| In this paper,the determination methods of Metabolizable Lipogenic Substances(MLS)levels in growing pig diet were studied.Based on this research,the effects of MLS levels in diets and ingredients of pigs and different MLS levels on growth performance,carcass quality and meat quality of growing pigs were studied.On the basis of the level of MG,the requirement of porcine metabolic fat producing substances(MLS)was determined,providing a basis for the formulation of dietary formula in the future.This paper is divided into three partsPart 1:Determination of MLS level in growing pig dietsA total of 18 pigs weighing 30 kg were selected and randomly divided into 3 treatments,6 replicates per treatment(1 pigs per replicate).Each pig was fed 3 different kinds of equal energy and equal nitrogen crude fiber levels.After a week of feeding,T type ileostomy fistula,portal vein,femoral artery and mesenteric vein fistula were installed in each pig.After the pigs returned to normal intake after operation,the ileal digesta was collected from the "T" fistula and the digestibility of crude fat was determined by Ti02 indicator method.The blood samples of portal vein and femoral artery were collected.The net absorption of acetic acid and butyric acid in portal vein was measured by arteriovenous concentration difference method.After that,animal slaughtering tests were carried out.The large intestine tissues of pigs were taken.The content of labeled and unlabeled butyric acid was determined by GC-MS,and the amount of acetic acid and butyric acid intestinal wall was obtained.The net absorption of large intestine acetic acid and butyric acid was calculated.The MLS level of the growing pigs was calculated according to the fat digestibility of the small intestine,the net absorption of acetic acid and butyric acid.The results showed that the fat content of the three diets was 3.24%,2.94%and 3.34%respectively,and there was no significant difference among the three groups(P>0.05).The content of chyme fat decreased first and then increased.The content of chyme fat in diet group ? was the lowest,but there were no significant differences among the groups(P>0.05).There were no significant differences in dietary titanium dioxide content and chyme titanium dioxide content among groups(P>0.05).The digestibility of intestinal fat in growing pigs increased first and then decreased.The digestibility of small intestine fat in diet group ? was significantly higher than that in diet group ?(P<0.05),and the digestibility of small intestine fat was the lowest in diet group ?,and there was no significant difference in digestibility of small intestine between group ? and group ?(P>0.05).There were no significant differences in portal vein blood flow,acetic acid concentration in portal vein and femoral artery among the three groups(P>0.05).The net absorption of acetic acid in portal vein of group ? was significantly higher than that of group ? and group ?(P<0.05),but there was no significant difference between group ?and group ?(P>0.05).The intestinal wall deposition in group ? was significantly higher than that in group ?(P<0.05),but there was no significant difference between group ?and groups ? and ?(P>0.05).Overall,with the increase of crude fiber level,the net absorption of acetic acid in portal vein and intestinal wall deposition showed a downward trend.There was no significant difference in portal vein blood flow,butyric acid concentration in portal vein and femoral artery between the three groups(P>0.05).The net absorption of butyric acid in portal vein of group ? was significantly higher than that of group ? and group ?(P<0.05),but there was no significant difference between group ?and group ?(P>0.05).There was no significant difference in the amount of butyric acid deposited in intestinal wall between groups(P>0.05).Overall,with the increase of crude fiber level,the net absorption of butyric acid in portal vein and intestinal wall deposition showed a downward trend.The net absorption of acetic acid and butyric acid in large intestine of group ? was significantly higher than that of group ? and group ?(P<0.05),but there was no significant difference between group ? and group ?(P>0.05).MLS levels in diet group ? and ? were significantly higher than those in diet group ?(P<0.05),but there was no significant difference between diet group ? and diet group ?(P>0.05)Under this experimental condition,the level of metabolizable lipid substances in 3 diets of growing pigs was 70.51 g/kg,68.09 g/kg and 40.58 g/kg respectivelyPart 2:In vitro determination of MLS levels in different diets and raw materialsThe diets in experiment 1 were crushed and screened(analysis sieve:pore size 0.42 mm(40 mesh))as substrates.After simulated "stomach-small intestine digestion" in vitro,the residues were dried and crushed.The acetic acid and butyric acid content produced by fermentation were determined by in vitro fermentation gas production method.According to the relationship between the MLS level of three diets and the acetic acid and butyric acid content produced in vivo,a line was established.The regression equation was used to establish a method for estimating the MLS value of pig diets in vitro,and the MLS values of several commonly used feed ingredients were determined by this method.The results showed that the optimum fermentation time was 48 hours in vitro.The regression equation for estimating the net absorption of acetic acid in vivo was Y=0.3394X+10.751(R2=0.9942),and the regression equation for estimating the net absorption of butyric acid in vivo was Y=0.1581X-0.1399(R2=0.9226).After digestion by simulated Stomach-Small intestine,the acetic acid produced by corn,soybean meal,wheat bran and soybean hull was 162.75,48.52,20.46 and 13.42 g/kg,and butyric acid was 57.98,16.98,21.30 and 21.84 g/kg,respectively.According to the formula,the endogenous MLS levels of each raw material were estimated to be 63.76,25.70,17.77 and 16.98 g/kg,respectively.Part 3:effects of 3 different MLS level diets on growth performance,carcass quality and meat quality of growing pigsA total of 18 pigs with good body weight and average body weight of 28.15+4.51kg were selected and randomly divided into 3 groups,6 replicates in each group and 1 pigs per replicate,fed 3 kinds of diets equal to nitrogen but with different MLS levels.The experimental period was 4 weeks.The daily feed intake was recorded and the average daily feed intake,average daily gain and feed-meat ratio were calculated.After the growth performance test,Pigs were slaughtered and their carcass quality and meat quality were analyzed.The results showed that there was no significant difference in daily average feed intake,daily gain and feed to meat ratio between the 3 groups(P>0.05).With the increase of fiber level,the daily average intake increased first and then tended to balance.When the crude fiber content reached 4.5%,it tended to balance basically.The daily gain showed a trend of first rising and then declining,and the most obvious was the daily gain when the crude fiber content was 4.5%(diet 2).The feed-meat ratio decreased first and then increased,and the feed-meat ratio of diet 2 was the lowest.Diets with different MLS levels did not significantly affect the carcass quality of growing pigs(P>0.05).With the increase of crude fiber level,the slaughter rate and carcass length had little effect,but the back fat thickness and eye muscle area increased first and then decreased.The back fat thickness in diet group ? increased by 2.5%compared with that in diet group ? and 7.7%higher than that in diet group ?.The area of eye muscle in group ? was 16.3%higher than that in group ? and 37.5%higher than that in group ? The cooked meat rate of group ?was significantly higher than that of group ?(P<0.05)when fed with diets with different MLS levels,but there was no significant effect on other indicators of growth pork quality(P>0.05).The brightness of group ? was 3.7%higher than that of group ? and 7.7%higher than that of group ?.The redness of group ? was 7.5%lower than that of group ? and 7.5%lower than that of group ?.The yellowness of group ? was 11.3%lower than that of group ? and 11.3%lower than that of group ?.The saturation of group ? was 3.6%higher than that of group ? and 7.0%higher than that of group ?.The pH value of muscle measured at 45 min and 24 h after slaughter showed little difference.The drip loss of group ? was higher by 53.1%than that of group ?.The marble score of group ? was 18.8%lower than that of group ? and 8.4%lower than that of group ?.The muscle tenderness of group ? was 9.5%lower than that of group ? and 16.1%higher than that of group ?Under the experimental conditions,the growth performance,carcass quality and meat quality of the growing pigs were the best when the level of metabolizable lipid substances in growing pigs was 68.09 g/kg. |
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