Optimum Dietary Protein Levels In Female Minks Of Breeding Season

This research was designed to study the effects of different levels of dietary protein on female minks of breeding season. Animal nutritional indicators, serum biochemical indicators and reproductive performance were measured and analyzed in search for the optimum dietary protein levels with best reproductive performance to provide a scientific basis for the establishment of mink nutrition standard. The study consisted of three tests:Test 1: Effect of dietary protein level during preparative mating period in female minks. One hundred and eighty female minks were assigned randomly to six groups with 30 females each. Groupâ… to Groupâ…£received diets of fresh material with protein level of 28.59%, 32.31%, 36.21% and 40.35% respectively. Groupâ…¤to Groupâ…¥received diets of dry powder with protein level of 32.66%, 40.47% respectively. The test included a 7-day pre-trial period and a 44-day test period. The results were as follows: There was no significant difference in DM digestibility, CP digestibility, EE digestibility, Nitrogen deposition, NPU and BV between groups fed fresh material diet (P>0.05).With the dietary protein level increased,the indicators metioned above firstly increased and then decreased,reaching the peak when dietary protein level was 36.21%; Contents of TP, GLU and activity of GOT were significantly lower in the 28.59% protein level group(P<0.05), but all the serum biochemical indicators showed no significant difference between groups with dietary protein level higher than 32.31%; Nitrogen deposition, NPU, BV, contents of BUN, ALB, GLU in groups fed dry powder diets were not significantly different with those fed fresh material diet of the same dietary protein level (P>0.05), but the DM digestibility, CP digestibility, EE digestibility, activity of GPT and GOT were significantly lower than their dry powder counterparts(P<0.05).Test 2: Effect of dietary protein level during gestation period in female minks. Using the minks and grouping in test, Groupâ… to Groupâ…£received diets of fresh material with protein level of 31.79%, 36.53%, 41.39% and 45.39% respectively. Groupâ…¤to Groupâ…¥received diets of dry powder with protein level of 36.55%, 44.47% respectively. The test included a 7-day pre-trial period and a 44-day test period. The results were as follows: In groups fed fresh material diet, CP digestibility, EE digestibility, Nitrogen deposition, NPU and BV increased with dietary protein level(R2 were 0.9811,0.9531,0.9047 and 0.8532 respectively). Indicators metioned above were significantly lower in the 31.79% protein level group (P<0.05) and reached the peak when protein level was 45.39% showing no significant difference with the 36.53% and 41.39% groups (P>0.05).No significant difference was observed in DM digestibility and EE digestibility in fresh material diet fed groups.Compared with groups fed fresh material diet of same dietary protein level, the dry powder ones showed significantly lower values in DM digestibility, CP digestibility, EE digestibility, Nitrogen deposition, NPU and BV(P<0.05). Different dietary protein levels showed no significant difference in Mating rate, Parturition rate, Litter size, Number of born alive, Birth survive rate,Individual birth weight among fresh material fed groups, but Parturition rate, Litter size, Number of born alive firstly increased and then decreased with increasing dietary protein level, reaching the peak at 36.53% dietary protein level. Mating rate, Parturition rate, Litter size, Number of born alive, Birth survive rate, Individual birth weight decreased or significantly decreased in groups fed dry powder diet compared with groups fed flesh material diet of same protein level(P<0.05).Test 3: Effect of dietary protein level during laction period in female minks.Performing badlly during test 1 and test 2, dry powder diet was removed in this test. Eighty pregnant minks with similar due date were selected and randomly assigned to four groups with 20 minks each. Groupâ… to Groupâ…£received diet of fresh material with protein level of 32.28%, 36.33%, 40.94%, 44.68% respectively. Test ended when the last litter was weaned with a 7-day pre-trial period at the beginning. The results were as follows: Dietary protein level significantly affected Weaning weight loss and Weaning weight loss rate of minks in laction period(P<0.05). Daily weight gain and Weaning survival rate of kits increased with the dietary protein level, although no significant difference was observed between the four groups. When the dietary protein was 44.68%, Daily weight gain and Weaning survival rate reached peak (R2 were 0.846 and 0.9987 respectively), Weaning weight loss and Weaning weight loss rate were the lowest. Values of BUN, TP, GLU and GOT were significantly affected by dietary protein level with the tendency of increasing with it, which showed that minks in laction had high utilization rates of high protein diet.The combination of feeding experiment, digestion metabolism experiment, serum biochemical indicators and reproductive performance showed that the optimum dietary protein levels in preparative mating period, gestation period and laction period were approximate 32%, 36% and 44% respectively.