后备母猪的营养与繁殖

后备母猪的繁殖能力关系到整个猪场的经济效益,其中营养水平和采食量在繁殖方面的影响不容忽视。本文简要叙述了有关营养在后备母猪各个阶段繁殖性能上的影响,以期为我国的养猪生产实践提供一定的帮助。     

Effects of deficiency and surplus dietary threonine on reproductive performance of primiparous pregnant gilts

Dietary threonine imbalance is known to impair reproductive performances of gestating sows, but the underlying mechanisms are largely unknown. In this study, effects of deficiency and surplus dietary threonine during gestation on reproductive performance, serum metabolites and hormones concentration, and colostral nutrient and immunoglobulin contents of primiparous sows were investigated. Ninety primiparous pregnant gilts were assigned to one of the three dietary treatments with different standardized ileal digestible threonine/lysine ratios at 0.59, 0.72 and 0.85, which represented deficient (DT), adequate (AT) and surplus (ST) dietary threonine concentration respectively. Maternal body weight gain from day 80–110 of gestation was highest (p < .05) for gilts fed AT than for gilts fed DT or ST. On days 30 and 110, serum threonine concentration increases in a dose‐dependent manner with the increasing of dietary threonine concentration in (p < .01), serum urea nitrogen concentration was lower (p < .01) in gilts fed AT than DT or ST, and serum insulin‐like growth factor‐I (IGF‐I) was lowest (p < .05) for gilts fed DT. On day 110, gilts fed AT had lower serum progesterone concentration but higher concentrations of serum prolactin (p < .05) compared to DT and ST. Concentration of colostral immunoglobulin A and G from gilts fed DT was lower (p < .05) compared with gilts fed AT or ST. In conclusion, gilts with the adequate threonine intake were more able to conserve dietary amino acids to support foetal and maternal tissue gain. Deficient or ST threonine intake may induce a delay in changes in progesterone and prolactin concentrations during the prepartum period impeding the transition from pregnancy to lactation.     

Behavior, preference for, and use of alfalfa, tall fescue, white clover, and buffalograss by pregnant gilts in an outdoor production system

Sustainable outdoor pig production requires vegetation that can maintain ground cover, assimilate manure nutrients, and prevent soil erosion. Two experiments were conducted to evaluate the suitability of four forages: alfalfa (Medicago sativa), tall fescue (Festuca arundinacea), white clover (Trifolium repens), and buffalograss (Buchloe dactyloides) for grazing or ground cover in pastures for pigs. Each forage plot covered 7.5 m2, with nine replicates in a randomized block design. In Exp. 1, eight pregnant gilts had free access to all forages during a 2-d adjustment period. Immediately thereafter, pairs of gilts were assigned randomly to one of each of four blocks of the four forages during a 2-d measurement period. The percentage of ground cover for each forage was visually estimated at 0, 24, and 48 h of study. Behavioral data, including walking, eating, grazing, rooting, drinking, standing, lying, and time spent in hut were video-monitored continuously for 48 h. Initial percentage of ground cover was 100% for all species. By 48 h, percentage of ground cover decreased (P < 0.001) for white clover (11.3 +/- 0.88%) and alfalfa (36.3 +/- 0.88%), but not for tall fescue (98.0 +/- 0.88%) or buffalograss (98.0 +/- 0.88%). Gilts spent more (P < 0.01) time grazing white clover (16.3 +/- 1.97 min/d) and alfalfa (11.2 +/- 1.97) than tall fescue (0.8 +/- 1.97) or buffalograss (0.3 +/- 1.97), and rooted more (P < 0.04) white clover than other forages. In Exp. 2, six gilts from the initial group were put on six blocks of the four forages. Each gilt was assigned randomly to three replicates of each forage, including alfalfa, tall fescue, or buffalograss (white clover was excluded because of damage by gilts during Exp. 1), and gilts grazed single forages for 2 d. After this grazing period, the percentage of ground cover was less (P < 0.01) for alfalfa than for buffalograss or tall fescue (37.5 +/- 0.38, 96.7 +/- 0.39, 96.3 +/- 0.39%, respectively). With access to a single forage, pregnant gilts spent more (P < 0.01) time grazing alfalfa (15.8 +/- 2.36 min/d) than buffalograss (1.5 +/- 2.36) or tall fescue (0.7 +/- 2.37). These gilts clearly preferred grazing white clover and alfalfa, and rooting and eating white clover compared with buffalograss or tall fescue. Rates of ground cover loss were less (P < 0.01) for tall fescue and buffalograss than for the more preferred forages. Less preferred forages could have potential as pasture for swine when the primary objective is ground cover maintenance rather than nutrient supply.     

Level of dietary energy during prepubertal growth and reproductive development of gilts.

Development of gilts that conceive early and continue to produce offspring is a primary objective of swine production. The objective of this study was to determine the degree of feed restriction during development required to optimize reproductive performance and efficiency in gilts. The effects that various patterns of growth had on reproductive development and performance of gilts through d 30 of gestation were investigated. At 13 wk of age and 41 kg BW, 192 white crossbred gilts were penned individually and assigned to receive 87.5%, 75%, 62.5%, and 50% of predicted ad libitum energy intake. The study was replicated in two seasons. At 25 wk of age, gilts were moved to group pens and allowed ad libitum access to feed, and estrous detection was initiated. Gilts were inseminated at first observed estrus and those recycling were remated. Post-mating gilts were fed 1.5x maintenance in stalls. Gilts that did not return to estrus 17 to 30 d after mating were slaughtered at 30 d of gestation. Reproductive tracts were collected and numbers of corpora lutea and live embryos were recorded. Feed restriction during development resulted in differences in BW and backfat thickness at the start of the breeding period and differences in feed intake during breeding. Gilts subjected to the greatest feed restriction during development consumed the greatest quantity of feed during breeding. Feed intake during breeding was associated with BW and backfat gain during breeding. The treatment group that entered breeding lightest and leanest (50% of predicted ad libitum intake) had the least number of days to first estrus, followed by the fattest, heaviest group (87.5% of predicted ad libitum intake). Treatment groups did not differ (P > 0.38) in ovulation rate or live embryo numbers. Significant relationships between quantity of GE consumed during development and variables considered important in reproductive development and performance were evident, such as BW and fatness at start of breeding and first detected estrus, and ovulation rate. Variation in dietary energy during the development period impacted many aspects of reproductive development and performance. However, coupling restricted energy intake during development with ad libitum intake during breeding negated many of the effects of feed restriction during the development period.     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

Safety and efficacy of vaccination of pregnant gilts against porcine reproductive and respiratory syndrome.

OBJECTIVE: To determine the safety and efficacy of vaccination of pregnant gilts with an attenuated strain of porcine reproductive and respiratory syndrome virus (PRRSV). ANIMALS: 16 pregnant gilts. PROCEDURE: Pregnant gilts free of antibodies for PRRSV were assigned (4 gilts/group) to the following groups: group I, untreated controls; group II, vaccinated on day 60 of gestation; group III, vaccinated on day 60 of gestation and exposed to virulent PRRSV on day 90 of gestation; and group IV, exposed to virulent PRRSV on day 90 of gestation. Safety and efficacy of vaccination was evaluated by group comparisons of prenatal and postnatal survival of fetuses and pigs, respectively, and by the condition and rate of weight gain of liveborn pigs. RESULTS: Collective (prenatal and postnatal) death losses up to day 15 after farrowing (conclusion of study) were similar for groups I (7/47, 14.9%) and II (7/44, 16.9%) but were greater for group III (18/49, 36.7%) and were greater still for group IV (23/37, 62.2%). Mean body weight 15 days after farrowing was greatest for pigs in litters of group I (4.46 kg) and progressively less for the other groups (3.87, 3.76, and 2.18 kg for groups II, III, and IV, respectively). CONCLUSIONS: Using these conditions, vaccination of gilts during midgestation appeared to be safe. However, it provided only partial protection against subsequent exposure to virulent virus. CLINICAL RELEVANCE: Attenuated-PRRSV vaccines may have to be administered to naive gilts > 30 days before conception to provide maximum protection throughout gestation.     

Expression of the uterine Mx protein in cyclic and pregnant cows,gilts, and mares

Pregnancy and interferon-tau (IFN tau) upregulate uterine Mx gene expression in ewes; however, the only known role for Mx is in the immune response to viral infection. We hypothesize that Mx functions as a conceptus-induced component of the anti-luteolytic mechanism and/or regulator of endometrial secretion or uterine remodeling during early pregnancy. This study was conducted to determine the effects of early pregnancy on uterine Mx expression in domestic farm species with varied mechanisms of pregnancy recognition. Endometrium from cows, gilts, and mares was collected during the first 20 d of the estrous cycle or pregnancy, and total messenger RNA (mRNA) and protein were analyzed for steady-state levels of Mx mRNA and protein. Northern blot analysis of Mx mRNA detected an approximately 2.5 Kb of mRNA in endometrium from each species. In pregnant cows, steady-state levels of Mx mRNA increased 10-fold (P < 0.05) above levels observed in cyclic cows by d 15 to 18. In cyclic gilts, slot blot analysis indicated that endometrial Mx mRNA levels did not change between d 5 and 18 of the cycle. However, in pregnant gilts, Mx levels tended (P = 0.06) to be elevated two-fold on d 16 only, and in situ hybridization indicated that this increase occurred in the stroma. In mares, Mx mRNA was low, but detectable, and did not change between ovulation (d 0) and d 20, regardless of reproductive status. Western blot analysis revealed multiple immunoreactive Mx protein bands in each species. One band was specific to pregnancy in cows. As in ewes, in situ hybridization analysis indicated that Mx mRNA was strongly expressed in the luminal epithelium, stroma, and myometrium by d 18 in cows. However, on d 14 in gilts, Mx was expressed primarily in the stroma, and on d 14 in mares, low levels of Mx expression were confined largely to the luminal epithelium. The uteruses of cows, gilts, and mares express Mx, and expression is upregulated during pregnancy in cows and gilts--animals whose conceptuses secrete interferons during early pregnancy, but that possess different mechanisms for pregnancy recognition.     

Porcine parvovirus: propagation in microcarrier cell culture and immunogenic evaluation in pregnant gilts

Porcine parvovirus was propagated in PK-15 cells cultured in roller bottles or on microcarrier beads. After inactivation, the virus was used as antigen in the preparation of vaccines. The immunogenic potency and safety of the vaccines were evaluated in specific pathogen free pregnant gilts and guinea pigs. Experimental challenge tests determined the efficacy of the vaccine in preventing porcine parvovirus transplacental infection. Neither viral antigens nor specific antibodies were detected in fetuses from vaccinated gilts. In contrast, fetal death and, or, mummification occurred when unvaccinated gilts were infected. Both virus and, or, antibodies were also detected in fetuses from these unvaccinated gilts. Serum conversion after vaccination was assayed by microserum neutralisation using guinea pig erythrocytes as cell indicators and by haemagglutination inhibition tests. Viral antigens in fetal tissues were detected using ELISA, the immunobeads technique, the haemagglutination test and by virus isolation.     

Evaluation of the uterine environment and embryos of prepubertal gilts

A series of three experiments was conducted to test the functional status of the uterus and embryos in prepubertal gilts. In Exp. 1, gilts were induced to ovulate by treating with gonadotropins followed by hCG 72 or 96 h later, and were artificially inseminated 24 h after hCG. Five of the 10 gilts treated at 120 d of age, but none of the gilts treated at 100 of age, maintained pregnancies. We next tested the function of the uterine environment by transferring embryos from postpubertal females into gilts of various ages that had been induced to ovulate but not inseminated (Exp. 2). Pregnancy rate at d 50 of gestation was 44% (4/9) for 100-d-old recipients, 67% (2/3) for 140-d-old recipients, and 60% (3/5) for postpubertal recipients (P > 0.20). Therefore, uteri of 100-d-old gilts are able to maintain pregnancies with conceptuses from postpubertal gilts. In Exp. 3, embryos from 100-d-old and postpubertal gilts were transferred into postpubertal recipients. Uterine horns of recipients were surgically separated before transfer, and embryos from 100-d-old and post-pubertal females were transferred to opposite horns of some recipients (experimental). Other recipients received embryos from postpubertal females in both uterine horns (control). When examined on d 50 to 60 of gestation, three of five control gilts were pregnant and three of seven experimental gilts were pregnant (P > 0.50). In experimental recipients, the survival of embryos from 100-d-old gilts was 38% (8/21) compared to 57% (15/26) for embryos from postpubertal gilts (P > 0.30). Because all uterine horns of pregnant recipients contained fetuses, these results support the hypothesis that embryos from 100-d-old gilts are able to initiate and maintain pregnancies in the uteri of postpubertal gilts. Therefore, the uterine environment of 100-d-old gilts provides an environment that supports development of embryos produced by postpubertal gilts, and the embryos produced by 100-d-old gilts can survive and develop in the uteri of postpubertal gilts. It was only the combination of embryos and uteri of 100-d-old gilts that did not permit pregnancy to be maintained.     

The effects of dietary fat or fiber addition on energy and nitrogen digestibility in lactating, primiparous sows housed in a warm or hot environment

Thirty primiparous sows were individually penned in a thermoneutral (20 degrees C) or hyperthermal (32 degrees C) environment and fed a high-starch (corn-soybean meal basal), high-fiber (48.5% wheat bran) or high-fat (10.6% choice white grease) diet from d 100 of gestation through a 22-d lactation to determine the effects of thermal environment and dietary energy source on energy and N digestibility in lactating sows. Voluntary feed intake and total feces and urine output were determined from d 12 through d 14 postpartum. Heat exposure (32 degrees C) depressed (P less than .05) voluntary feed, ME and N intake and lowered (P less than .05) apparent daily N retention. Heat exposure did not alter (P greater than .15) digestibility, expressed as percentage of intake, of dietary energy or N. Dietary additions of wheat bran depressed (P less than .05) the proportion of gross energy retained as ME by 12 and 14 percentage units and the apparent digestibility of N by 2.5 and 4.5 percentage units at 20 and 32 degrees C, respectively, compared with those of the basal diet. Dietary additions of choice white grease did not alter (P greater than .15) energy digestibility but increased (P less than .05) the proportion of N digested and retained in both environments. Apparent ME of the wheat bran, corn-soybean meal mix and choice white grease (determined by difference) was 2.72, 3.70 and 8.43 Mcal/kg DM and was independent of thermal environment. Digestibility of fibrous and starchy feedstuffs was similar in lactating sows and growing pigs allowed to consume feed ad libitum, whereas fat was more digestible in the sows.     

Experimental reproduction of swine infertility and respiratory syndrome in pregnant sows.

The purpose of this study was to experimentally reproduce swine infertility and respiratory syndrome (SIRS). Six multiparous sows were intranasally inoculated at 93 days of gestation with lung homogenates from clinically affected pigs, and 3 additional sows were similarly inoculated with a virus isolated in cell culture from the lung homogenate (SIRS virus, isolate ATCC VR-2332). Inoculated sows developed transient anorexia, farrowed up to 7 days prematurely, and delivered a mean of 5.8 live pigs and 6.0 dead fetuses/litter. Clinical signs of disease were not observed in 3 sham-inoculated control sows that delivered a mean of 12.7 live pigs and 0.3 stillborn fetuses/litter. The SIRS virus was isolated from 50 of 76 live-born and stillborn fetuses from the 9 infected litters. Virus was not isolated from 26 autolyzed fetuses or 15 control pigs. Six of 9 inoculated sows developed neutralizing antibodies to SIRS virus. The reproductive effects found in these experiments were identical to those found in field cases. On the basis of our findings, virus isolate ATCC VR-2332 causes the reproductive failure associated with SIRS.     

Genetic and environmental effects on carcass characteristics of Southdown x Romney lambs: I. Growth rate, sex, and rearing effects

Carcass data from more than 4,400 Southdown x Romney ewe and wether lambs collected over a 16-yr period were analyzed for the effects of sex, rearing status, and growth rate. Ewe lambs grew more slowly than wethers and had .78 kg less carcass weight at the same age. The carcass weight advantage for wethers was nearly all caused by heavier fat-free weight. Based on fat depths, the fat on ewe lambs was distributed in more anterior and ventral parts of the carcass relative to wether lambs. Lambs reared as twins had 1.73 kg less carcass weight and correspondingly reduced carcass measurements compared with lambs reared as singles. Sex and rearing status interacted for some traits. However, in no case was a significant sex difference reversed in single- and twin-related lambs. Growth rate effects were determined by regressing average change in carcass measurements on average carcass weight gain over a 5-wk period. When carcass weight remained constant over a 5-wk period, fat weight increased by .12 kg, fat-free weight and muscle measurements decreased, and bone lengths increased. For each kilogram of increase in 5-wk carcass weight gain, the marginal increase in fat weight was .41 kg and that of fat-free weight was .59 kg. At the average 5-wk carcass weight gain of 1.4 kg, fat and fat-free gains were As carcass weight gain increased above 1.4 kg, fat-free gain exceeded fat gain.