School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemFactors influencing the efficacy of the boar effect( 1996)Maximizing reproductive efficiency is of high potential benefit to the pig industry. Mature boar contact has proven to be very effective in stimulating gilt puberty, although the results tend to be variable. The experimental work in this thesis was conducted in order to elucidate some of the factors which may be contributing to this variation. Three experiments have been carried out to examine the possibility of improving the efficacy of the boar effect. The first experiment investigated the effects of boar contact and transportation on the stimulation of early puberty attainment in gilts. Gilts were allocated to one of six treatments: control - no boar contact or transportation (C); daily boar contact (B1); daily transportation (T); three times daily boar contact (B3); daily boar contact and transportation (B1+T); and three times daily boar contact plus daily transportation (B3+T). Results show that transport alone has little influence on the timing of gilt puberty (P>0.05), although there was a significant positive interaction between transport and boar contact (P<0.01). Frequent boar contact (three-times daily) stimulated a higher proportion of gilts to attain puberty within 20 days of commencement of treatment (P<0.05) than did either once-daily boar contact or no boar contact. In addition, the proportion of gilts reaching puberty was significantly lower when gilts were exposed to daily boar contact, compared to three times daily boar contact. The second experiment studied the efficacy of the boar effect when conducted in a modified Detection and Mating Area (DMA), with or without full boar contact, or in a pen which was not the boar's own. Gilts were assigned to treatments of: no boar contact (C); once daily boar contact (B); DMA exposure (DMA); and boar exposure plus DMA exposure (B+DMA). Mean days taken from the start of the experiment to puberty attainment were significantly fewer (P<0.01) for gilts receiving daily boar contact than for gilts not exposed to boars (36.1 vs. 56.8 days), although boar exposure in addition to DMA exposure tended to produce the lowest mean days to puberty (20.6 days). However, neither days taken to reach puberty, gilt age at puberty, nor gilt weight at puberty was significantly affected by daily exposure to a DMA. The third experiment examined the stimulatory effect of the presence of cycling females on puberty attainment in gilts, and whether the effect was a direct one, or whether it operated via an increase in the stimulus value of the boar. The gilt treatment groups in this experiment were: control - no contact with boars or cycling females (C); contact with cycling females, but not with boars (F); contact with boars, but not with cycling females (B); contact with both boars and cycling females, where the boars were not exposed to the cycling females (BF-1); and contact with both boars and cycling females, where the boars were exposed to the cycling females (BF-2). The proportion of gilts reaching puberty was not significantly influenced by treatment in this study. However, the mean days taken from commencement of treatment until puberty attainment were significantly fewer for those boar exposed gilts not exposed to cycling females than for those gilts receiving neither boar contact nor being exposed to cycling females. Cycling females may exert a minor stimulatory effect on the timing of gilt puberty in non-boar exposed gilts, but this effect is not significant. Results from these studies confirm the efficacy of mature boar contact as a means of inducing early puberty attainment in the young gilt (i.e. the boar effect). Transport did not exert a significant effect on days taken to reach puberty, although transport may be slightly stimulatory to puberty attainment in gilts when used in combination with frequent boar contact. Full boar contact, when given in a DMA, may be a more effective form of gilt puberty stimulation than full boar contact in an isolated pen. Preliminary data also suggest a possible negative interaction between puberty stimuli from the boar and those from cycling females which, if substantiated, may have implications for the management of the replacement gilt.
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ItemBoar contact frequency and the timing of puberty in gilts( 1995)The literature relating to the natural attainment of puberty and those factors involved in the early induction of puberty in gilts is reviewed. The first two experiments suggested that motivated/high stimulus value boar(s) may release sufficient stimuli to overcome the seasonal change that mediates the ability of the gilt to attain natural puberty. These experiments also demonstrated that increasing the, frequency of daily boar contact provided sufficient 'cumulative stimulus' to initiate earlier pubertal development, when compared with once-daily contact (P<0.05). In fact, boar exposure three times daily significantly reduced mean gilt age at puberty relative to once-daily boar exposure (183.2 � 2.71 vs. 196.0 � 3.00 days of age respectively, P<0.01). Twice-daily boar contact resulted in an intermediate mean gilt age at puberty (190.3 � 3.01 days). There was also a trend towards a higher proportion of gilts reaching puberty earlier with increasing frequency of boar contact but this effect became less evident after day 20 of commencement of treatment. In a third experiment increasing boar contact frequency to 8 times per day failed to improve the proportion of gilts attaining precocious puberty compared with 4 times daily contact. This suggests that maximum response to boar contact is achieved using 3-4 times exposure per day. The fourth experiment again confirmed that the boar effect is enhanced when boar contact occurs several times each day. It also indicated that transport 'stress' in conjunction with frequent boar contact may further reduce gilt age at puberty. However, transport alone did not significantly advance the timing of gilt puberty attainment. A final experiment suggested that the efficacy of the boar effect can also be maximised by increasing the frequency of boar - contact when large gilt group sizes are involved. However, it may be necessary to increase exposure times (>20 minutes per exposure) to obtain this benefit. No advantage of increasing the number of boars in the exposure groups from 2 to 4 or 6 was apparent in this study.
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