Study On The Optimum Net Energy Requirements In Gilts

The aim of this study was to determine optimal net energy(NE)requirements for gilts at first estrus and/or atfirst mating,and the relevant mechanism using plasma metabolomics.For this purpose,three experiments were included in this study.Experiment 1.The objective of this experiment was to determine the optimal net energy requirements for gilts at first estrus.A total of 120(Landrace x Large White)crossbred gilts(Body weight,84.0 ± 2.4 kg;Age,150.4 ± 3.5 d)were assigned to diet with different NE levels(2174,2274,2374,2474 and 2574 kcal/kg)based on their body weight,respectively.The results suggested that body weight and backfat thickness(BFT)showed dose-independent effect with the increase of dietary energy(P<0.05;Linear,P<0.05).The age of first estrus increased quadratically with increasing dietary energy(Treatment,P<0.05;Linear,P<0.05;Quadratic,P<0.05)(Age(d)= 0.0002(NE)2-0.9695(NE)+ 1339.2,R2 = 0.77).The optimal dietary net energy for gitls to reach the minimal age at first estrus,was 2424 kcal/kg.The estrus rate was 54%,70%,88%,91%and 58%for each treatment,respectively.Experiment 2.The objective of this experiment was to determine the optimal NE requirements for gilts at mating.A total of 120(Landrace x Large White)crossbred gilts(Age 175.0 ± 3.5 d,Body weight 99.0 ± 2.5 kg)were fed diets containing NE levels of 2174,2274,2374,2474 and 2574 kcal/kg,respectively.The treatments consisted of diets,and gilts were allocated to treatments based on their BW.The results showed that BW and BFT increased with increasing dietary energy(Treatment,P<0.05;Linear,P<0.05).Age at mating increased with increasing dietary energy(Treatment,P<0.05;Quadratic,P<0.05);based on the quadratic analysis,the optimal dietary net energy for gitls to reach the minimal age at mating,greatest litter birth weight and minimal birth weight variation was 2378,2435 and 2380 kcal/kg,respectively.Compared with other treatments,gilts fed diet with 2374 kal/kg of NE had the shortest estrus interval(Treatment,P<0.05;Quadratic,P<0.05)and greatest mating and gestating rate.The lowest litter size born alive was observed by gilts fed the 2174 and 2574 diet(P<0.01).Experiment 3.The objective of this experiment was to investigate the effects of energy on the reproducitive performance.Based on the results of experiment 1,gilts in treatment 1(Low),3(Medium)and 5(High)were used.On the day of first estrus,blood was collected.The results suggested that,the luteinizing hormone pulse in Low was the lowsest.Serum glucose concentration tended to be lower in Low(P = 0.08).Serum leptin concentration in High was lower than Low and Medium.Serum triglyceride concentration and triglyceride/high density lipoprotein cholesterol ratio was highest in High.A total of 29 compounds were indentified in serum by mass spectrometry.Energy affected the metabolism of sphingolipid,palmitic acid and bile acid.The fold change in High was greater than Low and Medium.Gilts in the Medium group with the greatest number of oocyte and highest oocyte quality(P<0.01).To summarize,the optimal dietary NE for gilts at first estrus and mating was 2424 and 2398 kcal/kg,respectively.Insufficient energy intake resulted in the decrease of serum glucose and cholesterol concentrations,which lead to the inhibition of luteinizing hormone secretion.Excessive energy intake also led to the disorder of sphingolipid and bile acid metabolism.The inbalance of energy intake decreased the oocyte quality.