| Under the modern intensive farming mode,the prominent problem that laying hens face in the late stage of laying is that with the increase of the age,the body is prone to redox imbalance and chronic inflammation,resulting in the decline of production performance and egg quality.Using green feed additives in layer production has become an effective method to improve production performance and egg quality.Taurine has strong anti-oxidation,anti-inflammatory,regulating lipid metabolism disorder and other functions,and has been widely used in medicine,food,and other fields,but its application in livestock and poultry farming is still in its infancy.Because of its various beneficial functions,taurine has been highly praised by some scholars for its role in livestock and poultry production in the post-antibiotic era.Previous studies have shown that taurine can improve the performance of laying hens in the late stage of laying,but the dosage of taurine is not uniform,and there are few reports on the effects of taurine on egg quality,nutritional composition and egg freshness.In this experiment,multiple taurine concentration gradients were set up to explore the effects of taurine on the production performance,conventional egg quality,nutritional components,egg antioxidant capacity and egg freshness under low temperature storage of laying hens in the late laying period.The recommended dosage of taurine in laying hens’ diets was determined to provide further basic data for the application of taurine in laying hens production.In this study,102 44-week-old Roman pink-shell laying hens were selected and randomly divided into six groups of 17 replicates each,and 1 layer hen per replicate.The control group was fed the basal diet,and the treatment group was supplemented with 0.01%,0.02%,0.05%,0.1% and 0.2% taurine on the basis of the basal diet,respectively.The pre-feeding period was 2 weeks,and the experimental period was16 weeks.During the experiment,the egg production rate,feed intake,and average egg weight of the laying hens in each group were counted every two weeks,and the feed-to-egg ratio was calculated.The eggs of each group were collected at the end of the4 th,8th,12 th,and 16 th weeks to determine egg quality.Eggs from each group were collected at the 16 th week to determine egg nutritional components,yolk fatty acid composition,yolk antioxidant capacity and egg freshness.The main findings are shown as follows:(1)Production performance: During the experiment,the addition of 0.01%,0.02%,0.05%,0.1% and 0.2% taurine to the diet significantly improved the laying rate and average egg weight,reduced the ratio of feed to egg of laying hens in the late laying period at different time periods(P < 0.05),but had no significant effect on average daily feed intake(P > 0.05).(2)Egg quality: The addition of taurine in the diet reduced egg yolk color,among which,0.02%(16th week),0.05%(16th week),0.1%(16th week),0.2% taurine group(12th and 16 th weeks)egg yolk color was significantly lower than the control group(P <0.05);The egg albumin height of the 0.01%,0.02%,0.05% and 0.1% taurine groups was higher than those in the control group at the 8th,12 th and 16 th weeks(P > 0.05);the Haugh unit of eggs in 0.05%(12th and 16 th weeks)and 0.1% taurine groups(12th week)were significantly higher than those in the control group(P < 0.05);the addition level of0.2% taurine had a negative effect on egg quality,reducing egg albumin height(4th week)and Haugh unit(4th and 16 th weeks)(P < 0.05).Taurine had no significant effect on egg shape index,eggshell strength and eggshell thickness(P > 0.05).(3)Nutritional components of eggs: Adding taurine to the diet can significantly reduce the TC(0.1% and 0.2% taurine)and TG(0.05%,0.1% and 0.2% taurine)content in eggs(P < 0.05),had no significant effect on the moisture,ash,crude fat,and crude protein in eggs(P > 0.05);the addition of 0.05% taurine in the diet had no significant effect on the fatty acid content in egg yolk(P > 0.05).(4)Antioxidant capacity: Taurine could significantly increase the levels of T-AOC(0.02%,0.05%,0.1% and 0.2% taurine)and T-SOD(0.1% and 0.2% taurine)of egg yolks stored for 1 day(P < 0.05);taurine had no significant effect on MDA content of egg yolk stored for 1 day and T-AOC,T-SOD and MDA content of egg yolk stored for 21 days(P > 0.05).In addition,the MDA content of eggs in the control group and the 0.01%,0.02%,0.05%,0.1%,and 0.2% taurine-treated group was increased by 30.80%,37.45%,30.40%,14.63%,17.96%,and 22.63%,respectively,on the 21 st day of storage compared with the first day.Among them,the MDA content of egg yolk in 0.05% taurine treatment group changed the least during storage,followed by 0.1% and 0.2% taurine groups.(5)Egg freshness under low temperature storage: After eggs were stored at 4 ℃ for different times,the weight loss rate of 0.01%(40 days),0.05%(30,40 days)and 0.2%(20,40 days)taurine group was significantly lower than that of the control group(P <0.05).On the first day of storage,the pH value of egg albumin in the 0.1% and 0.2%taurine groups was significantly lower than that in the control group and other taurine-treated groups(P < 0.05);with the increase of storage time,the pH of egg albumen in the 0.02%,0.05%,0.1% and 0.2% taurine groups were significantly lower than that in the control group on the 10 th and 30 th days(P < 0.05).Taurine had no significant effect on egg yolk index,Haugh unit and air chamber height(P > 0.05);Taurine tends to delay the decrease of egg Haugh unit and the increase of air chamber height during storage(P > 0.05).Within 30 days of storage,the egg Haugh unit of taurine treatment group was higher than that of the control group(P > 0.05).On the 10 th,20th,30 th and 40 th days of storage,the egg air chamber height of taurine treatment group was smaller than that of the control group(P > 0.05).To sum up,the conclusions of this study are shown as follows:(1)Adding 0.01%,0.02%,0.05%,0.1% and 0.2% of taurine to the diet of laying hens in the late laying period can significantly improve the laying rate and average egg weight of laying hens and reduce the ratio of feed to egg.(2)The addition of 0.01%,0.02%,0.05% and 0.1%taurine decreased the egg yolk color and increased the albumen height and Haugh unit.The addition level of 0.2% taurine had a negative effect on egg yolk color,Haugh unit and albumen height.(3)The addition of 0.01%,0.02%,0.05%,0.1% and 0.2% taurine to the diet can reduce the TC and TG contents of eggs to varying degrees.(4)The addition of 0.01%,0.02%,0.05%,0.1%,and 0.2% taurine to the diet can improve the antioxidant capacity of egg yolks and alleviate the weight loss of eggs and the increase of albumin pH during low temperature storage to varying degrees and prolong the freshness of eggs.Considering the comprehensive effect and cost,it is recommended to add 0.05% taurine to the diet of laying hens in the late laying period. |
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