Effect Of Different Light Conditions And Feeding Strategies On The Growth,development And Puberty Onset Of The Gilts

The onset of puberty for gilt is affected by many factors,among which environmental factors and nutritional factors are important factors influencing the onset of puberty.With the increasing influence of light conditions on gilt reproduction,it is important to study the effects of different nutrient supply strategies and lighting conditions on the onset of puberty for gilt to improve the reproductive performance of sows and save the cost of breeding enterprises.In this study,two-way cross gilts were used as experimental animals to study the effects of different light conditions and feeding strategies on the onset of puberty for gilts.The effects of light and feeding strategies on the onset of puberty for gilts are reflected by the effects of growth performance,estrous performance and hormonal changes of the gilts.An estimated model for estimating the weight of gilts was established by measuring the morphology of the gilts.The study is divided into three experiments:Experiment 1 Effects of different photoperiod and feeding strategies on the growth and development of the gilts,puberty onset and the secretion of the hormoneThe test was divided into four treatment groups,and the light intensity of each treatment was maintained at 100 lx.Treatment 1:photoperiod 10L:14D,phase-feeding;treatment 2:photoperiod 10L:14D,blend-feeding;treatment 3:photoperiod 16L:8D,phase-feeding;treatment 4:photoperiod 16L:8D,blend-feeding.6 replicates per treatment,2 pigs per replicate（pen）.The test lasted for11 weeks and was divided into two phases,60-80 kg for the first phase and 80-135 kg for the second phase.The feed intake and body weight of the pigs were recorded weekly and the health status of the pigs was observed and recorded daily.After 150days of age,the gilts commenced exposure to mature boars twice a day,once in the morning and the next in the afternoon,to record the age,backfat and the situation of estrus.Sow blood samples were collected at 170 days and 200 days,respectively,and serum levels of hormones were determined by ELISA.The results showed that:1.Production performance:The phase-feeding significantly increased（P<0.05）the average daily gain in the second and full periods,significantly reducing（P<0.05）the F/G at 24 weeks of age;16L:8D photoperiod significantly increased（P<0.05）the average daily gain at 25 and27 weeks of age,significantly reducing（P<0.05）the F/G in the second and full stages,but reducing the average daily gain at 26 weeks of age.2.Estrous performance:Different photoperiod and feeding strategies had no significant effect（P>0.05）on estrus rate,age of puberty and weight of puberty,but blend-feeding had a tendency to reduce weight of puberty of gilts（P=0.09）.3.Hormonal change:The effects of different photoperiod and feeding patterns on serum melatonin,leptin,LH and E₂ levels in gilts were not significant（P>0.05）,but the 16h long photoperiod significantly（P<0.05）increased the serum FSH concentration of the170-day-old gilts and decreased the serum leptin concentration at 200 days of age（P=0.06）.The 10h short photoperiod significantly（P<0.05）increased the serum IGF-I concentration at 170 days of age.Experiment 2 Effects of different light intensities and feeding strategies on the growth and development of the gilts,puberty onset and the secretion of the hormoneThe test was divided into four treatment groups,and the photoperiod of each treatment was maintained at 16L:8D.Treatment 1:light intensity 100 lx,phase-feeding;treatment 2:light intensity 100 lx,blend-feeding;treatment 3:light intensity 50 lx,phase-feeding;treatment 4:light intensity 50 lx,blend-feeding.6replicates per treatment,2 pigs per replicate（pen）.The feeding management,sample collection and data analysis are the same as experiment 1.The test results are as follows:1.Production performance:Different feeding strategies and light intensity had no significant effect（P>0.05）on the average daily gain and F/G of the first stage,the second stage and the whole stage.blend-feeding significantly increased（P<0.05）the average daily gain at 29th week of age,and the F/G decreased significantly（P<0.05）,but significantly reduced（P<0.05）the average daily gain at 20th week;The 50 lx light intensity significantly increased（P<0.05）the average daily gain at week 24,reduced the F/G,but significantly increased（P<0.05）the F/G at the 23rd week of age.2.Estrous performance:Different light intensity and feeding strategies had no significant effect（P>0.05）on the estrus rate of the gilts and the age of puberty,but the 50 lx light intensity had a tendency to reduce the weight of puberty（P=0.06）.There was a significant interaction between feeding strategy and light intensity（P<0.05）.3.Hormonal change:The 100 lx light intensity significantly increased（P<0.05）the serum FSH concentration and LH concentration of the gilts at 170 days and 200 days.But the 50lx light intensity significantly increased（P<0.05）the serum leptin concentration at200 days and inhibited the secretion of melatonin.Different feeding strategies had no significant effect on the secretion of FSH,LH and melatonin in gilts（P>0.05）.Different light intensity and feeding strategies had no significant effect on serum E₂and IGF-I concentrations in gilts（P>0.05）.Experiment 3 Establishment of weight estimation model for giltsThis experiment carried out correlation analysis and multiple linear regression analysis on the morphological indicators of gilts,and selected the best equation for the gilt weight estimation model:body weight（kg）=-140.659+1.298×HG（heart girth）-0.019×（age）-0.034×P2（backfat of P2）+0.408×LSNP（length snout to posterior）+0.285×HFH（height floor to hip）+1.22×WH（width of ham）（R2=0.929;P<0.001）.In summary,the following conclusions are drawn:The 16-hour light photoperiod can effectively reduce the average F/G of gilts,improve feed conversion ratio,and promote follicular development by increasing the secretion of FSH in gilts;100lx light intensity is conducive to the increase of FSH and LH concentration,but in terms of puberty onset,50lx light intensity can promote the increase of serum leptin concentration,inhibit the secretion of melatonin,and reduce the weight of puberty of gilts.Conducive to the onset of puberty of the gilts.phase-feeding strategy increased the average daily gain of gilts and promote the growth performance of the gilts.But the blend-feeding strategy can effectively promote the sexual maturity of the gilts,increase the estrus rate and reduce the weight of puberty of gilts,and improve the estrus performance of the gilts.