Current strategies for reproductive management of gilts and sows in North America.

Many advances in genetic selection, nutrition, housing and disease control have been incorporated into modern pork production since the 1950s resulting in highly prolific females and practices and technologies, which significantly increased efficiency of reproduction in the breeding herd. The objective of this manuscript is to review the literature and current industry practices employed for reproductive management. In particular the authors focus on assisted reproduction technologies and their application for enhanced productivity. Modern maternal line genotypes have lower appetites and exceptional lean growth potential compared to females of 20 yr ago. Thus, nutrient requirements and management techniques and technologies, which affect gilt development and sow longevity, require continuous updating. Failure to detect estrus accurately has the greatest impact on farrowing rate and litter size. Yet, even accurate estrus detection will not compensate for the variability in the interval between onset of estrus and actual time of ovulation. However, administration of GnRH analogs in weaned sows and in gilts after withdrawal of altrenogest do overcome this variability and thereby synchronize ovulation, which makes fixed-time AI practical. Seasonal infertility, mediated by temperature and photoperiod, is a persistent problem. Training workers in the art of stockmanship is of increasing importance as consumers become more interested in humane animal care. Altrenogest, is used to synchronize the estrous cycle of gilts, to prolong gestation for 2-3 d to synchronize farrowing and to postpone post-weaning estrus. P.G. 600® is used for induction of estrus in pre-pubertal gilts and as a treatment to overcome seasonal anestrous. Sperm cell numbers/dose of semen is significantly less for post cervical AI than for cervical AI. Real-time ultrasonography is used to determine pregnancy during wk 3-5. PGF2α effectively induces farrowing when administered within two d of normal gestation length. Ovulation synchronization, single fixed-time AI and induced parturition may lead to farrowing synchronization, which facilitates supervision and reduces stillbirths and piglet mortality. Attendance and assistance at farrowing is important especially to ensure adequate colostrum consumption by piglets immediately after birth. New performance terminologies are presented.

The role of neuropeptide Y and interaction with leptin in regulating feed intake and luteinizing hormone and growth hormone secretion in the pig.

Two experiments (EXP) were conducted in ovariectomized prepubertal gilts to test the hypothesis that neuropeptide Y (NPY) stimulates appetite and modulates LH and GH secretion, and that leptin modifies such acute effects of NPY on feeding behavior and LH and GH secretion. In EXP I, gilts received intracerebroventricular (ICV) injections of 0.9% saline (saline; n = 6), or 10 microg (n = 7), 50 microg (n = 5) or 100 microg (n = 7) NPY in saline and blood samples were collected. In EXP II, gilts received ICV injections of S (n = 4), or 50 microg leptin (n = 4), or 100 microg NPY (n = 4) or 100 microg NPY +50 microg leptin (n = 4) in saline, and feed intake was measured at 4, 20 and 44 h after feed presentation and blood samples collected. In EXP I, NPY suppressed LH secretion and the 100 microg dose stimulated GH secretion. In EXP II, NPY reversed the inhibitory effect of leptin on feed intake and suppressed LH secretion, but serum GH concentrations were unaffected. These results support the hypothesis that NPY modulates feed intake, and LH and GH secretion and may serve as a neural link between metabolic state and the reproductive and growth axis in the pig.

Perspectives for artificial insemination and genomics to improve global swine populations.

Civilizations throughout the world continue to depend on pig meat as an important food source. Approximately 40% of the red meat consumed annually worldwide (94 million metric tons) is pig meat. Pig numbers (940 million) and consumption have increased consistent with the increasing world population (FAO 2002). In the past 50 years, research guided genetic selection and nutrition programs have had a major impact on improving carcass composition and efficiency of production in swine. The use of artificial insemination (AI) in Europe has also had a major impact on pig improvement in the past 35 years and more recently in the USA. Several scientific advances in gamete physiology and/or manipulation have been successfully utilized while others are just beginning to be applied at the production level. Semen extenders that permit the use of fresh semen for more than 5 days post-collection are largely responsible for the success of AI in pigs worldwide. Transfer of the best genetics has been enabled by use of AI with fresh semen, and to some extent, by use of AI with frozen semen over the past 25 years. Sexed semen, now a reality, has the potential for increasing the rate of genetic progress in AI programs when used in conjunction with newly developed low sperm number insemination technology. Embryo cryopreservation provides opportunities for international transport of maternal germplasm worldwide; non-surgical transfer of viable embryos in practice is nearing reality. While production of transgenic animals has been successful, the low level of efficiency in producing these animals and lack of information on multigene interactions limit the use of the technology in applied production systems. Technologies based on research in functional genomics, proteomics and cloning have significant potential, but considerable research effort will be required before they can be utilized for AI in pig production. In the past 15 years, there has been a coordinated worldwide scientific effort to develop the genetic linkage map of the pig with the goal of identifying pigs with genetic alleles that result in improved growth rate, carcass quality, and reproductive performance. Molecular genetic tests have been developed to select pigs with improved traits such as removal of the porcine stress (RYR1) syndrome, and selection for specific estrogen receptor (ESR) alleles. Less progress has been made in developing routine tests related to diseases. Major research in genomics is being pursued to improve the efficiency of selection for healthier pigs with disease resistance properties. The sequencing of the genome of the pig to identify new genes and unique regulatory elements holds great promise to provide new information that can be used in pig production. AI, in vitro embryo production and embryo transfer will be the preferred means of implementing these new technologies to enhance efficiency of pig production in the future.

Concentration of neuropeptide Y, galanin, &bgr;-endorphin, vasoactive intestinal peptide and gonadotropin releasing hormone in the hypothalamus of gilts during the estrous cycle.

Numerous reports indicate that peptides isolated from the brain such as beta-endorphin (beta-END), neuropeptide Y (NPY), galanin (GAL) or vasoactive intestinal peptide (VIP), modulate secretion of gonadotropins and prolactin. The objective of the present experiment was to determine concentrations of NPY, GAL, beta-END, VIP and GnRH in the preoptic area (POA), medial basal hypothalamus (MBH) and pituitary stalk-median eminence (SME) during the estrous cycle in the pig. Gilts were slaughtered on Days 5, 10, 15 and 20 of the estrous cycle. Blood samples for analyses of progesterone were taken before slaughter. Neuropeptide concentrations in brain tissues were determined using RIA. The highest concentrations of all determined peptides occurred in SME. GnRH concentration in MBH was lower (p<0.05) in POA and SME on Day 20 than on Day 5. NPY concentration in POA was 5-6 times greater (p<0.05) on Days 10 and 20 than on Day 5. Similarly, concentrations of VIP in POA were greater (p<0.05) on Day 10, Day 15 and Day 20 than on Day 5. The concentration of GAL in POA was higher on Days 10 and 15 (p<0.05) than on Days 5 and 20. The concentration of GAL in SME was lowest on Day 5 and then significantly increased on Days 10, 15 and 20. In SME, concentration of beta-END increased 10 times on Days 15 and 20 when compared to Day 5 of the cycle. The correlation between concentration of GAL in the POA and MBH and progesterone concentration in the peripheral blood was positive, whereas this correlation associated with the SME was negative. These results indicate that considerable changes in various neuropeptide concentrations in different areas of the porcine hypothalamus are associated with stage of the estrous cycle and that GAL may be involved in control of the preovulatory LH surge in pigs.