Degus physiology

The Octodon degus is a diurnal rodent from South America. Of medium size, it remains one of the smallest caviomorphs on this continent. It is a rather unique rodent, often confused with other pet species like gerbils or chinchillas. Its physiology has allowed it to adapt to a semi-arid environment by adopting a crepuscular lifestyle and living in burrows.

Morphology

The Octodon degus is a medium-sized, stout-looking rodent. Its head is quite strong and has almond-shaped eyes and two large ears that allow it to detect predators. Its body is built for digging and moving quickly. It has powerful legs with five toes, the last of which is barely developed. A burrower⁰¹, it uses its claws to dig its burrow. Its tail is almost as long as its body and ends in a small brush of hairs. Octodons do not have a morphology adapted to a burrowing lifestyle⁰², but they rely heavily on their vision. Octodons also lack sexual dimorphism.

Octodon degus morphology

Physiological Data

Physical

Total length of the adult, including the tail: 250mm – 310mm
Total length of the adult body, excluding the tail: 150mm
Tail length: 65mm – 130mm

Average adult weight: 170g – 230g
Ideal weight in captivity: 180g – 250g

Ear size (height): 24mm – 32mm
Length of the hind leg: 35mm – 38mm

Adult age: 54 weeks – 1 year
Lifespan of the octodon in captivity: 5 – 9 years
Lifespan of the octodon in the wild: ≤ 2 years

Physiological

Body temperature: 36.0°C – 37.9°C (96.8°F – 100.2°F), which is the lowest body temperature among species in the suborder Caviomorpha⁰³.
Temperature during estrus (heat): ≈+ 4°C⁰⁴
Thermal neutral zone: 23°C – 32°C (73°F – 89°F).
Minimum temperature before activity outside the burrow: 24°C⁰⁵

Differentiated cecum: 33.60% specificity.
Haustrated cecum: 79.65% specificity.
Glandular stomach: 36.25% specificity.
Relative medullary thickness: 6.1.

Hematology

	Juveniles				Adults
Parameter	Mean (sd)	Median	Range	95% CI of mean	Mean (sd)	Median	Range	95% CI of mean	Age effect
Red blood cells (x 10^12/l)	7,3 (1,08)	7,60	4,72 - 9,01	6,89 - 7,64	8,7 (1,02)	8,98	5,34 - 9,93	8,35 - 9,06	***↑
Reticulocytes (x 10^9/l)	7,4 (16,27)	0,0	0,0 - 80,24	1,69 - 13,03	0,2 (1,23)	0,0	0,0 - 0,1	-0,23 - 0,66	*↓
%	0,1 (0,32)	0,0	0,0 - 1,7	0,02 - 0,24	0,0 (0,02)	0,0	0,0 - 0,1	0,0 - 0,01	NS
Haemoglobin (g/l)	113,7 (9,57)	116,0	89,0 - 134,0	110,4 - 117,0	117,6 (7,73)	119,0	99,0 - 131,0	114,9 - 120,3	NS
Haematocrit (l/l)	0,4 (0,04)	0,40	0,32 - 0,51	0,42 - 0,44	0,5 (0,03)	0,46	0,37 - 0,50	0,44 - 0,46	*↑
MCV (fl)	59,9 (5,41)	58,6	52,30 - 75,30	58,01 - 61,78	51,4 (3,15)	51,0	47,20 - 64,50	50,26 - 52,45	***↓
MCH (pg)	15,8 (1,52)	15,70	13,60 - 19,50	15,31 - 16,37	13,4 (0,62)	13,3	12,3 - 15,4	13,16 - 13,59	***↓
MCHC (g/l)	264,5 (10,43)	264,0	240,0 - 291,0	260,8 - 268,1	261,0 (11,36)	263,0	226,0 - 289,0	257,0 - 264,9	NS
Platelets (x 10^9/l)	453,4 (142,25)	455,0	57,0 - 896,0	403,9 - 503,0	383,0 (78,17)	362,0	223,0 - 530,0	233,7 - 410,2	*↓
White blood cells (x10^9/l)	7,2 (3,04)	7,0	2,0 - 12,30	6,10 - 8,22	7,4 (2,40)	7,1	3,5 - 14,6	6,55 - 8,23	NS
Neutrophils – bands (x10^9/l)	0,1 (0,20)	0,03	0,0 - 1,0	0,03 - 0,17	0,0 (0,07)	0,0	0,0 - 0,31	0,1 - 0,06	NS
%	1,0 (1,37)	0,05	0,0 - 6,0	0,52 - 1,48	0,4 (0,73)	0,0	0,0 - 3,0	0,15 - 0,65	NS
Neutrophils – segmented (x10^9/l)	2,2 (1,17)	2,05	0,38 - 4,80	1,82 - 2,63	3,1 (1,48)	2,89	0,70 - 7,01	2,53 - 3,58	NS
%	32,0 (13,07)	30,0	11,0 - 63,0	27,47 - 36,58	40,6 (13,09)	40,5	19,0 - 72,0	35,95 - 45,22	*↑
Lymphocytes (x10^9/l)	4,6 (2,39)	4,42	0,96 - 10,2	3,76 - 5,43	4,0 (1,40)	3,9	1,27 - 7,26	3,53 - 4,52	NS
%	63,2 (13,57)	66,0	33,0 - 85,0	58,47 - 67,93	54,9 (12,7)	54,0	27,0 - 77,0	50,38 - 59,38	*↓
Monocytes (x10^9/l)	0,1 (0,12)	0,09	0,0 - 0,41	0,09 - 0,17	0,1 (0,20)	0,07	0,0 - 0,89	0,06 - 0,20	NS
%	1,9 (1,62)	1,0	0,0 - 5,0	1,29 - 2,42	1,3 (1,51)	1,0	0,0 - 6,0	0,79 - 1,86	NS
Eosinophils (x10^9/l)	0,1 (0,12)	0,09	0,0 - 0,47	0,07 - 0,15	0,2 (0,26)	0,15	0,0 - 1,45	0,12 - 0,3	NS
%	1,8 (1,85)	1,0	0,0 - 8,0	1,13 - 2,42	2,6 (2,67)	2,0	0,0 - 12,0	1,67 - 3,56	NS
Basophils (x10^9/l)	0,0 (0,03)	0,0	0,0 - 0,12	0,0 - 0,02	0,0 (0,04)	0,0	0,0 - 0,19	0,0 - 0,03	NS
%	0,1 (0,40)	0,0	0,0 - 2,0	0,0 - 0,25	0,2 (0,45)	0,0	0,0 - 2,0	0,02 - 0,34	NS
* P<0,05; P<0,01; * P<0,001
↑ Values showed increases with increasing age
↓ Values showed decreases with increasing age
CI Confidence interval, MCH Mean corpuscular haemoglobin, MCHC Mean corpuscular haemoglobin concentration, MCV Mean corpuscular volume, NS Not significant

	Juveniles				Adults
Parameter	Mean (sd)	Median	Range	95% CI of mean	Moyenne (±ÉT)	Mean (sd)	Range	95% CI of mean	Age effect
TP (g/l)	54,7 (5,83)	53,8	46,50 - 73,70	52,68 - 56,74	63,1 (7,43)	63,9	45,8 - 77,70	60,35 - 35,91	***↑
Albumin (g/l)	34,0 (2,87)	34,4	28,60 - 40,60	32,97 - 34,97	33,1 (5,18)	33,3	19,0 - 45,10	31,21 - 35,07	NS
Globulin (g/l)	21,7 (7,62)	20,2	12,70 - 52,70	19,05 - 24,36	30,0 (6,10)	31,9	16,50 - 47,80	27,71 - 32,26	***↑
Albumin:globulin ratio	1,7 (0,43)	1,7	0,66 - 2,50	1,55 - 1,85	1,2 (0,35)	1,1	0,40 - 2,58	1,03 - 1,29	***↓
Glucose (mmol/l)	9,4 (1,69)	9,4	5,60 - 14,10	8,79 - 9,97	8,9 (1,68)	8,9	5,40 - 13,10	8,27 - 9,52	NS
Urea (mmol/l)	15,1 (2,57)	15,9	10,80 - 22,0	14,16 - 15,96	10,1 (1,78)	10,0	6,60 - 14,90	9,41 - 10,73	***↓
Creatine (μmol/l)	56,5 (12,94)	57,8	34,40 - 87,20	51,94 - 60,96	51,4 (9,50)	51,0	29,9 - 77,30	47,91 - 54,99	NS
Triglycerides (mmol/l)	1,8 (1,0)	1,5	0,01 - 4,47	1,47 - 2,16	1,9 (1,19)	1,59	0,44 - 4,85	1,46 - 2,34	NS
Cholesterol (mmol/l)	2,5 (0,70)	2,3	1,80 - 4,90	2,27 - 2,76	2,0 (0,39)	2,1	1,20 - 2,70	1,85 - 2,15	**↓
ALT (iu/l)	33,5 (18,32)	29,3	12,57 - 107,19	27,55 - 40,12	18,0 (8,02)	18,0	9,58 - 47,90	16,17 - 22,16	***↓
AST (iu/l)	61,1 (35,39)	53,3	10,18 - 192,81	48,50 - 73,65	17,9 (25,21)	36,5	19,16 - 137,72	37,72 - 56,29	*↓
APL (iu/l)	385,6 (247,26)	285,0	167,66 - 1077,84	299,40 - 471,86	65,9 (15,03)	65,3	40,72 - 105,99	62,87 - 74,25	***↓
Amylase (iu/l)	892,8 (298,38)	805,4	409,58 - 1947,90	788,62 - 996,41	820,4 (234,01)	755,7	481,44 - 1263,47	733,53 - 908,38	NS
Lipase (iu/l)	43,7 (21,50)	37,1	16,77 - 111,98	35,93 - 50,90	29,9 (5,45)	26,4	2,99 - 39,52	23,95 - 29,34	***↓
GGT (iu/l)	9,08 (1,50)	1,8	1,80 - 10,18	1,80 - 3,0	6,0 (0,05)	1,8	1,80 - 7,78	1,80 - 2,40	NS
CK (iu/l)	1159,3 (764,13)	1094,6	215,57 - 16012,0	752,69 - 2627,55	958,1 (846,19)	692,2	120,96 - 4245,51	643,71 - 1274,25	NS
LDH (iu/l)	679,0 (333,11)	591,0	35,33 - 1934,13	562,87 - 795,21	562,9 (111,02)	544,9	313,17 - 894,01	522,16 - 604,79	NS
Sodium (mmol/l)	142,3 (5,41)	141,9	131,60 - 156,50	140,40 - 144,20	142,1 (6,32)	142,7	121,0 - 151,20	139,80 - 144,50	NS
Potassium (mmol/l)	4,4 (1,0)	4,3	2,90 - 8,10	4,1 - 4,80	3,8 (0,40)	3,9	3,10 - 4,70	3,69 - 4,0	**↓
Chloride (mmol/l)	104,9 (5,56)	104,8	91,20 - 116,40	102,90 - 106,80	103,4 (5,54)	103,2	91,80 - 113,80	101,30 - 105,40	NS
Calcium (mmol/l)	3,2 (0,26)	3,1	2,69 - 3,73	3,075 - 3,26	2,5 (0,25)	2,6	2,01 - 2,96	2,45 - 2,64	***↓
Inorganic phosphore (mmol/l)	2,2 (0,57)	2,2	1,09 - 3,74	1,97 - 2,37	1,5 (0,36=	1,5	0,63 - 2,10	1,32 - 1,60	***↓
Total bilirubin (μmol/l)	2,4 (1,37)	2,4	0,90 - 5,40	1,91 - 2,86	2,8 (1,15)	0,9	0,90 - 5,40	1,40 - 2,33	NS
Total bile acids (μmol/l)	-	-	-	-	13,5 (12,21)	8,2	1,10 - 54,90	8,94 - 18,04	-
* P<0,05; P<0,01; * P<0,001
↑ Values showed increases with increasing age
↓ Values showed decreases with increasing age
ALP Alkaline phosphatase, ALT Alanine aminotransferase, AST Aspartate aminotransferase, CI Confidence interval, CK Creatine kinase, GGT γ-Glutamyl transferase, LDH Lactate dehydrogenase, NS Not significant, TP Total protein

It should be noted that the glucose level observed in captivity differs from that observed in the wild⁰⁶. In a sample of 16 wild degus of varying ages, the glucose level ranged from 3.89 to 5.39 mmol/l ⁰⁷.

Urinary concentration – 634 mOsmol l-1
- Average summer urine osmolality – 3137 mOsmoles kg-1
- Average winter urine osmolality – 1123 mOsmoles kg-1⁰⁸

Basal metabolic rate: 0.839 ml O2 g-1hr-1

Heart rate: 274 beats min-1

Resting respiratory rate: 123 breaths min-1 ⁰⁹
- Respiratory rate under anesthesia: 231 (+/-35) breaths min-1
  - Hypoxia (10% O2) – 179 (+/-17) breaths min-1
  - Hypercapnia (10% CO2) – 206 (+/-20) breaths min-1
- Anesthetized tidal volume: 0.18 (+/-0.04) ml
  - Hypoxia (10% O2) – 0.17 (+/-0.04) ml
  - Hypercapnia (10% CO2) – 0.16 (+/-0.03) ml
- Anesthetized minute volume – 40.6 (+/-11.7) ml min-1
  - Hypoxia (10% O2) – 32.3 (+/-10.2) ml min-1
    - Hypercapnia (10% CO2) – 34.6 (+/-8) ml min-1

Lowest average cortisol level reached – 500 ng ml-1¹⁰

Sexuality

Sexual maturity: between 7 weeks for females and 12 weeks for males¹¹
Estrous cycle duration: 18 to 21 days
Gestation period: between 87 and 95 days
Average litter size: 5.5
Minimum and maximum litters: 1 to 12¹²
Number of udders: 8

Young 12-day-old Octodon degus during nursing

Age at weaning: 72 to 75 days¹³
Average age at first gestation in the wild: 6 months
Average weight at the first gestation: 205g
Recommended minimum weight for the first gestation in captivity: 220g¹⁴
Sex ratio at birth: 100 females: 110 males¹⁵
Weight of the babies¹²

Age (days)	Average weight (grams)
1	13g
2	14g
3	14,5g
4	15g
5	18g
6	19g
7	20g
8	22g
9	23g
10	25g
11	25g
12	26g
13	27g
14	28g

As with the first days, weight variations can be observed throughout the growth, increasing with age.

Age (weeks)	Average weight (grams)
0	13g
1	20g
2	32g
3	41g
4	58g
5	72g
6	88g

Percentage of maternal body mass at birth: 5-6%
Growth rate of the pups during the first 14 days after birth: 1-3g/day
Duration of lactation: 21 to 40 days

Composition (%) of milk in mid-lactation.¹⁶.	Proteins	Carbohydrates	Lipids	Solids
Composition (%) of milk in mid-lactation.¹⁶.	4,4	2,7	20,1	30,5

Recommended weaning age: 6 weeks

Average cortisol level in lactating females: 1000 ng ml-1
Average testosterone level in adult breeding males: 2.35 ng ml-1¹⁷
Highest average testosterone level (male): 0.16 ng ml-1
Vitamin C content in caviomorph sperm: 2.5-12 mg dl-1
Gametic DNA content of spermatozoa: 2.7 pg
Average head length of spermatozoa: 6.0 μm
Average head width of spermatozoa: 4.6 μm
Average tail length of spermatozoa: 40.9 μm
Spermatozoal nuclear, nucleolar location: central

The reproduction of Octodon degus

Various

Field of vision overlap (frontal binocular): 50º
Number of cells in the retinal ganglion cell layer: 300,000
Maximum speed of a 180g degu: 4.9 m/s, approximately 17 km/h
Maximum jumping speed: 2.4 m/s, approximately 8 km/h

Developmental age of the circadian function: 10-12 months
Chromosome number (2n): 58
Genome size: 8.6 pg
Average number of chiasmata per bivalent: 1.6
Recombination index: 73

Harmful malathion dosage: 436 mg kg-1
Lethal dose of sodium pentobarbital: 60 mg kg-1

Skeleton

The skull of the degu has a well-developed large infraorbital foramen with a ventromedial groove and an open pterygoid fossa⁰². The tip of the pterygoid hamulus is in contact with the bulla. The bullae are of moderate size, but the auditory bulla is well-developed, and the paroccipital process conforms to the posterior edge and surface. Interestingly, the hammer and anvil ossicles are not fused. In the mandible, the two rami are closely connected, with the coronoid process appearing delicate and pointed. The clavicle and deltoid crest are well developed. The scapular spine extends from near the vertebral margin of the scapula to beyond the tip of the coracoid process. The scapular spine is a thin, unsupported finger-like projection from the medioscapular region to the ends of the large acromion and metacromion processes. There is an entepicondylar foramen in the humerus, and the proximal ends of the tibia and fibula are fused.

Musculature

There are several important myological features that distinguish the degu⁰². The maximum cutaneous muscle is complex and divided into four parts, with the anterior part extending to the lateral surface of the shoulder. There is a scapuloclavicular muscle, an anterior scalene muscle ventral to the brachial plexus, and the absence of a stylohyoid muscle despite the presence of a well-developed hyoid apparatus. There is also a mandibulolabial muscle composed of a complex group of multipartite masticatory muscles, with the medial masseter passing through the infraorbital foramen and the pars reflexa of the superficial masseter passing into the medial part of the mandible through a groove. It is interesting to note that the musculature of the degu is consistent with all other hystricognaths but is not found in any other group of rodents.

Vascular System and Thymus

Certain aspects of circulation in the degu have evolved¹⁸. The blood supply to the stapedial region has been replaced by the external carotid arteries. It has been reported that, with a few exceptions, the cephalic arteries of the degu are identical to those of other hystricognaths. The degu has both a left and right anterior vena cava. It has a double thymus with cervical and mediastinal components. The mediastinal component is multilobed and amorphous, morphologically similar to a typical rodent thymus. The cervical component is bilobed and remains active throughout the animal’s life, unlike the mediastinal component. The celiac artery and the mesenteric artery originate from the abdominal aorta. Degus appear not to have a gastroepiploic artery. The cecum is supplied with blood by the ileocolic artery in the direction from the head to the apex of the cecum. The liver is supplied by branches of the hepatic artery, with a right middle branch extending to the gallbladder. The pancreas is supplied by the cranial pancreaticoduodenal artery, the caudal pancreaticoduodenal artery, and the splenic artery. The dorsal spleen is supplied by a right branch of the dorsal gastro-splenic artery, while the ventral spleen is supplied by a right branch of the ventral gastro-splenic artery.

Brain

The degu’s brain follows the general pattern of rodents, but the olfactory bulb (used for distinguishing scents) is particularly well-developed¹⁹. Unlike other rodents, the vomeronasal nerve connects to the accessory olfactory bulb laterally. Furthermore, there is an indentation between the boundary of the rostral and caudal subdivisions of the olfactory bulb, and the rostral olfactory bulb is twice the size of the caudal bulb and exhibits biased sexual dimorphism toward males in terms of size. These unique features are likely related to semiochemical communication in degus. The brain’s surface is moderately folded, which is also an unusual characteristic among rodents, except those belonging to the suborder Hystricognathi. Blood is supplied to the brain only by the vertebral arteries, as the internal carotid arteries and tympanic stapedial arteries have been lost during evolution.

Dentition

Degus, like their relatives the chinchillas, have orange enamel on the front surface of their incisors with a multilayered microstructure. This coloration occurs during amelogenesis when the enamel is formed in ameloblasts (dental enamel-forming cells). Dental enamel amelogenins in development are specific proline-rich, leucine, histidine, and glutamyl residue-rich proteins synthesized by ameloblast cells of the inner enamel epithelium. These proteins mineralize to form mature enamel, presumably regulated by an enamel acid protein called tuftelin. The exact process by which enamel is colored orange is still debated, but it has been suggested that forming enamel is stained by oral enzymes present in degu saliva, although this is speculative. Chromogenic enzymes are assumed to be supported by the pellicle and originate from polyphenolic compounds that provide food color, such as carotenoid pigments. There may also be a link between enamel color and iron intake. Therefore, nutrition is believed to play a significant role in the color of degu’s tooth enamel.

The orange coloration of degus’ enamel develops slowly from birth¹³, with the young being born with pale cream-colored teeth that gradually darken over the first six months to reach the dark orange color of adulthood.

Dental disease and malocclusion in Octodon degus

Vision

Degus have well-developed vision and visual sensitivity during the day²⁰. Other nocturnal species of degus have vision specially adapted for nighttime, enhancing contrast and light sensitivity.

The degus’ lenses selectively absorb short-wavelength light²¹, with increasing optical density as the degus age. Degus’ retinas have one type of cone and two S-type cones, allowing them to see in dichromatic colors. Visible colors for degus include green and ultraviolet (UV). Rods have a spectral peak at 500 nm (green), while each cone type has spectral peaks at 507 nm (green) and 362 nm (UV). The retinas consist of approximately 9 million photoreceptors, with one-third being cones. The two cone types exist in a ratio of 13:1 (green:UV).

Having UV-sensitive S-cones is relatively rare among mammals. Degus have been shown to distinguish between UV and visible light in behavioral tests²².

Camouflage

The fur of degus is well adapted for camouflage. Their ventral fur is lighter and highly UV-reflective, reflecting up to 20% of UV light²¹, this suggests a communication signal during alarm calls or vigilance when degus expose their bellies by standing on their hind legs.

Degus’ urine also reflects UV light, up to 40% of incident light, serving as a visual territorial marker.

Degus colors

Diet

How to feed my degu?

Water

As degus are adapted to a semi-arid climate, their anatomy is designed to use water more efficiently. Degus have a high degree of water reabsorption in the colon, allowing them to maximize the amount of water they can extract from their food. They have about twice the colonic reabsorption capacity of laboratory rats, which may be due to the presence of a mercurial agent known to inhibit water channels²³. Degus lack sweat glands, minimizing water loss through evaporation. They can also condense water in their nasal passages to avoid exhaling essential moisture. This process is accomplished through aquaporins in the nasal mucosa, first AQP-3 in non-olfactory epithelial cells and later AQP-1 in the capillary lumen. The most significant water loss occurs through urination, which is why degu urine is highly concentrated due to a long Henle’s loop in the kidneys. It is interesting to note that degus, especially males, produce more urine at night than during the day. Research has shown that degus can go without water for up to 13 days, and after seven days without drinking, the urine concentration can reach 4604 mOsmoles l-1.

Other studies of degu kidneys have shown that they have the unusual ability to concentrate urinary potassium more than sodium and (also unusual) retain magnesium.

Octodon degus prenant une pause le vendredi - Photo par Jonas Šileika (Ne pas donner d'alcool à vos octodons!) — Degu taking a break on Friday – Photo by Jonas Šileika (Do not give alcohol to your degus!)

Digestion

Degus are herbivores, and their digestive system is specifically adapted to a folivorous diet. Their gastrointestinal tract contains sucrase, an enzyme that hydrolyzes plant carbohydrates, allowing degus to digest plant-specific sugars. Due to abnormal insulin function, degus should avoid diets containing sugar. Degus have a cecum²⁴, which varies in shape and position among degus. The caput caeci is generally located on the left with cranial or caudal rotation, and the apex is on the left in front of the pelvis. The ascending colon is arranged in variable overlapping folds and often spirals. Degu feces are small, dry, and compact.

Newborns also possess the enzyme lactase, allowing them to digest maternal milk. s.

Reproductive System

Sexing a degu

Although degus have different genital anatomy for males and females, it can be quite challenging to distinguish them at a glance. Their urogenital anatomy is similar to that of other caviomorphs²⁵. Males have a pair of testicles, which are always located inside the abdomen. The penis points backward from the peri-anal circle, below which is (inside) the cremasteric sac. The penis is stored inside in an S-shape, and its tip is covered in small spines. Inside the body, the vas deferens and seminal vesicles open independently into the urethra. The testicular artery is short with few loops and a large diameter. A saccularis urethralis is present. Females have a bicornuate uterus, which divides into two sections. The vaginal opening is located immediately (posteriorly) behind the urethral projection. Externally, females also have four pairs of nipples, with three positioned high on the sides between the front and rear limbs. One pair is positioned on the belly between the rear limbs for nursing while the female is in a state of vigilance.

There is a greater distance between the anus and the urethra in males, while females have virtually no space between the urethra and the anus.

How to differentiate the sex of the male or female degus?

Spermatozoa

The spermatozoa of degus differ from those of other species²⁶. The head measures 7.7 µm long by 5.9 µm wide, while the tail measures 41 µm long. The head is dorsoventrally flattened and has an oval shape. The gametic DNA content is about 2.7 pg. An interesting feature is that there is a high recombination index for rodents.

The acrosome is the most distinctive feature in the degu spermatozoon. When viewed from the front, the acrosome’s edge has the shape of an inverted ‘U’. The acrosomal region has dome-like protrusions that are regular (non-random). The acrosome represents about 60% of the length of the head. There are also subtle differences in spermatozoon morphology between degu species. The spermatozoon head of Octodon bridgesi is more elliptical than round, while that of Octodon lunatus is paddle-shaped and wider at the base. On average, the common degu has the smallest spermatozoon head length, Octodon bridgesi has the smallest spermatozoon head width, and the degu with crescent teeth has the shortest spermatozoon tail length.

Ovaire et placenta

During gestation, the placenta exhibits a hemo-monochorial placental barrier with continuous non-fenestrated capillaries²⁷.On the 27th day of gestation, the sub-placenta emerges beneath the wall of the central excavation, and the outermost trophoblasts of the ectoplacental cone begin to differentiate. These secondary giant trophoblast cells are located outside the placenta, forming an interface with maternal decidua cells. These cells contain cytokeratin and placental lactogen until the end of pregnancy. During gestation, extra-sub-placental trophoblast emerges from the sub-placenta to the decidua. The vascular mesenchyme of the central excavation invades the chorioallantoic placenta during gestation to form two fetal lobes, constituting the area of the placental barrier. The activity of the sodium-potassium ATPase pump in the placental barriers remains constant throughout gestation. The residual syncytium at the edge of the placental disk/between the lobes is not invaded by fetal mesenchyme and forms the marginal and interlobular labyrinthine syncytium. It is likely that these cells have a secretory process between maternal blood vessels. Placentas expelled from the body during birth present a large single lobe, have no sub-placenta, and reduced interlobular labyrinthine syncytium. The reversed visceral yolk sac can be seen on day 27 of gestation and has features suggesting that it functions as an early secretory organ. The parietal yolk sac epithelium covers the entire placenta and comes into direct contact with the uterine lumen. The weight of the placenta at term is about 8 g and has a diameter of about 13 mm.

Even at a young age, females have an antral follicle in their ovaries that does not ovulate but becomes atretic. Interstitial tissue is abundant, and interstitial cells are vacuolated and are potentially involved in steroid synthesis. During pregnancy, the corpus luteum persists but may regress before giving birth. Several small accessory corpus luteums form toward the end (days 75-80) of pregnancy, persisting up to 20 days after birth. Other structures present in the ovaries include epoo-phoron tubules and the ovarian network.

Sources

Much of this article has been taken/inspired from Degutopia.