Effects of different protein sources on milk performance and amino acid profile in early lactating dairy cows
Protein content of feed plays an important role in dairy amino acid profile of bovine milk protein. This study was aimed to investigate different protein sources on milk production performance and milk amino acid profile. Thirty-two Chinese Hostein dairy cows were blocked based on DIM (60±25 d) and milk yield (31.0±3.17kg/d) and randomly divided into group soybean (diet protein, soybean meal 11.29%, extruded soybean 2.06%, whole cottonseed 10.44%, rapeseed meal 4.19%, beet pulpand 4.16% and cottonseed meal 2.13%) and group non-soybean (whole cottonseed 10.44%, rapeseed meal 9.63%, cottonseed meal 6.71% and beet pulp 7.49%). Two diets contained similar forage with the same concentrate-to-forage ratio of 65:35 (DM basis).Experiment lasted for 12 weeks with first 2 weeks as adaption period. Milk samples were collected weekly and analyzed for milk composition and amino acid profile. Data were analyzed as repeated measurements using PROC MIXED of SAS.
Milk yield, milk protein content, milk fat content, milk protein yield and milk fat yield showed no difference between two groups. Compared with group soybean, Cows in group no-soybean increased DMI (20.31vs 17.43kg/d, P<0.01) and milk Pro content (8.48 vs 8.37 g/100g AA, P=0.04) but decreased milk Phe content (5.54 vs 5.60 g/100g AA, P=0.02) and BCAA (23.49 vs 23.68 g/100g AA, P=0.08), especially Leu content (11.69 vs 11.88 g/100g AA, P<0.01) in milk protein. There were no difference on content of EAA, NEAA between 2 groups. Results suggest that soybean meal can be partly replaced by miscellaneous meal (rapeseed meal, cottonseed meal and beet pulp) in diets for lactating dairy cows.
Keywords: protein source, milk amino acid profile, dairy cow