Dietary protein restriction during lactation in primiparous sows with different live weights at farrowing: I. Consequences on sow metabolic status and litter growth

The hypothesis that the restriction of dietary protein during lactation has different impacts on sow metabolic status and milk production according to body weight was evaluated. From 5-months of age until farrowing, the gilts were fed to achieve body weights of 180 or 240 kg at farrowing. At this time, 38 sows were assigned to one of three groups: " 180 kg" sows not restricted in dietary protein during lactation (180CP); "180 kg" restricted in protein (180LP), or "240 kg" sows restricted in protein (240LP). Catheters were fitted in the jugular vein of 24 sows and serial blood samples were collected 1 d before and 1 d after weaning. Amongst the protein-restricted animals, heavy sows (240LP) had a smaller appetite than light sows in early lactation, resulting in lower energy and protein intakes in the 240LP than in the 180LP sows. Body protein losses were 8, 11 and 13.5% of calculated body protein mass at farrowing in the 180CP, 180LP and 240LP sows, respectively. At the end of lactation, IGF-I concentrations were lower in the 180LP than in the sows from the other groups, probably because of the uncoupling between GH and IGF-I secretions. Low IGF-I concentrations likely promote lean tissue mobilization. Glucose and insulin profiles suggested an insulin resistance state in the 240LP sows compared with the 180LP sows, which may explain, at least in part, the lower feed intake and body reserve mobilization in these sows. Plasma pre- and post-prandial concentrations of amino acids in late lactation differed among the three treatment groups. Throughout lactation, litters from the 180LP and 240LP sows had a slower growth rate than litters from sows which were not restricted, suggesting that endogenous protein mobilization throughout lactation does not completely compensate for a low protein intake.     

Relationships between backfat depth and plasma leptin during lactation and sow reproductive performance after weaning

The aim of this study was to determine relationships between sow backfat depth, plasma leptin concentrations, and reproductive performance after weaning. On the day of farrowing (day 0), and at weaning (day 21), single blood samples were obtained from 120 mixed-parity sows and their backfat depth (P2) measured. Based on backfat depth at day 0, sows were classified as FAT (>24 mm, n = 16), MEDIUM (16-24 mm, n = 54), or THIN (<16 mm, n = 14). Sows were further classified on the basis of P2 backfat changes during lactation of <2 mm, 2-4 mm, or >4 mm. Reproductive performance was measured as weaning-to-oestrous intervals (WOI) of <6 d, 6-9 days, or > or =10 d, and pregnancy rates. There was a positive relationship (P < 0.0001) between backfat depth at day 0 and backfat loss during lactation. The WOI was not associated with backfat depth at day 0 or 21 (P > 0.1 for both). Pregnancy rate was not associated with backfat depth at day 0 (P > 0.1) but pregnant sows had a greater backfat depth at weaning (16.5 +/- 0.3 and 14.9 +/- 0.6 mm, P < 0.04). Backfat loss during lactation was positively associated with WOI (P < 0.01) and negatively associated with pregnancy rate (P < 0.04). Plasma leptin concentrations were higher (P < 0.001) in FAT sows than in MEDIUM or THIN sows on both days but there was no relationship between plasma leptin concentrations and reproductive performances after weaning. It is concluded that plasma leptin is associated with backfat depth and that loss of backfat depth during lactation is associated with reproductive performance. However, there is no direct association between plasma leptin and reproductive performance.     

Effect of exogenous gonadotropins on the weaning-to-estrus interval in sows

The efficacy of PG 600 (400 IU PMSG and 200 IU hCG) for accelerating the onset of estrus was determined for sows weaned during the summer. Yorkshire sows (average parity = 4.6), nursing 8.6 +/- 0.2 pigs (mean +/- SEM) were weaned after 27.7 +/- 0.4 d of lactation and were treated intramuscularly with either PG 600 (n = 35) or with 0.9% saline (n = 35). Sows were checked for estrus once daily in the presence of a mature boar. Treatment with PG 600 increased (P < 0.05) the percentage of sows in estrus within 7 d after weaning (97.1 vs 82.9%). Relative to controls, sows given PG 600 expressed estrus sooner (3.8 +/- 0.1 d vs 4.5 +/- 0.1 d; P < 0.01). Sows exhibiting estrus within 7 d after treatments were artificially inseminated 0 and 24 h after first exhibiting estrus. The percentage of inseminated sows that farrowed tended to be higher (P < 0.07) for control than for PG 600-treated sows (96.6 vs 82.3%). The number of pigs born live was similar (P > 0.1) for sows treated with PG 600 and with saline, and was 12.7 +/- 0.6 and 11.7 +/- 0.7, respectively. Pigs farrowed by saline-treated sows, however, tended to be heavier (P < 0.09) than pigs farrowed by sows treated with PG 600 (1.49 +/- 0.06 kg vs 1.34 +/- 0.06 kg). In summary, PG 600 accelerated the onset of estrus in sows weaned during the summer. Sows mated during the induced estrus, however, tended to have a lower farrowing rate and farrowed lighter pigs than control sows inseminated during a natural estrus occurring within 7 d after weaning.     

Correlation between LH response to challenges with GNRH and naloxone during lactation, and LH secretion and follicular development after weaning in the sows.

The aim of this study was of establishing a correlation between endogenous LH secretion and the magnitude of the LH response to challenges with GnRH and the opioid antagonist naloxone during lactation, and between these characteristics and LH secretion and follicular development after weaning. Sows (n = 9) were sampled for 6 h at day 2 post-partum, for 12 h on day 26 of lactation and for 6 h immediately after weaning at day 27 of lactation. Four hours after the beginning of sampling at day 26 of lactation all sows were injected with 2 mg/kg i.v. of naloxone hydrochloride and 5 h later with 100 microg/sow of GnRH. Follicular development was studied in all sows at slaughter the day after weaning. There was an effect of time (sampling period; P < 0.001) on mean plasma LH, with an increase (P < 0.05) in LH the day after weaning compared to mean LH concentrations during lactation. Naloxone and GnRH treatment both increased (P < 0.05) mean LH concentrations. A positive relationship (r = 0.58, P < 0.01) between mean plasma LH after GnRH and after weaning was established. Although there were differences (P < 0.001) between sows in follicular fluid volume, there were no correlations between mean follicular fluid volume and mean LH concentrations after GnRH or after weaning. These data indicate that the LH response to GnRH during late lactation could be useful predictor of LH activity after weaning. However, none of the measures of endogenous or induced LH secretion were associated with differences in ovarian follicular size after weaning. Direct evidence is therefore still needed for a functional link between differences in LH in lactation and differences in fertility after weaning.     

Dietary supplementation with maize distillers dried grains with solubles during late gestation and lactation: Effects on sow and litter performance,and on colostrum and milk composition

The objectives of this study were to determine the effects of maize distillers dried grains with solubles (DDGS) during late gestation and lactation on sow and piglet performance, and on colostrum and milk composition. Thirty-six second- and third-parity (2.43 parity) sows (Yorkshire) were allotted to 1 of 3 groups and fed diets containing 0 (control), 200 or 400 g DDGS/kg during the last 20 d of gestation and throughout a 21 d of lactation. Experimental diets contained 12.9 MJ metabolizable energy/kg and 9.7 g lysine/kg. The colostrum and milk samples were obtained on d 0 (farrowing) and d 21 (weaning). There were no differences (P>0.05) in the sows’ average gestation lengths, weaning-to-estrus interval, average daily feed intake, and the lactation backfat and body weight change between dietary treatments. There were no dietary effects (P>0.05) of DDGS on the numbers of total, born alive piglets, average birth weights, piglets per litter at weaning or piglets average daily gain during lactation. No differences (P>0.05) were observed in total solids, protein, fat and lactose among the sows fed the DDGS diets compared with the control. The composition of total solids and protein of sows colostrum and milk were higher at farrowing (d 0) than at weaning (d 21) (P<0.001). However, the fat and lactose content of sows colostrum and milk were increased (P<0.001) from d 0 (farrowing) to d 21 (weaning). In conclusion, the results suggest that 400 g DDGS/kg (87 g lysine/kg) supplemented with 5.2 g lysine/kg included in late gestation and lactation diets is sufficient to replace all the dietary soybean meal without significantly affecting sow and litter performance or colostrum and milk composition.     

Induction of lactational estrus in organic piglet production

The longer lactation period required in organic piglet producing herds reduces the potential number of produced litters per sow per year compared with that of conventional production. Induction and use of lactational estrus may be a way to increase the productivity in organic production. However, if lactational estrus is to be beneficial under practical husbandry conditions, it is crucial that the majority of sows are successfully mated within a few days to make batch farrowing procedures possible. The objective of this study was to investigate the occurrence and timing of lactational estrus in an organic outdoor system based on ad libitum feeding, individual housing until Day 35 in lactation, followed by grouping and introduction of a boar and weaning of piglets after 8 wk. Five groups with four sows ((Danish Yorkshire × Danish Landrace) × Danish Duroc) in each were observed, and rank was determined by a food competition test. All sows showed lactational estrus, and 84% of these sows showed estrus within 1 wk, on average 43.5 d and 7.3 d after farrowing and boar introduction, respectively. The number of days from boar introduction to estrus increased significantly with increasing feed competition rank (the lowest number being the top rank position). Eighty-four percent of all sows were diagnosed pregnant 5 wk after estrus. Behavioral observations revealed that the average total number of copulations per estrus sow was 2.3 with a range of 0 to 5 copulations. The findings of the current study indicate that it is possible to combine lactational estrus and batch farrowing procedures to increase the number of weaned piglets per year per sow in organic piglet production based on 8 wk of lactation or more.     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Induction of lactational estrus in organic piglet production

The longer lactation period required in organic piglet producing herds reduces the potential number of produced litters per sow per year compared with that of conventional production. Induction and use of lactational estrus may be a way to increase the productivity in organic production. However, if lactational estrus is to be beneficial under practical husbandry conditions, it is crucial that the majority of sows are successfully mated within a few days to make batch farrowing procedures possible. The objective of this study was to investigate the occurrence and timing of lactational estrus in an organic outdoor system based on ad libitum feeding, individual housing until Day 35 in lactation, followed by grouping and introduction of a boar and weaning of piglets after 8 wk. Five groups with four sows ((Danish Yorkshire × Danish Landrace) × Danish Duroc) in each were observed, and rank was determined by a food competition test. All sows showed lactational estrus, and 84% of these sows showed estrus within 1 wk, on average 43.5 d and 7.3 d after farrowing and boar introduction, respectively. The number of days from boar introduction to estrus increased significantly with increasing feed competition rank (the lowest number being the top rank position). Eighty-four percent of all sows were diagnosed pregnant 5 wk after estrus. Behavioral observations revealed that the average total number of copulations per estrus sow was 2.3 with a range of 0 to 5 copulations. The findings of the current study indicate that it is possible to combine lactational estrus and batch farrowing procedures to increase the number of weaned piglets per year per sow in organic piglet production based on 8 wk of lactation or more.     

Synchronization of ovulation and fertility in weaned sows treated with intravaginal triptorelin is influenced by timing of administration and follicle size

A 100 μg dose of triptorelin was tested for synchronizing ovulation in sows. In Experiment 1, conducted in April through June, sows (n = 125) were assigned to Control (untreated), TG-96 (Triptorelin Gel (TG) given intravaginally at 96 h post-weaning), or TG-E (given intravaginally at estrus). To optimize AI timing, sows were inseminated at 2 and 26 h after estrus for Control and TG-E and at 8 and 32 h following TG-96. Ovulation by 48 h post-treatment tended to be affected by treatment (P = 0.08) and more (P < 0.05) TG-96 sows ovulated (57.9%) compared to Controls (34.2%), but TG-E (45.1%) did not differ (P > 0.10). Duration of estrus was reduced (P < 0.005) in TG-96 (51 h) and TG-E (58 h) compared to Controls (65 h). There was no treatment effect on farrowing rate (71%) or total born (10.4). Average follicle size <6.5 mm at 96 h after weaning was associated with reduced (P < 0.01) estrus, ovulation and farrowing rate. Experiment 2 was conducted in August through September using 503 weaned sows. The TG-96 treatment reduced duration of estrus (P = 0.03), but treatment did not affect estrus expression, farrowing rate or total pigs born. In conclusion, use of a 100 μg dose of triptorelin intravaginally at 96 h or at estrus advanced ovulation and when used with timed insemination, resulted in similar farrowing rates and litter sizes comparable to sows mated based on estrus. However, ovulation induction and timed AI success may benefit from an approach that ensures sows have adequate follicle development at time of treatment.     

Estrogen induces estrus unaccompanied by a preovulatory surge in luteinizing hormone in suckled sows

The objective was to determine if progressive changes occurred in incidence of estrus and patterns of luteinizing hormone (LH) after estradiol benzoate (EB) administration at three stages of lactation. Estradiol benzoate (800 micrograms) was injected at the beginning of the second (7.8 +/- 0.3 days, range 7-8, n = 4), third (15.6 +/- 0.3 days, range 15-16 days, n = 5), or fourth (23.3 +/- 0.5 days, range 22-24, n = 4) wk of lactation. Interval to estrus (h) and proportion in estrus (in parentheses) were 72 (1/4), 88.5 (4/5), and 99 (4/4; pooled SEM = 3.5) for the second, third, and fourth weeks, respectively. Only one animal ovulated during lactation (third week). This animal had a progesterone concentration of 17 ng/ml 1 wk after estrus and an LH concentration above 2.0 ng/ml for 72 through 90 h after EB. In other sows, LH remained less than 1.0 ng/ml after EB. Patterns of LH after EB in sows treated during the fourth week of lactation were increased to a maximum of 0.76 ng/ml by 120 h after EB, which was greater than for those treated during the second or third week (maxima of 0.38 and 0.32 ng/ml, respectively; pooled SEM = 0.07; p less than 0.05). Concentrations of LH in sows that exhibited estrus were greater both before and after treatment than in sows that did not exhibit estrus after EB (p less than 0.05). By 2 wk after weaning, 8 sows had ovulated (6 of these exhibited estrus), and there were no effects of stage of lactation on these responses. We concluded that the behavioral responsiveness to EB increased as lactation progressed. The increased LH in sows treated during the fourth week indicated a partial recovery of the positive feedback response to EB. These data suggested that separate mechanisms caused behavioral and gonadotropin responses to EB in lactating sows.     

The influence of insulin administration after weaning the first litter on ovulation rate and embryo survival in sows

Primiparous crossbred sows (n = 43), lactating for an average of 21.1 +/- 0.1 d and weaning 8.7 +/- 0.1 pigs, were used to evaluate the influence of insulin on ovulation rate and embryo survival. The sows were maintained on 2.3 kg/head/d of a 14% protein gestation diet during pregnancy, fed ad libitum during lactation, given 2.7 kg/head/d from weaning until re-breeding and fed 2.3 kg/head/d after mating. Beginning the day after weaning (Day 0) sows were treated with 0.4 IU/kg body weight (BW) insulin (n = 21) or were administered an equivalent volume of saline (n = 22) for 4 d. Beginning on Day 3 and continuing until Day 14 after weaning, the sows were checked for estrus twice daily and were artificially inseminated using pooled semen from 2 fertile boars. At slaughter (days 30 to 40 of gestation), ovaries and uteri were collected, and the ovulation rate, embryo number and viability, and uterine weight and length were evaluated and recorded. Use of insulin decreased the average interval from weaning to estrus compared with saline by increasing percentage in estrus by Day 14 after weaning (5.0 +/- 0.57 vs 6.9 +/- 0.56 d, respectively; P < 0.03). Ovulation rate, number of embryos, embryo survival, and average uterine length and weight were not influenced by insulin treatment. Overall, insulin affected reproductive efficiency in primiparous sows by increasing the percentage of sows in estrus.     

Factors influencing the postweaning reproductive performance of sows on commercial farms

The objective of this study was to investigate the effects of various factors, including lactational feed intake, on the reproductive performance of sows in commercial herds. The 4 measures of reproductive performance were weaning-to-first-service interval, weaning-to-conception interval, litter weight at weaning, and subsequent litter size. Parity, farrowing season, lactation length, farrowing-to-conception interval, litter size, and lactation feed intake were investigated as risk factors common to the 4 measures of post-weaning reproductive performance. Using 4 basic multiple regression models for each measure, the least-square means for sets of factors were compared using the GLM procedure of SAS. Parity 1 sows had the longest weaning-to-first-service interval and weaning-to-conception interval, and the lighter litter weight at weaning (P < 0.05) than mid-parity sows. Sows in Parities 2 to 5 had larger subsequent litter size (P < 0.05) than those in Parities 1 and >/= 7. Sows farrowing in summer and spring had the longest and second longest weaning-to-conception interval (P < 0.05), respectively, while sows farrowing in summer had longer weaning-to-first-service interval than those that farrowed in spring (P < 0.05). Sows farrowing in summer produced the lightest litter weight at weaning (P < 0.05). No differences in subsequent litter sizes were found due to farrowing season (P > 0.10). As lactation length increased, weaning-to-first-service interval and weaning-to-conception interval decreased, and litter weaning weight increased. Longer lactation length and farrowing-to-conception interval were associated with larger subsequent litter size (P < 0.05). Litter size did not affect weaning-to-first-service interval or weaning-to-conception interval. Larger litter sizes were associated with heavier litter weight at weaning. Greater lactation feed intake improved the 4 measures of reproductive performance.     

The importance of farrowing to service interval in sows served during lactation or after shorter lactation than 28 days

In a retrospective study, based on data from the national litter recording system, farrowing rate and litter size of sows served (inseminated or mated) during the lactation period (n = 574) or after a lactation period shorter than 28 days (n = 14,219) were analysed. The results were compared with the corresponding figures for sows with lactation length between 28 and 35 days and weaning to first service interval of 4 or 5 days (reference group; n = 41,741). The farrowing rate of the reference group was 80.9% and subsequent litter size was 13.7 total piglets born. Among sows served prior to weaning, the farrowing rates and litter sizes were significantly lower for those served earlier than 22 days post-farrowing compared to those served later (P < 0.05). Shorter lactations than 28 days and service within 10 days post-weaning led to lower farrowing rates than in the reference group (P < 0.01). Significant differences were seen after different lactation lengths. After correction for weaning to service interval, preceding litter size weaned, parity, breed and the interaction between parity and breed, litter size was significantly and positively associated with the preceding lactation length. The study shows that service within the first 3 weeks post-farrowing results in reduced reproductive performance.     

Returns to service after mating and removal of sows for reproductive reasons from commercial swine farms

We studied the records of 30 herds with an average inventory of 11,705 sows, 25,719 farrowings and 25,040 daily feed intake logs. Production events were recorded by producers using the PigCHAMP production information system. Of 21,505 matings, 7.2% of sows subsequently returned to estrus after service. The proportionate rates of intervals from service to the subsequent post service event were 0 to 17 d, 2.1%; 18 to 25 d, 27.9%; 26 to 37 d, 13.8%; 38 to 46 d, 15.8%; 47 to 108 d, 30.4%; and >108 d, 10.0%. Sows returned to service after mating were categorized into groups that either regularly or irregularly returned to service after mating. Of a total inventory of 19,076 sows, 10.0% were removed following weaning for reproductive reasons. The reasons for removal included those of anestrus (25.2%), failure to conceive (37.0%), failure to farrow (15.0%), not pregnant (1.4%), negative pregnancy check (14.0%), and abortion (7.4%). The last 5 types of post weaning reproductive failure were grouped into the category of did not farrow. Categorical additive models and comparisons using contrasts were used to analyze the influence of risk factors on reproductive failure. Parity 1 sows had a higher proportion (P < 0.01) of returns to service and a greater proportion of sows remaining anestrous post weaning relative to Parity 3 sows. The proportion of sows that did not farrow was higher (P < 0.01) in Parities 9 and 10 than in Parity 3. More sows were removed for anestrus during the spring (P < 0.01) and summer (P = 0.06) than during the winter. All categories of lactation length had similar rates of reproductive failure except for the lactation length 1 to 7 d, which had a higher (P < 0.05) proportion of reproductive failure. Lower lactational feed intake was associated with an increased risk of occurrence of each reproductive failure category. The odds ratios of lactation feed intake in logistic regression analyses were 0.84, 0.89, 0.82 and 0.88 for regularly and irregularly returned to service, anestrus, and did not farrow groups, respectively. This means, for example, that a sow was 0.88 times less likely to have an occurrence of not farrowing for each 1 kg increase in average daily feed intake during lactation. Our results indicate that lower and higher parities, spring and summer seasons, a lactation length of less than 8 d and lower feed intake during lactation affect the occurrence of return to service after mating and of herd removal for reproductive reasons.     

Review: Nutrient requirements of the modern high-producing lactating sow,with an emphasis on amino acid requirements

Sow productivity improvements continue to increase metabolic demands during lactation. During the peripartum period, energy requirements increase by 60%, and amino acid needs increase by 150%. As litter size has increased, research on peripartum sows has focused on increasing birth weight, shortening farrowing duration to reduce stillbirths and improving colostrum composition and yield. Dietary fibre can provide short-chain fatty acids to serve as an energy source for the uterus prior to farrowing; however, fat and glucose appear to be the main energy sources used by the uterus during farrowing. Colostrum immunoglobulin G concentration can be improved by increasing energy and amino acid availability prior to farrowing; however, the influence of nutrient intake on colostrum yield is unequivocal. As sows transition to the lactation period, nutrient requirements increase with milk production demands to support large, fast-growing litters. The adoption of automated feed delivery systems has increased feed supply and intake of lactating sows; however, sows still cannot consume enough feed to meet energy and amino acid requirements during lactation. Thus, sows typically catabolise body fat and protein to meet the needs for milk production. The addition of energy sources to lactation diets increases energy intake and energy output in milk, leading to a reduction in BW loss and an improvement in litter growth rate. The supply of dietary amino acids and CP close to the requirements improves milk protein output and reduces muscle protein mobilisation. The amino acid requirements of lactating sows are variable as a consequence of the dynamic body tissue mobilisation during lactation; however, lysine (Lys) is consistently the first-limiting amino acid. A regression equation using published data on Lys requirement of lactating sows predicted a requirement of 27 g/day of digestible Lys intake for each 1 kg of litter growth, and 13 g/day of Lys mobilisation from body protein reserves. Increases in dietary amino acids reduce protein catabolism, which historically leads to improvements in subsequent reproductive performance. Although the connection between lactation catabolism and subsequent reproduction remains a dogma, recent literature with high-producing sows is not as clear on this response. Many practical aspects of meeting the nutrient requirements of lactating sows have not changed. Sows with large litters should approach farrowing without excess fat reserves (e.g. <18 mm backfat thickness), be fed ad libitum from farrowing to weaning, be housed in a thermoneutral environment and have their skin wetted to remove excess heat when exposed to high temperatures.     

The effects of zearalenone on reproduction in swine. II. The effect on puberty attainment and postweaning rebreeding performance

Eighty-five prepuberal, crossbred gilts received, ad libitum, a diet containing 0 or 10 ppm purified zearalenone for 30 d beginning at 145 to 193 d of age. At the end of this period all gilts were placed on the control diet and exposed daily to a mature boar for 60 d. Within 3 to 5 d of zearalenone ingestion, gilts showed marked vulval swelling and reddening, which continued for the 30-d feeding period. Thereafter symptoms slowly subsided. Zearalenone treated gilts showed first estrus significantly later than controls (P < 0.05), but the proportion of gilts showing estrus within 60 d of boar exposure was similar (P > 0.05). The length of the first estrous cycle was not affected by the ingestion of zearalenone before puberty (P > 0.05). In a second study, 65 multiparous, crossbred sows were full-fed twice daily a ration containing 0 or 10 ppm of purified zearalenone beginning 14 d before weaning. Postweaning, all sows were fed the control diet, were checked for estrus daily, and inseminated at the first postweaning estrus. Neither sows nor gilts from their litters exhibited signs of hyperestrogenism during treatment. Weaning to estrus interval was significantly extended in zearalenone treated sows (P < 0.05), but all other variables of fertility assessed were similar. These data suggest that zearalenone ingestion before puberty delays the stimulation of puberty associated with boar exposure, but does not affect subsequent cyclicity if zearalenone is removed from the ration. Similarly, zearalenone ingestion during lactation delays the return to estrus after weaning, but does not affect subsequent fertility when removed from the ration at weaning.     

Changes in the hypothalamic-hypophyseal-ovarian axis of primiparous sows following weaning or pulsatile gonadotropin releasing homrone administration and weaning

Lactating primiparous sows were used to examine relationships among hypothalamic gonadotropin releasing hormone (GnRH), serum, and anterior pituitary gonadotropins and follicular development after weaning or after administering GnRH pulses (1.5 ug) once hourly for 72 h before weaning. Control sows were either slaughtered at 0 or 72 h after weaning or were cannulated for collection of blood samples until 24 h after estrus. Sows pulsed with GnRH were either slaughtered 72 h after beginning of GnRH treatment or were cannulated for collection of blood samples until 24 h after estrus. Exogenous GnRH pulsed hourly during 72 h prior to weaning stimulated follicular growth as demonstrated by an increase in number of surface follicles >5 mm in diameter and a decrease in number of follicles <5 mm in diameter. Interval (h) from weaning to an increase in estradiol (>16 pg/ml) was less in GnRH-pulsed than in control sows (P < 0.05), but hours from weaning to estrus were similar between groups. Amounts of GnRH in the medial basal hypothalamus (MBH), stalk median eminence (SME), and hypophyseal portal area (HPA) were similar among control sows killed at 0 or 72 h and sows pulsed with GnRH. Serum concentrations of luteinizing hormone (LH) and frequency of release of LH were similar between GnRH-pulsed and control sows, but concentrations of LH and follicle stimulating hormone (FSH) in anterior pituitary were lower in GnRH-pulsed sows than control sows. Administration of GnRH for 72 h prior to weaning in primiparous sows stimulated follicular growth as manifested by increased secretion of estrogen; however, the amount of follicular growth was apparently inadequate to hasten the onset of estrus after weaning.     

In primiparous sows, plasma insulin-like growth factor-I can be affected by lactational feed intake and dietary energy source and is associated with luteinizing hormone

During a 21-day lactation period, 48 primiparous sows were fed a fat- or a starch-rich diet (131 g fat and 183 g starch + sugar x kg(-1) vs. 31 g fat and 351 g starch + sugar x kg(-1)) at a high or a low level of feeding (44 vs. 33 MJ net energy per day) according to a factorial design. Blood samples were collected at days 7, 14, 21, 22 (weaning), 24, 25, 26, and 27 post-partum (p.p.). IGF-I levels were higher with the starch-rich than with the fat-rich diet at days 7, 21, 22, and 24 p.p. Plasma IGF-I concentrations on day 22 p.p. were positively related with LH pulse frequency on day 22 p.p. and the height of the pre-ovulatory LH surge. Sows with low body weight at farrowing and high lactational body weight loss had lower plasma IGF-I concentrations than others, before and after weaning. These results indicate that IGF-I concentrations are affected by both feeding level and dietary energy source and are related to the secretion of LH. Furthermore, body weight at farrowing interacts with lactational body weight loss to affect IGF-I concentrations.     

Reproductive endocrinology and postweaning performance in the multiparous sow. Part 2. Influence of nursing behavior

The reason for variation in postweaning reproductive performance among multiparous sows is to a large extent unknown. In the present study, the influence of nursing behavior was explored. Blood samples were collected during lactation and after weaning from 18 multiparous sows for cortisol, LH, estradiol-17beta (E2), and progesterone analysis. Sow and piglet behavior was videotaped. The sows were fed according to litter size and slaughtered after the second postweaning estrus. The sows were divided into two groups based on average values for the different behavioral parameters. Sows with a long average nursing duration (long group) had lower average and basal LH levels on Day 14 and 21 of lactation as compared to the sows having a short average nursing duration (short group). In the long group, concentrations of E2 were lower the day after weaning, but on Day 15 and 21 of lactation no differences were noted between the two groups. Postweaning performance seemed impaired in the long group, though, differences were not significant. The sows in the long group were heavier and tended to lose less weight during lactation. To conclude, nursing duration seems to influence the extent to which reproductive functions are inhibited during lactation.     

The influence of time of insemination relative to time of ovulation on farrowing frequency and litter size in sows, as investigated by ultrasonography

The objective of this experiment was to identify the optimal time of insemination relative to the time of ovulation, based on ultrasonographic detection of embryonic survival at 10 days after ovulation, number of sows farrowing, and litter size. Furthermore, the possible value of the interval from weaning to onset of estrus for prediction of the time of ovulation was examined. Crossbred sows (n = 143) that had farrowed 2 to 9 litters were weaned (Day 0) and observed for estrus every 8 h from Day 3 until end of estrus. Ultrasonography was performed every 6 h, from 12 h after onset of estrus until ovulation had been observed. The sows were inseminated once at various time intervals from ovulation. At Day 16, 25 of the sows were slaughtered and their uteri were flushed for embryos. In the remaining sows, the number of viable and dead piglets and mummified fetuses per sow was recorded at farrowing, with the sum of the 3 constituting the total number of piglets born per sow. The highest number of embryos recovered per sow was found after insemination during the interval from 24 h before to 4 h after ovulation. The lowest frequency of non-pregnant sows and the highest total number of piglets born per sow were found after insemination from 28 h before to 4 h after ovulation. Consequently, the optimal time for insemination was found to be in the interval 28 h before to 4 h after ovulation. The interval from weaning to onset of estrus and from onset of estrus to ovulation were negatively correlated, allowing a rough prediction of the time of ovulation from the interval from weaning to onset of estrus.