weight between cows offered LF or C100 diets as heifers. Lactation body weight, dry matter intake, and feed efficiency of cows did not differ between treatments at 45 or 90 d in milk. Milk yield and milk components also were not different between cows that were offered C100 or LF diets as gravid heifers. At 45 d in milk, rumen digesta volume was greater (99.1 vs. 66.1L) for cows offered L85 compared with cows offered L80+I as gravid heifers, but this effect was not observed at 90 d in milk. Limit feeding of gravid Holstein heifers for 180 d did not result in any carryover effects during their first lactation for rumen digesta volume, dry matter intake, or milk yield.

Effects of spontaneous heating on estimates of total digestible nutrients for alfalfa-orchardgrass hays packaged in large round bales

Large round or large square hay packages are more likely to heat spontaneously during storage than hay packaged in conventional (45 kg) bales, and the effects of this phenomenon on the associated energy estimates for these hays can be severe. Our objectives for this project were to assess the relationship between estimates of total digestible nutrients (TDN) and spontaneous heating and to describe any important differences in energy estimates that may result specifically from 2 methods of estimating truly digestible fiber (TD-Fiber). Using the summative approach to estimate TDN, TD-Fiber can be estimated from inputs of protein-corrected neutral detergent fiber (NDFn) and acid detergent lignin (TD-FiberLIG) or from NDFn and 48-h neutral detergent fiber digestibility (TD-FiberNDFD). Throughout 2006 and 2007, mixed alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hays from 3 individual harvests were obtained from the same 8.2-ha research site near Stratford, Wisconsin. Both options for estimating TD-Fiber (TD-FiberLIG or TD-FiberNDFD) were then used independently via the summative approach to estimate the total TDN concentrations (TDN-LIG or TDN-NDFD, respectively) within these hays. Estimates of both TDN-LIG and TDN-NDFD then were related to heating degree days >30 degrees C accumulated during storage by various regression techniques. Changes (poststorage - prestorage) in TDN-LIG that occurred during storage (DeltaTDN-LIG) were best fitted with a nonlinear decay model in which the independent variable was squared [Y=(11.7 x e(-0.0000033xxxx)) - 11.6; R(2)=0.928]. For changes in TDN-NDFD (DeltaTDN-NDFD), a quadratic regression model provided the best fit (Y=0.0000027x(2) - 0.010x+0.4; R(2)=0.861). Generally, DeltaTDN-LIG estimates were 2.0 to 4.0 percentage units lower than DeltaTDN-NDFD estimates when heating exceeded 500 HDD. For regressions on maximum internal bale temperature, both DeltaTDN-LIG (Y=-0.38x+16.3; R(2)=0.954) and DeltaTDN-NDFD (Y=-0.25x+10.2; R(2)=0.848) were best fitted by linear models with heterogeneous (P<0.001) slopes and intercepts. In both cases, coefficients of determination were high, suggesting that simple measures of spontaneous heating are excellent predictors of energy losses in heated forages. Regardless of method, reductions in TDN were associated primarily with losses of nonfiber carbohydrate, which is known to occur via oxidation of sugars during spontaneous heating. For heated forages, some discrepancy between TDN-LIG and TDN-NDFD existed because the relationship between NDFD and spontaneous heating was shown previously to be very poor, resulting in minimal changes for estimates of TD-FiberNDFD as a consequence of heating. In contrast, TD-FiberLIG declined in close association with heating, largely because TD-FiberLIG was sensitive to changes in concentrations of both NDFn and acid detergent lignin. Discrepancies between TDN-LIG and TDN-NDFD were exacerbated further when neutral detergent fiber rather than NDFn was used to estimate TD-FiberNDFD. Estimates of TDN declined by as much as 13.0 percentage units within severely heated hays, and this is a serious consequence of spontaneous heating.

Storage characteristics, nutritive value, and fermentation characteristics of alfalfa packaged in large-round bales and wrapped in stretch film after extended time delays1

The production of baled silage is attractive to producers because it offers advantages over dry hay, particularly by limiting risks associated with wet or unstable weather conditions. Our objectives were to test the effects of delayed wrapping on silage fermentation, storage characteristics, and the nutritive value of baled alfalfa silages. To accomplish this, large-round bales of alfalfa were wrapped in plastic film within 4h of baling (d 0), or after delays of 1, 2, or 3 d. A secondary objective was to evaluate a prototype bale wrap containing an O2-limiting barrier (OB) against an identical polyethylene wrap without the O2 barrier (SUN). Sixty-four 1.19×1.25-m bales of alfalfa were made from 4 field blocks at a mean moisture concentration of 59.1±4.3% with a mean initial wet bale weight of 473±26.4kg. Two bales per field block were assigned to each combination of bale wrap (SUN or OB) and wrapping time (0, 1, 2, or 3 d postbaling), and one bale of each pair was fitted with a thermocouple placed in the geometric center of each bale. All bales were sampled after a 97-d storage period. Internal bale temperatures, recorded at the time bales were wrapped, were greater for all bales with wrapping delays compared with bales wrapped on d 0 (54.9 vs. 34.9°C), and increased to a maximum of 63.9°C after a 3-d delay exhibiting a linear effect of time delay. Total silage fermentation acids (lactic, acetic, propionic, butyric, and isobutyric) were greatest when bales were wrapped on d 0 compared with all bales wrapped with time delays (4.64 vs. 2.26% of DM), and declined with linear and quadratic effects of wrapping delay. Total fermentation acids also were related quadratically to internal bale temperature by regression [y (% of DM)=0.0042x(2) - 0.50x + 17.1; R(2)=0.725]. Similar responses were observed for lactic acid, except that trends were linear, both for orthogonal contrasts evaluating length of wrapping delay, and in regressions on internal bale temperature [y (% of DM)=-0.046x + 3.5; R(2)=0.663]. Butyric acid also was detected, regardless of treatment, but was greatest within bales wrapped on d 0 compared with those with wrapping delays (0.99 vs. 0.38% of DM), and a similar response (0.68 vs. 0.52% of DM) was observed for NH3-N, suggesting that clostridial activity occurred during silage fermentation. Based on these results, silage fermentation characteristics and the nutritive value declined with time delays before wrapping, but responses were exacerbated when delays exceeded 1 d.