Proportion Of Gilts Research Articles

Vaccination against Clostridium perfringens type C enteritis in pigs: a field study using an adapted vaccination scheme

BackgroundClostridium perfringens type C induced necrotizing enteritis (NE) causes high mortality in newborn piglets. Immunization programs employing commercially available vaccines are used to prevent disease. Sows are vaccinated during every gestation period and piglets take up antibodies from the colostrum. Antibodies against the major clostridial toxin beta-toxin (CPB) are considered essential for protective immunity. Because the pathogen can persist for several years on farms, continuous vaccination is essential to protect pig herds from the re-occurrence of NE.ResultsIn two field trials using commercially available vaccines we monitored neutralizing anti-CPB antibodies in pigs after vaccination. The first trial compared antibody titers in primiparous (gilts) and multiparous sows and their piglets after vaccination. A proportion of gilts and their piglets’ showed no or low antibody titers. All multiparous sows developed significantly higher serum and colostrum antibody titers after a booster vaccination shortly before their next farrowing. These colostral antibody titer highly correlated with the serum antibody titer of their piglets after consumption of colostrum. In a second field trial, we adapted the vaccination schemes using 3 instead of 2 initial vaccinations before the first farrowing of gilts. This significantly increased serum and colostrum antibody titers in gilts and serum antibody titers in piglets.ConclusionWe demonstrate that despite following recommended vaccination protocols, a proportion of gilts might not sufficiently seroconvert to provide efficient passive immunity to their offsprings. A simple adaptation of the vaccination scheme can however improve passive protection of piglets from NE.

Porcine circovirus type 2 associated reproductive failure in a specific pathogen free (SPF) piglet producing herd in Norway: a case report

BackgroundSince 1999, scientists have published evidence of transplacental infection by porcine circovirus type 2 (PCV2) and reproductive failure in pigs. Affected herds have frequently been start-up herds, either naïve or with a high proportion of PCV2 susceptible gilts. Here, delayed farrowing in non-vaccinated gilts was observed in a commercial specific pathogen free (SPF) herd. Mummified fetuses and stillborn piglets recovered from these gilts were PCV2 positive.Case presentationThe case herd was a self-recruiting, piglet producing unit of 240 sows. After detecting livestock associated methicillin resistant Staphylococcus aureus (LA-MRSA, CC398), stamping out was imposed by the authorities. An SPF herd was re-established and all dams were vaccinated against PCV2 until the farmer decided to exclude this vaccine. The first non-vaccinated batch consisted of 76% gilts. Here, one gilt showed signs of impending farrowing. This gilt was slaughtered three to four weeks after the expected farrowing date without having expelled any uterine contents. In the subsequent batch consisting of 79% gilts, three gilts showed similar clinical signs. Delayed farrowing was observed in two of these gilts and the uterine contents from the third gilt were recovered at the abattoir. Mummified fetuses and stillborn piglets were recovered from all three gilts. High levels of PCV2 DNA (>107 viral genomic copies/ 500 ng tissue) were found in myocardial samples by real-time PCR analysis. One myocardial sample submitted for immunohistochemical (IHC) analysis showed moderate amounts of PCV2 antigen. In the subsequent batch consisting of 77% gilts, several weak-born piglets were seen across different litters.ConclusionsThis case report describes an apparent link between in utero PCV2 infection, pre partum nest-building behaviour, mammary development and delayed farrowing. To date, no reports have described imminent signs of farrowing and delayed farrowing as clinical signs in conjunction with transplacental PCV2 infection in Norway. Reinitiation of PCV2 vaccination was strongly advised in this herd due to recent depopulation and repopulation and the high proportion of gilts. Vaccination was effective because no further cases have occurred since.

Two different strategies for housing gilts after mating did not affect the proportion of gilts culled

Two different strategies for housing gilts after mating did not affect the proportion of gilts culled

Single fixed-time laparoscopic intrauterine insemination as a tool to obtain low-diversity porcine embryos

Double fixed-time insemination after ovulation induction is commonly used in pigs to obtain in vivo produced embryos at defined stages of development for downstream biotechnological applications. However, variations in the time of ovulation and fertilisation of the ovulated oocytes by spermatozoa, mainly in one of the inseminations, can cause diversities in embryo development. The aim of the present study was to reduce embryo diversity and to achieve a ‘uniform outcome’ of porcine embryo stages using single laparoscopic fixed-time insemination (LIUI). Altogether, 48 puberal German Landrace gilts were included in the study. Estrus of gilts was synchronized by 15-day long altrenogest (Regumate<sup>®</sup>) feeding and follicle development was stimulated with 850 IU eCG 24 h after the final altrenogest application. Ovulation was induced with 500 IU hCG 80 h after eCG. LIUI was performed 31 h after hCG treatment. Gilts under general anaesthesia were fixed in a dorsal position, a pneumoperitoneum was produced and three trocar cannulas were inserted into the abdomen for optics and instruments. Each uterine horn was carefully punctured 10–15 cm caudal from the utero-tubal junction with a 2.5 mm trocar. A 2.2 mm catheter was inserted about 3 cm into the uterine lumen and 20 ml of extended fresh boar semen (32.2 × 106 sperm cells/ml) were injected. Embryos were surgically flushed from the genital tract two (Day 2) and three (Day 3) days after insemination. Altogether, 778 oocytes/embryos were recovered (recovery rate 68 ± 17%); 45 of 48 gilts (93.8%) revealed fertilisation and 76.1% of the recovered embryos (n = 592) were at the 2- and 4-cell stage. On Day 2 (n = 22 gilts), a higher percentage of gilts (72.7%, P < 0.05) displayed only 2-cell embryos compared with gilts which had 2- and 4-cell (22.7%), or only 4-cell embryos (4.6%). On Day 3 (n = 23 gilts), the proportion of gilts with 2-cell, 2- and 4-cell, and only 4-cell embryos shifted to 4.3%, 0% and 95.7%, respectively (P < 0.05). The results of the present study demonstrate high rates of fertilisation and homogenously developed embryos after single fixed-time laparoscopic intrauterine insemination in gilts. Additionally, these results were achieved by inseminating a 60% lower number of sperm cells per insemination dose compared to usual doses used for transcervical insemination. In conclusion, LIUI can be recommended for the in vivo production of embryos in a homogeneous developmental stage, and also as an alternative method for low-dose insemination.  

9 SINGLE FIXED-TIME LAPAROSCOPIC INTRAUTERINE INSEMINATION IN PIGS TO PRODUCE LOW-DIVERSE EMBRYOS

In vivo-derived embryos at a defined stage of development are often a necessary requirement for ongoing biotechnological applications. Because double fixed-time insemination after ovulation induction is commonly used in pigs to produce embryos, variations in the time of ovulation and fertilization of the ovulated oocytes by spermatozoa mainly of 1 of the 2 inseminations can cause, however, diversities in embryo development. To moderate embryo diversity and to realize a uniform outcome of porcine embryo stages, single laparoscopic fixed-time insemination can be used to minimize embryo diversity. The potential of laparoscopic intrauterine insemination (LIUI) has been demonstrated in sperm-mediated gene transfer (Fantinati et al. 2005) and evaluation of sperm migration (Brüssow et al. 2006, 2011). The aim of the present study was to analyze the development and possible diversity of embryos after LIUI. Forty-eight puberal German Landrace gilts were included in the study. Estrus of gilts was synchronized by 15-day Regu-Mate® (Intervet, Millsboro, DE, USA) feeding and follicle development was stimulated with 850 IU of eCG 24 h after Regu-Mate® treatment. Ovulation was induced by 500 IU of hCG 80 h after eCG treatment. The LIUI was performed 31 h after hCG treatment. To that, ketamine/azaperone-anaesthetized gilts were fixed in a dorsal position, a pneumoperitoneum was produced and 3 trocar cannulas were inserted into the abdomen for optics and instruments. Laparoscopic handling was observed on a television monitor. Each uterine horn was carefully fixed with an atraumatic forceps 10 to 15 cm caudal from the utero-tubal junction and the uterine wall was punctured with a 2.5-mm diameter trocar. A 2.2-mm catheter connected to a syringe was inserted about 3 cm into the uterine lumen and 20 mL of extended, fresh boar semen (32.2 × 106 sperm cells mL–1; 65% motility) was deposited in the lumen. Embryos were surgically flushed from the genital tract on Day 2 and 3, respectively. Altogether, 778 oocytes were recovered (recovery rate 68 ± 17%); 45 of 48 gilts (93.8%) revealed fertilization and 76.1% of the recovered embryos (n = 592) were at the 2- and 4-cell stage. On Day 2 (n = 22 gilts), a higher percentage of gilts displayed only 2-cell embryos compared with both 2- and 4-cell, and only 4-cell embryos (72.2 v. 22.7 and 4.6%, P < 0.05; chi-square test). On Day 3 (n = 23 gilts), there was a shift regarding the embryo stage. The proportion of gilts with 2-cell, 2- and 4-cell, and only 4-cell embryos was 4.3, 0, and 95.7%, respectively (P < 0.05). Results of the present study demonstrate high rates of fertilization and of non-diverse developed embryos after single fixed-time LIUI in gilts. Additionally, these results were achieved after inseminating a 75% lower number of sperm cells per insemination dose. Laparoscopic intrauterine insemination can be suggested as an alternative for insemination of sex-sorted semen where the number of available sperm cells after the sorting procedure is restricted.

Indução de puberdade em leitoas com diferentes idades em dois sistemas de manejo

O objetivo deste trabalho foi determinar o efeito do método de exposição ao macho e da idade da leitoa, por ocasião da exposição, sobre o percentual de manifestação do primeiro estro, idade de início da puberdade e intervalo entre estímulo e puberdade. Leitoas Danbred F1 Landrace x Large White foram induzidas à puberdade com dois sistemas de exposição ao macho - Baia, estímulo feito pela introdução de macho na baia das fêmeas; Bear, estímulo feito pela colocação de fêmeas na área de permanência de machos - , em três idades de início do estímulo - 150, 170 e 200 dias. Não houve diferença entre os sistemas de estimulação quanto à percentagem de leitoas em estro, idade à puberdade e intervalo entre estimulação e puberdade. Esse intervalo foi menor, quando a exposição das fêmeas foi feita aos 200 dias de idade, e a proporção de fêmeas que atingiram a puberdade aos 10, 20, 30 e 42 dias após o início da exposição foi maior. A indução da puberdade tem maior sucesso quando a exposição da fêmea ao macho é feita aos 200 dias de idade, independentemente do sistema de estimulação.

Lean meat prediction with HGP, CGM and CSB-Image-Meater, with prediction accuracy evaluated for different proportions of gilts, boars and castrated boars in the pig population

Prediction equations for the percentage lean meat in pig carcasses in The Netherlands were derived for the Hennessy Grading Probe 7, Capteur Gras/Maigre — Sydel and CSB-Image-Meater. Because castrated males are expected to vanish from the Dutch pig population in the near future, accuracy of prediction was evaluated for different scenarios representing a wide range of different proportions for entire males, castrated males and females in the Dutch pig population. The prediction equations for the instruments are in compliance with the EC regulations for prediction accuracy for the different scenarios. So, these equations will remain valid when castrated males are (gradually) removed from the Dutch slaughter population. Results of this study are of interest for researchers from countries or areas contemplating the use of one of the aforementioned instruments. The statistical approach for evaluation of prediction accuracy is of particular interest when changes in proportions of important subpopulations in the target population are foreseen.

Age, body weight and backfat thickness at first observed oestrus in crossbred Landrace × Yorkshire gilts, seasonal variations and their influence on subsequence reproductive performance

The objective of the present study was to investigate puberty attainment in crossbred Landrace × Yorkshire (LY) gilts reared under tropical conditions and their subsequent reproductive performance. This study was carried out in a 2400-sow herd over a 1-year period. A total of 696 crossbred LY replacement gilts were included. Faecal samples from 214 gilts were collected to determine the faecal progesterone profiles around the time of first oestrus. Solid-phase 125I-radioimmunoassay was used to determine the progesterone concentrations in the faecal extract. The gilts entered the herd at an average age of 177.5 ± 12.6 days, 95.7 ± 10.2 kg body weight (BW) and a backfat thickness (BF) of 12.0 ± 2.9 mm. On average, the gilts expressed first standing oestrus at 195 days of age, 106 kg of BW and a BF of 13.0 mm. The interval from entry to the gilt pool to the first observed oestrus (EOI) was 24.4 ± 18.0 days (range 0–88 days). The hormonal profile indicated that the gilts that actually ovulated during the first observed oestrus was 34% (group A), the gilts that had ovulated before the first observed oestrus was 21% (group B) and the gilts that did not ovulate during the first observed oestrus was 45% (group C). During summer the proportion of group A gilts was significantly lower than during the winter and the rainy seasons ( P < 0.05). The BW of gilts at entry significantly correlated with the BF at entry ( r = 0.31, P < 0.001), the age at entry ( r = 0.47, P < 0.001), the BW at first oestrus ( r = 0.65, P < 0.001) and the BF at first oestrus ( r = 0.33, P < 0.001). An increase of BW at entry of 1 kg resulted in a decrease of EOI of 0.28 days. The age, BW and BF of gilts at the first observed oestrus significantly influenced the total number of piglets born per litter (TB) and the number of piglets born alive per litter (BA) in the first three parities. Gilts expressing their first oestrus between 181 and 200 days had a significantly larger TB than gilts that expressed first oestrus between 150 and 180 days ( P = 0.03) and between 201 and 220 days ( P = 0.003). Gilts that showed first oestrus between 110.1 and 120.0 kg had a larger TB and BA than gilts that showed first oestrus between 80.0 and 100.0 kg ( P < 0.05). Gilts that showed first oestrus with a BF between 13.1 and 15.0 mm had a larger TB and BA than gilts that showed first oestrus with a BF between 11.1 and 13.0 mm ( P < 0.05). Group A gilts had a significantly larger TB than group B (10.5 piglets/L versus 9.4 piglets/L, P = 0.02), while farrowing rate (FR) did not differ significantly among groups A, B and C (78.1, 76.9 and 77.6%, respectively). Gilts that farrowed in the summer had a larger TB and BA than gilts that farrowed in the winter (TB, P = 0.03; BA, P = 0.09) and the rainy season (TB, P = 0.006; BA, P = 0.003). In conclusion, LY gilts reared under tropical conditions expressed first standing oestrus at 195 days of age, 106 kg BW and a BF of 13.0 mm. Under field conditions, 21% of the gilts with an observed oestrus had ovulated. The proportion of gilts that showed first oestrus and ovulated normally was lowest during the summer. The age, BW and BF at first observed oestrus influenced subsequent reproductive performance over the first three parities. The mean litter size (TB and BA) in the first three parities were highest in gilts that had a first observed oestrus between 181 and 200 days with 110.1–120.0 kg BW and 13.1–15.0 mm BF.

Effect of altering dose of PG600 on reproductive performance responses in prepubertal gilts and weaned sows

This study evaluated the effects of altering dose of PG600 on estrus and ovulation responses in prepubertal gilts and weaned sows. Experiment 1 tested the effects of one (1.0×, 400 IU eCG + 200 IU hCG, n = 74), one and a half (1.5×, n = 82), or two (2.0×, n = 71) doses of PG600 for prepubertal gilts. Estrus (58%) and ovulation (90%) were not affected ( P > 0.10) by dose. Higher doses increased ( P < 0.01) numbers of corpora lutea (17, 24, and 25), but not ( P > 0.10) the proportion of gilts with cysts (26, 36, and 46% for 1.0×, 1.5×, and 2.0×, respectively). Experiment 2 tested the effects of 0× ( n = 30), 0.5× ( n = 32), 1.0× ( n = 29), or 1.5× ( n = 30) doses of PG600 in weaned sows. Dose did not influence return to estrus (90%, P > 0.10). There was an effect of dose ( P < 0.05) on incidence of cysts (3.4, 1.8, 6.4, and 29.8%, for 0×, 0.5×, 1.0×, and 1.5× doses, respectively). The 0.5× dose increased ( P < 0.01) farrowing rate (83.2%) compared to 0× (72.1%) and 1.5× (58.6%), but was not different from 1.0× (76.4%). Total pigs born (10.5 ± 0.8) did not differ ( P > 0.10) among treatments. These data suggest that increasing dose of PG600 to 1.5× for gilts increases the number of corpora lutea but does not alter the proportion expressing estrus or ovulating. Reducing dose of PG600 for weaned sows did not alter estrus or ovulation, but the 0.5× dose increased farrowing rate compared to no PG600.

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts.

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.

The Use of an Immunomodulator to Enhance the Reproductive Performance of Gilts Transported for Long Distances from Breeding to Commercial Units

ContentsThe reproductive performance of gilts transported for long distances from three high‐health breeding farms to six commercial farms was tested after the use of a Parapox‐ovis‐virus‐based immunomodulator, Baypamun N (Bayer AG, Germany). Sixty (60) gilts were injected with Baypamun N, three times (2 days before departure, 2 h before departure and 2 days after their arrival at the commercial farms), while the remaining 60 gilts were injected with placebo at the same times. The results indicated that: (i) no adverse reactions or adverse effects were noticed related to the treatment with Baypamun N, (ii) treatment with Baypamun N improved the reproductive performance of gilts; the proportion of gilts farrowed/total gilts examined, the total number of piglets born, the number of piglets born alive and the body‐weight of piglets at farrowing were significantly increased (p &lt; 0.05), and (iii) treatment with Baypamun N reduced (p &lt; 0.05) the cost of medication per gilt examined and per served gilt.

The effect of virginiamycin supplementation in sow diets on the reproductive performance of the gilt/sow

AbstractThis trial investigated the effects of virginiamycin on sow and litter performance. Virginiamycin was added to the sow diet during the period of gestation and lactation at the levels of0, 40 and 60 mg/kg, throughout two breeding cycles. Virginiamycin did not significantly affect sow weight change during gestation or lactation, or litter size and weight; there were no significant effects on food consumption (P &gt; 0·05). However, when added at a level of 40 mgl kg virginiamycin tended to produce a better condition of sows which resulted in a significant reduction of replacement rate (P &lt; 0·05), even though the proportion of gilts culled in the treated and untreated groups was high. The most evident result was a significantly shorter weaning-to-conception interval for the virginiamycin group at the end of the second reproductive cycle (first period, 5·9 days less than the control group, 2·5 days less than the 60 mg/kg group; second period, -9·5 days v. control group, P &lt; 0·05, and -7·1 days v. 60 mg/kg group, P &lt; 0·05), allowing a numerical improvement in productivity. Piglet performance was not significantly improved by the use of virginiamycin even though there was an evident trend in favour of the 40 mg/kg group which presented a higher proportion of heavier piglets (P &lt; 0·05) and a reduction of pre-weaning mortality. A significant quadratic regression was found for weaning-to-conception interval and numeric productivity, indicating that the dosage more efficient to improve these parameters was 32 mg/kg. The results obtained in the virginiamycin 60 group were generally inferior to those of the 40 mg/kg group and also to the control group and seem to demonstrate that the 60 mg/kg dosage was too high.

The efficacy of the boar effect when conducted in a modified detection-mating area (DMA)

Fifty-six Large White/Landrace crossbred gilts from 14 litters were allocated to four treatments by litter and liveweight in a 2x2 factorial experiment. The two factors tested were boar contact v. no boar contact and exposure to a modified Detection-Mating Area (DMA) v. no DMA exposure. All treatments began at a mean gilt age of 160 days and continued on a daily basis for 60 days. Daily boar exposure significantly reduced mean gilt age at puberty (196.2�3.88 v. 216.6�3.26 days respectively, P &lt; 0.01) and increased the proportion of gilts attaining puberty within 60 days of commencement of treatment (0.79 v. 0.30 respectively, P &lt; 0.01), compared with gilts receiving no boar exposure. In contrast, daily exposure to a modified DMA failed to significantly reduce mean gilt age at puberty (202.8�4.63 v. 209.7� 3.35 days respectively) or to increase the proportion of gilts attaining puberty within 60 days of commencement of treatment (0.50 v. 0.59 respectively) compared with gilts receiving no DMA exposure. However, daily exposure to a modified DMA did significantly increase the proportion of gilts pubertal over a 2-day period (days 27-28 of treatment) relative to gilts not exposed to a DMA. It is concluded that (1) daily boar exposure is a potent stimulus for early puberty attainment in gilts, (2) full physical contact with the boar must occur in order to achieve the boar effect, and (3) the current recommendation that gilt puberty stimulation can be adequately achieved by exposing them to a DMA on a daily basis should be re-examined.

Daily gain and age and weight at puberty in purebred and crossbred Duroc, Landrace and Large White gilts

Average daily gain and age and weight at puberty were studied in purebred Landrace (LD) and Large White (LW) and crossbred LD×LW, LW×LD, Duroc (DR)×LD and DR×LW gilts, in order to compare performance and sexual maturity in different breed combinations.Gilts (44–47) from each breed combination were available. Estrus was checked twice daily from 154 d and on, until at least 80% of the gilts from each breed combination had their first estrus. Differences between breed combinations were observed for daily gain and weight at puberty (P<0.05). The correlation between the two traits was r=0.64, and the correlation between daily gain and age at puberty was r=−0.17. Growth rate, age and weight at puberty and proportion of gilts in estrus up to 200, 220 and 244 d of age improved linearly from white-purebred (LD and LW) to Duroc-crossbred (DR × LD and DR × LW) gilts (P<0.05), with white-crossbred (LD × LW and LW × LD) gilts being intermediate. Results indicate that growth rate and sexual maturity did not significantly differ between Duroc- and white-crossbreds. The use of DR×LD or DR×LW gilts and sows in the breeding hard would depend on their litter productivity.

Attainment of puberty in domestic gilts reared under long-day or short-day artificial light regimens

The effect of photoperiod on attainment of puberty was examined in four studies using controlled long- or short-day light regimens. Gilts were reared together under natural photoperiod until divided between two controlled environment rooms at a mean age of 106.6 ± 0.52 days on 25 September 1987 (Study 1, n = 32) or 23 March 1988 (Study 2, n = 26). In Study 3 (21 September 1988; n = 35) and Study 4 (21 March 1989; n = 36) the gilts were transferred to the controlled environment rooms at 56.5 ± 0.82 days of age. In all studies the light: dark ratio was initially 12 h light: 12 h dark (12 L: 12 D) in both rooms and it was then either increased or decreased by 10–15 min per week. In Studies 1 and 2 the ratio was increased to 16 L: 8 D or decreased to 8 L: 16 D over 16 weeks. In Studies 3 and 4 it was increased to 14.5 L: 9.5 D or decreased to 9.5 L: 14.5 D over 12 weeks then returned to 12 L: 12 D over a further 12 weeks. Temperature was maintained at 23°C. In Studies 1 and 2 all gilts commenced daily exposure to mature boars at 173.5 ± 0.52 days of age and 82.9 ± 1.63 kg. In Studies 3 and 4 all gilts remained isolated from boars. In Studies 1 and 2 the light regimens during rearing had no significant effect on either the proportion of gilts which reached puberty in response to boars or the interval from first exposure to boars until puberty (overall, long-day 21 29 , 21.9 ± 2.83 days ; short-day 18 29 , 22.1 ± 2.66 days ). However, when gilts remained isolated from boars more of those housed under the short-day regimens reached puberty in both Study 3 ( 10 18 vs. 1 17 , P < 0.01 ) and Study 4 ( 10 19 vs. 0 17 , P < 0.01 ). The mean age at puberty was 209.3 ± 3.13 days in Study 3 and 214 ± 2.61 in Study 4. These data, obtained from gilts housed at constant cool temperatures under controlled light regimens which closely mimicked natural photoperiods, show conclusively that long days are inhibitory to attainment of puberty in the gilt. This finding provides compelling evidence that photoperiod is the major environmental factor responsible for the delay in puberty often seen during the summer under field conditions.

Boar-induced puberty in gilts handled pleasantly or unpleasantly during rearing

The effect of handling during rearing on attainment of puberty in response to daily exposure to a mature boar was studied using 70 gilts. The gilts were either handled pleasantly (patted and stroked) or unpleasantly (given a brief electric shock) when they approached the experimenter during handling sessions which were imposed for 3 min, 3 days per week for 12 weeks from 80 to 164 days of age. In a 3-min behavioural test at 164 days of age, pleasantly handled gilts were quicker to approach within 0.5 m of the experimenter ( P < 0.01), spent more time within 0.5m ( P < 0.05) and interacted more quickly ( P < 0.01) and more frequently ( P < 0.05) than gilts handled unpleasantly. There was no difference between treatment groups in growth rate or in the overall proportion of gilts which attained puberty but the mean interval from first boar exposure to puberty was shorter for unpleasantly handled gilts (20.6 vs. 27.3 days, P < 0.05). At 10, 15 and 20 days after first boar exposure, significantly more unpleasantly handled gilts had reached puberty than had pleasantly handled gilts ( P < 0.05). The ratio of the cross-sectional area of the adrenal cortex to the adrenal medulla was not affected by handling treatment (3.41 ± 0.24 vs. 3.57 ± 0.27 for pleasantly and unpleasantly handled gilts, respectively). We conclude that the unpleasantly handled gilts were not chronically stressed but were more sensitive to acute stress making them more, not less, responsive to puberty stimulation by a boar. The data also suggest that grouped gilts respond differently to gilts housed alone and that fear of humans is not necesarily indicative of chronic stress in the gilt.

Influence of manure gases on the onset of puberty of replacement gilts

AbstractTo determine whether gases generated during the breakdown of accumulated manure in an environmentally regulated building affects the onset of puberty in gilts, 42 crossbred gilts, born from 1 o t 15 September 1985, were reared indoors from 10 to 30 weeks of age on concrete slats over a pit that was drained and refilled with clean water biweekly (clean group). Forty-two gilts were reared over a pit where manure was allowed to accumulate (control group). These two groups had similar feeding, water, floor space, lighting and room temperature. A third group of 42 crossbred gilts was reared from 10 to 30 weeks of age in an open-front building with a concrete apron (outdoor group). Concentration of aerial ammonia in the control environment was three- to five-fold higher than in either the clean or the outdoor environment (P &lt; 0·001). Average daily gain and food conversion efficiency were similar for the two indoor treatment groups, but the outdoor group gained less weight than either indoor group (P &lt; 0·05). At 26 weeks of age all gilts were exposed to mature boars daily for 2 weeks, then every 2nd day for an additional 2 weeks. A greater proportion of gilts in the clean environment attained puberty 7 days (P &lt; 0·05) and 10 days (P &lt; 0·07) after first exposure to boars. These data suggest that odorous gases, such as ammonia, in the air of environmentally regulated buildings may diminish the stimulatory influence of boars on the onset of puberty in gilts.

Study of follicular development and heredity of morphological types of ovaries in prepuberal gilts.

Two different morphological types of ovaries ("grape" and "other" types) previously described by microscopic examination were studied on 107 live gilts. The ovarian type and distribution of macroscopic follicles during the prepuberal period were determined at 140, 160 and 180 d of age by laparoscopic examination. The incidence of grape-type (GT) ovaries was higher (P less than .05) at 140 d of age (50.5%) than at 160 d (38.3%) or 180 d (35.5%). At maturity (d 19 of the first postweaning estrus), 37.7% of the ovaries were classified as GT. The proportion of gilts that maintained their initial type (at 140 d of age) at 160 d, 180 d and at maturity was higher (P less than .05) for the gilts having the other-type (OT) ovaries (49% and 25% for OT and GT, respectively). The mean number of small follicles (1 to 3 mm in diameter) was higher (P less than .05) for the OT ovaries at 140 d (71.5 vs 18.0), at 160 d (79.3 vs 26.2) and at 180 d (77.0 vs 32.8). The number of follicles of 4 to 5 mm was higher (P less than .05) for GT ovaries at 140 d (16.4 vs 4.8), at 160 d (20.9 vs 4.8) and at 180 d of age (21.4 vs 5.7). The large follicles (greater than or equal to 6 mm) were more numerous for the GT at 140 d (7.0 vs .3), at 160 d (5.7 vs .5) and at 180 d (4.4 vs .6). No statistical difference was observed at maturity in the distribution of follicles between the two types.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of duration of boar exposure on the frequency of gilts reaching first estrus.

One-hundred crossbred gilts were used in an experiment that was designed to examine the effects of duration of boar exposure on the proportion of gilts reaching first estrus. Two replicates (summer and fall) of 50 gilts each were randomly assigned, within litter, to one of the following treatments: 1) 30 min of daily boar exposure, 2) 15 min of daily boar exposure, 3) 5 min of daily boar exposure, 4) continuous fence-line boar exposure, plus walked to a neutral pen and exposed to a different boar for 10 to 15 min daily, or 5) continuous fence-line boar exposure. Boar exposure lasted for 30 d. The percentage of gilts exhibiting first estrus by 210 d of age ranged from a high of 65.0 for treatment 4 to a low of 10.0 for treatment 5. Treatments 1, 3 and 4 were greater than treatment 5 (P less than .05), but not different from treatment 2. There were no differences in average age at first estrus. Treatment means for days to puberty after boar exposure were not different (P greater than .05). However, a significant treatment X season interaction occurred. This interaction appears to suggest seasonal trends. These results indicate that treatments 1 and 4 (30 min daily and continuous fence-line boar exposure plus 10 to 15 min, respectively) were the most effective methods tested for the induction of first estrus.

The effect of boar contact on the maintenance of cyclic activity in gilts after the hormonal induction of puberty

A single injection of 400 i.μ. pregnant mare's serum gonadotrophin (PMSG) plus 200 i.μ. human chorionic gonadotrophin (HCG) has been shown to induce puberty in a high proportion of gilts treated (Burnett and Walker, 198S). However, studies indicate that the hormone treatment may fail to initiate normal oestrous cycling after the pubertal ovulation. The work of Paterson and Lindsay (1981) has shown that housing gilts in contact with boars throughout the cycle after puberty induction will enhance the proportion of animals which maintain cyclic activity to a second ovulation. The purpose of the experiment reported here was to examine the effect of boar contact and the timing of the introduction of boar contact on the maintenance of cyclic activity after puberty induction by PMSG + HCG.