Effects of different dietary forage sources on milk performance and amino acid profile in early lactating dairy cows
The objective of this study was to evaluate the effects of different dietary forage sources on performance and milk amino acid profile in early lactation dairy cows. Thirty-two Chinese lactating Holstein cows with similar DIM (55±15 d) and milk yield (31.4±3.49kg/d) were randomly assigned to two groups and fed total mixed ration(TMR) using automatic feeding system. Diets contained similar concentrate mixtures with the same forage-to-concentrate ratio of 36:64 [dry matter (DM) basis]. Different forage sources were then added: 17.30% alfalfa hay and 18.77% corn silage (MF); 36.07% corn straw (CS).Experiment lasted for 90 days including first 14 days dietary adaption. Animal health condition, milk yield, amount of feed offered and refused for individual cows were recorded every day in experimental period. Milk samples of each cow on 91 d were collected to analysis milk composition and amino acid profile in milk protein.
MF group had increased daily DMI(21.35 vs 17.43 kg/d, P<0.01), milk yield(30.45 vs 23.12 kg/d, P<0.01), milk protein content (3.66 vs 3.32 %, P<0.01), milk protein yield(1.11 vs 0.75 kg/d, P<0.01), milk fat yield(1.36 vs 1.01 kg/d, P<0.01) and milk lactose yield(1.47 vs 1.13 kg/d, P<0.01) compared with CS group. The content of Thr(3.79 vs 3.71 g/100g AA, P<0.01), Ser(4.48 vs 3.36, P=0.03), Met(3.50 vs 3.38, P=0.02), Lys(7.71 vs 7.55, P<0.01) and Arg(3.35 vs 3.31, P=0.02) in milk protein were elevated significantly in MF group while the two kinds of BCAA (Leu 11.72 vs 11.88, P=0.02 and Val 5.98 vs 6.09, P<0.01) showed an opposite trend. Otherwise, the concentrations of amino acids in milk were greater (P<0.01) in response to MF group compared with CS group. But no difference was observed in content of milk fat and milk lactose between two treatments (P>0.05).
Keywords: forage, milk performance, amino acid