Effects Of Dietary Supplemenation Of Methionine And Di-Peptide DL-Methionyl-DL-Methionine On The Crop Milk Protein Synthesis Of Breeding Pigeon And Growth Performance Of Squabs

After the squabs are shelled,the pigeon crop milk is the main source of nutrients.The secretion amount of crop milk directly affects the growth performance and survival rate of the squabs.Therefore,exploring the synthetic mechanism of crop milk is essential for the growth and development of squabs.Based on the correlation between the PRLR/JAK2/STAT5 signaling pathway and the protein synthesis of crop milk,this paper explores the effects of dietary supplemental of DL-methionine and di-peptide DL-methionyl-DL-methionine on the performance amd the crop milk protein synthesis of the breeding pigeons,and the growth performance of the squabs.We hope to provide theoret ical basis and nutritional solutions for milk protein synthesis and the improvement of squabs’ growth.The study was divided into three parts.In Experiment 1,a total of 324 pairs of breeding pigeons,with similar production and reproductive performance,were selected,and were randomly divided into 9 treatment groups.The 9 treatment diets contains,basic diet,(CP=15%,Met=0.25%),and the diets supplemented with 0.15%,0.30%,0.45% and 0.60% DL-methionine or supplemented with 0.15%,0.30%,0.45% and 0.60% di-peptide DL-methionyl-DL-methionine The effects of dietary supplemental with DL-methionine and di-peptide DL-methionyl-DL-methionine on the performance,crop morphology,crude protein levels in crop milk of breeding pigeons,and the growth performance,slaughter performance,and meat quality of squabs were determined.Meanwhile,the protein expression of PRLR/JAK2/STAT5 signaling pathway in crop tissues of breeding pigeons were also investigated.In Experiment 2,10 pairs of breeding pigeons during the non-lactation period and 10 pairs of breeding pigeons during the lactation period were selected,and the expression of PRLR/JAK2/STAT5 signaling pathway-related proteins in the crop of different breeding cycles were determined.In Experiment 3,a total of 40 pairs of pigeons,with similar production and reproductive performance,were randomly divided into 4 treatment groups.The wing veins of the breeding pigeons were respectively injected with 0(dissolved medium saline),0.5,1.0,and 2.0 mg/kg BW/d of bromocriptine mesylate.The effects of bromocriptine mesylate injection on the morphology of the crop milk protein synthesis,the growth performance of squabs,and the proteins expression of PRLR/JAK2/STAT5 signaling pathway were investigated.The results showed that,(1)Compared with the basal diet group,dietary supplemental with different levels of DL-methionine or di-peptide DL-methionyl-DL-methionine significantly increases the average daily feed intake,the thickness and relative weight of the crop tissues,and the crude protein levels of crop milk,and decreased the body weight loss of breeding pigeons(P<0.05).In addition,the DL-methionine or di-peptide DL-methionyl-DL-methionine supplementation also improved the average daily gain,slaughter performance,meat quality,relative small intestine weight,and d,and decreased the mortality of squabs(P <0.05).(2)A non-linear exponential regression model indicated that di-peptide DL-methionyl-DL-methionine was found to be more bioavailable than DL-Met with calculated relative bioavailability values of 211%,346%,467%,and 376% based on the body weight loss of breeding pigeons,average daily weight gain,carcass rate and breast muscle rate of the squabs,respectively.(3)Dietary supplementation of DL-methionine and di-peptide DL-methionyl-DL-methionine significantly up-regulated the proteins expression of PRLR/JAK2/STAT5 signaling pathway in the crop tissues of breeding pigeons(P<0.05).(4)Compared with the non-lactation period,the proteins expression of PRLR/JAK2/STAT5 signaling pathway were up-regulated in the crop tissues of the breeding pigeons(P<0.05).(5)In vivo injection of bromocriptine mesylate significantly down-regulate the proteins expression of PRLR/JAK2/STAT5 signaling pathway in the crop tissues,decreased the thickness and relative weight of the pigeon crop,the crude protein content in the crop milk of breeding pigeons(P<0.05).Meanwhile,the injection of bromocriptine mesylate decreased the growth performance of the squabs(P<0.05).In conclusion,the supplementaton of DL-methionine and di-peptide DL-methionyl-DL-methionine in the breeding pigeon diet(CP=15%,Met=0.25%)significantly increased the performance and the protein synthesis of crop milk of breeding pigions,and increased the growth performance of the squabs.The differences in bioavailability do exist between sources of synthetic DL-methionine,and the di-peptide DL-methionyl-DL-methionine is more available than DL-methionine.The improvement of growth performance of breeding pigeons and the squabs by the supplemental of DL-methionine and di-peptide DL-methionyl-DL-methionine may be related to the up-regulated protein expression of the PRLR/JAK2/STAT5 signaling pathway in the crop tissue of the pigeons,which promotes the synthesis of crop milk proteins.