PorkNet Papers Collection
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The key to establishing nutrient requirements for lactating sows is not limited to maximizing milk yield for nursing pigs, but extends also to maintaining optimum body condition for the subsequent parities (Noblet et al., 1990; Pettigrew et al., 1992a; 1992b; NRC, 1998).
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Milk is a pivotal factor in piglet survival, growth, development, and pre-weaning piglet body composition. The demonstration that heavier weaning piglets attain market weight faster than lighter weaning piglets (Mahan and Lepine, 1991) has sparked increasing interest in exploiting the lactation period to enhance overall piglet growth and pork production. With increasing desire for piglets that grow at a faster rate and attain greater lean mass deposition, tailoring milk quantities and milk composition to optimize these traits would be of great value to the swine producer.
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Mammary gland involution in sows after weaning is an important part of the normal cycle of mammary growth, lactation, and involution. The process of mammary gland involution is initiated at cessation of milk removal, which results in regression of lactation function. In swine, cessation of milk removal occurs the day the piglets are weaned. The act of weaning initiates a process of active tissue involution that involves both functional and structural changes in the mammary gland. Mammary gland involution often is characterized by substantial histological changes in mammary tissue, changes in mammary gland secretions, and loss of lactating epithelial cells. There is a general lack of information available about the process of mammary gland involution in swine.
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At parturition, all mammary glands undergo lactogenesis and glands which are routinely suckled continue to grow (Kim et al., 1999). Piglets begin to develop a preference for specific teats within the first few hours after birth. Once teat order is established, mammary glands which are not regularly suckled begin regressing by a process of involution. Although not producing milk, non-suckled mammary glands may impact the physiology of the sow during lactation. The presence of non-suckled glands may affect the total amount of lactating mammary tissue which develops in suckled glands and, therefore, must be supported by the sow during lactation. Regression of the non-suckled glands should contribute to the pool of endogenous amino acids available for lactation, although the extent of this contribution is not known. In addition, the speed with which the non-suckled glands undergo involution and the type of tissue changes which occur during that involution will determine how long after parturition non-suckled glands may retain lactation function and be available for cross-fostering.
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Reproductive performance in swine is most related to inseminations occurring near the time of ovulation. This is due to the time-span for normal fertilization of eggs being limited by both the egg after the occurrence of ovulation (<12 h) and the sperm after insemination (<24 h). Therefore, the number of eggs that are fertilized, the percentage of normal embryos, the resulting pregnancy rates (Hunter and Dzuik, 1968, Soede et al., 1995), farrowing rates (Nissen et al., 1997), and litter size (Kemp and Soede, 1996; Rozeboom et al., 1996) are all related to time of insemination relative to ovulation. Insemination within 12 h before ovulation, appears to produce the most optimal pregnancy rates (>90%) and litter sizes (10.5-11, Kemp and Soede, 1996) but Nissen et al has observed that inseminations occurring from 28 h before to 4 h after ovulation result in high reproductive rates (Nissen et al., 1997). Unfortunately, the time of ovulation is difficult to predict since the only obvious marker for this event is the expression of standing estrus. Further, the time of ovulation varies between 24 to 60 h after onset of estrus (Soede et al., 1992). This high level of variation is important since insemination protocols are set from estrus, with inseminations typically occurring twice between 0 and 48 h. There appears to be a normal distribution for ovulation time after onset of estrus, with 20% of weaned sows ovulating by 24 h, 55% ovulating between 24 and 48 h, and 25% ovulating after 48 h (Knox et al., 1999a). It would appear then, that current insemination protocols may not fully account for the total variation in ovulation times within the breeding herd. This would help explain why average USA reproductive rates are less than optimal.
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The "wean-to-finish" production system is being advocated largely because of claims of improved animal performance and a reduction in labor needed for animal movement compared to conventional two- or three-stage systems. However, there has been little, if any, research carried out with this system and consequently limited research data are available to evaluate such claims or to provide an objective basis for developing the optimum design and management approach for a wean-to-finish system.
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Economics drive profitability in hog production units. Inputs such as buildings and equipment are the second leading expense behind feed costs. Hoop structures offer a low cost alternative form of swine housing, however, production levels must be evaluated in any new system.
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Pharmacologic levels of supplemental Zn are well established as growth promoters for newly weaned pigs. Feed-grade zinc oxide (ZnO) manufactured by the Waelz process dominates the feed-grade Zn market for pigs, and this source of ZnO also has been most heavily researched as a growth promotant for nursery pigs (Hahn and Baker, 1993; Hill et al., 1999; Mahan et al., 2000; Mavromichalis et al., 2000). Our research with chicks has demonstrated that Waelz ZnO (72% Zn) has a relative Zn bioavailability (RBV) of around 43% relative to analytical-grade ZnO (80.3% Zn). Another source of feed-grade ZnO is manufactured by the hydrosulfide process and contains about 78% Zn. Our research has shown that the RBV of Zn in this product is somewhat higher than that in analytical-grade ZnO (Edwards and Baker, 1999).
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The efficacy of supplemental microbial phytase for improving phytate-phosphorus (P) utilization has been investigated extensively, and phytase has been shown to consistently improve phytate-P utilization in both swine and poultry (Simons et al., 1990; Cromwell et al., 1993; Biehl et al., 1995). Improved utilization of dietary phytate-P caused by phytase supplementation offers producers a viable means of reducing inorganic P supplementation, and it also effectively reduces P excretion. Concerns pertaining to nitrogen (N) pollution present another environmental challenge facing swine producers, and microbial phytase may have a role in the liberation and utilization of phytate-bound amino acids. Phytase addition to swine and poultry diets, therefore, may improve not only the utilization of dietary phytate-P but also protein, although research dealing with the latter is inconsistent and controversial (Kornegay, 1996; Kornegay et al., 1998a; 1998b; Ravindran et al., 1999; Boling et al., 1999; Zhang et al., 1999; Peter et al., 2000). Phytase-mediated responses in protein digestibility, if any, are of lower magnitude than responses in phytate-P utilization, and the potential improvements have seldom manifested in improved growth performance. The ability of phytase to not only liberate phytate-bound P, but also improve protein-amino acid utilization would provide swine and poultry producers a means to further aid in the alleviation of social and environmental concerns presently encompassing large-scale livestock production. In addition to reductions in inorganic P supplementation, phytase-mediated increases in protein-amino acid utilization would also enable producers to feed lower-protein diets and reduce N excretion, thereby creating both economic and environmental advantages.
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Signature-tagged mutagenesis is a functional genomics approach to identify bacterial virulence genes by simultaneously screening multiple mutants in a single host animal. Avirulent (attenuated) mutants are identified by negative selection (failure to colonize the host). The method was recently developed to investigate Salmonella typhimurium in a mouse model of human typhoid fever. We modified the protocol to investigate virulence genes of S. choleraesuis in its natural host, the pig. First, we generated random, knock-out (null) mutations in S. choleraesuis using transposon-mediated insertion of unique, signature-tagged (40 bp), kanamycin resistance cassettes. To validate the modified protocol, a test pool of 45 mutants was inoculated orally or intraperitoneally (systemic infection) into pigs. Three of the mutants were not identified from cultures of the mesenteric lymph nodes obtained four days after infection. Attenuation of these three candidate attenuated mutants was confirmed by mixed challenge growth experiments (growth of a 1:1 mixture of mutant and wild type S. choleraesuis) in broth cultures and in pigs. All three mutants were attenuated for infection of pigs as the mutants were at a marked disadvantage relative to the wild type bacteria for growth. For one mutant, the competitive indices (ratios of mutant to wild type bacteria) were 0.15 and 0.03 for bacteria in the intestines and mesenteric lymph nodes, respectively; for the other two mutants, the indices were about 0.001 in either tissue. In contrast, none of the mutants were at a growth disadvantage in broth cultures. As an additional control, two random mutants recovered from the pigs inoculated with the pool (and therefore not candidates for attenuation) were also tested in the mixed challenge experiments. As expected, the competitive growths of these mutants in culture medium and in pigs were similar to that of the wild type. In one of the three attenuated mutants the inactivated gene has been identified, after cloning and sequencing, as hilA . In mouse models of S. typhimurium infection, hilA is associated with enteric invasion, but not systemic proliferation. Because the hilA mutant failed to colonize pigs irrespective of oral or systemic inoculation, its function in pigs is likely to be more complex than in the mouse. Our data show signature-tagged mutagenesis can be used to identify Salmonella genes associated with virulence in pigs. As we continue screening mutants, we expect to identify novel genes related to pathogenicity and we are expanding our studies to include S. typhimurium.
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There has been limited research carried out on the effects of environmental factors such as group size and crowding on carcass and meat quality characteristics in pigs. A number of studies investigating the effects of rearing environment on carcass and meat quality traits have compared outdoor versus indoor rearing systems and have shown variable results. Pigs reared outdoors have been reported to have darker meat color and no difference in ultimate pH when compared to confinement reared pigs (Wariss et al., 1983). Enfalt et al. (1996) showed that pigs reared in confinement had higher ultimate pH and marbling and lower drip loss than pigs reared outdoors. Other studies have shown no effect of rearing environment on these traits (van der Wal et al., 1993).
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Late finishing swine (n = 408) with an average initial weight of 84 kg were used to evaluate the effects of supplementing microbial phytase to corn-soybean meal diets in which sources of supplemental inorganic phosphorus (P), zinc (Zn), copper (Cu), and manganese (Mn) were removed. The dietary treatments employed were: A) positive control which included a standard trace-mineral premix and inorganic P supplementation (0.16% available P, 0.46% Ca); B) negative control in which a trace-mineral premix without Zn, Cu, and Mn was fed, and no inorganic P was added (0.06% available P, 0.46% Ca); and the negative-control diet supplemented with either C) 300 U/kg microbial phytase; or D) 500 U/kg microbial phytase. With the exception of available P, Zn, Mn and Cu, diets were formulated to meet or exceed NRC (1998) nutrient recommendations for late-finishing pigs. Each supplementation regimen was fed to six pens of 17 pigs (triplicate replicates of both of barrows and gilts) from 84 to 123 kg body weight. Reducing inorganic P and selected trace minerals, or the addition of either 300 or 500 U/kg phytase to the negative control diet did not affect (P > 0.10) weight gain, feed intake, or feed efficiency (gain/feed). Moreover, carcass characteristics were not affected (P > 0.10) by any of the supplementation strategies employed in this experiment. Metacarpal III and IV bone ash (g), however, was reduced (P < 0.05) for pigs fed the negative control diet compared to the fully-supplemented positive-control diet and the diets containing added phytase. These data indicate that supplemental levels of inorganic P, Zn, Cu, and Mn can be reduced or eliminated without deleteriously affecting growth performance and carcass characteristics of late-finishing swine.
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There have been numerous studies reporting the differences in performance levels and carcass characteristics between contrasting breeds and lines of pigs. Additionally, there is also a body of literature reporting that increased group size and reduced floor space allowance (crowding) results in reduced feed intakes and growth rates (Edmonds et al., 1998; Hyun et al., 1998). It is well known that the animal's environment dictates the level to which it will express its genetic potential. Thus, the concept of genotype × environmental interactions (G × E) becomes important. Merks (1986), defined a G × E as a change in the relative performance of two or more genotypes measured in two or more environments. Several researchers have shown that genotype × environmental interactions may exist in swine populations (Bidanel and Ducos, 1996; Merks, 1989). As commercial producers continue to try new techniques to increase the efficient use of their facilities such as large group sizes and increased stocking densities, the presence of genotype × environmental interactions may become more important. The objective of this study was to investigate the interaction between genetic growth potential and rearing environment.
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Soybean meal is a major protein source for swine and other monogastric animals. However, soybeans, like other legume seeds, contain anti-nutritional factors. Scientists have been successful in eliminating the principle growth inhibitors in soybeans through physical and chemical processing. However, galactosyl oligosaccharides, i.e., -galactosides and -galactomannan, known as flatulence-producing factors are still present in soybean meal produced by conventional processes (Rackis, 1981). The content of -galactosides (raffinose, 1.0% and stachyose, 4.6%) and -galactomannan (1.2%) is relatively high in soybean meals and these -galactosides and -galactomannan are not digestible by pigs and other monogastric animals because of the lack of nzymes that target -1,6- and -1,4-galactosyl bonds. Consequently, the levels of indigestible galactosyl oligosaccharides are negatively related to energy and protein digestibility and growth in swine (Veldman et al., 1993; Gdala et al., 1997) and poultry (Coon et al., 1990).
