Influence of number of gilts per pen on estrous traits in confinement-reared gilts

One hundred forty-four Yorkshire (Y) x Landrace (L) and Chester White (CW) x Large White (LW) reciprocal cross gilts (Trial I) and 147 CW:LW x Y:L reciprocal cross gilts (Trial II), 4.5 to 5 months old, were penned in groups of 3, 9, 17 or 27 (1.1 m(2)/gilt). Estrus was checked daily from seven to nine months of age. Reproductive tracts of all noncyclic gilts were examined at nine months of age. Between seven and nine months of age, 12% to 16% fewer (P<0.05) gilts in pens of three had regular estrous cycles, and the percentage of gilts with regular estrous cycles did not differ with more (9, 17 or 27) gilts/pen. At nine months of age, 56.9% of the gilts penned in groups of three were cyclic as compared to 78%, 80.4% and 80.7% of the gilts penned in groups of 9, 17 and 27, respectively. In Trial I, more (P<0.05) CW x LW reciprocal cross gilts were cyclic compared to Y x L reciprocal cross gilts at nine months of age. The CW x LW group had fewer behaviorally anestrous gilts and more cyclic gilts, regardless of the number of gilts/pen. The social cues involved in the process of sexual development of gilts remain undefined, but extremes in the number of gilts/pen should be avoided.     

Estrous activity in different breeds and breed crosses of sheep

Estrus was monitored in 715 straightbred and crossbred ewes during spring lactation, postweaning, summer and/or late summer breeding periods. Straightbred ewes were comprised of seven breeds, and crossbreds consisted of Rambouillet- and Finnsheep-sired ewes of the seven breeds. Estrus was detected in 5.4% of the Rambouillet and Finnsheep crossbred ewes during lactation. After weaning, the incidence of estrus was 1.1% in all crossbred and straightbred ewes. The incidence of estrus was 5.2% for all ewes during the summer period. During late summer (July 28 to August 17), 42% of all ewes showed estrus and both breed of sire and breed of dam influenced estrous activity (P<0.01). Straightbred Rambouillet, Targhee, Dorset and most Rambouillet-sired crossbred ewes showed the greatest estrous activity and could be the genetic stock of choice for early lamb production. Straightbred Hampshire, Suffolk and most Finnsheep crossbred ewes showed estrous activity later in the season. Results support the conclusion that certain sheep breeds and breed crosses show estrous activity during August, while other breeds and breed crosses begin estrous activity later and continue until March or April. Thus, lambs may be produced from January through September each year by maintaining several different breeds or breed crosses in the breeding flock.     

Effect of lighting regimen,rearing in isolation and olfactory bulbectomy on growth and puberty in Yorkshire gilts

This study was designed to determine the effects of isolation or group rearing, total darkness or constant light, and olfactory bulbectomy on growth and onset of puberty in Yorkshire gilts. Forty-eight gilts, 90 days old, were assigned randomly to the following treatments: rearing in isolation with constant darkness, IS-CD; isolation with constant light, IS-CL; isolation with natural summer daylength, IS-NL; group rearing with natural daylength, GR-NL. They were reared in these environments to 245 days of age, without exposure to a boar. Twelve gilts, ～ 100 days old, were olfactory-bulbectomized (OB) and ten sham-operated (SC) littermates served as controls. They were reared in natural daylength in their respective groups, without exposure to a boar. Average weekly gains were similar among all treatment and control groups, ranging from 4.5 to 4.8 kg. Percentages of gilts in groups IS-CD, IS-CL, IS-NL and GR-NL that exhibited pubertal estrus by 245 days of age were 50, 50, 50 and 75, respectively (P>0.05), and the corresponding average ages of them at puberty were 208, 220, 213 and 205 days (P>0.05). In OB gilts, the percentage of them cycling at 270 days (33) was less (P<0.05) than that of SC (80). Sequential profiles of peripheral blood serum concentrations of progesterone confirmed normal estrous cycles after pubertal estrus of individual gilts among all treatment and control groups. These results indicate that rearing of gilts in isolation with either total darkness or constant light has no significant detrimental effect on their growth, age at onset of pubertal estruc and subsequent estrous cycles. Olfactory bulbectomy during the prepubertal period, however, delays onset of puberty but does not result in permanent loss of ovarian function.     

Failure of the orally active progestin, Regu-mate, to overcome confinement-induced delayed puberty in gilts

Thirty-three crossbred gilts that were raised in total confinement were randomly allotted to two adjacent pens in a finishing unit at 144.7 +/- .5 days of age and 58.0 +/- 1.7 kg body weight. At approximately 253 days of age, 16 gilts were group fed a daily dose of 20 mg of Regu-mate per gilt for 18 days and 17 control gilts were group fed the same diet without Regu-mate for 18 days. Ovarian morphology was examined on 11 or 12 days after the last feeding of Regu-mate. Based on estrous behavior and ovarian morphology only one Regu-mate gilt displayed an estrus but did not ovulate and only three of the control gilts displayed estrus and ovulated at least once before the start of treatment. Three of the 16 Regu-mate gilts displayed estrus and ovulated 7.3 +/- .3 days after the last feeding and within the same time period the 3 control gilts, which previously displayed estrus, continued to have estrous cycles. One additional control gilt displayed estrus and ovulated 5 days after the last feeding of the control diet. Therefore, the proportion of gilts that displayed estrus and ovulated by the end of the experimental period were similar for the treated (25.0%) and control (23.5%) groups. Based on these results we conclude that treatment of gilts in a state of confinement-induced delayed puberty with 20 mg Regu-mate daily for 18 days failed to result in a synchronized onset of puberty in a significant proportion of gilts.     

Delayed puberty in gilts in total confinement

Two hundred fourteen crossbred gilts, born in January through March and June through July of two different years, were raised in total confinement until 100 to 120 days of age and then moved to an outside dirt lot (non-confined) or to a single pen in a confinement, finishing building (confined). Beginning at 150 days of age, estrus was checked daily with a boar to determine percentage of gilts that attained puberty and age at first estrus, and weekly blood samples were collected and analyzed for progesterone by radioimmunoassay to determine age at first ovulation. In the Jan.-Mar. born gilts, 75.4% of the non-confined gilts and 37.4% of the confined gilts attained puberty by 270 days of age (P<.001). Although differences were not significant in the gilts born in June-July, more non-confined gilts (62.6%) than confined gilts (50.9%) attained puberty. Of the 121 gilts that ovulated, only 1 non-confined and 3 confined gilts did not exhibit estrus. Average age at first estrus or at first ovulation were similar for confined and non-confined gilts. Adrenal gland weights at 250 to 270 days of age were similar also for confined and non-confined gilts. Based on the results of this study, we conclude that total confinement housing can reduce, by as much as 50%, the proportion of gilts that attain puberty by 8 to 9 months of age and that time of year may influence the extent of delayed puberty.     

Alteration of the estrous cycle of gilts by movement to a confinement housing system

Thirty-six crossbred gilts were maintained in outside dirt lots for 2 or more estrous periods. Eighteen of the gilts were moved to another outside dirt lot (non-confined) and the other eighteen were moved to a single pen in a confinement finishing building (confined). A blood sample was collected on the day of movement and every 7 days thereafter for 12 weeks and quantitated for progesterone to verify the occurrence of each ovulation. Any estrous cycle shorter than 18 days or longer than 23 days was classified as abnormal. The duration of estrous cycles of non-confined gilts were not different before, during or after movement, whereas the duration of estrous cycles were greater (P=.005) during movement than before movement in the confined gilts. The duration of estrous cycles of confined gilts were greater (P=.020) than those of non-confined gilts during movement. The percentage of abnormal estrous cycles were greater during movement than before (P=.007) or after (P=.052) movement for the confined gilts, whereas the percentage age of abnormal estrous cycles were greater (P=.050) during movement than before movement in non-confined gilts. Therefore, the greatest percentage of abnormal estrous cycles occurred during movement in both groups. A single incident of silent estrus followed by normal estrous cycles was observed. In addition, an estrus occurred while plasma progesterone concentration was elevated (51 ng/ml) and was followed by normal estrous cycles.     

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.     

A note on the effects of contact frequency and time of day of boar exposure on the efficacy of the boar effect

Sixty-four Large White/Landrace crossbred gilts were used in this study, 16 gilts being allocated to each of four treatments to compare the effects on puberty attainment of exposure to boar contact either 0, 1 or 2 times daily. The once-daily exposure occurred in either the morning or the afternoon (AM vs. PM). Treatments were of 20-min duration starting at a mean gilt age of 160 days and continuing for 60 days. Boar exposure significantly increased the proportion of gilts attaining puberty within 60 days of the commencement of treatments (P < 0.05) compared with gilts not receiving boar contact. Gilts receiving boar exposure twice daily attained puberty significantly earlier than did gilts in the two treatment groups (AM and PM, respectively) given a single daily boar exposure period (mean gilt ages at puberty 176.4 vs. 192.7 and 189.2 days of age, respectively, P < 0.05). It is concluded that (a) twice-daily boar contact enhances the efficacy of the boar effect in gilts above that seen with a single daily boar exposure period and (b) this enhanced response of the gilt is due to the frequency of boar contact and not to the time of day at which the contact occurs.     

Determination by echography of uterine changes around puberty in gilts and evaluation of a diagnosis of puberty

Three experiments were carried out to evaluate the use of ultrasonography in assessing the onset of puberty in gilts. In experiment 1, gilts (n = 17) were scanned 3 times per week beginning at 133 and continuing until 187 days of age. The ultrasonic appearance of the uterus was described, quantified and compared with the reproductive status observed at slaughter. The quantification of the pictures showed a different correlation in time for infantile, impubertal, prepubertal and pubertal stages. For pubertal females, "uterine area" increased at around 180 days of age, well-defined sections of the uterine horns appeared 3 +/- 0.5 days before puberty. In infantile and impubertal gilts during the same period of age, uterine images remained dark and homogeneous; no significant change in the "uterine area" was observed. This difference in images allowed an evaluation of the diagnosis of puberty. In experiment 2, the gilts (n = 123) were scanned, the result was verified at slaughter the day after by examination of the genital tract. The uterine weight of the gilts that had reached a prepubertal or pubertal stage was significantly greater (P = 0.0001) than that in impubertal gilts. The sensitivity and the specificity of the diagnosis were 91.9% and 96.5% respectively. Experiment 3 was performed on a farm and echographic examinations were carried out one and five days after gilts (n = 117) arrived at the piggery. Oestrus detection or blood sampling for progesterone determinations were used as tools to determine the reproductive status. The sensitivity and the specificity of the diagnosis were 98.9% and 100% respectively. This diagnosis of puberty is thus accurate.     

Age, body weight and backfat thickness at first observed oestrus in crossbred Landrace x 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 x 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.     

Metabolic clearance and production rates of oestradiol and progesterone during pubertal and postpubertal development in gilts

The crossbred gilts studied were aged 80 days (prepubertal), 180 days (prepubertal or postpubertal) and 260 days (postpubertal or pregnant). Estimates of metabolic clearance rate (MCR) of oestradiol and progesterone were consistently less (21 and 27%) in plasma than in blood, and these differences were not influenced by age of gilt. The MCR (1/day per kg body weight) for oestradiol and progesterone in plasma was greater (P less than 0.05) for 80-day-old prepubertal gilts than for older gilts. The MCR values of oestradiol and progesterone were similar in 180-day-old and 260-day-old gilts independent of reproductive state. Production rate (PR) of oestradiol and progesterone increased with age (80-180 days), and age and reproductive state differences were much more pronounced for PR of progesterone than of oestradiol. These results support the hypothesis that a reduction in the MCR and an increase in PR of oestradiol and progesterone in the gilt are associated with the process of pubertal development, and changes in gonadal steroid concentrations appear not to alter the MCR of oestradiol and progesterone.     

Absence of brain opioid peptide modulation of luteinizing hormone secretion in the prepubertal gilt

Three experiments were conducted to evaluate the role of endogenous opioid peptides (EOP) in modulating luteinizing hormone (LH) secretion in the prepubertal gilt. In Experiment I, 8 prepubertal (P) gilts, 160-170 days of age (puberty = 197 +/- 10 days), received either 1 (n = 2), 3 (n = 3), or 6 (n = 3) mg/kg BW of naloxone (NAL), an opiate antagonist, in saline i.v. Blood was collected by jugular vein cannula every 15 min for 2 h before and 2 h after NAL. All doses of NAL failed to alter serum LH concentrations. In Experiment II, 21 P gilts 160-170 days of age and 21 mature (M) gilts were ovariectomized (OVX). At the time of OVX, gilts were classified as prepubertal if their ovaries were devoid of corpora albicantia and corpora lutea. Three weeks after OVX, P and M gilts were injected twice daily for 10 days with either 0.85 mg/kg BW of progesterone (P4) or oil vehicle (V), resulting in the following groups: PP4 (n = 11), PV (n = 10), MP4 (n = 11), and MV (n = 10). All gilts received 1 mg/kg BW of NAL on the last day of treatment. Blood samples were collected via a jugular cannula every 15 min for 4 h before and 2 h after NAL treatment. NAL treatment resulted in an increase (p less than 0.05) in serum LH concentrations only in the MP4 gilts. In Experiment III, 15 OVX gilts 280 days of age were used. Ten of the 15 gilts were OVX prior to puberty at 160 days of age and were classified as chronologically mature (CM) at the time of treatment. The remaining 5 gilts were OVX after puberty, and were classified as sexually mature (SM) at the time of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the presence of a mature female on puberty attainment in gilts

At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment O) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at weekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during estrus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7 19 ) than in Treatment O (0 19 ) even though the average age at puberty was similar (I, 231 +/- 24 days; O, 243 +/- 12 days; mean +/- SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment O but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estrus were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen.     

Effect of prior FSH treatment on the estrus and ovulation responses to eCG in prepubertal gilts

The objective of this study was to determine the effect of pre-treatment of prepubertal gilts with FSH on the estrus and ovulatory responses to eCG injection at two ages. A total of 149 prepubertal Hypor gilts were selected at 150 days (n=76) or 180 days (n=73) of age and assigned to injection of 400 IU eCG plus 200 IU hCG (PG600), 600IU eCG alone (Folligon), pre-treatment with 72 mg FSH (Folltropin) administered as 6 x 12 mg injections at 12 h intervals with 600 IU Folligon 12h after last FSH injection, or non-injected controls. To facilitate detection of estrus, gilts were exposed to a mature boar for 15 min daily for 7 days. To determine ovulatory responses, blood samples were obtained on the day of injection and 10 days later and assayed for progesterone content. Following treatment at 150 days, one control gilt (5.3%) was deemed estrus but ovulation did not occur. Compared to treatment with Folligon alone, PG600 injection tended (P=0.1) to increase the estrus response (52.6% compared with. 26.3%) and increased (P<0.01) the ovulatory response (89.5% compared with. 47.4%). The estrous response in gilts pretreated with Folltropin was intermediate (42.1%) but the ovulatory response (47.4%) was the same as for Folligon alone. Following treatment at 180 days, two control gilts (10.5%) were deemed estrus and ovulation did occur in these gilts. There was no difference between hormone-treated groups for estrus or ovulatory responses, although the ovulatory response of PG600-treated gilts tended (P=0.1) to be greater than for the Folligon-treated group (89.5% compared with 66.7%), with Folltropin-pretreated gilts being intermediate (76.5%). These data demonstrate that the estrus and ovulatory responses of gilts were greater for PG600 than for Folligon and that while responses to PG600 were not affected by gilt age, for the combined Folligon groups, estrous response (P<0.02) and ovulatory response (P<0.05) improved with increased gilt age.     

The incidence of,and factors associated with,failure to mate by 245 days of age in the gilt

The incidence of, and factors associated with, gilts failing to mate between 29 and 35 weeks of age were studied over 12 months at a large intensive piggery in southern Australia. After excluding gilts culled as physically unsound, 10.5% of the remaining 2484 gilts failed to mate and were slaughtered.Seventy percent of unmated gilts had ovulated, and of these, 54% had shown negative or low responses to the back-pressure test (BPT) and 16% had shown moderate or high responses. Few prepubertal gilts (1%) had abnormal reproductive tracts.When group size was greater than 50 gilts (< 0.9 m²/gilt) immediately prior to mating (27–28 weeks of age), there was a higher incidence of unmated gilts and an increase in the proportion of unmated gilts which had shown negative or low BPT response than when groups were less than 50 gilts (12.9 vs. 8.6%, P < 0.001; and 8.0 vs. 3.6%, P < 0.001, respectively).The incidence of prepubertal gilts at 35 weeks was lower during spring than other seasons (1.48 and 3.36%, P < 0.05) and higher during summer than other seasons (4.61 and 2.37%, P < 0.01).Fewer Large White gilts remained unmated at 35 weeks of age than Landrace or Large White-Landrace synthetic breed gilts (7.7 and 14.1% of those selected, P < 0.001). More purebred gilts were prepubertal at 35 weeks of age than crossbred gilts (5.4 and 2.4%, P < 0.01).     

Pre- and Postpubertal LH and Estradiol Pattern in Gilts Subjected to Intermittent Inescapable Electroshock

The effect of intermittent electroshock on LH and es-tradiol secretory pattern and on reaching puberty was studied in 24 prepubertal gilts. Twelve gilts 115-168 days of age received unpredictable and inescapable electroshocks 0-5 times daily between 8 am and 4 pm and 12 gilts served as controls. At an age of 168 ± 0.7 days all gilts were moved, regrouped and exposed to a boar for 30 min. Observa-tions for signs of oestrus were carried out twice daily. Indwelling jugular catheters were inserted into 8 gilts on each treatment after the initial boar contact. Blood samples were collected to determine LH profiles for 4 h every 15 min on day 2 and day 4 after the in-itial boar contact. The remaining 4 gilts on each treatment were catheterized one day prior to the initial boar contact and blood was collected to determine LH profiles the day before initial boar contact and day 1 and day 2 after initial boar contact for 6 h every 15 min. In addition, blood samples were collected and analyzed for LH and estradiol from all gilts daily at 8 am, 12 am and 4 pm for the first 3 days following the initial boar con-tact and thereafter every 4 h until the end of oestrus (diurnal samples). Samples taken daily at noon the first 5 days following initial boar contact were analyzed for Cortisol. The electroshock treatment significantly increased the age at puberty (p=0.04) and tended to decrease the mean LH concentration prior to the preovulatory LH surge (p=0.08) and the maximal concentration of LH during the preovulatory LH surge (p=0.07). The apparent down regulation of the plasma concentration of LH was not as-sociated with increased activity in the hypothalamus-pituitary-adrenal axis in that the basal concentration of Cortisol was not affected by treatment. This indicates that other physiological mechanisms are involved in stress-induced suppression of LH.     

Seasonal inhibition of puberty in domestic gilts is overcome by melatonin administered orally, but not by implant.

The ability of exogenous melatonin, applied either orally or by implant, to overcome the seasonal inhibition of puberty in domestic gilts was tested in two experiments. In Expt 1, 24 gilts received two melatonin implants at 126 days of age and again at 161 days and 196 days, while 24 gilts acted as controls. All gilts were slaughtered at a mean age of 223 days. Blood samples were collected by venepuncture from eight gilts in each treatment at 126, 144 and 178 days of age and the plasma was assayed for melatonin concentration by direct radioimmunoassay. In Expt 2A, four gilts (125 days of age) were fed either 0, 1, 2 or 4 mg of melatonin at 14:00 h on each of four consecutive days. Blood samples for melatonin assay were collected via indwelling jugular catheters every 30 or 60 min from 12:00 to 22:00 h. In Expt 2B, 27 gilts were fed 1 mg of melatonin at 15:00 h each day from 129 days of age until slaughter at 221 days, while 25 gilts acted as controls. In both experiments, the presence of morphologically normal corpora lutea at slaughter was the criterion for puberty. In Expt 1, constant-release melatonin implants had no effect on the percentage of gilts which reached puberty. Among the 24 control gilts, two (8.3%) reached puberty compared with one of the 24 (4.2%) gilts with implants. In all the samples from control gilts, and in the samples taken from treated gilts prior to implantation at 126 days of age, mean plasma melatonin concentration was below the sensitivity of the assay (3.6 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.