Growth, Development and Survival and Pork Composition

Chapters 8 & 9 of McGlone and Pond, 2002.

Pigs grow according to a growth curve. The usual growth curve has a sigmoidal-shape with a slow start, an exponential phase and then a plateau phase.

Body parts also grow in a non-linear manner. The size of body parts are important – for example, the size of the toes influences the size of slotted floors.

To calculate ADG, use the formula:

Larger weight – smaller weight

ADG = __________________________

Time in days

Growth is in the form of increases in muscle, fat and bone. Growth can be differential, that is, if muscle grows more than fat, then the animal has increased lean gain.

Differential Growth and Body Composition. Note the slow onset of fat and the large deposition of protein in early life.

Muscle (and other cells) can increase in:

Numbers of cells (hyperplasia)
Size of cells (hypertrophy; atrophy is the decrease in cell size, for example a decrease in muscle mass)

Stages of development – Prenatal period

Fertilization
Implantation
Organ differentiation
Placental growth (simultaneous with fetal growth)

Maternal tissues: uterine endothelium, uttering connective tissue, uterine epithelium
Fetal chorion: trophoblasts, connective tissuelayer and endothelium
The placenta is about 10% of fetal weight (40 lb of pigs have about a 4 lb placenta)

Fetal membranes (most growth completed by day 70 of gestation)

Yolk sac
Amnion
Serosa
Allantois

Uterus also grows during pregnancy

Fetal membranes and the placenta

Prenatal mortality = 20-45% -- most in the first 25 days of gestation
Deaths after about day 30 and before day 90 of gestation are termed ‘mummy’.

Piglets rapidly adapt at birth

· Oxygen obtained from lungs instead of umbilical cord

· The umbilical artery and vein breaks at birth, which can result in excessive bleeding (it is made worse in certain conditions such as vitamin K deficiency) – typically the umbilical blood clots rapidly

· Stillborn piglets die shortly before or during parturition

o To determine if the piglet was born dead – float the lungs in water – if they sink, the piglet never took a breath – if they float, the pig breathed.

Stages of development – Postnatal period

Birth weight and piglet survival – small pigs are at risk!

Feeding small or weak piglets improves their chance of survival.

Preweaning mortality

Most piglet deaths occur in the first 3 days of life. From d 3 to weaning, the loss of piglets is small but steady
Piglets must nurse to obtain energy within hours of birth or they will become hypoglycemic (as low as 10 mg/100 mL glucose is possible and would indicate a serious problem).
Hypoglycemia leads to lethargic piglets which further reduces nursing ending in coma and death of piglets – oral or intravenous glucose can be given to recover these piglets
Cold and fasting leads to a drop in body temperature and death
Piglets do not have the ability to thermoregulate until over 3 days of age
Colostrum is consumed and piglets obtain energy and immunoglobulins (passive immunity).
Piglets can not build antibodies until they are about 3 weeks of age

Digestive system development

· Piglets can be weaned at birth – if so, they need to be fed often since they have little reserves of energy (glucose or fat).

· CHO: Piglets can readily absorb glucose but not sucrose or polysaccharides (other than lactose – they have lactase which breaks lactose into glucose and galactose)

· FAT: Piglets can digest and absorb fat at birth.

· PROTEIN: Piglets absorb large molecular weight proteins whole for about 48 h after birth (immunoglobulins) due to presence of a trypsin inhibitor in colostrum and a lack of pepsin (in the stomach) and after that, the piglet produces trypsin and pepsin and proteins are not absorbed whole (but amino acids are absorbed).

Pig teeth