Effects Of Dietary Protein, Lys, Met On The Production Performance, Regularation Of Metabolism And Intestinal Characteristics At The Growth Period

As a kind of precious fur animals, mink (Carnivora mustelidae mustelia) has high daily proteinrequirements. The current study was conducted to investigate the effects of proteins, lysine andmethionine in dry-powder diet on production performance of growing mink. A combined strategycomprising of feeding trials, digestion and metabolism experiments, slaughter experiment, histology,molecular biology and chromatography of amino acid were employed to study the mechanisms ofproteins and amino acids digestion, absorption and metabolism in minks at different day-age. Thenutritional requirements of proteins and amino acids in mink were estimated to provide the data fordry-powder feed application in animal husbandry. This study was divided into two parts.Part1: Effects of protein levels on production performance, regularation of metabolism andintestinal characteristics in growing minksOne hundred and twenty healthy weaned50-day minks were randomly assigned into six treatments(the average body weight of each treatment had no significant difference, P>0.05), half male (averagebody weight of0.778±0.119kg) and half female (average body weight of0.577±0.073kg). Everygroup had20replications, with one mink in each replication. Each mink was fed in an individual pen.Minks from six groups were supplemented with28%(group Ⅰ),30%(group Ⅱ),32%(group Ⅲ),34%(group Ⅳ),36%(group Ⅴ) and38%(group Ⅵ) proteins, respectively. The main results were as follow:1The optimal protein intakes of minks at50-65day,65-68day,80-95day and95-110day were30-33g/d,28-35g/d,30-32g/d and29-40g/d, respectively.2The optimal protein intakes of male minks at early, middle and late winter hair period were42-48g/d,36-42g/d and41-47g/d. However, taking25-27g/d or30-32g/d were beneficial for those femaleminks at middle or late winter hair period to produce high-quality fur.3The digestibility of main nutrient had the sigenificantly difference at various physical stage in themink by the experiment of metabolism and digestibility(P<0.05). The mink fed with34%~36%dietary protein levelvs had higher digestibility of protein and nitrogen deposition at the grwoing period.The mink fed with32%~34%dietary protein levelvs had the same regularity at the fur bearingperiod(P<0.05). Dietary protein could enhance the digestibility of crude fat in the growth period(P<0.05).4The average body weight gain of growing female minks in group Ⅰ was minimum, whilemaximum in group Ⅳ. The activity of aspartate aminotransferase, total amino acid and total proteinconcentrations in serum of growing female minks in group Ⅴ were higher than those in other groups.5The villus height, crypt depth and mucosa thickness of jejunum in group Ⅳ and group Ⅴ werehigher than those of other groups, indicating that protein concentrations could adjust the morphology ofintestinal tract in mink.6The expression level of gene MC1R were significantly differently (P<0.01) among groups.Compared with group Ⅰ, MC1R expression level was highest in group Ⅲ and lowest in group Ⅵ, suggesting that protein concentrations contributed to color and maturation of fur.Part2: Effects of methionine levels on production performance, regularation of metabolism andintestinal characteristics in growing minksTwo hundred60-day minks were randomly assigned into ten treatments (the mean body weight ofeach treatment had no significant difference, P>0.05), half male and half female. Every group had20minks, half male and half female. The two factors and three levels experimental design was carried outto add0,0.3%or0.6%lysine/methionine to32%protein group, and the34%protein group was used aspositive control. The main results were as follow:1The concentrations of lysine and sulfur amino acid were1.64%-1.94%and0.91%-1.21%in dietof growing mink. Growing performance of minks in treatment group supplemented with amino acid wasbetter than those in34%protein group. The optimum concentrations of lysine and sulfur amino acidwere1.39%-1.69%and1.24%-1.54%for production performance of male minks at winter hair period,while1.59%-1.89%and0.94%-1.24%in female minks.2Lysine and methionine had effects on fur quality of minks. The optimum concentrations of lysineand sulfur amino acid were1.29%and0.94%. The fur area was biggest, when concentrations ofmethionine and cystine were1.2%and0.35%. The optimum concentration of sulfur amino acid was1.24%-1.54%and lysine/methionine was1:0.83-1.28.3The concentrations of lysine and methionine were1.64%-1.94%and1.39%-1.69%in diet ofgrowing male minks, while those were1.59%-1.75%and1.24%-1.61%in female minks. The digestionefficiency in basal diet supplemented with amino acid was comparative to that of34%protein group.4The concentrations of serum urea nitrogen in growing male minks supplemented with0.3%Lysand0.6%Met were significantly lower (P<0.01) than that of basal diet group. The growing femaleminks supplemented with0.3%Lys and0.6%Met showed good protein and amino acid metabolism,and high serum TAA.5The pepsin activity was improved by0.3%-0.6%Met.The absorption area of jejunum was highest in minks supplemented with0.3%Met or0.3%-0.6%Lys and0.3%Met. Addition of0.3%Lys and0.3%Met could enhance catalytic activity of duodenumtrypsase of minks. Those diets supplemented with0.6%Met or high level proteins could improve theactivities of amylopsin and pancreatic lipase.In summary, the requirements and metabolism of protein and amino acids vary in minks ofdifferent growing periods. Diets supplemented with moderate proteins and amino acids are capable toimprove production performance of minks. It is desirable to use properly formulated rations forreducing the nitrogen emission and cost in mink feeding.