144 



NORTH AMERICAN FAUNA 74 



Table 22. Estimated mean daily intake of artificial walrus milk, in relation to 

 body weight, of walrus calves reared in captivity. 



Gross energ\- 



Age 

 lonths) 



Total 

 bod>' 

 wt (kg) 



Milk 

 Liters 



per day 

 % TBWa 



(kcal per day) 



Per kg'/^ 

 Total of TBW 



Source t> 





4d 



3 



6.5 



4,440 



251 



R 





54 



4.2 



7.8 



7.812 



393 



BA 





5b 



4.7 



8.3 



8,742 



462 



BA 







4.7 



7.4 



8,742 



390 



BA 



ic 



bb 



5. i 



o.b 



8,436 



364 



P 





70 



4.7 



6.7 



8,742 



361 



BA 



2 



62 



5.4 



8.7 



7,992 



362 



Ra 



4 



90 



7 



7.8 



10,360 



355 



R 



4c 



127 



10.9 



8.7 



16.132 



427 



Ra 



8 



154 



14.3 



9.3 



26,598 



609 



BA 



8 



161 



12.9 



8.0 



23,994 



532 



BA 



8 



170 



14.9 



8.8 



27,714 



590 



BA 



8 



186 



14.9 



8.0 



27,714 



550 



BA 



^Percent of total body weight (TBW), assuming milk weight of 1 kg/L. 



bBA = Brown and Asper (1966). P = Pournelle (1961), R = Reventlow (1951), Ra = 



G. C. Ray (personal communication). 

 ^Three animals; data given as mean for group. 



suggest that either the walrus calves had a higher caloric requirement than is 

 normal for domestic animals, or they were not able to use their food very 

 efficiently. The latter seems to me more probable, for the following reasons: 



• The gross energy value per unit volume of the artificial milk was about half 

 that of natural walrus milk, hence the calves probably had to ingest at least twice 

 the volume that would have been required had they been feeding on natural 

 milk. 



• At that rate, the calves would have consumed about two-thirds as much fat, 

 but more than twice as much protein and 200 times more carbohydrate than 

 would have been available in the caloric equivalent volume of natural milk. 



• At least half of that carboh>'drate was lactose, which would not have been 

 available to the calves as digestible energ}', because of their lack of lactase. 



• Much of the protein also may have been unused, if it were greatiy in excess of 

 the normal (natural) rate of intake. 



Thus it seems likely that the prepared diet was greati>- unbalanced and that the 

 net energy available from it was appreciably lower than would have been 

 available from a caloric equivalent volume of natural walrus milk. The natural 

 milk must be assumed to be optimally balanced, with very high net digestible 

 energ}', perhaps comparable to the 84 % available to human infants on mother's 

 milk (Ebbs 1966). 



The daily net digestible energy intake by calves probably is comparable to that 

 of young domestic mammals (about 350 kcal/kg TBW3'4 pgr day). This intake of 

 natural milk would amount to about 6.8% of the TBW per day. The rate of 

 intake for walrus calves under natural conditions may be slightly higher because 



