Lactocrine term is used to describe the milk borne bioactive factors (MbFs) that transfer from mother to offspring/s via lactation. The MbFs play significant role in providing immunity, survival, growth and development of new-born. Milk is not only a nutritive food for the young one but also possessing many bioactive molecules/ bioactive factors that enhance the growth and development of the internal organs. The mechanism by which these factors stimulate the neonatal organs is not fully known. The MbFs might act through receptor-system or through another compound.
The first secretion of mammary gland after birth is called colostrum, having high concentration of immunoglobulins, antibacterial compounds, proteins, fat and other bioactive compounds. It not only provides nutrition but also protection and survival in a new environment after birth. The nutritive colostrum having high amount of solid or macromolecules that have to absorb or uptake by the neonatal gut. There is a time limit window to uptake the macromolecules where the neonatal gut is permeable to macromolecules. This window is remained open up to 48 hours of birth but the rate of absorption in the neonatal gut might decrease as the hours increases after birth. Therefore, feeding of colostrum might be done as soon as possible i.e., before closure of gut permeability. The delay in colostrum feeding leads to short-term and long-term effect. The time and duration of colostrum feeding is very essential for healthy growth of new-born. The new-born prone to infection from surroundings. The delay or deprive in colostrum feeding impact the growth and development of neonatal life. The immunoglobulin in the milk is the passive immunity to the offspring for protection against the infection. Failure to nurse the neonate during gut uptake window leads to poor health condition. The few hours delay in colostrum feeding might affect the number of mammotrope pre-pubertally in the offsprings.
Maternal nourishment begins at the time of conception, throughout the gestation and also continue postnatally till weaned. The effect of maternal nourishment on development is great. The maternal care continues after birth. Maternal signals on the developing fetus, neonatal and postnatal life is essential for growth. Postnatal nourishment of mother via lactation have impact on the development of the reproductive performance of the offspring in their adulthood. Lactation is a significant part of neonatal development. The mother sends signalling molecules via lactation (lactocrine hypothesis) for the development and growth of reproductive tract so that her offspring become suitable productive animals in future. This is a great economic benefit to the farmers. More piglet more economic returns. The selection of a good genotype may not be always successful because the phenotype of an organism is not fixed by genotype. The several factors (environmental, nutrition, bioactive molecules) affect the phenotype of an individuals. Any non-genetic factors that affect the expression of genes is epigenetics. The epigenetics during fetal and postnatal life influence the phenotype of an animal. A single genotype produces many phenotypes.
It is necessary to consider (1) feeding of sufficient colostrum (2) quantity and quality of colostrum, (3) report of mastitis, lack of colostrum in the sow, etc without compromising the genetic selection for reproductive and productivity performances. Lactocrine hypothesis is important to consider for continuous productive performance of progenies. When we talk about production, the reproductive performance of animals comes to our mind. The reproduction is the backbone of production. The studied on porcine reproductive tract shown the significant impact of MbFs via lactation. The development of porcine uterine function and capacity are influenced by the MbFs. The communication of mother to offspring through signalling molecule via lactation is significant. When the piglet fed with milk replacer for two days from birth, the histology of uterus did not differ as compared to nursing piglets, but the endometrial thickening and glandular development is affected. The deprive of colostrum reduces the uterine capacity or fecundity (ability to produce more offspring’s). The female new-born piglet complete devoid of colostrum permanently impair reproductive capacity and performances. The postnatal effect of maternal lactocrine on the development of porcine uterus, endometrial functionality and capacity is essential for healthy pig, also economic benefit to the farmers. The factors affecting the lactation, quality of colostrum and its abundance and the consumption is really important consideration for the selection and the sustainability of productive performance.
The litter bearing species or prolific breed is that which give number of new-borns per litter. The litter size (number of piglets per litter) is depended upon the quality of egg (oocytes), successful ovulation, fertilization, conception, implantation and gestation. There is a close contact between the cells of embryo and uterine epithelium or uterine wall during attachment and peri-attachment. There is always a communication between the maternal uterus and the developmental fetus. It very important that the functionality of uterus should operate or co-operate properly during the peri-attachment of embryo, and during utero-development. The uterine functionality and capacity enhance the litter size as well as the live healthy piglet. The MbFs via lactation improves the function and the capacity of the uterus. The piglet deprives of colostrum shown to reduce litter size. The MbFs might influence the Fecundity which is an important parameter to be considered for piggery farming or breeding.
The sufficient and timely (0 day) feeding of colostrum provide sufficient transmission of immunoglobulin and other milk-born bioactive factors (MbFs) that might have a long-term beneficial effect on uterine growth, development, capacity and fecundity. Colostrum might be a uterotropic support during early developmental stage. The growth factors, steroid, peptide hormones and the immunoglobulins may act as MbFs. The metabolic hormones like leptin, ghrelin, adiponectin, glucocorticoids in the milk have significant impact on the development of the neonatal life. These hormones might act upon the tissue or have interact with some molecule and helps in development during neonatal life. The MbFs deficiency may cause increase adiposity, altered hypothalamic gene expression even the development of organs delays than normal.
Milk also contain small, non-coding micro RNAs (mi RNAs) which are enclosed in the exosomes that protects from degradation. This milk borne mi-RNAs believed to play role for the development of neonatal immune system. The maternal somatic cells also transfer from milk to neonate during nursing, cross the neonatal intestine, colonized in the neonatal tissue and influence the postnatal development by way of micro-chimerism. Based on this information we can say that the milk is not just a nutritive food but more than that.
Male reproduction (testis): Seroli cells and its number is important for the daily spermatozoa production in the testis. The number of Sertoli cells determined the rate of daily spermatozoa production. The increase of the spermatozoa production is needed for profitable animal production system. The Sertoli cell number established before puberty, these cells maintain the blood-testis-barrier. The number of Sertoli cell reported lower in piglet fed commercial milk-replacer for 2 days as compared to nursing piglet. It might have role in proliferation of Sertoli cells. The absent of relaxin i.e., lactocrine-null can alter the normal testicular development in nursing male piglets.
Relaxin: a prototypical lactocrine active factor
Relaxin, a neohormone is an example of MbFs that support the uterine growth and endometrial functionality. The immunoreactive relaxin is detected in the milk, as well as the biologically active prorelaxin also detected in the peripheral circulation of neonatal nursing piglet. The relaxin pass through the neonatal gut and then into the circulation, may does its function on the reproductive tract during neonatal life.
Relaxin have many known physiological roles, it is also known as hormones of pregnancy. The growth promoting effect of relaxin is demonstrated in neonatal piglets. The relaxin receptors are detected in the uterus and cervix tissue. The uterine glandular and luminal epithelial cell proliferation decreases in piglet with commercial milk replacer than nursing. The deprive of colostrum for the first 48 hours fail to recover uterine functionality or capacity. Similarly, the cervix shows reduction of the cervical crypt’s depths and the stromal cell proliferation as compared to the nursing.
The presence of higher insulin like growth factors in the milk is a potential lactocrine-active factors for the growth and development of reproductive tract.
Swine, a prolific animal provide livelihood to many farmers in India. Piggery is a profitable source of income if it manages scientifically and economically. Selection of good breed (genetic) is essential but managing their progenies for profitable outcome requires a scientific knowledge of non-genetic factors. The colostrum feeding is one of the factors, negligence and delays feeding of colostrum resulted in future consequences. Therefore, improvement of colostrum quality and availability is necessary for the new-born piglets.