Dormant Forage Research Articles

Dormant Season Grazing: Effect of Supplementation Strategies on Heifer Resource Utilization and Vegetation Use

Grazing dormant forage under low-input heifer development strategies typically exposes cattle to low-quality forage. Protein supplementation while grazing dormant range can enhance heifer growth and reproductive performance. We examined resource utilization of heifers and the effects of dormant season grazing on residual vegetation characteristics under two supplementation management strategies. Approximately 100 weaned composite heifer calves were randomly selected and placed into one of two supplementation treatments in each of 2 yr, one receiving a free access 62% crude protein self-fed concentrate and the other receiving a daily hand-fed 20% crude protein cake. Grazing occurred from December (2015 and 2016) through March (2016 and 2017). Thirty transects were randomly located within each pasture for measuring vegetation quality and structure before and after grazing. Daily space use and behavior was evaluated for 21 individuals within each treatment using global positioning system (GPS) collars and resource utilization functions. Heifers supplemented with concentrated protein spent more time grazing per day than heifers supplemented with cake (6.92 ± 0.18, 6.24 ± 0.17 h). Relative use by heifers in the cake treatment was negatively related to horizontal distance from the supplement delivery site early to midwinter (β¯ˆ = −0.41 ± 0.16, −0.53 ± 0.17). Both treatments selected grazing locations relative to standing biomass of perennial grasses (β¯ˆ = 0.0005 ± 0.00004) and crude protein (β¯ˆ = 0.12 ± 0.007). However, resource selection was highly variable among individuals for both supplementation treatments. We found no treatment effects on pre-post grazing differences in residual cover of litter, grass, forbs and shrubs (P > 0.24). However, the time period when grazing occurred had an effect on residual vegetation conditions (P < 0.01). Our results indicate high levels of variability in grazing site selection by heifers, suggesting future research should incorporate individual animal measurements in an attempt to account for individual animal variability.

522 Evaluation of oats incorporated into annual ryegrass on performance of beef cattle

Forty crossbred beef steers (204.1 + 18.9 kg BW) were used in a randomized complete block to determine the effects of incorporating oats (Avena sativa) into annual ryegrass (Lolium multiflorum) pastures. Ten warm-season perennial pastures (1.21 ha) were killed with glyphosate and then burned, after which pastures were scratched with a disk. Pastures were randomly assigned to 1 of 2 treatments: 1) oats drilled into the pasture at a depth of 2.54 cm, at a rate of 90 kg/ha, after which annual ryegrass was broadcast at the rate of 56 kg/ha (OATS) or 2) annual ryegrass broadcast at the rate of 56 kg/ha (RG). Fertilization rates and application were similar across both treatments. When pastures had sufficient forage to support 4 beef cattle (5 kg forage DM/kg of BW), cattle were weighed and then moved into pastures. Forage biomass was determined weekly with the use of a rising plate reader, and when forage became limiting (less than 5 kg of forage DM/kg of BW), cattle were weighed and then removed. Between forage grazing periods, cattle had access to a commercial feed supplement and dormant forage. Pasture cost of establishment per hectare was greater for OATS (P= 0.001; US$332.5 and $219.7 for OATS and RG, respectively). Average daily gain did not differ (P= 0.90) between treatments (1.00 vs. 0.99 kg/d for OATS and RG, respectively. Pastures planted with OATS had more grazing days (124 vs. 98) and overall greater gain per pasture (P= 0.003; 383.8 kg compared with 291.6 kg for OATS and RG, respectively). Pasture-only cost of gain was similar (P= 0.24) for both OATS and RG; however, when the cost of supplementation (when not grazing) was factored into the overall cost of gain, OATS had a more economical cost of gain compared with RG (P= 0.002). Results suggest incorporation of a small grain such as oats may increase the winter grazing period and reduce cost of gain.

Overcoming challenges to utilization of dormant forage in year-round grazing systems1

Overcoming challenges to utilization of dormant forage in year-round grazing systems1

Effect of Supplemental Corn Dried Distillers Grains with Solubles Fed to Beef Steers Grazing Native Rangeland during the Forage Dormant Season.

Two experiments were conducted to evaluate the effects of the level of corn dry distillers grains with solubles (CDDGS) supplementation on growing performance, blood metabolites, digestion characteristics and ruminal fermentation patterns in steers grazing dormant forage. In Exp. 1, of growth performance, 120 steers (204±5 kg initial body weight [BW]) were distributed randomly into 3 groups (each of 40 steers), which were provided with the following levels of CDDGS supplement: 0%, 0.25%, or 0.50% BW. All groups of steers were grazed for 30 days in each of 3 grazing periods (March, April, and May). Approximately 1,000 ha of the land was divided with electric fencing into 3 equally sized pastures (333 ha in size). Blood samples were collected monthly from 20 steers in each grazing group for analysis of glucose (G), urea-nitrogen (UN) and non-esterified fatty acids. Final BW, average daily gain (ADG) and supplement conversion (CDDGS-C) increased with increasing levels of CDDGS supplementation (p<0.05).The CDDGS supplementation also increased the plasma G and UN concentrations (p<0.05). In Exp. 2, of digestive metabolism, 9 ruminally cannulated steers (BW = 350±3 kg) were distributed, following a completely randomized design, into groups of three in each pasture. The ruminally cannulated steers were provided the same levels of CDDGS supplementation as in the growing performance study (0%, 0.25%, and 0.50% BW), and they grazed along with the other 40 steers throughout the grazing periods. The dry matter intake, crude protein intake, neutral detergent fiber intake (NDFI), apparent digestibility of dry matter (ADDM), crude protein (ADCP) and neutral detergent fiber (ADNDF) increased with increasing levels of CDDGS supplementation (p<0.05). The ruminal degradation rates of CP (kdCP), NDF (kdNDF) and passage rate (kp) also increased with increasing levels of CDDGS supplementation (p<0.05). Ruminal ammonia nitrogen (NH3-N) and propionate concentrations also increased with increasing levels of CDDGS supplementation (p<0.05). However, acetate concentrations decreased with increasing levels of CDDGS supplementation (p<0.05). Liquid dilution rate increased with increasing levels of CDDGS supplementation but ruminal liquid volume decreased (p<0.05). On the basis of these findings, we can conclude that CDDGS supplementation enhanced the productive performance of cattle grazing native rangeland without negatively affecting forage intake, glucose and urea-nitrogen blood concentrations, ruminal degradation and ruminal fermentation patterns.

Heifer Body Weight Gain and Reproductive Achievement in Response to Protein and Energy Supplementation While Grazing Dormant Range Forage

Heifers grazing winter range require supplemental nutrients to complement dormant forage to achieve optimal growth and performance. A study was conducted to evaluate nutritional envi- ronment and effect of different supplementation strategies for developing heifers grazing dor- mant winter range. Eighty-four Angus crossbred heifers were stratified by body weight at weaning, allocated to one of six replicated pastures, and randomly assigned one of three supplemental treatments: 1) 908 g/d of a control supplement providing 340 g·hd −1 ·d −1 of CP with 130 g of rumen undegradable protein (RUP) and 614 MJ of ME (LRUP); 2) 908 g/d of a RUP supplement providing 340 g·hd−1·d−1 of CP with 170 g of RUP and 567 MJ of ME (HRUP); or 3) 1814 g/d of a protein and energy supplement providing 340 g·hd−1·d−1 of CP with 120 g of RUP + 100 g of propionate salt (NutroCal ™ , Kemin Industries, Inc.) and 1222 MJ of ME (LRUP + E). Body weights were taken in No- vember, with monthly 12 h shrunk BW from January thru April, and again in September (at time of pregnancy diagnosis). Heifer average daily gain was similar throughout the developmental period except from d125 to d159 where LRUP + E supplemented heifers had greater gains (P < 0.01) than LRUP and HRUP supplemented heifers (0.33, 0.04, and 0.14 ± 0.05 kg/d, respectively). LRUP + E heifers had a greater percentage (P = 0.04) of heifers pubertal at time of artificial insemination compared to LRUP and HRUP heifers (57, 29, and 30, respectively). However, no differences were * Corresponding author.

Metabolizable protein supply while grazing dormant winter forage during heifer development alters pregnancy and subsequent in-herd retention rate

Two studies were conducted to evaluate the effects of postweaning management of British crossbred heifers on growth and reproduction. In Exp. 1, 239 spring-born, crossbred heifers were stratified by weaning BW (234 ± 1 kg) and allotted randomly to 1 of 2 treatments. Treatments were fed at a rate equivalent to 1.14 kg/d while grazing dormant forage (6.5% CP and 80% NDF, DM basis) and were 1) 36% CP containing 36% RUP (36RUP) or 2) 36% CP containing 50% RUP (50RUP). Supplementation was initiated in February (1995 and 1996) or November (1997 and 1998) and terminated at the onset of breeding season (mid May). Heifers were weighed monthly up to breeding and again at time of palpation. After timed AI, heifers were exposed to breeding bulls for 42 ± 8 d. In Exp. 2, 191 spring-born, crossbred heifers were stratified by weaning BW to treatments. Heifer development treatments were 1) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 36% RUP (36RUP), 2) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 50% RUP (50RUP), and 3) corn silage-based growing diet in a drylot (DRYLOT). Heifers receiving 36RUP and 50RUP treatments were developed on dormant forage. Treatments started in February and ended at the onset of a 45-d breeding season in May. Heifer BW and hip height were taken monthly from initiation of supplementation until breeding and at pregnancy diagnosis. In Exp. 1, BW was not different (P ≥ 0.27) for among treatments at all measurement times. However, 50RUP heifers had greater (P = 0.02; 80 and 67%) pregnancy rates than 36RUP heifers. In Exp. 2, DRYLOT heifers had greater (P < 0.01) BW at breeding than 36RUP or 50RUP developed heifers. However, BW at pregnancy diagnosis was not different (P = 0.24) for between treatments. Pregnancy rates tended to be greater (P = 0.10) for 50RUP heifers than 36RUP and DRYLOT. Net return per heifer was US$99.71 and $87.18 greater for 50RUP and 36RUP heifers, respectively, compared with DRYLOT heifers due to differences in pregnancy and development costs. Retention rate after breeding yr 3 and 4 was greatest (P ≤ 0.01) for 50RUP heifers. Thus, increasing the supply of MP by increasing the proportion of RUP in supplements fed to heifers on dormant forage before breeding increased pregnancy rates, cow herd retention, and net return compared with heifers fed in drylot.

Energy and Carbon Costs of Selected Cow-Calf Systems

Abstract Fossil fuel-derived inputs can increase cow-calf production per unit of land or labor but can raise financial and environmental concerns. Eleven US cow-calf systems from nine ecological regions in Iowa, South Dakota, Tennessee, and Texas were analyzed to determine quantities of energy used and carbon (C) emitted due to fossil fuel use (excluding emissions from soils and biota) and to determine how management and environment influenced those quantities. Total energy and C cost, calculated cow −1 or ha −1 , were highly correlated (0.99). Energy use cow −1 and ha −1 varied greatly across systems, ranging from 3 000 to 12 600 megajoules (MJ) · cow −1 · yr −1 and from 260 to 20 800 MJ · ha −1 · yr −1 . As stocking rate increased, MJ · cow −1 increased at an increasing rate. Differences in quantity of fertilizer accounted for most variation in energy use. Fertilizer allowed higher stocking rates but reduced energy efficiency of liveweight marketed. Compared to intensive, higher stocking rate systems, rangeland systems based on native or naturalized forages used little or no fertilizer, but used more energy cow −1 for crude protein (CP) supplementation, fencing, and pickup trucks. Across all systems, energy used to produce winter feed ranged from 0% to 46% of total energy. Northern systems used higher percentages of total energy for winter feed and fed for more days year −1 , but southern systems that included large amounts of bermudagrass ( Cynodon dactylon L.) hay used the most MJ · cow −1 for winter feed. Systems with high MJ · cow −1 were vulnerable to shocks in energy prices. Reducing energy use and C emissions from cow-calf operations is possible, especially by reducing fertilizer and hay use, but would likely reduce productivity ha −1 . Forages with high nitrogen use efficiency, locally adapted plants and animals, and replacement of hay with unfertilized dormant forage and CP supplementation could reduce energy use.

Effect of reduced heifer nutrition duringin uteroand post-weaning development on glucose and acetate kinetics

Energetic efficiency was evaluated in composite bred heifers born from dams receiving 1·8 or 1·2 kg/d winter supplementation for approximately 80 d before parturition. Heifers were then developed post-weaning and randomly assigned to heifer development treatments of either control (100 %; ad libitum; n 8/year) or restricted (80 %; fed 80 % of supplementation fed to controls adjusted to a common body weight: n 8/year) in a 2-year study. A glucose tolerance test (GTT) and acetate irreversible loss test (AILT) were administered to heifers at the termination of a 140 d development period when the heifers were approximately 403 d of age and consumed a silage-based diet, and again at 940 d of age when pregnant with their second calf and grazing dormant forage. No differences were measured (P>0·08) for dam winter nutrition or heifer development treatment for baseline serum metabolites or measures in either the GTT or the AILT. However, changes in baseline serum concentrations (P>0·05) were different between metabolic challenges, which occurred at different stages of development. No difference in acetate disappearance (P = 0·18) and half-life (P = 0·66) was measured between the two metabolic challenges. A trend for glucose half-life to be shorter in heifers born from dams receiving in utero winter treatments that supplied 1·2 kg/d of winter supplementation was observed (P = 0·083). Heifers developed with lower total DM intake during a 140 d development period had similar glucose and acetate incorporation rates as ad libitum-fed heifers when evaluated at two different production stages.

Effects of summer management and fall harvest date on ruminal in situ degradation of crude protein in stockpiled bermudagrass

Limited information is available describing digestive kinetics of crude protein (CP) in stockpiled bermudagrass ( Cynodon dactylon (L.) Pers.) during late fall and early winter. ‘Greenfield’ bermudagrass was stockpiled at two sites following summer hay or pasture management, and samples were taken at 4-week intervals under caged exclosures (UNGRAZED) and outside exclosures (GRAZED) between 17 October 1997 and 9 January 1998. Forage samples were subsequently incubated in situ in five ruminally cannulated, crossbred steers to determine effects of fall harvest date and previous summer management on in situ degradation kinetics of forage CP. At the hay site, concentrations of total plant CP declined ( P<0.05) for UNGRAZED forages between 17 October (134.4 g kg −1) and 12 December (119.4 g kg −1), but concentrations of CP did not differ ( P>0.05) on the 17 October and 9 January harvest dates. From the pasture site, concentrations of total CP for UNGRAZED forages did not change ( P>0.05) throughout the trial. In situ degradation rates of CP from the hay site were not different ( P>0.05) for UNGRAZED forages on 17 October and 9 January (overall mean=0.056 h −1). The ruminal degradation of CP decreased ( P<0.05) by 63 g kg −1 CP between 14 November and 12 December, but did not change during the first and last sampling intervals. At the pasture site, rates of CP degradation increased ( P<0.05) for UNGRAZED forages between 17 October (0.044 h −1) and 9 January (0.080 h −1) due to the presence of immature, winter annual weeds. Similarly, the ruminal degradation of CP increased ( P<0.05) between 12 December (580 g kg −1) and 9 January (624 g kg −1) in response to winter annual weed presence. Ruminal availability of CP in stockpiled bermudagrass decreases as the dormant forage ages, but may be adequate to meet the minimum CP requirements of dry, pregnant beef cows.

Influence of supplementation on behavior of grazing cattle.

Dormant grasses are usually deficient in nutrients needed to meet cattle requirements. Research results indicate that grazing activities are sensitive to some environmental variables and vegetative (sward) characteristics; however, minimal information is available on the influence of supplementation regimens on cattle grazing activities. Supplementation studies reviewed had forage N levels that ranged from .9 to 1.2% and forage intakes that ranged from 12.3 to 31.0 g of OM/kg of BW. Protein supplementation affected (P < .05) time spent grazing: unsupplemented (NS) cattle grazed approximately 1.5 h/d more than did supplemented (S) cattle. Type of supplemental protein and time of daily feeding did not affect (P > .10) this response. Different types and timing of starch-based supplements produced variable results; however, increasing the level of supplemental starch decreased (P < .05) daily grazing time. Protein supplementation increased (P < .05) harvesting efficiency (HE; grams of forage intake.kilogram of BW-1.minute spent grazing-1); however, high-starch supplements either did not alter (P > .10) or decreased (P < .05) HE compared with NS. Progressive defoliation can influence grazing behavior in both sheep and cattle grazing actively growing forage; however, evaluation of vegetative characteristics of dormant forage and the corresponding effect on grazing behavior are not known. The effects of various grazing management strategies on cattle behavior are inconclusive and deserve additional attention. Methods and (or) management practices that modify behaviors to control feed intake, improve efficiency, or reduce stress could be major contributions to the livestock industry.

Digestion of ruminal masticate dried by three different methods

Masticate was collected by ruminal evacuation of four steers grazing intermediate wheatgrass ( Thinopyrum intermedium Host) pasture during dormant and active plant growth periods. Masticate was either lyophilized, or oven dried (60 °C) after the material was spread either 1 cm deep on two (1935 cm 2) trays or spread 3 cm deep on a pan (1290 cm 2). In vitro organic matter (OM) disappearance differed ( P < 0.05) among all drying methods for dormant forage; however, differences ( P < 0.10) were not of a similar magnitude for actively growing forage. The rates (polyester bag procedures) of OM and neutral detergent fiber (NDF) degradation were not altered ( P > 0.10) by the drying method; however, the extent of OM and NDF digested was altered ( P < 0.05) by the drying method. Current data suggest that detrimental effects may be minimized by proper handling during oven drying. Lower temperatures, as well as increasing the surface area of samples allowing for rapid drying may minimize the effect of heat damage on the digestibility of the forage.

Influence of increasing amounts of supplemental alfalfa hay on intake and utilization of dormant, winter-harvested, bluestem-range forage by beef steers (1991)

Sixteen, ruminally cannulated, beef steers were used in an intake/digestion experiment to determine the effects of supplementing a dormant, winter-harvested, bluestem range, forage diet with increasing amounts of moderate quality alfalfa. Steers were allowed ad libitum access to dormant forage and were supplemented with alfalfa hay at: 1) .23, 2) .47, 3).70, and 4) .94 % of BW on a dry matter (DM) basis. As the amount of supplemental alfalfa increased, dormant forage intake decreased, but total DM intake increased. Dry matter digestibility was unaffected by treatment, and only minor changes were noted for ruminal fermentation characteristics. Changes in ruminal fill and liquid dilution rates indicated an increase in digesta passage with increasing amounts of supplemental alfalfa hay. Although these results indicate that maximal digestible nutrient intake is attained at the highest level of supplementation, levels of nutrient intake and fermentation patterns indicate that adequate performance may be attained at lower levels of supplementation.

Sheep Grazing Behavior as Affected by Supplementation

Behavioral characteristics of supplemented (S; 23% crude protein, 3.41 mcal DE/kg) and nonsupplemented (N) ewes grazing native New Mexico rangeland were monitored from December 1983 to August 1984. Four marked ewes were observed per treatment group. Behavioral data were collected by simultaneous observations of both treatment groups by 2 observers starting 0.5 hour before sunrise, and continuing until 0.5 hour after sunset. Trials were conducted during the winter breeding season while ewes grazed dormant forage, during spring lambing that coincided with the onset of active forage growth, and during summer lactation, during both a quiescent period and active forage growth. Supplement was not fed during the summer. Total grazing (min/day) was less (P=0.01) in winter, equal in spring, and greater (P=0.01) in summer for S than N ewes. Mean daily periods of loafing for S ewes was greater (P=0.01) in winter; equivalent in spring, and less (P0.01) in summer than for N ewes. Daily travel time did not differ between S and N ewes during the winter; however, S ewes traveled more (P=0.02) in spring and less (P=0.01) in summer than N ewes. Supplemented ewes tended (P=0.06) to weigh less after the winter breeding season, and weaned similar, but slightly heavier, lambs (P=0.14) than N ewes. There were no differences (P>0.22) in ewe live weights during the remainder of the study. Mean fleece weights were not different (P=0.52) between S and N ewes. Supplemental feeding of range ewes, under the conditions of this study, did not appear to improve overall production by S ewes. Slower weight gains for S ewes during breeding may have resulted from reduced grazing time noted for this period.

Supplementation of dormant tallgrass-prairie forage: I. Influence of varying supplemental protein and(or) energy levels on forage utilization characteristics of beef steers in confinement.

Three experiments were conducted to evaluate effects of supplemental protein vs energy level on dormant forage intake and utilization. In Exp. 1, 16 ruminally cannulated steers were blocked by weight (avg wt = 242 kg) and assigned randomly to a negative control or to one of three isocaloric supplement treatments fed at .4% BW: 1) control, no supplement (NS); 2) 12% CP, low protein (LP); 3) 28% CP, moderate protein (MP); 4) 41% CP, high protein (HP). In Exp. 2 and 3, 16 ruminally cannulated steers were blocked by weight (avg wt = 332 kg, Exp. 2; 401 kg, Exp. 3) and assigned randomly to a 2 x 2 factorial arrangement of treatments. The treatments contrasted low (LP) and high (HP) levels of supplemental protein (.66 g CP/kg BW vs 1.32 g CP/kg BW) with low (LE) and high (HE) levels of supplemental ME (9.2 kcal/kg BW vs 18.4 kcal/kg BW). In Exp. 1, forage DMI as well as ruminal DM and indigestible ADF fill at 4 h postfeeding were greater (P less than .10) with the MP and HP steers than with control and LP steers. Total DM digestibility increased (P less than .10) for supplemented steers (35.5% for control vs 47.3 for supplemented steers); however, LP depressed (P less than .10) NDF digestibility. In Exp. 2, forage DMI, indigestible ADF flow and liquid flow were depressed (P less than .10) in LP-HE supplemented steers. In Exp. 3, HP steers had greater (P less than .10) forage DMI, indigestible ADF fill values (4 h postfeeding), liquid volume and tended (P = .11) to have greater ruminal DM fill (4 h postfeeding). In summary, increased levels of supplemental protein increased intake and utilization of dormant tallgrass-prairie forage (less than 3% CP). Increasing supplemental energy without adequate protein availability was associated with depressed intake and digestibility.

Supplementation of dormant tallgrass-prairie forage: II. Performance and forage utilization characteristics in grazing beef cattle receiving supplements of different protein concentrations.

Two experiments were conducted to evaluate the influence of supplemental protein concentration on the intake and utilization of dormant range forage by beef cattle. In Exp. 1,97 pregnant Hereford x Angus cows (avg wt = 454 kg) were assigned randomly to three isocaloric treatment supplements: 1) low protein (LP), 13% CP; 2) moderate protein (MP), 25% CP; and 3) high protein (HP), 39% CP. In Exp. 2, 15 ruminally and 12 esophageally cannulated steers (avg wt = 319 and 355 kg, respectively) were assigned randomly to LP, MP and HP treatments and were used in a 22-d winter grazing trial to evaluate forage intake and utilization characteristics. In Exp. 1, cow body condition (BC) and BW changes responded in linear (P less than .01) and quadratic (P less than .01) fashions to increasing protein concentration, with MP and HP displaying the least BC and BW loss from trial initiation (d 1) through d 84. From d 84 to calving (avg calving date = d 120), only the HP supplement continued to be effective in minimizing BC loss (P less than .01). Calf birth weight tended (P = .17) to increase in a linear fashion to increasing supplemental protein concentration, but calf ADG and cow reproductive efficiency were unaffected (P greater than .10). In Exp. 2, forage OM intake responded in a quadratic fashion (P less than .10), with the MP treatment having the highest NDF digestibility and ruminal OM fill. In conclusion, beef cow BC and BW losses during the winter grazing period were minimized with increasing supplemental CP concentration. Intake and utilization of dormant forage by steers were improved with moderate (26%) levels of CP in the supplement.

Influence of supplemental protein concentration on intake, utilization, and quality of diet selected by steers grazing dormant tallgrass-prairie (1989)

Fifteen ruminally and 12 esophageally cannulated steers were randomly assigned to receive low (LP), moderate (MP), and high (HP) crude protein (CP) supplements in a 23-day winter grazing trial designed to evaluate dormant tallgrass forage intake and utilization. Supplemental CP levels were 13, 26, or 39%, respectively. Forage organic matter (OM) intake was greatest (P<.05) for the MP steers. Likewise, fiber (NDF) digestibility and ruminal fill were largest (P<.10) for the MP treatment. Furthermore, the quality of diet selected tended to improve with increasing supplemental protein concentration. Increasing CP concentration in supplements dramatically improves the intake and utilization of dormant forage. In this study, intake and digestibility were optimized with the MP supplement.

Nomographic Estimation of Forage Intake by White-Tailed Deer

Nomographic Estimation of Forage Intake by White-Tailed Deer

Seasonal Changes in Heart Rates, Activity, Metabolism, and Forage Intake of White-Tailed Deer

White-tailed deer (Odocoileus virginianus) exhibited seasonal rhythms in heart rates, activities, and metabolism, with the lowest ecological metabolism occurring in the winter and highest in the summer. This rhythm is an adaptation for energy conservation; resource needs are lower when range resources are reduced. A series of equations is used to estimate ecological metabolism and forage consumption from measured heart rates and activity patterns throughout the year. The highest energy expenditure (about 4 times baseline metabolism) is estimated for a female with 2 fawns during the lactation period, and the lowest (about 1.5 times baseline metabolism) for deer in midwinter. As metabolism rises in March and April, the intake of dormant forage should also rise until more digestible spring growth is available. The timing of the arrival of spring seems to be an important factor in population dynamics, with its effect being most pronounced 2 years later when the fawns should become members of the breeding population. J. WILDL. MANAGE. 42(4):715-738 The free-ranging animal presents several acute problems for the physiological ecologist interested in quantifying the animal's of living over the annual cycle. Knowledge of this cost is fundamental to an understanding of productivity, for an animal can be productive only if the range supplies nutrients in excess of the level necessary for maintenance. There is ample evidence for this in the literature; it is well known that deer on overstocked range are smaller in size, have fewer fawns, and have smaller antlers than those on range that is properly stocked. Difficulties in the direct measurement of the metabolism of free-ranging animals are sufficiently great to compel one to seek alternate methods of estimation. This paper presents a method for predicting ecological metabolism (Moen 1973) and forage intake of white-tailed deer based on equations derived from several years of physiological telemetry measurements at the Wildlife Ecology Laboratory, Cornell University, and additional data from the literature. Funds for this research have been provided by the New York State Department f Environmental Conservation through Pittman-Robertson Project W-124-R and the N.Y. State College of Agriculture and Life Sciences, Cornell University. Special thanks are due Anne Hiller and Barbara Buxton for their part in the training and measurements on experimental deer, Joanne Paul for summarizing data, and Elyse Egan for verifying each of the equatio s. I wish to recognize Helenette Silv r for her pioneering work on the metabolism of white-tailed deer in the 1950's which served as an important foundation for my research in the 60's and 70's.