The association between growth rate, body weight, backfat thickness and age at first observed oestrus in crossbred Landrace x Yorkshire gilts

The present study aims to investigate the association between growth rate (GR), body weight (BW), backfat thickness (BF) and age at first observed oestrus in crossbred Landrace x Yorkshire (LY) replacement gilts in the tropics. The study was carried out on five commercial swine herds in Thailand between 2004 and 2006. A total of 6946 LY gilts were included. The gilts entered the herd at about 163 days of age. The BW (kg) and BF (mm) of the gilts were measured when the gilts entered the gilt pools and again when the gilts were sent to the breeding house. The GR from birth to entry into the gilt pools (birth to 90 kg BW) (GRe), the GR from entry into to exit from the gilt pools (91-134 kg BW) (GRi) and the GR from birth until the gilts were sent to the breeding house (birth to 134 kg BW) (GRs) were calculated. The relationship between age at first observed oestrus and GRe, GRs, GRi, BW and BF were analyzed. Pearson's correlation and four general linear models (GLMs) were conducted. On average, the gilts showed first observed oestrus at 200+/-28 days of age. The means of age at first observed oestrus varied from 188 to 251 days (P<0.001) among the herds. The GRs of the gilts significantly correlated with the BW (r=0.55, P<0.001) of the gilts when they were sent to the breeding house and the age at first observed oestrus (r=-0.40, P<0.001). Gilts with a high GRe and GRs were younger at first observed oestrus compared to gilts with a low GRe and GRs. On average, the gilts with GRs of over 604 g/day showed first observed oestrus before 5 months of age. GRi was not correlated with the age at first observed oestrus (P>0.05). Neither the BF of the gilts at entry nor the BF that the gilts gained within the gilt pools significantly correlated with age at first observed oestrus (P=0.29 and P=0.69, respectively). But the gilts with a higher BF at entry tended to have a higher BW when they were sent to the breeding house (r=0.44, P<0.001). The present study indicates that replacement gilts with a high GR (both GRe and GRs) tend to show sign of oestrus earlier than gilts with a low GR (both GRe and GRs).     

Effect of birth litter size, birth parity number, growth rate, backfat thickness and age at first mating of gilts on their reproductive performance as sows

The present study was performed to evaluate retrospectively the influence of birth litter size, birth parity number, performance test parameters (growth rate from birth to 100kg body weight and backfat thickness at 100kg body weight) and age at first mating (AFM) of gilts on their reproductive performance as sows. Traits analysed included remating rate in gilts (RRG), litter size, weaning-to-first-service interval (WSI), remating rate in sows and farrowing rate (FR). Data were collected from 11 Swedish Landrace (L) and 8 Swedish Yorkshire (Y) nucleus herds and included 20712 farrowing records from sow parities 1-5. Sows that farrowed for the first time during 1993-1997, having complete records of performance test and AFM, were followed up to investigate their subsequent reproductive performance until their last farrowing in 1999. Analysis of variance and multiple regression were applied to continuous data. Logistic regression was applied to categorical data. The analyses were based on the same animals and the records were split into six groups of females, i.e. gilts, primiparous sows, and sows in parities 2-5, respectively. Each additional piglet in the litter in which the gilt was born was associated with an increase of her own litter size of between 0.07 and 0.1 piglets per litter (P<0.001). Gilts born from sow parity 1 had a longer WSI as primiparous sows compared with gilts born from sow parity 4 (0.3 days; P<0.05) or parity 5 (0.4 days; P<0.01). Gilts with a higher growth rate of up to 100kg body weight had a larger litter size (all parities 1-5; P<0.05), shorter WSI (all parities 1-5; P<0.05) and higher FR (parities 2 and 5; P<0.05) than gilts with a lower growth rate. Gilts with a high backfat thickness at 100kg body weight had a shorter WSI as primiparous sows (P<0.001) compared with low backfat gilts, and 0.1 piglets per litter more as second parity sows (P<0.01). A 10 day increase in AFM resulted in an increase in litter size of about 0.1 piglet for primiparous sows (P<0.001) and a decrease (P<0.05) for sow parities 4 and 5.     

Effect of insemination of estrus-induced prepuberal gilts on ensuing reproductive performance and body weight

Prepuberal gilts reared and managed to 85-90 kg live weight in a common system were allocated at random to one of three first-mating treatments in an experiment conducted over a period of more than 5 years. In two of the treatments, gilts received a single i.m. injection of 400 IU equine chorionic gonadotropin (eCG) and 200 IU human chorionic gonadotropin (hCG) (PG600; Intervet) and were either inseminated 4 and 5 days later on a fixed-time basis regardless of oestrus (treatment A), or at the second oestrus following treatment (treatment B). The third group of gilts remained untreated and was inseminated on the first spontaneous oestrus (treatment C). Thereafter, all gilts were managed in the same way and those observed in oestrus were re-inseminated. Significantly more gilts returned to oestrus after the first service in treatment A (35%) than in treatment B and C (12 and 17%, respectively; P<0.01). Gilts farrowed to the first or repeat inseminations at a significantly younger age (P<0.01) in treatment A (304 days) than treatment B (324 days) and C (320 days). The age difference at farrowing remained in surviving gilts at the end of their third parity. The first farrowing performance of the gilts was significantly affected by treatment in terms of litter size at birth (A 7.0, B 8.4 and C 8.3 live piglets per gilt; P<0.01), litter size at weaning (A 6.2, B 7.2 and C 7.2 live piglets per gilt, P<0.05), and piglet birth weight (A 1.4, B 1.3 and C 1.3 kg; P<0.05) but piglet survival rate and weaning weight were not affected by treatment. The live weights of the gilts were significantly different between the treatments at first insemination (A 95.7, B 106.5 and C 109.2 kg; P<0.01) but not when the first litter was weaned (A 133.6, B 135.1 and C 136.6; P>0.05). After the first farrowing there were no differences between the treatments in terms of the survival rate, productive or reproductive performance of the gilts/sows and their offspring. Without conducting a detailed cost-benefit-calculation it was deduced that, from an economical point of view, differences between treatment A and treatments B and C are negligible because the savings associated with farrowing at a younger age on this treatment just about compensated for any additional costs associated with the treatment and the lower number of piglets born at the first farrowing.     

Relationships between ovulation rate and litter size in purebred Landrace and Yorkshire gilts

The aim of the present study was to investigate the ovulation rate and its relationship to number of total piglets born in purebred gilts under tropical climatic conditions. This study was conducted in two swine breeding herds (A and B) in the northeastern part of Thailand. The sources of swine genetic material originate from West Europe. Gilts were mated (AI) on the second or later observed estrus at a body weight of at least 130 kg. In most cases, they were mated at third estrus. One hundred and twenty-seven gilts, 24 Landrace and 24 Yorkshire from herd A, and 42 Landrace and 37 Yorkshire from herd B were used. Gilts were examined once by laparoscopy under general anesthesia between days 8 and 15 after mating. The ovaries were examined and the pathological findings were recorded. The number of corpora lutea was counted, and was assumed to equal the ovulation rate. Subsequent mating results and farrowing data were recorded. The data were analyzed with analysis of variance. Single or double unilateral cysts and par-ovarian cysts did not affect mating results. Landrace gilts were significantly younger at first mating than Yorkshire gilts (244 versus 249 days, P < 0.05). At first mating, Yorkshire gilts had a significantly higher ovulation rate compared to Landrace gilts (15.3 versus 13.8, P < 0.001). There was no difference in the number of total piglets born per litter between the two breeds, but the total prenatal loss from ovulation to farrowing was significantly higher in Yorkshire than in Landrace gilts. Both the low ovulation rate and the high prenatal loss contribute to the low litter size in gilts raised under tropical climatic conditions.     

Age at puberty, ovulation rate, uterine length, prenatal survival and litter size in Chinese Meishan and Yorkshire females

Studies on the ovulation rate, prenatal survival and litter size of Chinese Meishan pigs have given widely divergent results depending on the extent of inbreeding of the animals, their original genetic diversity, the age and parity, and the conditions of management. To obtain meaningful results, it is necessary to characterize the population under study. The following report characterizes populations of Meishan and Yorkshire of a widely diverse background. First farrowing data were collected on 21 Meishan and 20 Yorkshire gilts. Meishan gilts had 12.4 fully formed piglets and Yorkshire gilts had 7.4 fully formed piglets (P < 0.01). Meishan gilts averaged 1.86 mummified fetuses per litter vs 0.05 per Yorkshire litter (P < 0.01). Yorkshire piglets averaged 1.3 kg body weight at birth vs 0.9 kg for Meishan piglets (P < 0.01). At 47 days of second gestation, 19 Meishan and 12 Yorkshire sows averaged 22.7 and 16.3 corpora lutea (CL), respectively (P < 0.01). Uterine length and number of fetuses were not different (P > 0.40) in the two breeds. Daily estrous detection of 50 Meishan and 34 Yorkshire gilts began at 60 and 120 days of age, respectively. Meishan gilts reached sexual maturity at 95 days of age, which was 105 days earlier than Yorkshire gilts (P < 0.01). Meishan gilts were in estrus nearly 1 day longer than Yorkshire gilts at first, second and third estrus (P < 0.05). No differences in cycle length between breeds were detected for the first or second estrous cycle (P > 0.60). Nineteen Meishan gilts were slaughtered at 51 days of gestation and their reproductive tracts were recovered. The mean number of dissected CL (17.0), number of fetuses (13.1), total uterine length (396 cm), spacing per fetus (29.9 cm), allantoic (124.9 ml) and amniotic (32.2 ml) volumes, crown-rump length (82.8 mm), weight (35.4 g), sex, and direction of each fetus were determined. Chinese Meishan gilts reached puberty much earlier and were in estrus longer than Yorkshire gilts and Meishan sows had more CL than Yorkshire sows.     

Endocrine and ovulatory responses of the gilt to exogenous gonadotropins and estradiol during sexual maturation

Three studies were conducted to investigate the endocrine and ovulatory responses of the prepubertal gilt to exogenous estradiol and gonadotropins. In Study One, prepubertal gilts of 190 days of age were injected s.c. with pregnant mare's serum gonadotropin (PMSG) or physiological saline (SAL). Following PMSG injection, circulating levels of estradiol-17 beta (E2) increased. This increase was followed by a surge of luteinizing hormone (LH), estrus, a rise in progesterone (P4) levels, and ovulation. None of the gilts given SAL had increased levels of E2, LH or P4, and none ovulated. In Study Two, prepubertal gilts of 165 days of age were treated with varying doses of PMSG. A positive correlation was observed between dose of PMSG and peak levels of E2 (r = 0.83, P less than 0.001) and between dose of PMSG and number of corpora lutea (r = 0.96, P less than 0.001). In Study Three, gilts were treated at ages of 70 to 190 days with estradiol benzoate (EB), PMSG, or corn oil plus saline (CO/SAL) followed in 72 to 96 h by human chorionic gonadotropin (hCG) or SAL. All gilts treated with EB at 100 to 175 days of age had two surges of LH at an approximately 24-h interval. Gilts responding to EB at 70 and 190 days had only one surge of LH. Gilts of 100 days of age or older responded to PMSG with a single surge or two surges of LH. Ovulation in response to treatment was observed in gilts of 100 days of age or greater but not at 70 days. The conclusions drawn from these studies are that 1) PMSG-induced ovulation is preceded by an increase in circulating levels of E2 and in some gilts by a surge of LH, and 2) prepubertal gilts are able to respond to exogenous endocrine stimulation with either a single surge or multiple surges of LH at 70 to 190 days but are unable to ovulate in response to exogenous gonadotropins until 100 days of age.     

Litter size and piglet traits of gilts with different prolactin receptor genotypes

Seventy-seven Large White x Meishan F2 crossbred gilts with prolactin receptor (PRLR) genotype AA (n = 26), AB (n = 36) and BB (n = 15) were compared for teat number (FTm), age at first estrus, gestation length (GL), litter size, and litter means of functional teat number (FTp), birthweight (BW), and pre-weaning growth rate (GR). Own placental information was available for 88% of 620 live-born piglets (62 gilts), since placentae were labeled during farrowing. The effect of PRLR genotype of the mother on average placenta weight (PLW) and placenta efficiency (EFF = BW/PLW), was therefore, also analyzed, PRLR genotype significantly (P < 0.05) affected age at first estrus and, as a result (since the gilts were inseminated at a fixed estrus number), age and bodyweight at insemination. Furthermore, PRLR genotype affected total number of piglets born (TNB, P = 0.056) and number of piglets born alive (NBA, P = 0.072), but it did not affect (P > 0.3) GL, BW or GR, neither before nor after correction for litter size. BB gilts were significantly younger at first estrus and younger and lighter at insemination than AA gilts (P < 0.05). AA gilts had larger TNB (P = 0.047) and tended to have a larger NBA (P = 0.062) than BB gilts. TNB was 11.4 +/- 0.7, 10.8 +/- 0.6, and 8.8 +/- 0.9; NBA was 11.1 +/- 0.6, 10.5 +/- 0.6, and 8.7 +/- 0.9; BW was 1309 +/- 40, 1277 +/- 34, and 1290 +/- 53 g; and GL was 113.6 +/- 0.3, 113.8 +/- 0.3, and 113.5 +/- 0.4 days for AA, AB and BB gilts, respectively. The effects on litter size and age at first estrus are independent effects. PRLR affected PLW (P = 0.050) and EFF (P = 0.066), resulting in a difference between AA and BB gilts. PLW was 160 +/- 9, 181 +/- 7 and 196 +/- 11 g and EFF was 7.6 +/- 0.2, 7.3 +/- 0.2 and 6.7 +/- 0.3 for AA (n = 19), AB (n = 29) and BB (n = 14) gilts, respectively. After correction for TNB, the differences disappeared. Functional teat number of the AA. AB and BB gilts was 15.35 +/- 0.22, 15.53 +/- 0.18, and 15.60 +/- 0.29, respectively, and was not affected by PRLR genotype (P = 0.7). Functional teat number of piglets from AA, AB and BB mothers was 14.20 +/- 0.10, 14.37 +/- 0.08, and 14.63 +/- 0.13, respectively. Piglets from BB mothers had on average larger numbers of functional teats compared to piglets from AA mothers (P = 0.028). In conclusion, PRLR gene is a major gene or marker for age at first estrus, litter size, and litter average of number of functional teats in the Large White x Meishan F2 crossbred gilts studied. The favorable allele for litter size (A allele) is the unfavorable allele for age at first estrus and for litter mean of functional teat number.     

The effect of modified eros centre, outdoor raising or conventional group housing on breeding gilts and its effects on reproductive performance over four parities

The present study was conducted in a large Croatian "built up unit". The objective of the study was to determine if an indoor modified eros centre (MEC) compared to indoor or outdoor group housing of gilts, influenced the onset of puberty of gilts and the reproductive performance of the evaluated females (n = 783) over four parities. The gilts were from the same nucleus herd. Gilts of same age (140-150 days of age), body condition (body condition score of 3-4) and similar genetics (four-way cross females), during the same season (January to April 1999), were randomly divided at arrival into three groups and treated as follows:MEC gilts (n = 279): These were placed into indoor MEC pens in groups of 8-10. The gilts had continuous fenceline contact to boars (one boar to two groups of gilts, boars were changed daily) and to shortly weaned oestrous sows. Gilts were regrouped and dislocated at 10-day intervals. Outdoor gilts (n = 263): These were kept in groups of 8-10 on a large pasture (80-100 m2 per group). The animals had fenceline contact to mature boar for 5-10 min daily. Control indoor gilts (n = 241): These were housed indoors in large pens in groups of 8-10. The animals had fenceline contact to mature boars for 5-10 min daily. Each outdoor group had an insulated hut with straw bedding. All gilts were fed ad libitum with the same commercial diet. Housing gilts in MEC resulted in earlier (P < 0.001) onset of estrus (MEC: 174.8 +/- 2.4 days, indoor group housing: 207.6 +/- 4.1 days, outdoor group housing: 187.4 +/- 2.1 days) and lower (P < 0.001) farrowing rate to first service (MEC: 70.97%, indoor group housing: 89.73%, outdoor group housing: 89.62%). Farrowing rate of regularly returning MEC gilts to second service was 95.00%. First total-born litter size, first liveborn litter size, first wean-to-estrus interval (WEI), percent of sows bred after first weaning, second total-born litter size, second liveborn litter size, average third and fourth total-born and liveborn litter size, number of sows having four litters, number of litters per sow, total number of pigs per sow, total number of liveborn pigs per sow showed no significant differences between the groups. More (P < 0.05) sows were culled in outdoor group. Compared to MEC and outdoor housing, indoor housed sows suffered higher (P < 0.05) percentage of anoestrus.     

The effect of early contact with mature boars on reproductive efficiency in the gilt

The effect of first contact of gilts with a mature boar at 23 or 28 weeks of age on their subsequent reproductive efficiency was studied over a 12-month period at a large intensive piggery in southern Australia. Following this contact, the gilts entered the mating shed at 29 weeks of age and were checked daily for oestrus, as assessed by the back-pressure test in the presence of the boar. Gilts that showed moderate or high responses were taken to a boar for mating. Sexual receptivity was then assessed by the time taken to “stand” after the first mount by the boar. Gilts that remained unmated at 35 weeks of age were culled, and their ovaries were examined.Of the 2660 gilts in the study, 2349 were mated and they had a farrowing rate of 88.2% with a mean litter size of 9.5 piglets, of which 0.7 piglets (7.4%) were born dead. The reproductive efficiency of the gilts following earlier contact with the boar was consistently higher than that of gilts exposed later. The mating rate of the week 23 gilts was greater than that of the week 28 gilts (70.1 vs 66.0%, P < 0.01), more appeared to show a high level of sexual receptivity (97.0 and 94.6%, N.S.) and fewer failed to mate when put to a boar (6.1 vs 9.5%, P < 0.01). The percentage of prepubertal gilts at 35 weeks of age was also lower (1.46 vs 3.03%, P < 0.01). The improved reproductive performance was estimated to be equivalent to 0.24 extra piglets born per gilt.     

Factors influencing age at first mating in purebred Swedish Landrace and Swedish Yorkshire gilts

The aim of the present study was to retrospectively analyze causes of the variation in age at first mating in Swedish Landrace (L) and Swedish Yorkshire (Y) gilts. Production traits including growth rate from birth to 100kg body weight and backfat thickness at 100kg body weight were also studied. Data analyzed were obtained from 11 L and 11 Y nucleus herds and included gilts born during a 5-year-period from October 1993 until September 1998. The complete data set included information on 14,761 gilts (6997 L and 7764 Y). Traits analyzed included age of gilt at first mating, growth rate and backfat thickness. Seven statistical models were used for analyzing the data. Factors included were gilt breed, birth month, parity number and size of the litter in which the gilt was born as well as their interactions. Compared with Y gilts, L gilts grew faster (571 versus 556 g/day; P<0.001), had a thinner backfat (11.9 versus 12. 3mm; P<0.001) at 100kg body weight and were 12 days younger at first mating (237 versus 249 days; P<0.001). Birth month significantly (P<0.001) influenced age at first mating, growth rate and backfat thickness. Gilts born from smaller litters were mated at younger age than gilts born from larger litters even when age at first mating was adjusted for the effect of growth rate and backfat thickness. Growth rate of the gilts decreased when 'birth litter size' increased. Gilts born from primiparous sows grew slower, had a thinner backfat at 100kg body weight and were older at first mating compared with gilts born from multiparous sows. Gilts with a higher growth rate were younger at first mating than those with a lower growth rate. Gilts with a thicker backfat at 100kg body weight were mated earlier than the thin ones. However, the effect of growth rate on age at first mating was more pronounced in the gilts with a thinner backfat rather than the ones with a thicker backfat.     

Effect of a GnRH analogue (Maprelin) on the reproductive performance of gilts and sows

The ability of peforelin (l-GnRH-III) to stimulate follicular growth, FSH release, and estrus in gilts after altrenogest treatment and in sows after weaning was investigated. In three farrow-to-wean herds, with at least 600 sows and average production performance, 216 gilts, 335 primiparous, and 1299 pluriparous sows were randomly allocated to three treatments: peforelin (M group: Maprelin), eCG (F group: Folligon), and physiological saline solution (C group). Animals were treated 48 hours after their last altrenogest treatment (gilts) or 24 hours after weaning (sows). The weaning-to-estrus interval, estrus duration, estrus rate (ER), pregnancy rate, and total born (TB), live born, and stillborn (SB) numbers were recorded and compared between treatments for the different parity groups (gilts and primiparous and pluriparous sows). Follicle sizes were measured in representative animals from each group on the occasion of their last altrenogest treatment or at weaning, and also on the occasions of their first (FS1) and second (FS2) attempted inseminations. Blood samples were taken to determine FSH concentrations at weaning and 2 hours after injection, and progesterone concentrations 10 days after the first insemination attempt. The relative change in FSH concentrations was calculated. Significant differences were found for ER within 7 days of weaning in pluriparous sows (95%, 91%, and 90% for the M, F, and C groups, respectively, P = 0.005). Gilts in the F-group had high TB numbers, and pluriparous sows in the M group had high SB numbers (TB gilts = 13.6, 15.4, and 14.9 [P = 0.02] and SB pluriparous sows = 1.8, 1.4, and 1.7 [P = 0.05] for the M, F, and C groups, respectively). The M group had the highest FS1 (for gilts) and FS2 (for pluriparous sows) values: FS1 = 5.4, 4.9, and 4.9 mm [P = 0.02] and FS2 = 6.8, 5.3, and 6.3 mm [P = 0.03] for the M, F, and C groups, respectively. There were no significant differences between the different treatments within each parity group with respect to any of the other variables. Overall, peforelin treatment had small but positive effects on the ER and follicle growth in certain parity groups but did not seem to affect litter sizes or FSH and progesterone levels in sows on the occasions of the corresponding examinations.     

Influence of time of insemination relative to ovulation and frequency of insemination on gilt fertility

The objectives of this study were to determine the optimal time of insemination in the pre-ovulatory period (from 32 to 0 h before ovulation) and to evaluate once-daily versus twice-daily inseminations in gilts. In Experiment 1, pre-puberal gilts (n=102) were observed for estrus every 8h and ultrasonography was performed every 8h from the onset of estrus to confirmation of ovulation. The gilts were inseminated once with 4 x 10(9) spermatozoa at various intervals prior to ovulation. Pregnancy detection was conducted 24 days after AI and gilts were slaughtered 4-6 days later. Corpora lutea and the number of viable embryos were counted and the embryo recovery rate was calculated (based on the percentage of corpora lutea). Inseminations performed <24h before ovulation resulted in a higher embryo recovery rate (P=0.02) and produced 2.1 more embryos (P=0.01) than inseminations >or=24h before ovulation. However, the pregnancy rate was reduced when inseminations were performed >16 h before ovulation (P=0.08). In Experiment 2, pre-puberal gilts (n=105) were observed for estrus every 12h and ultrasonography was performed every 12h from the onset of estrus to confirmation of ovulation. Gilts were inseminated (with 4 x 10(9) spermatozoa) 12h after the onset of estrus, with inseminations repeated either every 12h (twice-daily) or 24h (once-daily) during estrus. The gilts were allowed to farrow. There were no differences (between gilts bred twice-daily versus once-daily) for return to estrus rate (P=0.36) and adjusted farrowing rate (P=0.19). However, gilts inseminated once-daily had 1.2 piglets less than those inseminated twice-daily (P=0.09). In conclusion, gilts should be inseminated up to 16 h before ovulation, as intervals >16 h reduced pregnancy rate and litter size.     

Increased ovulation rate in gilts after oral administration of epostane

In Phase I of this study to enhance ovulation rate and hence litter size, gilts received 0 (sham control), 0.625, 1.25, 2.5 or 5.0 mg epostane/kg body weight on Days 10, 11 and 12 of the oestrous cycle (5 gilts/group). After epostane treatment, plasma progesterone concentrations were reduced (P less than 0.01) in a dose-related manner, % progesterone decline = 21.30 x square root of (dose) + 10.45, R2 = 0.70, but recovered to pretreatment levels by 24 h. In Phase II the effects of epostane on ovulation rate and litter size were tested at two study centres. At each centre 108 gilts were treated with the same doses of epostane as used in Phase I and the doses were given for 7 days (Days 15-21) or 12 days (Days 10-21) during the first oestrous cycle. Gilts were inseminated twice during the oestrus after treatment and were slaughtered 30 days later. Mean (+/- s.d.) ovulation rate was 16 +/- 2.7 (N = 8) and 21 +/- 4.0 (N = 61) for control and epostane-treated gilts in Centre A and 12 +/- 2.4 (N = 5) and 17 +/- 3.8 (N = 55) respectively in Centre B (P less than 0.01 for both) and was dose related (ovulation rate = 3.38 x square root of (dose) + 16.17, R2 = 0.31). The effects of 7- or 12-day epostane treatment on ovulation rate were not different (P greater than 0.05), indicating that effects of treatment after Day 14 of the oestrous cycle are most important to subsequent ovulation frequency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reproductive performance of high growth rate gilts inseminated at an early age

The aim of this work was to determine if gilts, which have a high growth rate (GR) could be mated earlier without reducing the reproductive performance or increasing the culling rate up to the third parity. Gilts of Camborough 22 (C22, n=568) breeding were mated and allocated into three groups according to weight and age on the insemination day. G1 (n=164)-gilts with a GR>or=700 g/d and inseminated at <210 d. G2 (n=165)-gilts with a GR>or=700 g/d and inseminated at >or=210 d. G3 (n=239)-gilts with a GR<700 g/d and inseminated at >or=210 d. All females were fed ad libitum from 150 d on and were inseminated at their second estrus or later. The minimum weight at mating was 127 kg. Three parities were studied, with farrowing rate, litter size and culling rate being compared. At the first parity, G2 gilts produced, on average, one more piglet than the other groups (P<0.05). However, when analyzing three parities, there were no differences in total born (11.6 x 12.3 x 11.7), farrowing rate (87.1% x 88.7% x 89.8%) and culling rate (30.2% x 25.3% x 28.2%) among G1-G3 groups, respectively (P>0.05). In conclusion, gilts, which had a minimum weight of 127 kg can be inseminated at their second or greater estrus, between 185 and <210 d of age, without impairing their productive performance over three parities.     

Productive performance, carcass and meat quality of intact and castrated gilts slaughtered at 106 or 122 kg BW

A total of 200 (Landrace × Large White dam × Pietrain × Large White sire) gilts of 50 ± 3 days of age (23.3 ± 1.47 kg BW) were used to investigate the effects of castration (intact gilt, IG v. castrated gilt, CG) and slaughter weight (SW; 106 v. 122 kg BW) on productive performance, carcass and meat quality. Four treatments were arranged factorially and five replicates of 10 pigs each per treatment. Half of the gilts were ovariectomized at 58 days of age (8 days after the beginning of the trial at 29.8 ± 1.64 kg BW), whereas the other half remained intact. The pigs were slaughtered at 106 or 122 kg BW. Meat samples were taken at Musculus longissimus thoracis at the level of the last rib and subcutaneous fat samples were taken at the tail insertion. For the entire experimental period, CG had higher (P < 0.05) BW gain and higher (P < 0.001) backfat and Musculus gluteus medius fat thickness than IG. However, IG had higher (P < 0.05) loin and trimmed primal cut yields than CG. Meat quality was similar for IG and CG but the proportion of linoleic acid in subcutaneous fat was higher (P < 0.001) for IG. Pigs slaughtered at 122 kg BW had higher (P < 0.001) feed intake and poorer feed efficiency than pigs slaughtered at 106 kg BW. An increase in SW improved (P < 0.001) carcass yield but decreased (P < 0.05) trimmed primal cut yield. Meat from pigs slaughtered at the heavier BW was redder (a*; P < 0.001) and had more (P < 0.01) intramuscular fat and less thawing (P < 0.05) and cooking (P < 0.10) loss than meat from pigs slaughtered at the lighter BW. In addition, pigs slaughtered at 122 kg BW had less (P < 0.01) linoleic acid content in subcutaneous fat than pigs slaughtered at 106 kg BW. Castration of gilts and slaughtering at heavier BW are useful practices for the production of heavy pigs destined to the dry-cured industry in which a certain amount of fat in the carcass is required. In contrast, when the carcasses are destined to fresh meat production, IG slaughtered at 106 kg BW is a more efficient alternative.     

Effects of transferred ova per recipient and dual use of donors as recipients on production of transgenic swine

The purpose of the study was to determine whether the number of transferred ova per recipient influenced the efficiency of producing transgenic pigs and whether donor gilts were as effective as unmated gilts as recipients of microinjected ova. Eight genes were microinjected into 4,232 ova that were transferred into 169 recipients over a 5-yr period. Although the farrowing rate and litter size was highest for recipients receiving 31 to 41 ova per recipient, the percentage of transferred ova developing into piglets was highest for recipients receiving 13 to 20 ova (P = 0.021 for all recipients and P = 0.011 for pregnant recipients). Based on these data we conclude transferring more than 20 ova per recipient may incur some loss due to uterine crowding. Gilts used as recipients of microinjected ova immediately after their own ova were flushed from their oviducts had the same farrowing rate, litter size, and ovum development efficiency as unmated gilts that were only used as recipients. However, donor-recipients that ovulated 21 or more ova had smaller litters (P = 0.009) and were less efficient in producing pigs (P = 0.024) and transgenic pigs (P = 0.054) from transferred ova than donor-recipients that ovulated 20 or fewer ova. Dual use of donors as recipients was an effective method of reducing the number of recipients in a transgenic pig project by nearly one-half.     

Synchronisation of oestrus in dairy cows using prostaglandin F2alpha,gonadotrophin-releasing hormone,and oestradiol cypionate

An oestrous synchronisation protocol was developed for use in lactating dairy cows using PGF(2alpha), GnRH, and oestradiol cypionate (ECP). In experiment 1, lactating dairy cows received two injections of PGF(2alpha) (on days 0 and 11) (PP; n=10) or two injections of PGF(2alpha) (days 0 and 11) and 100 microg of GnRH on day 3 (PGP; n=10). In experiment 2, cows were treated with PGP (n=7), or PGP and 1 mg of ECP at the same time (PGPE(0); n=7) or 1 day after the second PGF(2alpha) injection (PGPE(1); n=7). In experiment 3, 101 lactating dairy cows in a commercial herd were assigned to one of three treatments; PP, PGP, or PGPE(1). Follicular growth was measured by ultrasound in experiments 1 and 2. Every cow (experiments 1, 2, and 3) was blood sampled at selected intervals for progesterone and oestradiol assays and inseminated at oestrus. In experiment 1, a higher percentage of GnRH-treated cows ovulated after the first PGF(2alpha) injection (90% versus 50%; P<0.05). The GnRH-treated cows tended to have a larger dominant follicle present at the time of the second PGF(2alpha) injection (16.5+/-0.5 mm versus 15.0+/-0.7 mm; P<0.10). The percentage of cows that ovulated after the second PGF(2alpha) injection was similar (60%). In experiment 2, cows treated with ECP had higher peak preovulatory concentrations of oestradiol in plasma (6.99+/-0.63 versus 3.63+/-0.63; P<0.01) following the second PGF(2alpha) injection and a higher percentage ovulated (86% versus 43%; P<0.05). A higher percentage of PGPE(1)-treated cows in experiment 3 were observed in standing oestrus and ovulated after the second PGF(2alpha) injection (standing oestrus, 26.4, 34.3, and 62.6%, P<0.01; ovulated, 56, 63, and 78%, P<0.05; PP, PGP, and PGPE(1), respectively). In conclusion, the PGP protocol increased the number of cows that ovulated after the first PGF(2alpha) injection and produced a more mature dominant follicle at the time of the second PGF(2alpha) injection. Adding ECP to PGP (PGPE(1)) enhanced the expression of oestrus and increased ovulation percentage. The combination of PGP and ECP is potentially a new method to routinely synchronise oestrus and ovulation in dairy cows.     

The involvement of boar submaxillary salivary gland secretions in boar-induced precocious puberty attainment in the gilt

The involvement of secretions from boar submaxillary salivary glands in mediating the induction of precocious puberty in the gilt was investigated as follows. Forty-eight Large White × (Large White × Landrace) prepubertal gilts from 12 litters were randomly allocated within litters by weight, to four treatment groups of six, in two replicates, at 145 days of age. Treatments commencing at a mean group age of 165 days, were: (1) control (no boar exposure); (2) gilts exposed to a mature sialectomised boar (submaxillary salivary glands were removed at 9 weeks of age); (3) gilts exposed to a mature sham-operated boar; (4) gilts exposed to a mature unoperated boar.Boar exposure occurred for 30 min per day for 75 days, or until pubertal oestrus was observed. Gilts showing pubertal oestrus were removed and slaughtered. Ovaries were examined to confirm reproductive status. Gilts failing to exhibit oestrus by 240 days of age were slaughtered and nominally ascribed a pubertal age of 245 days. Age at puberty was significantly earlier in all three boar-exposed treatments than in the control treatment (P<0.05 for treatments 2 and 3, P<0.001 for treatment 4; median ages at puberty being 227.0, 203.5 , 202.0 and 179.0 days for treatments 1 to 4 respectively). No frothy saliva was ever produced by the sialectomised boar, and chromatographic analysis of saliva produced by the sham-operated boar during mating revealed very low levels of 16-androstene pheromones, while levels in the unoperated boar's saliva were normal. These results provide further evidence for an important role of boar salivary pheromones in the induction of precocious puberty attainment in the gilt.     

Oestrous behaviour in relation to fertility and fecundity of gilts

The reproductive performance of 2484 gilts was recorded over a 12-month period at a large intensive piggery in southern Australia. Between 29 and 35 weeks of age, gilts were examined daily for response to the back-pressure test (BPT). Those subjectively assessed as showing a moderate or high response were taken to a boar for mating. Gilts that had showed a moderate response to the BPT on their first day of mating had lower average litter size than gilts showing a high BPT response (9.05 and 9.35 piglets, respectively; P < 0.05). A quantitative assessment of sexual receptivity was made while the gilt was with the boar. Gilts that were mated while showing low sexual receptivity on the first day of mating had poorer farrowing rate (78.1 vs. 83.1%, respectively; P < 0.05), as well as lower litter size (9.03 vs. 9.35 piglets, respectively; P < 0.05) than gilts that were mated when showing high sexual receptivity. A moderate BPT response was followed by either low sexual receptivity or failure to mate on 81.4% of occasions, compared with 12.8% for a high BPT response. Since 75% of gilts that showed a moderate BPT response on the first day of mating showed a high response on the following day, it was concluded that mating should only be attempted when gilts exhibit a high response to the BPT. The mean farrowing rate and litter size for gilts at their first farrowing was 82.4% and 9.31 piglets (8.62 alive and 0.69 dead), respectively.     

The extent and timing of prenatal loss in gilts

The potential litter size of gilts that is based on the ovulation rate is much higher than the actual litter size, which depends on the fertilization rate and subsequent prenatal mortality. Prenatal mortality is divided into embryonic mortality (before Day 30) and fetal mortality (after Day 30). Prenatal loss includes both fertilization failure and prenatal mortality. Crossbred gilts (n = 149) were bred at the first observed estrus after being exposed to the boar at 200 days of age. Time of the first insemination after estrus detection was determined by measurement of vaginal conductivity using a Walsmeta meter. A second insemination was administered either 8 or 16 hours later. Artificial insemination with fresh semen (0 to 3 days old) was used throughout the experiment. Gilts were slaughtered on Day 3 (n = 26), Day 10 (n = 42), Day 30 of gestation (n = 45) or they were allowed to farrow (n = 36). Gilts slaughtered on Day 3 were used to estimate the fertilization rate. Gilts slaughtered on Day 10 and Day 30 were used to calculate embryonic mortality, while fetal mortality was calculated from the gilts that farrowed. The mean (+/-SEM) number of corpora lutea (CL) was 13.15+/-0.46, 13.36+/-0.37 and 12.97+/-0.39 for gilts slaughtered at Days 3, 10 and 30, respectively (P>0.05), and the mean (+/-SEM) number of normal embryos recovered was 11.12+/-0.69, 9.46+/-0.55 and 9.33+/-0.58, respectively. Litter size at parturition was 9.10+/-0.54. There was a significant difference between the number of normal embryos on Day 3 and Day 30 (P=0.05) and also between the number of normal embryos at Day 3 and the number of piglets at term. Ninety percent of the ova were recovered at Day 3. The fertilization rate was calculated either 1) assuming that unrecovered ova had a similar fertilization rate as the recovered ova (FRER=94.5+/-2.0%) or 2) assuming that unrecovered ova were unfertilized (FROR=84.5+/-2.5%). It was concluded that FRER was a more accurate estimation of the fertilization rate. Based on this fertilization rate, embryonic mortality between Day 3 and Day 10 was 20.8+/-8.3%, with an additional 12.5+/-7.1% loss between Day 10 and Day 30, when all gilts were included (P = 0.308). Thus the total prenatal loss, including fertilization failure, up to Day 10 was 26.3% and to Day 30 it was 38.8%. Fetal mortality was 2.2%, giving a total prenatal mortality (excluding fertilization failure) of 35.5% and a prenatal loss of 41%. Most of the prenatal loss was due to embryonic mortality. In those gilts that remained pregnant most of the embryonic loss occurred before Day 10 (19.0+/-6.3%; P=0.003). There was no further loss between Day 10 and 30 of pregnancy. There was a significant difference between the loss from Day 3 to Day 10 compared with the loss from Day 10 to Day 30 (P=0.05); therefore, most of the embryonic loss in pregnant gilts occurred before Day 10. Since fetal mortality was 3.2+/-6.3%, most of the prenatal loss was due to embryonic mortality.