| Three different experiments were conducted to evaluate the effects of lactoferrin in milk replacer.Experiment 1 30 Holstein bull calves were selected and assigned to 5 groups randomly. Calves in 5 groups were respectively fed milk replacer(CK) or milk replacer supplemented with 125 mg/d LF (MR1), 250 mg/d LF (MR2), 500 mg/d LF (MR3)and 1000 mg/d LF (MR4). After 6w's feeding, The results showed that:supplementation of LF with different had the positive effects on growth of the pre-ruminant calves and promote calves'health.1. In different weeks, the daily body weight gain in MR2, MR3 and MR4 were significantly higher than in the others(P﹤0.05) There was no significant difference in body weight between MR2, MR3 and MR4 during whole experiment(P>0.05).. During the whole 6 weeks, the daily body weight gain of 5 groups are 0.44kg/d,0.49kg/d,0.62kg/d,0.61kg/d,0.58kg/d, respectively;2. There was no significant change in plasma glucose, urea nitrogen, total protein and triglycerides concentration between different groups(P>0.05), but IgA,IgG,IgM concentration were different in 5 groups. At 6th week , plasma IgG of MR2, MR3 and MR4 was significantly higher than CK(P﹤0.01), MR1 was significantly higher than CK(P﹤0.05), At 4th week , IgA in MR2 and MR4 were also significantly higher than CK (P﹤0.01) ,MR3 was significantly higher than CK(P﹤0.05), At 8th week , IgA of MR1,MR2, MR3 and MR4 were significantly higher than CK(P﹤0.01),and plasma IgG of MR1,MR2, MR3 and MR4 were significantly higher than CK(P﹤0.05),at 6th week, At 8th week, IgG of MR2, MR4 were significantly higher than MR1, CK(P﹤0.01), MR3 was significantly higher than CK and MR1(P﹤0.05).Experiment 2 Nine Holstein bull calves were selected and assigned to three groups randomly. Calves in three groups were respectively fed m milk replacer(CK) or milk replacer supplemented with 250 mg/d LF (MR2),and 1000 mg/d LF (MR4). Determine calves digestibility during 20~25 and 40~45 days old. The results showed that:Between 20~25 days old, the digestibility of dry matter, crude protein and fat,in MR2 and MR4 significantly higher than CK(P﹤0.05), there was no difference between MR2 and MR4 (P>0.05).The nitrogen retention rate of 20~25d calves with CK was 5.65g/d, significantly lower than that in MR2 and MR4(7.46g/d and 7.59g/d, respectively)(P<0.05); meanwhile,40~45d calves had the higher nitrogen retention rate in MR2 group (10.91g/d) and MR3group (10.94g/d ) ,respect to 40~45d calves in CK (8.32g/d)(P<0.05).Experiment 3 Experiment design was in same with the Experiment 1, all the tested calves were slaughter after 8 weeks old . Digesta in rumen,duodenum and proximal, middle, distal of jejunum were colleted to determine the activity of different kinds of digestive enzymes. Tissue samples of duodenum and proximal, middle, distal of jejunum were collected to analyze gut morphology. The results showed that:1. The ruminal volatile fatty acids concentration of MR2 and MR4 were higher than CK. The activity of trypsin,chymotrypsin,amylase,lipase in MR2 and MR4 were much higher than CK. The trypsin activity in proximal and middle of intestine of MR2 and MR4 were significantly higher than CK (P﹤0.05),in the duodenum and middlel of jejunum chymotrypsin activity higher than CK(P﹤0.05),The activity of amylase in CK was significantly lower than MR2 and MR4(P﹤0.05);2. The villi size in MR2 and MR4 were long, tapering, integrated and the crypt depth were normal .In CK, the villi size was inferior to MR2 and MR4 slightly. Villus atrophy and crypt elongation were occurred in CK, even Villus shedding was observed in individual calf.
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