Pig

The following description of pig embryos is taken from the work of Paten ³⁴ and Marrable. ³⁵ Patten’s account of pig development is based on the Carnegie Institute collection and the data of Minot. ³⁶ He records the postcopulatory age of the various embryos. Marrable ³⁵ cautions about the difficulty of accurately aging embryos and notes that errors of aging may range from 20 to 60% at 5 days, and from 10 to 30% at 10 days. He also gives an equation for estimating age from length and presents a key for the preliminary estimation of pig embryos from their external appearance. Carnegie stages 1 to 8 of pig embryos are presented in Table 12. Table 12 Carnegie Stages 1 To 8 Of Pig Embryos

Carnegie stage

PC age (days)

Features

1

1

Fertilization

2

2—3.5

2 — 16 cells

3

4—7

Free blastocyst

4

7—8

Bilaminar embryo

5

8

—

6

9

Primitive streak

7

10—12

Notochordal process

8

13

Neural folds

Figure 109 Dorsal view of a Carnegie stage 9 pig embryo. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351069939/5bbd806d-0715-46b3-b0f7-7252d28d5864/content/fig_109.tif"/> (From Marrable, A. W., The Embryonic Pig. A Chronological Account, Pitman Medical, London, 1971. With permission.)