Author Institution: Ohio Division of Wildlife, New Marshfield and Department of Food Science and Nutrition, The Ohio State University, ColumbusMilk was collected from eight female gray squirrels (Sciurus carolinensis) and pooled for analysis, in an effort to determine the best substitute for gray squirrel milk for preweaned young squirrels. The sample, about 2 cc, contained 9.0 percent protein, 12.1 percent fat, 3.0 percent lactose, 1.3 percent ash, 0.36 percent calcium, and 0.45 percent phosphorus. This analysis is similar to that reported for two samples from single specimens. 

Infra-red spectroscopy was used for a portion of the analysis. This method provides a useful means of analyzing the small quantities (<0.5 ml) of milk obtainable from a variety of small mammals

Harper, W. J.

Nixon, Charles M.

The Ohio Journal of Science

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No. 1 RESPONSIBILITY OF THE PROFESSIONAL ECOLOGISTCOMPOSITION OF GRAY SQUIRREL MILK1- 2CHARLES M. NIXON AND W. J. HARPEROhio Division of Wildlife, New Marshfield3 and Department of Food Science and Nutrition,The Ohio State University, ColumbusABSTRACTMilk was collected from eight female gray squirrels (Sciurus carolinensis) and pooledfor analysis, in an effort to determine the best substitute for gray squirrel milk for pre-weaned young squirrels. The sample, about 2 cc, contained 9.0 percent protein, 12.1 per-cent fat, 3.0 percent lactose, 1.3 percent ash, 0.36 percent calcium, and 0.45 percent phos-phorus. This analysis is similar to that reported for two samples from single specimens.Infra-red spectroscopy was used for a portion of the analysis. This method providesa useful means of analyzing the small quantities (<0.5 ml) of milk obtainable from a varietyof small mammals.The gray squirrel is wholly dependent upon milk for about seven weeks post-partum and is not entirely weaned for another three to four weeks (Shorten, 1954,p. 127). If gray squirrels must be reared in the absence of their mother duringthe preweaning stage, a suitable substitute for squirrel milk must be provided forup to 23^ 2 months postpartum.This paper presents a partial analysis of a pooled sample of milk taken fromeight female gray squirrels and compares the analysis with two published analyses1A contribution of Federal Aid in Wildlife Restoration Project, Ohio W-105-R.2Manuscript received April 29, 1971.3Present address: Illinois Natural History Survey, Urbana, Illinois 61801.THE OHIO JOURNAL OF SCIENCE 72(1): 3, January, 1972.34 CHARLES M. NIXON AND W. J. HARPER Vol. 72of milk obtained from single females. The use of infra-red spectroscopy for thepartial analysis of a small volume of milk from a wild rodent is also reported.METHODSLactating female gray squirrels were livetrapped at intervals between 1966and 1968 on the 1,250-acre Waterloo Experiment Station, Athens County, Ohio.Trapping sites were located in mature upland oak-hickory and mixed-mesophyticforests.Each female was injected intermuscularly with A/i cc of Oxytocin. After 20minutes, the teats were stripped by hand and any expelled milk removed by eye-dropper. Unfortunately, only 10 to 20 drops of milk could be obtained fromeach milking, and attempts to remilk females 12 to 18 hours later were not success-ful. Nearly 2 cc of milk were finally collected from eight females, with each femalecontributing a nearly equal amount of milk.Because conventional methods of analysis for fat, carbohydrate, and proteinwould have consumed nearly all of the milk sample, analyses of these constitutentswere attempted by infra-red spectroscopy, using the principles of the infra-redmilk analyzer initially developed in England (Goulden, 1964, p. 273). Theanalysis was made with a Beckman IR-5 double-beam scanning infra-red spectro-photometer. A 0.1-ml milk sample was placed in a calcium fluoride cell with a0.100-cm light path, with double distilled water in a matching cell as the samplereference. Fat was determined by absorption at 5.73 microns and lactose byabsorption at 9.6 microns. Fat and lactose from purified cow's milk were utilizedto develop standard curves for the determination of concentration. It was as-sumed that the extinction coefficients of fat and lactose in cow's milk would bethe same as the extinction coefficients of these constituents in gray squirrel milk.Five replicate analyses were made, which were in agreement with a standard devia-tion of less than ±3.5 percent for both the lipid and carbohydrate. The sampleswere then recovered for use in other analyses.An attempt was made to determine the protein content of squirrel milk byadsorption at 6.46 microns. Because of a lack of resolution of the instrument,the standard deviation was ±11.7 percent. As a result of this wide variationbetween replicate analyses, attention was directed to other methods for derivingthe protein content. A 0.1-ml sample of squirrel milk was diluted 1 to 10, 1 to20, and 1 to 50 times, and the adsorption was determined in a Hytachi model No.139 UV spectrophotometer. All quantities were measured in a 100-microlitersyringe. Skim cow's milk, of varying dilutions, in which the protein was deter-mined by the standard micro-kjedahl procedure, was utilized as a reference stand-ard. Analysis was also made by the Lowry procedure and both methods were ingood agreement.The total solids present in duplicate 100-mg samples of gray squirrel milkwere determined by drying them to a constant weight in a vacuum oven held at80°C. These dried samples were then heated for one hour at 650°C in a mufflefurnace for ash determination. Calcium and phosphorus analyses, using AOAC-approved micromethodology, required the largest samples of milk, 0.3 ml and 0.5ml respectively.RESULTS AND DISCUSSIONThe analysis of the milk sample is shown in Table 1, along with two publishedanalyses, presumably each from a single specimen. For comparative purposes,analyses of whole cow's milk and of evaporated cow's milk, both of which havebeen used to feed preweaned gray squirrels at the Waterloo Experiment Station,have also been included in Table 1.All three samples of gray squirrel milk are similar in composition, with theexception of the higher fat content found in the sample reported by Jenness andSloan (1970, p. 609). Each sample shows squirrel milk to be higher in protein andNo. 1 GRAY SQUIRREL MILK 5fat, and somewhat lower in ash and carbohydrate than is whole cow's milk (Table1). Gray squirrel milk is similar in composition to those of mouse (Mus musculus),rat {Rattus norvegicus), and hamster (Mesocricetus auratus) milks (Jenness andSloan, 1970, p. 609). Young of each of these rodents and also of the gray squirrelare inclined to nurse on schedule rather than on demand, because the female isoften absent for extended periods in search of food. The small volume of milkavailable per feeding and the often-disrupted feeding schedule require a milkparticularly high in fat, known for its satiety value. The nestling squirrel, byingesting a milk with a protein content of about nine percent, should double itsweight by six to eight days postpartum (Blaxter 1961, p. 336). Shorten (1951, p.448) reported weight gains of this magnitude for one captive litter reared by themother.TABLE 1Average percent composition of two samples of gray squirrel milk compared withcomposition of whole cow's milk and of undiluted, evaporated cow's milkSpeciesGray SquirrelGray SquirrelGray SquirrelCow (whole milk)Cow (evaporated milk)TotalSolids25.439.627.613.826.2Water74.660.472.486.273.8Protein9.07.49.23.87.0F a t12.124.712.64.47.9Carbo-hydratelactose3.03.73.44.99.8Ash1.31.01.4.721.5Calcium.36———Phosphorus Source.45 This studyJenness and Sloan,1970, p. 609— Ben Shaul, 1962. p.336— Wright etol., 1939,p. 640— Silver, 1961, p. 69We recognize that the composition of milks differs markedly between the earlyor colostrum stage and the stage of established lactation (Ling et al., 1961, p. 231).The stage of lactation was not known for any of the eight females milked for thisstudy, nor was it reported by either Jenness and Sloan (1970) or Ben Shaul (1962)for their milk samples. Therefore these analyses should be used only as a guidein formulating a milk substitute for preweaned gray squirrels.Use of emission spectroscopy to analyze for minerals, coupled with infra-redspectroscopy for measuring the contents of protein, fat, and carbohydrate shouldprovide a useful method for analyzing milk from a variety of small mammals.Although we were only able to analyze fat and carbohydrate by the infra-redmethod, an instrument with a better resolution could also be utilized for thesimultaneous analysis for protein. The analytical technique is applicable tosamples as small as 0.1 ml.ACKNOWLEDGMENTSWe wish to acknowledge the assistance of Roger Beal and Milford W. McClain,Ohio Division of Wildlife, in collecting the milk samples, and of Dr. TheodoreBookhout, The Ohio State University, in expediting the analysis. Mrs. HelenSchultz and Mr. W. R. Edwards, Illinois Natural History Survey, critically re-viewed the manuscript.LITERATURE CITEDBen Shaul, Devorah. 1962. The composition of the milk of wild animals. Zool. Soc. London,International Zoo Yearbook, 4: 333-342. Hutchinson, London.Blaxter, K. 1961. Lactation and the growth of the young. Pp. 305-361. In Kon, S. and6 CHARLES M. NIXON AND W. J. HARPER Vol. 72A. Cowie (eds.). Milk: The mammary gland and its secretion. Vol. 2. Academic Press,New York. 423 p.Goulden, J. 1964. Analysis of milk by infra-red adsorption. J. Dairy Research 31(3): 273-284.Jenness, R., and R. Sloan. 1970. The composition of milks of various species: a review. DairyScience Abstracts 32(10): 599-612.Ling, E., S. Kon, and J. Porter. 1961. The composition of milk and the nutritive value of itscomponents. Pp. 195-263. In Kon, S. and A. Cowie (eds.). Milk: The mammary glandand its secretion. Vol. 2. Academic Press, New York. 423 p.Shorten, Monica. 1951. Some aspects of the biology of the gre}^ squirrel (Sciurus carolinensis)in Great Britain. Proc. Zool. Soc. London, 121 (pt. 2): 427-459.1954. Squirrels. Collins, London. 212 p.Silver, Helenette. 1961. Deer milk compared with substitute milk for fawns. / . Wildl.Mgmt., 25: 66-70.Wright, P., E. Deysher, and C. Cary. 1939. Variations in the composition of milk. Pp. 639-648. In Food and life. Yearbook of Agriculture, U.S.D.A., Washington, D.C. 1165 p.

Composition of Gray Squirrel Milk

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Composition of Gray Squirrel Milk

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