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Weight estimation for axis, fallow, sika and white-tailed deer in Texas.

Abstract. -- Predictive equations provide wildlife managers and sportsmen with a practical and reliable estimate of deer weight. These equations have not been reported for axis (Axis axis), fallow (Dama dama), sika (Cervus nippon), or white-tailed deer (Odocoileus virginianus) in Texas. To address this need, the relationships between heart girth, live weight, dressed weight, and carcass weight were assessed for these cervid species in central Texas. Separate predictive equations were required for each species, age class, and season. General models using heart girth to provide an estimate of weight had [R.sup.2] values of 0.76, 0.75, and 0.75 for live weight, dressed weight, and carcass weight, respectively. General models using dressed weight to predict live weight and using live weight to predict carcass weight had [R.sup.2] values of 0.89 and 0.83, respectively.

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Predictive equations based on heart girth or partial body weight provide a simple and reliable estimate of deer weight. The low cost and convenience of weight equations makes them practical for use by wildlife managers and sportsmen (Smart et al. 1973).

Viable populations of non-native deer species are present in Texas and offer a popular sporting alternative to indigenous big game. Axis, fallow, and sika deer are the most common species of exotic deer present on Texas rangelands (Traweek 1989). However, weight estimation equations have not been reported for these species nor for native white-tailed deer in the Edwards Plateau Region of Texas. The objectives of this study were to test for effects of season, age, and species on regression models for body weights of axis, fallow, sika, and white-tailed deer and to develop predictive equations of body weight for each species.

Study Area and Methods

Deer were harvested on four privately owned ranches located in Kerr and Real Counties, Texas during two winter (15 December 1987-15 January 1988 and 15 December 1988-15 January 1989) and two summer (15 July 1988-15 August 1988 and 15 July 1989-15 August 1989) sampling periods. These ranches were predominantly rangeland used for the production of domestic livestock and wildlife and were characteristic of the Edwards Plateau Region (Butts et al. 1982; Landers 1987). Body weights and heart girth measurements were recorded for 111 axis, 100 fallow, 90 sika, and 102 white-tailed deer. All deer were female and classified as either subadult (1.0-1.5 years-old) or adult (> 1.5 years-old) based on tooth eruption and wear criteria (Severinghaus 1949; Graf & Nichols 1966; Chaplin & White 1969; Duff 1969).

A linear measurement of heart girth (Smart et al. 1973) using a flexible steel tape and recorded to the nearest 0.5 cm was taken with the deer lying on its side prior to evisceration. Live weight, defined as the weight of a recently harvested deer minus blood loss from the gunshot wound to the head, was measured using a spring scale. An electronic scale was used to determine carcass weight, defined as the weight of the eviscerated deer minus the head, hide, and feet. The combined weight of the head, hide, and feet was then measured using a spring scale and added to the carcass weight to arrive at the field dressed weight. Spring scales were calibrated with the electronic scale, prior to each weighing session, and all weights were recorded to the nearest 0.45 kg.

Statistical analyses were performed with the PC version of the computer program SHAZAM (White et al. 1988) on an IBM PC-AT. Linear regression equations were developed describing the weight-girth and weight-weight relationships. Differences among age, season, species and the various interaction terms in the regression equations were tested with the creation of dummy variables (Leistritz 1973).

Results

Coefficient of determination ([R.sup.2]) values suggested most of the variability in our data were accounted for in the various regression models. General models using heart girth to provide an estimate of weight had [R.sup.2] values of 0.76, 0.75, and 0.75 for live weight, dressed weight, and carcass weight, respectively. General models using dressed weight to predict live weight and using live weight to predict carcass weight had [R.sup.2] values of 0.89 and 0.83, respectively.

Equations developed to estimate live weight from heart girth (Table 1) varied by age and season. For each species, the live weight to girth relationship was different between age-classes during winter requiring separate equations for adults and subadults. Age-specific equations were needed for fallow and white-tailed deer in the summer but not for axis or sika deer.

The dressed weight of a deer can be estimated from a linear heart girth measurement (Table 2). Separate equations were required for axis, fallow, sika, and whitetail adults harvested during summer. However, sika and whitetails each showed little variation in the dressed weight to girth relationship among adults harvested during the winter or subadults in either season. Age-related variation was apparent for axis and fallow deer.

The relationship of carcass weight to heart girth (Table 3) observed for axis, sika, and white-tailed deer differed from that of fallow deer; however, none of the species showed an age or season effect on this relationship. Seasonal variation in intercept existed; therefore, separate equations in summer and winter were needed for fallow, sika, and white-tailed deer. Four equations were necessary for axis deer because of age- and season-related variation in intercept terms.

Equations designed to predict live weight from dressed weight (Table 4) and carcass weight from live weight (Table 5) reflect age-related differences for axis, fallow, sika, and white-tailed deer. Variation in the live weight to dressed weight relationship also occurred by season for all species. Only axis and fallow deer required season-specific equations to estimate carcass weight from a live weight measurement.

Discussion

Strong correlation among body weights and heart girth has been reported for white-tailed deer in the southeastern United States (Smart et al. 1973; Urbston et al. 1976; Weckerly et al. 1987). Results of this study verify this relationship for axis, fallow, sika, and white-tailed deer in Texas with standard errors for specific estimates similar to those reported for white-tailed deer in Illinois (Roseberry & Klimstra 1975) and Tennessee (Weckerly et al. 1987).

Analyses revealed the need for separate weight estimation equations among cervid species, age classes, and seasons in the Edwards Plateau Region of Texas. Although separate regression equations presented in this study have been determined to be statistically different (Tables 1-5), biologically significant differences may not exist in cases where both intercepts and slopes are very similar.

Models were developed using data collected exclusively from female deer and, therefore, may or may not be applicable for males of the respective species (Smart et al. 1973; Weckerly et al. 1987). Also, the Edwards Plateau Region of central Texas supports a very dense deer population. Because deer weights may be population specific, caution should be used when applying these predictive equations to other deer populations.
Table 1. Linear regression equations developed to estimate live weight
from heart girth for axis, fallow, sika, and white-tailed deer in Texas,
1987-89.

 Live Weight (kg)
Species Age Season n [bar.X] SE (a) Equation (bc)

Axis Adult & Summer 55 44.1 3.6 Y = -14.38 +
 Subadult 0.08(HG)
 Adult Winter 46 46.8 3.0 Y = - 2.67 +
 0.07(HG)
 Subadult Winter 10 39.5 3.7 Y = - 2.67 +
 0.06(HG)
Fallow Adult Summer 38 37.1 4.1 Y = -22.02 +
 0.08(HG)
 Adult Winter 42 38.0 2.6 Y = -10.31 +
 0.07(HG)
 Subadult Summer 16 29.5 2.9 Y = -20.47 +
 0.08(HG)
 Subadult Winter 4 33.8 2.8 Y = - 8.75 +
 0.06(HG)
Sika Adult & Summer 44 37.1 3.7 Y = -20.46 +
 Subadult 0.08(HG)
 Adult Winter 40 39.1 3.3 Y = - 8.75 +
 0.07(HG)
 Subadult Winter 6 33.4 2.7 Y = - 8.75 +
 0.06(HG)
Whitetail Adult Summer 47 34.5 3.2 Y = -22.88 +
 0.09(HG)
 Adult Winter 50 34.3 2.7 Y = -11.17 +
 0.07(HG)
 Subadult Summer (d) 2 24.5 Y = -20.46 +
 0.08(HG)
 Subadult Winter 3 27.8 0.2 Y = - 8.75 +
 0.06(HG)

(a) Standard error of the estimate.
(b) Based on the general model Y = - 8.745 + 0.058(HG) + 6.078 (Axis) -
11.714 (Summer) - 1.564 (Fallow*Adult) - 2.421 (Whitetail*Adult) + 0.007
(Adult*Girth) + 0.018 (Summer*Girth) - 0.003 (Axis*Summer*Adult*Girth) +
0.003 (Whitetail*Summer*Adult*Girth). [R.sup.2] = 0.7615, Adj.
[R.sup.2] = 0.7561, N = 403, F = 139.5.
(c) Y = live weight in kg, HG = heart girth in mm.
(d) Too few observations to calculate SE.

Table 2. Linear regression equations developed to estimate dressed
weight from heart girth for axis, fallow, sika, and white-tailed deer in
Texas, 1987-89.

 Dressed Weight (kg)
Species Age Season n [bar.X] SE (a) Equation (bc)

Axis Adult Summer 45 30.1 2.2 Y = -15.11 +
 0.06(HG)
 Adult Winter 56 (d) 28.5 1.7 Y = -13.95 +
 0.06(HG)
 Subadult Winter 10 24.6 2.9 Y = -13.95 +
 0.05(HG)
Fallow Adult Summer 38 21.7 2.4 Y = -17.33 +
 0.06(HG)
 Adult Winter 42 22.7 2.2 Y = -16.18 +
 0.05(HG)
 Subadult Combined 20 19.4 1.6 Y = -13.95 +
 0.05(HG)
Sika Adult Summer 37 23.6 2.6 Y = -15.11 +
 0.06(HG)
 Adult & Winter 53 23.8 2.7 Y = - 8.75 +
 Subadult 0.07(HG)
Whitetail Adult Summer 47 21.9 2.0 Y = -12.44 +
 0.05(HG)
 Adult & Winter 55 22.3 2.1 Y = -11.28 +
 Subadult 0.05(HG)

(a) Standard error of the estimate.
(b) Based on the general model Y = - 13.953 + 0.048(HG) + 2.669
(Whitetail) - 2.223 (Fallow*Adult) - 1.156 (Summer*Adult) + 0.004
(Adult*Girth) + 0.003 (Summer*Girth) + 0.005 (Axis*Girth) - 0.004
(Whitetail*Adult*Girth). [R.sup.2] = 0.7543, Adj. [R.sup.2] = 0.7493,
N = 403, F = 151.2.
(c) Y = dressed weight in kg, HG = heart girth in mm.
(d) This equation also represents axis subadults during the summer.

Table 3. Linear regression equations developed to estimate carcass
weight from heart girth for axis, fallow, sika, and white-tailed deer in
Texas, 1987-89.

 Carcass Weight (kg)
Species Age Season n [bar.X] SE (a) Equation (bc)

Axis Adult Summer 45 24.2 1.9 Y = -13.24 +
 0.05(HG)
 Adult Winter 46 23.4 1.6 Y = -14.19 +
 0.05(HG)
 Subadult Summer 10 19.8 1.8 Y = -14.95 +
 0.05(HG)
 Subadult Winter 10 19.6 2.6 Y = -15.91 +
 0.05(HG)
Fallow Adult & Summer 54 15.9 2.1 Y = -10.22 +
 Subadult 0.04(HG)
 Adult & Winter 46 16.8 2.1 Y = -11.18 +
 Subadult 0.04(HG)
Sika Adult & Summer 44 17.7 2.1 Y = -17.07 +
 Subadult 0.05(HG)
 Adult & Winter 46 18.8 2.3 Y = -18.03 +
 Subadult 0.05(HG)
Whitetail Adult & Summer 49 17.2 1.7 Y = -15.98 +
 Subadult 0.05(HG)
 Adult & Winter 53 17.6 1.8 Y = -16.93 +
 Subadult 0.05(HG)

(a) Standard error of the estimate.
(b) Based on the general model Y = - 18.025 + 0.049 (HG) + 2.119
(Axis) + 6.850 (Fallow) + 1.094 (Whitetail) + 0.953 (Summer) + 1.718
(Axis*Adult) - 0.012 (Fallow*Girth). [R.sup.2] = 0.7505, Adj. [R.sup.2]
= 0.7460, N = 403, F = 169.7.
(c) Y = carcass weight in kg, HG = heart girth in mm.

Table 4. Linear regression equations developed to estimate live weight
from dressed weight for axis, fallow, sika, and white-tailed deer in
Texas, 1987-89.

 Live Weight (kg)
Species Age Season n [bar.X] SE (a) Equation (bc)

Axis Adult Summer 45 45.7 2.3 Y = 7.20 +
 1.28(DW)
 Adult Winter 46 46.8 2.1 Y = 13.98 +
 1.12(DW)
 Subadult Summer 10 37.1 1.0 Y = 7.20 +
 1.18(DW)
 Subadult Winter 10 39.5 2.3 Y = 13.98 +
 1.02(DW)
Fallow Adult Summer 38 37.1 3.3 Y = 8.54 +
 1.31(DW)
 Adult Winter 42 38.0 2.5 Y = 15.31 +
 1.01(DW)
 Subadult Summer 16 29.5 1.9 Y = 7.20 +
 1.21(DW)
 Subadult Winter 4 33.8 1.8 Y = 13.98 +
 0.91(DW)
Sika Adult Summer 37 38.2 2.3 Y = 7.20 +
 1.31(DW)
 Adult Winter 40 39.1 2.0 Y = 13.98 +
 1.01(DW)
 Subadult Summer 7 31.5 2.3 Y = 7.20 +
 1.21(DW)
 Subadult Winter 6 33.4 1.9 Y = 13.98 +
 0.91(DW)
Whitetail Adult Summer 47 34.5 1.9 Y = 0.50 +
 1.55(DW)
 Adult Winter 50 34.3 1.8 Y = 7.27 +
 1.19(DW)
 Subadult Summer (d) 2 24.5 Y = 0.50 +
 1.39(DW)
 Subadult Winter 3 27.8 0.6 Y = 7.27 +
 1.09(DW)

(a) Standard error of the estimate.
(b) Based on the general model Y = 13.975 + 0.906 (DW) - 6.705
(Whitetail) - 6.773 (Summer) + 1.337 (Fallow*Adult) + 0.103 (Adult*DW) +
0.115 (Axis*DW) + 0.184 (Whitetail*DW) + 0.300 (Summer*DW) - 0.141
(Axis*Summer*DW) + 0.059 (Whitetail*Adult*Summer*DW). [R.sup.2] =
0.8855, Adj. [R.sup.2] = 0.8825, N = 403, F = 303.0.
(c) Y = live weight in kg, DW = dressed weight in kg.
(d) Too few observations to calculate SE.

Table 5. Linear regression equations developed to estimate carcass
weight from live weight for axis, fallow, sika, and white-tailed deer
in Texas, 1987-89.

 Carcass Weight (kg)
Species Age Season n [bar.X] SE (a) Equation (bc)

Axis Adult Summer 45 24.2 1.3 Y = 0.57 + 0.52(LW)
 Adult Winter 46 23.4 1.6 Y = 0.57 + 0.49(LW)
 Subadult Summer 10 19.8 1.1 Y = -1.46 + 0.57(LW)
 Subadult Winter 10 19.6 1.5 Y = -1.46 + 0.54(LW)
Fallow Adult Summer 38 16.3 1.8 Y = 2.97 + 0.36(LW)
 Adult Winter 42 16.9 2.2 Y = -1.46 + 0.36(LW)
 Subadult Summer 16 14.9 1.5 Y = 2.97 + 0.53(LW)
 Subadult Winter 4 15.3 2.0 Y = -1.46 + 0.53(LW)
Sika Adult Combined 77 18.5 1.8 Y = -1.46 + 0.52(LW)
 Subadult Combined 13 17.0 2.4 Y = -1.46 + 0.57(LW)
Whitetail Adult Combined 97 17.5 1.3 Y = -0.27 + 0.52(LW)
 Subadult Combined 5 14.4 0.9 Y = -1.46 + 0.57(LW)

(a) Standard error of the estimate.
(b) Based on the general model Y = - 1.459 + 0.567(LW) + 4.432 (Fallow*
Summer) + 2.025 (Axis*Adult) + 1.194 (Whitetail*Adult) - 0.050 (Adult*
LW) - 0.031 (Axis*LW) - 0.037 (Fallow*LW) + 0.031 (Axis*Summer*LW) -
0.123 (Fallow*Summer*LW). [R.sup.2] = 0.8256, Adj. [R.sup.2] = 0.8216,
N = 403, F = 206.7.
(c) Y = carcass weight in kg, LW = live weight in kg.


Acknowledgments

We thank the owners and managers of the Bowman, Johnson, Two-Dot, and Y.O. ranches for their hospitality and assistance. We would also like to thank the Texas Wild Game Cooperative, All That's Deer, Inc., J. J. Jackley, M. Bailey, and several students at Texas Tech University for their assistance in data collection and R. S. Lutz, L. M. Smith, and J. J. Jackley for reviewing the manuscript. This research was supported by the Exotic Wildlife Association, Texas Tech University, the Houston Livestock Show and Rodeo, and various private landowners. This manuscript is Texas Tech University, College of Agricultural Sciences Contribution T-4-590.

Literature Cited

Butts, G. L., M. J. Anderegg, W. E. Armstrong, D. E. Harmel, C. W. Ramsey & S. H. Sorola. 1982. Food habits of five exotic ungulates on Kerr Wildlife Management Area, Texas. Texas Parks and Wildlife Dept. Technical Series, No. 30.

Chaplin, R. E. & R. W. G. White. 1969. The use of tooth eruption and wear, body weight and antler characteristics in the age estimation of male wild and park Fallow deer (Dama dama). J. Zool., London, 157:125-132.

Duff, K. R. 1969. Tooth eruption as a guide to aging Japanese sika deer (Cervus nippon) in Dorset. Deer, 2:566-567.

Graf, W. & L. Nichols, Jr. 1966. The axis deer in Hawaii. J. Bombay Nat. Hist. Soc., 63(3):629-734.

Landers, R. Q. 1987. Native vegetation of Texas. Rangelands, 9:203-207.

Leistritz, F. L. 1973. The use of dummy variables in regression analysis. Dep. Agric. Econ., N. Dakota State Univ., Misc. Report 13, Fargo, N. Dakota.

Roseberry, J. L. & W. D. Klimstra. 1975. Productivity of white-tailed deer on Crab Orchard National Wildlife Refuge. J. Wildlife. Manag., 34(1):23-28.

Severinghaus, C. W. 1949. Tooth development and wear as criteria of age in white-tailed deer. J. Wildlife Manag., 13(2):195-216.

Smart, C. W., R. H. Giles, Jr. & D. C. Guynn, Jr. 1973. Weight tape for white-tailed deer in Virginia. J. Wildlife Manag., 37(4):553-555.

Traweek, M. S. 1989. State-wide census of exotic big game animals. Job Report, Federal Aid Project W-109-R-12, Texas Parks and Wildlife Dept., Austin, Texas.

Urbston, D. F., C. W. Smart & P. F. Scanlon. 1976. Relationship between body weight and heart girth in white-tailed deer from South Carolina. Proc. Annu. Conf. Southeastern Assoc. Game and Fish Comm., 30:471-473.

Weckerly, F. W., P. L. Leberg & R. A. Van Den Bussche. 1987. Variation of weight and chest girth in white-tailed deer. J. Wildlife Manag., 51(2):334-337.

White, K. J., S. A. Haun, N. G. Horsman & S. D. Wong. 1988. SHAZAM econometrics computer program. McGraw-Hill Book Co., New York.

David A. Osborn, Stephen Demarais and R. Terry Ervin

School of Forest Resources, University of Georga, Athens, Georgia 30602 and Department of Range and Wildlife Management and Department of Agricultural Economics, Texas Tech University, Lubbock, Texas 79409
COPYRIGHT 1995 Texas Academy of Science
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1995 Gale, Cengage Learning. All rights reserved.

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Author:Osborn, David A.; Demarais, Stephen; Ervin, R. Terry
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Nov 1, 1995
Words:3033
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