Litter Size: The number of offspring produced at one birth by a viviparous animal.Breeding: The production of offspring by selective mating or HYBRIDIZATION, GENETIC in animals or plants.Reproduction: The total process by which organisms produce offspring. (Stedman, 25th ed)Weaning: Permanent deprivation of breast milk and commencement of nourishment with other food. (From Stedman, 25th ed)Ovulation: The discharge of an OVUM from a rupturing follicle in the OVARY.Lactation: The processes of milk secretion by the maternal MAMMARY GLANDS after PARTURITION. The proliferation of the mammary glandular tissue, milk synthesis, and milk expulsion or let down are regulated by the interactions of several hormones including ESTRADIOL; PROGESTERONE; PROLACTIN; and OXYTOCIN.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Pregnancy: The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.Fertility: The capacity to conceive or to induce conception. It may refer to either the male or female.Body Weight: The mass or quantity of heaviness of an individual. It is expressed by units of pounds or kilograms.Pregnancy, Animal: The process of bearing developing young (EMBRYOS or FETUSES) in utero in non-human mammals, beginning from FERTILIZATION to BIRTH.Parity: The number of offspring a female has borne. It is contrasted with GRAVIDITY, which refers to the number of pregnancies, regardless of outcome.Animals, Suckling: Young, unweaned mammals. Refers to nursing animals whether nourished by their biological mother, foster mother, or bottle fed.Hybrid Vigor: The adaptive superiority of the heterozygous GENOTYPE with respect to one or more characters in comparison with the corresponding HOMOZYGOTE.Selection, Genetic: Differential and non-random reproduction of different genotypes, operating to alter the gene frequencies within a population.Birth Weight: The mass or quantity of heaviness of an individual at BIRTH. It is expressed by units of pounds or kilograms.Sheep: Any of the ruminant mammals with curved horns in the genus Ovis, family Bovidae. They possess lachrymal grooves and interdigital glands, which are absent in GOATS.Animal Husbandry: The science of breeding, feeding and care of domestic animals; includes housing and nutrition.Animals, Newborn: Refers to animals in the period of time just after birth.Sex Ratio: The number of males per 100 females.Crosses, Genetic: Deliberate breeding of two different individuals that results in offspring that carry part of the genetic material of each parent. The parent organisms must be genetically compatible and may be from different varieties or closely related species.Least-Squares Analysis: A principle of estimation in which the estimates of a set of parameters in a statistical model are those quantities minimizing the sum of squared differences between the observed values of a dependent variable and the values predicted by the model.Fetal Death: Death of the developing young in utero. BIRTH of a dead FETUS is STILLBIRTH.Fetal Viability: The potential of the FETUS to survive outside the UTERUS after birth, natural or induced. Fetal viability depends largely on the FETAL ORGAN MATURITY, and environmental conditions.Uterus: The hollow thick-walled muscular organ in the female PELVIS. It consists of the fundus (the body) which is the site of EMBRYO IMPLANTATION and FETAL DEVELOPMENT. Beyond the isthmus at the perineal end of fundus, is CERVIX UTERI (the neck) opening into VAGINA. Beyond the isthmi at the upper abdominal end of fundus, are the FALLOPIAN TUBES.Weight Gain: Increase in BODY WEIGHT over existing weight.Animal Nutritional Physiological Phenomena: Nutritional physiology of animals.Estrus: The period in the ESTROUS CYCLE associated with maximum sexual receptivity and fertility in non-primate female mammals.Organ Size: The measurement of an organ in volume, mass, or heaviness.Milk: The white liquid secreted by the mammary glands. It contains proteins, sugar, lipids, vitamins, and minerals.Embryonic and Fetal Development: Morphological and physiological development of EMBRYOS or FETUSES.Animal Population Groups: Animals grouped according to ecological, morphological or genetic populations.Models, Genetic: Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.Eating: The consumption of edible substances.Sexual Maturation: Achievement of full sexual capacity in animals and in humans.Arvicolinae: A subfamily of MURIDAE found nearly world-wide and consisting of about 20 genera. Voles, lemmings, and muskrats are members.Inbreeding: The mating of plants or non-human animals which are closely related genetically.Quantitative Trait, Heritable: A characteristic showing quantitative inheritance such as SKIN PIGMENTATION in humans. (From A Dictionary of Genetics, 4th ed)Sus scrofa: A species of SWINE, in the family Suidae, comprising a number of subspecies including the domestic pig Sus scrofa domestica.Fetal Resorption: The disintegration and assimilation of the dead FETUS in the UTERUS at any stage after the completion of organogenesis which, in humans, is after the 9th week of GESTATION. It does not include embryo resorption (see EMBRYO LOSS).Insemination, Artificial: Artificial introduction of SEMEN or SPERMATOZOA into the VAGINA to facilitate FERTILIZATION.Random Allocation: A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects.Carnivory: The consumption of animal flesh.Housing, AnimalAnimal Feed: Foodstuff used especially for domestic and laboratory animals, or livestock.Scrotum: A cutaneous pouch of skin containing the testicles and spermatic cords.Overnutrition: An imbalanced NUTRITIONAL STATUS resulting from excessive intake of nutrients. Generally, overnutrition generates an energy imbalance between food consumption and energy expenditure leading to disorders such as OBESITY.Dicamba: A chlorinated organic herbicide.Trenbolone Acetate: An anabolic steroid used mainly as an anabolic agent in veterinary practice.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Vaccines, Contraceptive: Vaccines or candidate vaccines used to prevent conception.Parturition: The process of giving birth to one or more offspring.Stillbirth: The event that a FETUS is born dead or stillborn.Fetus: The unborn young of a viviparous mammal, in the postembryonic period, after the major structures have been outlined. In humans, the unborn young from the end of the eighth week after CONCEPTION until BIRTH, as distinguished from the earlier EMBRYO, MAMMALIAN.Embryo Implantation: Endometrial implantation of EMBRYO, MAMMALIAN at the BLASTOCYST stage.Viviparity, Nonmammalian: The capability of bearing live young (rather than eggs) in nonmammalian species. Some species of REPTILES and FISHES exhibit this.Body Composition: The relative amounts of various components in the body, such as percentage of body fat.Estrus Detection: Methods for recognizing the state of ESTRUS.Seasons: Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Quadruplets: Four individuals derived from four FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.Fetal Development: Morphological and physiological development of FETUSES.Placenta: A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (CHORIONIC VILLI) derived from TROPHOBLASTS and a maternal portion (DECIDUA) derived from the uterine ENDOMETRIUM. The placenta produces an array of steroid, protein and peptide hormones (PLACENTAL HORMONES).Ovulation Inhibition: Blocking the process leading to OVULATION. Various factors are known to inhibit ovulation, such as neuroendocrine, psychological, and pharmacological agents.Maternal Behavior: The behavior patterns associated with or characteristic of a mother.