Robert J. Van Saun and Donald C. Wagner Various species of cervids have been used for food, sport and exhibits for much of human existence. White-tailed deer (Odocoileus virginianus) represent one of the most widely distributed and adaptable cervid species. Various subspecies of white-tailed deer are found throughout most of North America into Central and South America (Heffelfinger 2011). The Commonwealth of Pennsylvania maintains a large wild white-tailed deer population that attracts many hunters but also results in challenges for the local agricultural industry due to agricultural crop consumption. Pennsylvania is second to Texas in the number of deer farms (approximately 631 farms) in the United States that predominately manage white-tailed deer and elk (wapiti, Cervus elaphus canadensis). In contrast, deer parks in the United Kingdom manage a range of deer species, with red deer (Cervus elaphus) and fallow deer (Dama dama) predominating (https://bds.org.uk). The United Kingdom also has a small commercial deer farm industry holding almost exclusively red deer. Farmed, embarked and zoologic-exhibited deer provide some nutritional challenges in maintaining health and longevity. Nutrition plays a fundamental role in reproductive performance outcomes and disease susceptibility. Malnutrition is the primary nutritional disease manifested in wild deer populations, a function of weather conditions, population density and forage availability. As a prey species, they are reluctant to display clinical signs of disease, making diagnosis more challenging. Farmed, enclosed or exhibited deer may display a range of nutritional issues, as nutritional requirements for white-tailed deer or other cervid relatives are relatively unknown compared to other production species. Veterinarians servicing cervid farms should be versed in the nutritional triad (Box A) to provide critical service to their clients. This chapter will provide the general practitioner with detailed information on deer nutritional management and its assessment relative to farmed and captive deer. Antlered deer belong to the Cervidae family within the Suborder Ruminantia and Order Artiodactyla. Whilst deer are ruminant animals, direct extrapolation of common nutritional practices for domesticated ruminants, such as sheep and cattle, should not be employed. There are morphological and physiological adaptations amongst ruminant species as they evolved within an ecological niche and feeding pattern, and this is especially pertinent to cervid species. As ruminant species, deer have a three-compartment forestomach and a gastric stomach with the ability to regurgitate and continue masticating their ingested feed. Regurgitation and continued mastication facilitate greater rumen microbial attachment and fermentation of plant compounds indigestible to the host animal, allowing for more extensive fibre digestion compared to non-ruminant herbivores. End products of forestomach fermentation provide volatile fatty acids (VFA) and microbial protein to the host animal in support of their energy and amino acid needs. The extent to which a feed is rumen-fermented is a function of the competition between the inherent rate of passage and the rate of digestion (Van Soest 1994). The rate of passage generally slows with increasing body size, increases with increasing dry matter intake (DMI) and is influenced by dietary composition, namely plant fibre content (measured as neutral detergent fibre [NDF]) and particle size (Van Soest 1994). The rate of digestion is dependent upon the chemical and physical composition of the feed ingredient. Plant cell wall cellulose is slowly degraded, whereas hemicellulose is moderately degraded, with degradation rate and extent being influenced by cell wall lignification, a function of plant species and maturity. Rumen microbial populations are essential to plant material digestion as ruminant animals are incapable of enzymatically digesting complex plant carbohydrates such as cellulose, hemicellulose, pectin, galactan, fructosan and β-glucan (Russell 2002). Ruminant animals only have enzymes capable of digesting starch (e.g. amylose or amylopectin) and some disaccharides (e.g. lactose, sucrose, maltose). The rumen microbial ecosystem is quite complex and consists predominately of hundreds of bacterial species and protozoa as well as fungi. Differing populations of rumen bacterial species have preferred substrates for fermentation (Russell et al. 1992). Cellulolytic bacteria have slow generation times and require slower rates of passage and attachment to dietary fibre to be maintained in the rumen environment. Those bacterial species capable of fermenting sugars and starches have faster generation times and can potentially overwhelm the rumen environment with lactic acid, lowering pH. Fibre fermentation only occurs when the rumen fluid exceeds 6.0 pH units. Protozoa consume starch and bacteria within the rumen. Secondary fermenting bacterial species will utilise fermentation products (i.e. succinate and lactate) from other species. The collective population of rumen microbes ultimately produces three primary VFAs, including acetate, propionate and butyrate (Russell et al. 1992). Rumen-generated propionate, predominately from sugar and starch fermentation, is exclusively used to generate glucose via hepatic gluconeogenesis. Acetate and butyrate can serve multiple purposes in the animal’s metabolism. They are precursors to fatty acid synthesis in adipose tissue and mammary gland. They can be oxidised by many cells for energy generation. Acetate is the primary product of fibre, measured as NDF, fermentation. Butyrate is produced by the fermentation of many different carbohydrates, both fibrous and starch. Butyrate is preferentially metabolised by the rumen epithelium generating β-hydroxybutyrate (BHB). Of interest, it is the production of butyrate that is responsible for rumen papillae development and epithelial metabolism in calves, lambs and kids (Górka et al. 2018; Liu et al. 2019; Malhi et al. 2013), an essential process to facilitate a smooth dietary transition at weaning. It would seem reasonable that a similar association occurs in deer as fawns develop their functional rumen. Calf consumption of lush cool season grasses containing sucrose-based sugars may account for butyrate production in wild species contributing to rumen development in place of concentrate feeds fed to domesticated ruminants. Ruminant species populate a wide range of ecosystems and display various feeding behaviours to minimise interspecies competition, including with non-ruminant herbivores. Based on their diet selectivity (Table 12.1), ruminants can be generally categorised into concentrate selectors, intermediate browsers or grass and roughage grazers (Hofman 1989; Van Soest 1996). Concentrate selectors are those species that preferentially consume highly digestible plant materials, termed non-fibre carbohydrates (NFC) and have limited to no capacity to degrade plant cell wall (NDF) compounds. These ruminants generally are of small body size, but not exclusively. They will select the highly digestible plant components, primarily the cell contents and NDF-soluble fibre carbohydrates (i.e. pectin, galactan, β-glucan and fructans). These species will have a narrow muzzle, prehensile lips, tongue or both, and an extended large intestine compared to grazing ruminants (Hofman 1989; Van Soest 1996). Concentrate selectors will have a smaller rumen with greater surface area (more and larger papillae) and larger salivary glands to account for the more rapid fermentation of NFC. In contrast, grass and roughage grazers are generally larger body size ruminants, have a larger rumen capacity and a slower rate of passage, allowing them to take advantage of high NDF diets (Shipley 1999). Table 12.1 Comparison of ruminant species relative to feeding pattern (based on Hofman 1989). Intermediate browsers are those ruminants that are more adaptable to differing feed selectivity, which may be seasonal. Some species may be more selective of NFC, bringing them closer to concentrate selectors, while others may graze high-quality grasses during the spring growth season. Smaller body-sized deer generally will select a higher quality forage to meet metabolic needs (Luna et al. 2013). Most deer species anatomically have a narrow muzzle and are considered a browsing species, taking advantage of a wide range of plant food resources in their environment (Hofman 1989; Van Soest 1996). Roe deer (Capreolus capreolus), white-tailed deer, black-tailed deer (Odocoileus hemionus hemionus) and mule deer (Odocoileus hemionus) are all considered concentrate selectors. Still, they may display periods of being intermediate browsers. Intermediate browsers have greater variability in body size, moderately sized rumen and salivary gland size between the other two groups (Shipley 1999; Van Soest 1996). The feeding pattern of goats more closely resembles the intermediate browsing feeding pattern of most deer species. Deer generally will select against lignified NDF material when other feed resources are available. The recognised decline in deer DMI during the winter season may be an adaptation to slow the rate of passage potentially improving NDF degradation. Restricting the captive deer’s ability to selectively consume a diversity of vegetation can negatively affect their digestive ability, rumen dynamics and ability to meet their nutrient needs (Mason et al. 2019). In the United States, summarised literature describing deer nutrient requirements was published in the 2007 National Research Council (NRC) report. Although the report is available, one must recognise the limited understanding of deer nutrient requirements compared to domesticated ruminant species. Deer, like all other species, have requirements for all the essential nutrients, namely water, energy, protein (amino acids), fatty acids, minerals and vitamins (NRC 2007). Additionally, there is a need for some amount of dietary fibre to account for microbial needs and maintenance of rumen health. A factorial approach is used to determine the total daily requirement for a nutrient based on maintenance plus any additional physiologic state requirement (i.e. growth, pregnancy and lactation). Quantitative equations predicting nutrient requirements of deer have been developed (NRC 2007; Dryden 2011) and the reader is directed to these publications for detailed descriptions. Maintenance nutrient requirements are those needed to support day-to-day body metabolism. Essentially, this means no net loss or gain in body tissue, though body weight may vary due to gut fill differences. Maintenance metabolic needs account for body temperature regulation, digestive function, pelage growth and minimal activity. Maintenance needs will be further modified by increased activity in search of food resources or social interactions. Ambient environment will also alter maintenance needs relative to inducing cold or heat stress. Pregnancy requirements account for nutrients used to support fetal growth and associated support structures (e.g. uterus and placenta), collectively termed the conceptus. As seen in other species, fetal growth is exponential, with more than 60% of fetal growth occurring in the last third of pregnancy (Armstrong 1950), placing a greater nutritional burden on the female during late pregnancy (Figure 12.1). An established pregnancy will have a high nutritional priority and, during conditions of limited feed resources, the hind will mobilise both body fat and muscle protein to support the conceptus (Bauman and Currie 1980). Severe nutritional restriction in late pregnancy can result in lower birth weight, altered colostrum quality and quantity, and compromise the hind’s lactational performance, all leading to greater calf losses. Often overfeeding in late pregnancy is considered a cause of large birth weights; however, efficiency of energy deposition into the fetus is only 13–16% (NRC 2007; Dryden 2011). Heavy birth weights may be more a function of inadequate nutrition during mid-pregnancy, inducing compensatory growth of the placenta. Figure 12.1 Cumulative fetal weight for white-tailed deer fetus throughout gestation. Single fetus data from Armstrong (1950). Twin fetuses were predicted as 75% increase in total fetal weight. Lactation requirements are those nutrients needed to support mammary milk secretion. Requirements for lactation will be determined by the volume of milk generated and its composition (Dryden 2011). Milk volume is driven by lactose content acting as an osmotic agent drawing in water. Lactose is generated in the mammary gland and is a function of glucose availability. Deer milk lactose content ranges from 2.5 to 6.5 g/100 g with some variability between species (Wang et al. 2017). Fat and protein are the primary milk components in support of calf nutrition and account for predicted milk energy content. Deer milk is higher in fat and protein compared to domesticated ruminant species. Milk fat content is variable amongst deer species, ranging from 6 to 19 g/100 g (Wang et al. 2017). Casein is the primary milk protein and its total protein content ranges from 5.7 to 10 g/100 g (Wang et al. 2017). As observed in other species, milk composition will change relative to the day of lactation and with supplementation. Supplementing lactating deer with a high energy (12.5 MJ/kg) concentrate resulted in lower milk fat and protein content, with higher lactose content suggesting a similar response to domestic ruminants (Bovolenta et al. 2013). Milk mineral content for red deer was similar to other ruminant species where macrominerals predominated and trace minerals were below requirements (Gallego et al. 2006). Growth requirements encompass nutrients necessary for the accretion of body tissue. Requirements in support of average daily gain (ADG) are dependent upon the rate of gain (g/day) and composition of gain (fat versus protein). Prepuberal animals will have more protein gain and skeletal development, whereas after puberty the composition of gain increases in fat content. Protein gain is more efficient as muscle mass is primarily water. As the percentage of fat increases in tissue gain, the required energy to support the gain will increase. Calf growth rate will be directed by milk consumption, where milk yield is strongly influenced by maternal body condition and body weight (ADG, g/d = 0.0721 × g BW0.71; NRC 2007). Daily nutrient requirements are most often determined through feeding studies controlling many factors; these may not be completely adequate for animals under typical management environments. Direct extrapolation of feed energy content based on domesticated ruminants may not be appropriate for deer given the differences in digestibility. Thus, body weight and body condition should be routinely monitored to assess dietary adequacy. Factors known to affect nutrient requirements include species, physiological state (i.e. maintenance, growth, pregnancy, lactation and antler growth), age, gender, environmental temperature and humidity, activity level, season and health status. There are limited data to address all these factors in feeding deer. A more detailed comparison of domesticated small ruminant nutrient requirements is available (Gurung et al. 2020). Predicted deer nutrient requirements using NRC models are summarised in Table 12.2. Table 12.2 Predicted dietary energy and protein requirements (dry matter basis) of deer (NRC 2007). BW: body weight; ME: metabolisable energy; CP: crude protein; MP: metabolisable protein. aEnergy was calculated using an averaged coefficient of 565 kJ/kg (135 kcal/kg) and 724 kJ/kg (173 kcal/kg) across deer species for winter and summer requirements, respectively. Table 12.3 Predicted dietary calcium and phosphorus and vitamins A and E requirements for deer at different life stages (NRC 2007). Mineral concentrations are high and low dietary content (dry matter basis) to address the range in deer body weight. aRE (retinol equivalent) = 1 μg retinol = 6 μg ß-carotene = 12–16 μg of other pro-vitamin A carotenoids. bIU (international unit) = 1 mg D,L α-tocopheryl acetate. Table 12.4 Suggested dietary mineral concentrations (dry matter basis) for captive deer diets based on modified recommendations for goats (NRC 2007). aDietary copper availability will be dependent upon the dietary or water content of iron, molybdenum and sulphur. With the selective browsing behaviour of most deer species, it is challenging to appreciate the nutrient composition of the range of feeds consumed by the wild deer population. Depending upon the season and environment, a deer’s diet may consist of grasses, forbs, woody browse and mast (Pierce et al. 2022). Reported nutrient composition of forbs, browse and mast have been published (Adam 1994; Forsyth et al. 2002; Jones et al. 2008; Miller and Marchinton 2007; Pierce et al. 2022; Vangilder et al. 1982). Compositional analysis of these feeds would suggest deer could meet nutritional needs through selective feeding (Berteaux et al. 1998; Vangilder et al. 1982). In contrast, the nutrient composition of forages and supplements can be obtained from commercial forage testing laboratories for confinement feeding of managed deer. Although nutrient content can be determined in feed samples, the challenge with deer is determining what component of the feed was actually consumed. For example, deer-fed alfalfa hay may consume mostly leaves, leaving the stems. One could collect feed refusals (i.e. orts) and determine nutrient content, then calculate the missing nutrients. This approach is not practical on a regular basis but may be an option in a nutritional assessment situation. A suggested listing of testing parameters in feeding deer is provided in Box B. Forage laboratories can provide a range of sophisticated tests; however, most are designed for dairy cattle feeding practises and need to be interpreted with caution for deer (noted with ‘?’ in Box B). Any samples with water content above 20% should be frozen following collection and shipped to the laboratory in a frozen state to ensure accurate dry matter determination. A detailed description of feed test report interpretation is beyond the scope of this article and the reader is referred elsewhere (Arispe and Filley 2020; Van Saun 2023a).
Chapter 12
Nutrition of Deer
Introduction
Understanding the Beast
Nutritional Physiology
Feeding Patterns
Feeding pattern
Eating behaviour
Ability to select
Relative ability to digest NDF
Example species
Concentrate selector
Frequent feeding periods with short rumination bouts
++++
0 to +
Roe deer, white-tailed deer, black-tailed deer, mule deer, moose
Intermediate browser
Seasonal selectivity, Moderate feeding and rumination bouts
++ to +++
++ to +++
Goat, red deer, reindeer, fallow deer, elk (wapiti)
Grass and roughage grazer
Limited long feeding bouts with long rumination bouts
Limited to +
++++
Cattle, sheep, bison, buffalo
Nutrient Requirements
Life-stage Requirements
Essential Nutrients
Class/age/other
Winter season requirements
Summer season requirements
Body weight (kg)
Dry matter intake
Energy requirementa
Protein requirement
Dry matter intake
Energy requirement
Protein requirement
kg
%BW
ME (MJ/d)
ME (MJ/kg)
CP (g/d)
CP (g/kg)
MP (g/d)
kg
%BW
ME (MJ/d)
ME (MJ/kg)
CP (g/d)
CP (g/kg)
MP (g/d)
Young to mature maintenance only
–10
0.3
2.9
–2.9
–9.8
–25
–90
–18
0.3
3.4
–4.2
14.0
–35
100
–24
–20
0.5
2.5
–5.0
10.0
–43
–90
–30
0.6
2.9
–6.7
11.2
–59
100
–41
–30
0.7
2.2
–6.7
–9.6
–58
–90
–41
0.8
2.6
–9.2
11.5
–79
100
–56
–40
0.8
2.1
–8.4
10.5
–72
–90
–50
1 1
2.4
11.7
11.7
–99
100
–69
–50
1 1
2 1
10.0
10.0
–85
–90
–60
1.1
2.3
13.8
12.6
117
100
–82
–60
1.1
1.9
11.3
10.3
–98
–90
–68
1.3
2.2
15.5
11.9
134
100
–94
–80
1.5
1.9
15.1
10.0
121
–80
–85
1.6
2 1
19.3
12.0
166
100
116
100
1.8
1.8
18.0
10.0
143
–80
100
1.9
1.9
23.0
12.1
196
100
137
120
2 1
1.7
20.5
10.3
164
–80
115
2.6
2.2
26.4
10.1
225
–90
157
140
2.3
1.6
23.0
10.0
184
–80
129
2.9
2.1
29.3
10.1
252
–90
177
160
2.5
1.6
25.5
10.2
204
–80
143
3.3
2 1
32.6
–9.9
279
–90
195
180
2.8
1.5
27.6
–9.9
223
–80
156
3.6
2 1
35.6
–9.9
305
–90
213
200
3 1
1.5
30.1
10.0
241
–80
169
3.8
1.9
38.5
10.1
330
–90
231
220
4 1
1.8
32.2
–8.1
259
–60
181
4.1
1.9
41.4
10.1
354
–90
248
240
4.3
1.8
34.3
–8.0
276
–60
193
4.4
1.8
43.9
10.0
378
–90
265
260
4.6
1.8
36.4
–7.9
293
–60
205
4.7
1.8
46.9
10.0
401
–90
281
280
4.8
1.7
38.5
–8.0
310
–60
217
5 1
1.8
49.4
–9.9
424
–90
297
Single fetus
Twin fetuses
Breeding, early pregnancy
–40
0.9
2.2
–8.8
–9.8
–93
110
–65
0.9
2.3
–9.2
10.2
100
110
–70
–50
1 1
2.1
10.5
10.5
110
110
–77
1.1
2.1
10.9
–9.9
119
110
–84
–60
1.2
2 1
12.1
10.1
127
110
–89
1.2
2.1
12.1
10.1
138
110
–96
–80
1.6
2 1
15.9
–9.9
160
100
112
1.6
2.1
16.3
10.2
173
110
121
100
1.9
1.9
18.8
–9.9
190
100
133
2 1
2 1
19.7
–9.8
207
110
145
120
2.2
1.8
21.8
–9.9
219
100
154
2.3
1.9
22.6
–9.8
239
110
167
140
2.5
1.8
24.7
–9.8
248
100
173
2.5
1.8
25.5
10.2
270
110
189
160
2.9
1.8
28.2
–9.9
281
100
197
2.8
1.8
28.0
10.0
295
110
206
180
3.2
1.8
31.4
–9.9
312
100
218
3.1
1.7
30.9
10.0
324
110
227
Late pregnancy
–40
1.2
3 1
12.1
10.1
191
160
134
1.3
3.3
15.9
12.2
227
170
159
–50
1.4
2.9
14.2
10.2
214
150
150
1.5
3.1
18.4
12.3
253
160
177
–60
1.6
2.7
16.3
10.2
236
140
165
1.8
3.0
21.3
11.9
278
160
194
–80
2.2
2.8
22.2
10.1
278
130
195
2.4
3.0
28.5
11.9
326
140
228
100
2.6
2.6
25.9
10.0
319
120
223
2.8
2.8
33.9
12.1
373
130
261
120
3 1
2.5
29.7
–9.9
359
120
251
3.2
2.7
38.9
12.2
419
130
293
140
3.4
2.4
33.5
–9.8
398
120
279
3.6
2.6
43.5
12.1
464
130
325
160
3.7
2.3
36.9
–9.9
427
110
299
4.0
2.5
48.1
12.1
497
120
348
180
4.1
2.2
40.7
–9.9
463
100
324
4.4
2.4
53.0
12.1
538
110
376
Lactation
–40
1.6
4.1
19.7
12.3
207
130
145
2.0
5.0
24.3
12.1
266
130
186
–50
1.9
3.9
23.4
12.3
250
130
175
2.4
4.8
28.5
11.9
322
140
226
–60
2.2
3.7
26.8
12.2
292
130
204
2.7
4.6
33.1
12.2
377
140
264
–80
2.8
3.5
33.1
11.8
371
130
260
3.4
4.2
40.6
11.9
481
140
337
100
3.3
3.3
39.3
11.9
446
140
312
4 1
4 1
48.1
12.0
581
140
406
120
3.8
3.1
45.2
11.9
518
140
363
4.6
3.8
55.2
12.0
676
150
473
140
4.2
3 1
50.6
12.1
588
140
411
5.2
3.7
61.9
11.9
768
150
538
160
4.6
2.8
55.3
11.9
644
140
450
5.7
3.4
67.6
12.0
841
150
589
180
5.1
2.6
60.6
11.9
709
150
496
6.2
3.1
74.1
11.9
928
160
649
Moderate growth
Rapid growth
Adult males (includes allowance for antler growth)
–60
1.9
3.2
19.3
10.1
169
–90
118
2.1
3.5
21.3
10.2
188
–90
131
–80
2.4
3 1
24.3
10.1
211
–90
148
2.7
3.3
26.8
–9.9
236
–90
165
100
2.9
2.9
28.9
10.0
252
–90
176
3.2
3.2
31.8
–9.9
283
–90
198
120
3.3
2.8
33.1
10.0
290
–90
203
3.7
3.1
36.8
10.0
327
–90
229
140
3.7
2.7
37.2
10.1
327
–90
229
4.2
3 1
41.9
10.0
371
–90
260
160
4.2
2.6
41.4
–9.9
363
–90
254
4.7
2.9
46.5
–9.9
413
–90
289
180
4.6
2.5
45.6
–9.9
399
–90
279
5.1
2.8
51.1
10.0
454
–90
318
200
4.9
2.5
49.4
10.1
433
–90
303
5.6
2.8
55.7
–9.9
495
–90
347
220
5.3
2.4
53.1
10.0
467
–90
327
6 1
2.7
60.3
10.0
535
–90
374
240
5.7
2.4
56.9
10.0
500
–90
350
6.5
2.7
64.4
–9.9
574
–90
402
260
6.1
2.3
60.7
–9.9
532
–90
373
6.9
2.6
69.1
10.0
613
–90
429
Physiologic state
Calcium (g/kg DM)
Phosphorus (g/kg DM)
Vitamin Aa (RE/BWkg)
Vitamin Eb (IU/BWkg)
Maintenance – winter
1.7–3.3
1.3–1.8
31.4
5.3
Maintenance – summer
1.6–3.7
1.7–1.8
31.4
5.3
Breeding/early pregnancy
31.4
5.3
–––Single fetus
2.3–4.1
2.1–2.7
–––Twin fetuses
3.0–6.0
2.5–3.6
Late pregnancy
45.5
5.6
–––Single fetus
2.3–4.4
2.1–2.7
–––Twin fetuses
3.0–6.2
2.4–3.3
Lactation
53.5
5.6
–––Single fetus
2.5–4.6
2.6–3.8
–––Twin fetuses
2.3–3.9
2.4–3.4
Males/growing
1.4–1.8
1.2–1.6
100
10
Mineral
Units
Life stage
Maintenance
Pregnancy
Lactation
Growth
Magnesium
g/kg
0.8–1.1
0.8–1.1
0.8–1.1
0.8–1.1
Potassium
g/kg
6.5–10
6.5–15
7.5–15
6.5–10
Sodium
g/kg
0.5–1.0
0.5–1.0
1.0–1.5
0.5–1.0
Sulphur
g/kg
1.2–1.8
1.4–2.0
1.8–2.5
1.2–1.8
Cobalt
mg/kg
0.1–0.15
0.1–0.15
0.1–0.15
0.1–0.15
Coppera
mg/kg
8–10
10
8–10
8–10
Iron
mg/kg
35
35
35
95
Iodine
mg/kg
0.5
0.5
0.8
0.5
Manganese
mg/kg
15–20
15–20
15–20
15–20
Selenium
mg/kg
0.1–0.15
0.15–0.2
0.15–0.2
0.1–0.15
Zinc
mg/kg
20–30
25–35
30–40
20–30
Feed Composition
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