Chapter 4: Muskox Nutrition

How much must the muskox eat in summer and in winter, to maintain its body weight and to grow?

Robert G. White, Dan F. Holleman and co-workers, Institute of Arctic Biology, University of Alaska, Fairbanks, report in Biol. Pap. Univ. Alaska Spec. Rep. No. 4:193-194 (1984) Abstract, about the "Seasonal changes in voluntary intake and digestibility of diets by captive muskoxen":

The 7 muskoxen, used in these studies, were captured on Nunivak Island as calves in February 1979. The regression of weight change versus food intake in winter gave a projected dry matter intake for maintenance of 35 g/kg^0.75.d, while in summer it was 28% higher at 45 g/kg^0.75.d. The mean dry matter digestibility (DMD) of the pellet diet was 76 ± 4%.

In winter, the projected daily digestible DMI at maintenance was 28 g/kg^0.75.d, compared with 34 g/kg^0.75.d in summer. Assuming a metabolizability of 83% (Blaxter 1962. The energy metabolism of ruminants. C. C. Thomas, Springfield IL.) the daily MER (metabolic energy requirement) was 425 kJ (101 kcal)/kg^0.75.in winter and 28% higher in summer. At this range of body weights (200-240 kg), the mean MER based on ARC (Agricultural Research Council 1980). This study showed, that the voluntary food intake and MER of young muskoxen varied seasonally. The MER in winter was 28% lower, than in summer... Crude protein in pelleted feed: 18.1% CP. - R. G. White et al. (1984:193)

Seasonal changes involuntary food intake, maintenance energy requirement and digestibility of a mixed pellet plus hay diet in muskoxen.

Summer 1979 102±7 g/kg^0.75.d, 74±1 % dry matter digestibility.

Maintenance metabolizable energy, 544 kJ(130 kcal)/kg^0.75.d.

Winter 1980 38±3 g/kg^0.75.d voluntary food intake. Dry matter digestibility 81±2%.

Maintenance metabolizable energy 425 kJ(101 kcal)/kg^0.75.d. - R. G. White et al. (1984:194)Table 2

The calculated daily digestible DMI (dry matter intake) for the summer pasture muskoxen was 49 g/kg^0.75. The daily metabolizable energy intake, based on this intake, was approximately 604 kJ/kg^0.75 (144 kcal/kg^0.75) and was 43% greater, than the winter maintenance energy requirement of pen-fed muskoxen (White et al. 1984b). - Holleman, D. F. et al. (1984:191)

Food conversion efficiency and growth rates of hand-reared muskox calves

By Kathleen Frisby, Robert White and Barbara Sammons, Institute of Arctic Biology, University of Alaska, Fairbanks, in: Biol. Pap. Univ. Alaska Spec. Rep. No. 4:196-202 (1984)

Maintenance requirements for muskox

Our data suggest, that dry matter intake by muskoxen on these diets is low at 45 to 55 g/kg^0.75 Compared with sheep at 80g/kg^0.75, but similar to cattle at 30 to 60 g/kg^0.75 (Stobo and Roy 1973). Frisby, K. (1984:200) Table 4.

Robert G. White and co-workers, Institute of Arctic Biology, University of Alaska, Fairbanks, report in Biol. Pap. Univ. Alaska Spec. Rep. No. 4:205-206 (1984) Abstract, about "Seasonal changes in water metabolism of captive muskoxen":

Maintenance water intake of yearlings, weighing 90 to 100 kg, was 5.5 liter/d at a food intake of 1.9 kg dry matter (DM)/d. Therefore the minimum water requirement for maintenance was 2.88 liter/kg DM or 112 liter/kg N. These values are in the same range, as those for reindeer in winter (Cameron et al. 1982).

Comparative water requirements of muskoxen and Rangifer

From: R. G. White et al. (1984:206) Table 1

J. Z. Adamczewski, R. K. Chaplin and co-workers, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. In: Can. J. Anim. Sci. 74: 305-313 (1994) "Seasonal variation in intake and digestion of a high-roughage diet by muskoxen":

Body weights and voluntary intake were monitored during 16 trials from late March 1990 to December 1991, in four annual breeding females and in three hysterectomized (= uterus removed) females. Mean body weights of breeding females were greatest in February and March (248 kg) and lowest following calving in late May or early June (216 kg), while mean weight of hysterectomized females declined little from a peak of 228 kg in February-March to a low of 213 kg in July.

Mean dry matter intake of breeding females was highest in July and August (62 g/d/kg^0.75). Then it declined slowly to its lowest point in March and April (41 g/kg^0.75 d). Dry matter intake of hysterectomized cows was less clearly seasonal, but averaged 42 g/kg^0.75 d in late winter and 50 g/kg^0.75 d in mid-summer.

High quality forage is only briefly available in summer, and access to nearly all forage may be severely restricted by snow for 8-10 months annually. The ability of muskoxen, to subsist on sparse winter forage, is essential to their survival ... Hubert (1977) measured digestibility of diets, fed to captive muskoxen in Alaska at 62-65%, and estimated dry matter (DM) digestibility in free-ranging muskoxen on Devon Island at 65% in early winter and at least 75% in summer.

White et al. (1984) measured a high digestibility (74%) for brome hay, and up to 81% for mixed high-quality diets in young muskoxen: voluntary intake in winter was a relatively low 38 g/kg⁷⁵. Chaplin (1984) showed that 6-mo-old muskox calves digested a timothy-brome hay better, than domestic lambs of similar weight. Sixteen feed intake trials were conducted approximately every 4-6 week from March 1990 to December 1991. Seven mature (± 4 yr old) muskox females were used; four bred annually during the study period. - Adamczewski, R. K et al. (1994:305, 306)

Apparent Digestibility and Energy Intake. Because mean body weights were stable throughout these trials, daily metabolizable energy intake (ME) for maintenance, in MJ, was estimated as 0.82 times DE intake (ARC 1980) and expressed as MJ kg^0.75. (1994:307)

Results. Peak intake occurred during July in 1990 (66.0 g/kg^0.75) and during August in 1991 (59.1 g/kg^0.75) and was followed by a slow decline through autumn and early winter to a low point during March in 1990 (42.1 g/kg^0.75) and during April in 1991 (40.9 g/kg^0.75). p. 308

Digestibility and Energy Intake

Overall diet quality was very similar in March and July, although CP and most fiber and lignin fractions were slightly higher in March (Table 3). The hay, eaten, was consistently higher in protein and lower in fiber and lignin, than the hay offered. Apparent OM (= organic matter) digestibility was significantly greater in March (73.8%), than in July (60.8%) and similarly CP and most fiber fractions were more digestible during the winter trial (Table 4).

The muskoxen consumed 12.6% more DM in July, than in March (44.6 vs 39.0 g/kg^0.75), but owing to the lower digestibility in July, estimated maintenance ME (metabolizable energy) intake was similar during the two trials (0.441 vs 0.413 MJ/kg^0.75 = 105 vs 99 kcal/kg^0.75). The body weights of the muskoxen were stable during each trial, but the mean body weight was significantly higher in March (266 kg) than in July (253 kg). The decrease in weight of the six animals occurred in April and May.

Mean apparent digestion and intake of hay and pellet diet

by muskoxen in March and July 1991

From: Adamszewski et al. (1994:310) Table 4

Maintenance requirements of muskoxen are relatively low in winter, compared with those of most ruminants. Our estimates of their maintenance ME and DM intake in winter are comparable to those of White et al. (1984a): 0.425 vs 0.441 MJ/kg^0.75, (101.53 vs 105.35 kcal) 38 vs 39 g/kg^0.75 day, although the diets were quiet different. The low relative energy requirement, combined with a large gut fill and very slow rate of passage, allows muskoxen to thrive on low-quality forage.

Breeding muskox cows ate about as much in winter, as non-breeding females and castrate males, but substantially more in summer. Peak intake of lactating females was about 48% higher, than in non-breeding muskoxen. This value gives an indication of the energy cost of lactation, but may not reveal their full extent. Body weights of lactating females changed little during early summer, as found in captive muskoxen in Alaska by White et al. (1989). However, free-ranging lactating muskoxen on Victoria Island catabolized (broke down, digested) body fat rapidly in early lactation (Adamczweski et al. 1992). Adamczweski et al. (1994:310, 313).

Muskox Nutrition

(1 Joule = 0.2389 Cal. 1 Cal = 4.186 Joule)

544 kJ ME/kg^0.75 d maintenance in summer (Adamszewski) = 129.957 kcal ME/kg^0.75 day

DE x 0.82 = ME/kg^0.75 day ARC 1980. (Adamszewski 1994:307)

101.529 kcal ME/kg^0.75 day maintenance (White, R. G.)

105.351 kcal ME/kg^0.75 day maintenance (Adamczewski, J. Z. et al. 1994)

38 g DMI/kg^0.75 day maintenance (White, 1984)

39 g DMI/kg^0.75 day maintenance (Adamsczewski, J. Z. 1994).

75.9% of CP digested in March (Adamsczewski, J. Z. et al. 1994)

220 kg muskox = 57.124 kg^0.75 metabolic body weight

2.664 g DCP/kg ^0.75 day maintenance in winter. Calculated from: 39 g DMI/kg^0.75 day maintenance. In winter 75.9% of CP digested (Adamcz.). 9% CP in food (Barrow meadow tundra) in winter (Chapin III, F.S. 1975)

152 g DCP/day for 220 kg muskox in winter for maintenance

ME (metabolizable energy) = 0.82 times DEI (digestible energy intake)

425 kJ ME/kg ^0.75 maintenance in winter = 101.529 kcal ME/kg ^0.75 day. - White, R. G.

= 38 g DMI/kg ^0.75 day

441 kJ ME/kg ^0.75 maintenance in winter 0 105.351 kcal ME/kg^0.75 day (Adamszewski. 1994)

= 39 g DMI/kg^0.75 day

75.9% of CP digested in March, 54.6% CP digested in July

Muskoxen on Victoria Island

How much food does the muskox pasture on Victoria Island contain? And how much crude protein (dry weight) is there in these plants during the long arctic winter?

J. Adamczweski and P.F. Flood, Dept. of Veterinary Anatomy, Univ. of Saskatchewan, Saskatoon. A. Gunn, Dept. of Renewable Resources, Government of Northwest Territories, Coppermine, N.W.T. B. Laarveld, Dept. of Animal Science, Univ. of Saskatchewan, Saskatoon. In: Rangifer, 12 (3): 179-183 (1992) they report about the "Seasonal changes in weight, condition and nutrition of free-ranging and captive muskox females":

"Wild muskoxen calve several weeks before snowmelt and begin costly lactation, without access to green forage; retaining substantial body fat until late winter may be essential to reproductive success. Captive muskox females tend, to regain body weight rapidly at the end of summer (White et al. 1989), but little is known of seasonal changes in body reserves of wild muskoxen. We began a study of weight and body composition in female muskoxen in 1989, on Victoria Island, Northwest Territories (NWT). Our objective was, to assess seasonal changes in nutrition and body reserves of females, and to relate these changes to reproductive status, particularly to early lactation in late winter." Adamczewski, J. et al. (1992:179).

"Collections on Victoria Island were conducted in April, May, August and November 1989, 1990, and April and May 1991. Approximately 20 muskoxen, mostly adult females and calves, were shot by Inuit hunters during each collection. Diet quality in wild muskoxen was estimated from analysis of nitrogen (N) in freeze-dried samples of rumen contents from shot animals." Adamczewski, J. et al. (1992:179)

"Values for wild females were summed for each month (1989-91), since there was little between-year variation (e.g. April data for 1989, 1990, 1991 are used together). Seasonal values for wild and captive females were compared by season. Diet quality varied markedly with season on Victoria Island, with a peak in July, followed by a rapid decline." Adamczewski, J. et al. (1992:180) (Fig. 1)

Per cent crude protein (dry wt) in rumen contents of Victoria Island muskoxen

Seasonal changes in the quality in Victoria Island muskoxen: % nitrogen in freeze-dried rumen contents. After Adamczewski, J. et al. (1992:180). During the winter months, from the beginning of November, till the end of May, the food of the Victoria Island muskox contains about 15.852 % (15.000-16.705 %) percent crude protein (dry weight). The muskox fertilizes with his dung and urine these pastures. That is, why these pastures have much more protein, than polar desert, which the muskox does not use at all or only very rarely. Victoria Island muskox females, 4 years old or older. They weigh from April till June about 150-170 kg. And from August to November about 200-220 kg. Adamczewski, J. et al. (1992:181) Figure 3a.

How much aboveground plant matter is growing on Victoria Island? That is, on the most fertile places, where the muskox is grazing.

J. Adamczewski. et al.: "Lactating wild females tended to regain weight, lost during winter, with a rapid surge in August, while non-lactating females regained it throughout summer and were clearly fatter by November. Lactating cows lost fat much more rapidly after giving birth, than during pregnancy... Captive muskox females maintained higher body weights, than wild ones all year, but mean weight of the 4 breeding cows did decrease from a winter peak of 250 kg to a low of 218 kg following calving." (1992:180).

"A strong seasonal cycle of changes in weight and nutritional status occurs in wild female muskoxen; changes in fat are primarily related to reproductive status. Substantial changes in body protein also occur annually, although there is no clear association with reproduction. Newly-lactating females lose more of their fat in the last 5-6 weeks of winter, than during the previous 4-6 months, and lactating females compress much of their compensatory growth into late summer and fall, past the peak of forage quality, as found by Thing et al. (1987).

"This tendency persists in captivity in Saskatoon, as it does in Fairbanks (White, et al., 1989), although the seasonal variation is much reduced. This pattern may reflect priorities, which change with season: initially (May-July) priority is given to calf support, and later to maternal tissues. Weight gain, despite reduced food quality, is possible in muskoxen, due to their very efficient digestion of graminoid forage and low metabolic rate (Adamczewski et al., 1991)." – Adamczewski, J. et al. (1992:181)

"The low pregnancy rate among muskox cows on Victoria Island indicates, that few cows are currently calving in successive years, although this can occur in wild muskoxen. This may reflect the large energetic cost of lactation, particularly in the initial weeks before spring, when fat stores are depleted rapidly. Nursing females apparently do not catch up to non-lactating cows in condition during the fall weight surge, in this population. Should this poorer condition coincide with poor nutrition in fall or early winter, conception or early pregnancy might be adversely affected." Adamczewski, J. et al. (1992:181)

Annual aboveground Plant-Production

How much aboveground dry plant-mass is growing now per year in the Far North, where reindeer and muskox are grazing? What do we find at 70°-80°North?

J. Svoboda (1977:206) reports about the standing stock and annual aboveground plant production on Victoria Island Island. He describes it as a "Polar Semi-desert site":

Result: Annual aboveground plant production on Victoria Islands is only 31.3 gDM/m² year. And these most fertile areas are only found near to the coast, at low elevations. In Tsavo East N. Park, Kenya, East Africa, during the great drought of 1970-72, the elephants and rhinos were starving to death with a full stomach. Because only about 200 gDM/m² had grown there per year.

Crude protein for maintenance

The muskox in its wild state, adapted to food, low in protein and high in fiber, is able, to maintain its body weight, when its food contains at least 5% crude protein (dry weight), not 6 or even 7%. Food, which contains 3.5% crude protein (dry wt) or less, the muskox is not able to digest anymore. The muskox needs in winter, when it is on winter maintenance, with its reduced metabolic rate, food, which contains at least 3.6% crude protein (dry wt).

The muskox still needs the additional protein (3.5-6.0% CP), which it does not get then through its food. This additional protein, which the muskox needs, but does not get then through its food, it will get from its own muscle tissue. It will loose then during the winter 10-15% of its body weight. This emergency protein, taken from its own body, will enable the micro-flora in its digestive tract, to survive and to break down and digest the food, which the muskox has eaten. Without this emergency protein, which the animal takes from its own body, the micro-flora would starve to death. When the micro-flora is gone, the muskox may eat food. But it will not be able to digest it anymore. It will then also starve to death, with a full stomach.