Supported by NIH grants RR00166 and HD02274.

Data are presented for birthweights from 5,376 pigtailed macaque monkeys born at the Primate Center Medical Lake Breeding Colony or the Seattle Infant Primate Research Laboratory Nursery between the years 1970 - 1997. The data represent the total population of all liveborn vaginally delivered animals with first body weights measured within 7 days of birth. Most of these values (67.3%) were taken during the first 24 postnatal hours (days 0-1). The remaining were from days 2-3 (22.1%), 4-5 (8.2%), and 6-7 (2.0%). Data are presented by sex and primary location during the last 30 days of pregnancy. A preliminary analysis showed that birth weights differed significantly for both females and males between each of three primary locations defined next (p range .02-.0001 by 2-sample Kolmogorov-Smirnov tests).

The primary locations were (i) Colony Social Group, (ii) Colony Single Cage, and (iii) Nursery Single Cage. Social groups were either harem groups containing one adult male and 6-10 females or 6-10 females with no male. Primary locations were defined as follows. If the animal was in its birth location for more than 14 days prior to birth, that location was designated primary. If the animal was in its birth location less than 15 days, it received a primary location based on its location prior to the one at birth. This could be any of the locations i, ii, or iii. However, colony locations were never preceded by the nursery location. There were very few cases in which a social group birth location less than 15 days was preceded by a cage location. However, the colony and nursery cage locations less than 15 days were preceded by the social group location very frequently. The nursery location less than 15 days was also frequently preceded by the colony cage location.

The table below presents summary birth weight statistics by sex and primary location. Figures present cumulative birth weight distributions. Figure 1 shows female and male distributions in one centile units for all individuals regardless of primary location. Figures 2a and 2b show distributions by location for each sex. It can be seen that location differences are small at the low birth weight end, but become quite large – as much as .75 SD units -- above the 25^th centile.

Some Cautions and Limitations

A number of variables are associated with birthweights of captive primates in addition to sex and primary pregnancy location. Among these are maternal age and parity. It is likely that parity effects underlie the cage versus social group differences presented here. The modal parity for group pregnancies is one. Cage pregnancies, especially those in the nursery, are more likely to involve multiparous females, who deliver larger newborns than primipara on average. Other factors to consider include wild versus colony born parents, generation in captivity among colony born parents, dominance status among social group members, medical conditions of the mother, the mother or father’s own birthweight, and the number of location changes during pregnancy. We have found significant relationships with birthweight for all of these factors. However, in studies to date, sex and primary pregnancy location taken together appear to account for the largest variance in the total population data.

A major variable not considered here is gestation length. Unfortunately, most of the births in this data base had either no gestation estimates or estimates based on manual palpation. The latter is very unreliable. Although gestation specific birth weights are desirable for both husbandry and scientific purposes, they could not be accurately calculated with this data base. On the other hand, these birthweight data represent population values for the total history of the Medical Lake Colony liveborn, non-caesarian section delivered, neonates – as the colony was formally closed at the end of 1996.

Readers can obtain exact birthweight centile values for a given sex and either the overall data or more precise values using the primary locations. Entering a birthweight and checking a sex and a location will yield the centile value to the nearest whole number.

Related References

Blakley, G.A., Morton, W.R., & Smith, O.A. (1972). Husbandry and breeding of Macaca nemestrina. Medical Primatology, 61-72, Lyon:France.

Dukelow, W.R., & Erwin, J. (Eds) Reproduction and Development. In Comparative Primate Biology, Vol. 3. 1986, many of the sections on growth. New York:Alan Liss, Inc.

Sackett, G.P., & Ruppenthal, G.C. (1992). Growth of nursery-raised Macaca nemestrina infants: Effects of feeding schedules, sex, and birth weight. American Journal of Primatology, 27, 189-204.

Swindler, D.R., & Emel, L.M. (1990) Dental development, skeletal maturation, and body weight at birth in pig-tail macaques (Macaca nemestrina). Archives of Oral Biology, 35, 289-294.