P.E. Hughes

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25-28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P < 0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P < 0.01) and 87% for CW sows (P > 0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P < 0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P > 0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.

The effect of repeated boar exposure on cortisol secretion and reproduction in gilts

It has been proposed that short-term activation of the hypothalamo-pituitary adrenal axis, with a consequent increase in the secretion of cortisol, amy disrupt the endocrine events prior to ovulation and thereby impair reproduction in females. We investigated this concept in gilts in which oestrus was detected by introduction to boars, where intense physical contact is possible, or by applying pressure to the back of gilts (back-pressure test) during fence-line exposure to boars, where intense physical contact is prohibited. We expected that there would be a greater release of cortisol and that reproduction would be inhibited in gilts introduced to boars compared to gilts in which the back-pressure test was used. As expected, introduction of gilts to boars resulted in a significant transient increase in plasma concentrations of cortisol while there was no significant effect of using the back-pressure test on plasma cortisol. Nevertheless, introduction of gilts to boars did not impair reproduction and there was no effect of method of detecting oestrus on duration of oestrus, sexual receptivity, fertility or fecundity. The length of the oestrous cycle was decreased and ovulation rate increased in gilts that were introduced to boars compared to gilts that underwent the back-pressure test, indicating that introduction of gilts to boars may have stimulated these aspects of reproduction. These stimulatory effects may have been due to an increased exposure of gilts to sexual behaviour and stimuli from boars when introduced to boars and/or to stimulatory effects of the hypothalamo-pituitary adrenal axis on some aspects of reproduction.

The effect of season, frequency and duration of contact with boars on the attainment of puberty in gilts

Abstract The effect of varying the frequency and duration of exposure to a mature boar on attainment of puberty in gilts was examined in two experiments. In Experiment 1, gilts received full boar contact for 30 min per day from 175 days of age on (a) 0 days per week (isolated), (b) 2 days per week (c) 5 days per week or (d) 7 days per week until puberty or 235 days of age. These treatments were replicated in January, May and October and a total of 97 gilts were used. In Experiment 2, conducted in September, gilts received full boar contact from 160 days of age for (a) 0 min per day (isolated), (b) 2 min per day, (c) 10 min per day or (d) 30 min per day each day until puberty or 240 days of age. In Experiment 1, neither frequency of contact nor month affected the proportion of gilts which reached puberty in response to boar exposure (0.92 overall). Among gilts isolated from boars, the proportion reaching puberty was significantly affected by month, being lower than that for boar-exposed gilts in January (0.0 vs 0.88, P 0.05). The mean interval to puberty for isolated gilts in both May (48.0 days) and October (44.6 days) was longer (P In Experiment 2, the proportion of gilts which reached puberty in the 2 min (1.0), 10 min (0.71) and 30 min (0.92) per day groups did not differ significantly. Overall, more boar exposed than isolated gilts reached puberty (0.88 vs. 0.46, P All boar exposure treatments stimulated puberty in a high proportion of gilts but the response was either fast, resulting in a short interval to puberty or slow, resulting in a longer interval. We conclude there is a threshold level of stimulus required for a fast response and that this level changes throughout the year being highest in January (summer) and lowest in October (spring).

The effects of contact frequency and transport on the efficacy of the boar effect

Ninety six Large White/Landrace cross-bred gilts were used in this study, sixteen gilts being allocated to each of six treatments. The treatments compared the effects on puberty attainment of exposing gilts to boar contact either 0, 1 or 3 times daily (C, D and 3D), with or without the addition of transport stress (T). Treatments began at a mean gilt age of 160 days and continued for 40 days. The duration of each period of boar contact was 20 min. Those gilts receiving transport stress were placed on a trailer daily for the first ten days of the study and driven at a constant speed for 20 min. There was no significant effect of transport alone on the timing of gilt puberty attainment. Boar exposure significantly increased the proportion of gilts attaining puberty within 40 days of the commencement of treatments (P < 0.05) compared with gilts not receiving boar contact. Boar exposure three times daily significantly reduced mean gilt age at puberty relative to no boar exposure (190.2 vs. 202.3 days of age respectively, P < 0.01) while once-daily boar exposure gave an intermediate value (196.7 days). In addition, a significant (P < 0.01) interaction occurred between boar contact frequency and transport in this study. It is concluded that (a) transport alone does not provide a significant stimulus for early puberty attainment in the gilt, (b) the pubertal response of the gilt to the boar effect is enhanced when boar contact occurs several times each day compared with a single boar contact period, and (c) a combination of frequent boar contact and transport may result in a greater degree of gilt puberty stimulation than frequent boar contact alone.

The role of contact frequency in modifying the efficacy of the boar effect

Sixty-four Large White-Landrace crossbred gilts were used in each of two experiments in this study. The two experiments compared the effects on puberty attainment of exposing gilts to boar contact on either alternate days (ADB), daily (DB) or twice daily (2DB) in Experiment 1, and daily (D), twice daily (2D) or three times daily (3D) in Experiment 2. In each experiment, puberty attainment by gilts in the boar exposure regimens was compared with puberty attainment in a non-boar exposed control group of gilts. Boar exposure began at a mean gilt age of 160 days and continued for 60 days. The duration of boar contact was for 20 min per exposure period in Experiment 1, and for 60 min, 30 min and 20 min per exposure period, respectively, for Treatments D, 2D and 3D in Experiment 2. Experiment 1 commenced in the summer whereas Experiment 2 began in the winter months. All boar exposure regimens significantly increased the proportion of gilts attaining puberty within 20, 40 and 60 days of the commencement of treatments (P<0.05) compared with control gilts in both experiments. In Experiment 1, twice daily boar contact resulted in a significantly higher proportion of gilts reaching puberty in the first 20 days of treatment than for either daily or alternate day boar contact (0.86 vs. 0.21 and 0.07 for Treatments 2DB, DB and ADB, respectively, P<0.01). No significant effect of boar contact frequency was observed in Experiment 2, although there was a tendency for three times daily boar contact to increase the proportion of gilts pubertal within 20 days of the start of treatments (0.25, 0.27 and 0.62 for Treatments D, 2D and 3D, respectively). Both the mean days taken to reach puberty after the imposition of treatments and mean gilt age at puberty were significantly reduced by increasing boar contact frequency in both experiments. It is concluded that the pubertal response of the gilt to the boar effect is enhanced when boar contact occurs several times each day compared with a single boar contact period. Preliminary data suggest that the actual frequency of daily boar contact required to maximise puberty stimulation in the gilt may be dependent on season.

The influence of boar libido on the efficacy of the boar effect

Eighty-one Large White/Landrace crossbred gilts were used in three replicates in this study. These gilts were allocated to one of three treatments, these being (1) control—no boar contact, (2) daily exposure to a low-libido boar, and (3) daily exposure to a high-libido boar. All treatments began at a mean gilt age of 160 days and continued for 60 days. The ‘libido’ boars used were designated as high or low on the basis of their sexual behaviour at 9–10 months of age in three 15-min mating tests, the variables measured being total number of copulations achieved and mean time to first mount an oestrous female. Results from the combined data of the three replicates show that gilts in both boar exposure treatments were younger at puberty than were nondashboar exposed gilts (P<0.05). Exposure to a high-libido boar stimulated puberty at a significantly earlier age than did exposure to a low-libido boar (179.6 vs. 194.1 days, P<0.05). These data demonstrate that differences in the stimulus value of mature boars to prepubertal gilts do occur. However, the causes of these differences remain to be identified.

The effect of limiting the number of days of contact with boars, season and herd of origin on the attainment of puberty in gilts

Abstract The effect of limiting the number of days of boar exposure on the attainment of puberty in gilts was examined in two herds (Medina and Muresk) and in two seasons (winter and summer). The treatments used were full boar contact for 20–30 min per day from 165 days of age for (a) 1 day, (b) 10 consecutive days or (c) daily until puberty or slaughter and (d) an isolated control. Those not detected in oestrus were slaughtered 80 days (Medina) or 135 days (Muresk) after first boar exposure. In the winter neither treatment nor herd had any significant effect on the proportion of gilts which reached puberty (0.93 in both herds). In the summer a lower proportion of control gilts reached puberty at Medina than in the winter (0.33 vs. 1.0, P

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.

The influence of mating frequency and nutrition on the stimulus value of boars

Abstract Two experiments were conducted to investigate the possible influences of mating frequency and nutrition levels on the stimulus value of individual boars. In Experiment 1, eight young boars were assigned to one of four mating frequencies: 0, 1, 3 or 6 matings week −1 from 9 to 14 months of age. Between 12 and 14 months of age all boars were used as stimulus males to induce early puberty attainment in groups of prepubertal gilts. This involved 60 days of daily exposure of a group of eight prepubertal gilts to each boar for a period of 20 min from a mean gilt age of 163 days. There was no significant effect of the number of copulations per week that the boar was allowed on his ability to induce early puberty attainment in gilts. There was also no effect of mating frequency on the sexual behaviour of boars, as measured in standardised sexual motivation tests. However, the data collected in this area were limited and therefore the results are inconclusive. In Experiment 2, eight boars were fed either a ‘high’ ( n = 4) or ‘low’ ( n = 4) plane of nutrition from 5 to 9 months of age, these nutritional planes representing feed levels of ad libitum and 1.5 times maintenance, respectively. From 9 months of age until the conclusion of the study, two of the ‘high’ plane boars and two of the ‘low’ plane boars were fed ad libitum (Treatments HH and LH, respectively) while the remaining two ‘high’ plane and two ‘low’ plane boars were fed at a level of 1.5 times maintenance (Treatments HL and LL, respectively). Each of the boars was exposed to a group of eight prepubertal gilts from 9 months of age in order to assess stimulus value (as described for Experiment 1). There was no significant effect of boar nutritional planes on the stimulus value of the boars as measured by gilt puberty attainment in response to daily boar contact. These results suggest that factors other than mating frequency and nutrition are responsible for the determination of a boars stimulus value.

The effects of duration of boar exposure, number of gilts in the exposure group and size of the exposure pen on the efficacy of the boar effect

Forty-eight Large White×Landrace gilts were allocated to treatment in each of three 3×2 factorial experiments within this study. The three experiments used boar exposure durations of either 20, 12.5 or 5 min day−1. The factors examined were number of gilts in the boar-exposure group (8, 4 or 2) and size of the exposure pen (large — 22.2 m2, small — 11.1 m2). Boar exposure began at a mean gilt age of 160 days and continued on a daily basis for 80 days. The frequency of boar-gilt interactions was assessed in the replicate employing 5 min day−1 of boar exposure by video-recording the exposure period for all treatment groups on Days 1–3 and 6–8 of treatment. Increasing group size significantly decreased boar-gilt interactions (P<0.05) as did increasing the size of the exposure pen (P<0.01). Twenty minutes day−1 of boar exposure significantly reduced gilt age at puberty (P<0.05) and increased the proportion of gilts attaining puberty in response to boar exposure within 21 days of commencement of treatment (P<0.01) compared with 12.5 or 5 min day−1 of boar exposure. Neither group size nor exposure pen area exerted a significant influence on gilt puberty attainment when boar exposure occurred for either 5 or 20 min day−1. However, at 12.5 min day−1 of boar exposure gilts reached puberty significantly earlier in pairs than in groups of four or eight (P<0.001) and the proportion of gilts reaching puberty within 21 days of commencement of treatment was significantly higher for pairs than for groups of four (P<0.001) or eight (P<0.05). Additionally, when 12.5 min day−1 of exposure was allowed those gilts receiving boar contact in the large exposure pen attained puberty significantly earlier (P<0.05) than did those gilts exposed in the small pen. It is concluded that daily boar exposure is required for at least 12.5 min day−1 to maximise the boar effect. Furthermore, when the adequacy of boar contact duration is marginal (approximately 12.5 min day−1) both group size and exposure pen area may influence the efficacy of boar-induced puberty stimulation in the gilt.