The objectives of this study were to optimize the protein supplies and replacement of SBM with locally available ingredients in the rations of high producing Holstein Friesian cows at mid lactation. On the basis of these objectives, three experiments were conducted. Multiparous cows in mid-lactation received three treatments in a 3×3 Latin square design with a period length of 20 d. Number of animals used were nine in 1st and 3rd experiments and 12 in 2nd experiment (Table 6.1). The trials were conducted at a corporate dairy farm. When we compare the initial and final values of milk yield, milk fat and milk protein contents, there is not a big difference of our diets with that currently being practiced in Pakistan (Table 6.1). This also reveals that the experimental milk production was close to pre-experimental milk production indicating that a successful dietary transition was achieved. Table 6.1: Demonstration of parameters before and during the experiments Exp.
Cows
No.
Initial Parameters During Experiment Parameters
DIM Milk
yield (kg)
Milk
fat (%)
Milk
protein (%)
Milk
yield (kg)
Milk fat
(%)
Milk
protein (%)
1 9 113±25 32±4.1 3.65 3.25 29.7±3.1 3.70 3.27
2 12 153±44 23.3±2.1 3.99 3.34 24.7±1.8 3.98 3.31
3 9 109±19 34±3.7 3.71 3.19 30.7±2.5 3.64 3.21
Exp., experiment; DIM, days in milk In the 1st experiment, three dietary treatments were designed to provide similar energy and increasing supply of MP (g/d)—2371 (low), 2561 (medium), and 2711 (high). Increasing the MP supplies did not modify DMI; however, it increased milk protein, fat, and lactose yield linearly. Similarly, FCM increased (9.3%) linearly due to an increase in both milk yield (5.2%) and milk fat content (7.8%). Milk nitrogen efficiency decreased from 0.26 to 0.20, whereas, the
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metabolic efficiency of MP decreased from 0.70 to 0.60 at low to high MP supplies and it average value across the treatments was 0.64 (Table 6.2). In conclusion, increasing the MP supplies resulted in increased milk protein yield; however, a higher BUN and low MNE indicated an efficient utilization of dietary protein in low MP supplies. Milk nitrogen efficiency ranges from 20 to 30% in dairy cows at mid stage of lactation. Milk nitrogen efficiency increases slightly but linearly with the increase of dietary protein up to a certain level of supply of protein. At high protein levels of dietary protein MNE is low and vice versa. In the 2nd experiment, the response of balancing metabolizable Lys to Met ratio (3:1) in low protein diets was investigated. Three experimental diets; 1) LP−: low protein diet (13.6% CP) with imbalanced Lys to Met ratio (3.33), 2) LP+: low protein diet (13.5% CP) with balanced Lys to Met ratio (2.94) through HMBi; and 3) HP−: high protein diet (14.7% CP) without balancing Lys to Met ratio (3.39) in a 3×3 Latin square design were designed. Milk yield of LP- was 0.85 kg/d less as compared with the average milk yield of LP+ and HP-. Dry matter intake decreased by 0.7 kg/d in LP+ compared to HP- treatment whereas milk yield tended to be higher by 0.7 kg/d and protein yield by 23 g/d. Balancing the Lys to Met ratio by supplementing HMBi through feed increased feed, N, and MP conversion efficiencies to milk by 4.4, 1.6, and 13.1% respectively compared to the HP- diet. Similarly, 4% FCM was increased by 4.4% in LP+ diet as compared to HP- diet. Moreover, plasma urea concentration was numerically less in LP+ compared to LP- and HP- treatments whereas no effect was observed on plasma glucose and TG concentrations. In the 3rd experiment, three diets 1) Control: with low protein with SMB as a protein source, 2) SBMD: high protein diet with SBM as a major protein source and 3) CGMD: high
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protein diet with CGM as a major protein source. Increasing the protein supplies did not affect DMI, milk fat yield, and milk fat and lactose contents in SBMD and CGMD diets compared to the control diet. Similarly, MP balance and MP/NEL increased by 31.5 and 9.1%, respectively. Increasing the protein supplies tended to increase milk yield. Similarly, milk protein and lactose yield increased by 3.5 and 3.3%, respectively. Milk protein contents tended to increase by 1.5% in SBMD and CGMD treatments compared to the control. Increasing the dietary protein supplies increased FE in SBMD and CGMD treatments compared to control, whereas, MNE decreased by 10.9%. No effect was observed on DM, N and NEL intakes when SBM was partially replaced with CGM. Consequently, milk yield, milk components’ yield, milk composition and feed efficiency remained unaffected. Contrary to this, MNE decreased by 5% in CGM treatment compared to SBM. There were no dietary treatment effects on blood metabolites including BUN, glucose and TG concentrations, which means neither replacement of SBM nor concentration of protein in the diet affected the blood metabolites profile. There was no change in lactation performance of cows by the partial replacement of SBM with CGM. Therefore, SMB could be partially replaced with CGM with urea without affecting animal performance, and saving the feed cost. Table 6.2: Effects of experimental diets on different parameters Exp.
MP
efficiencies
Δ MP
efficiencies (%)
Δ MY
(kg)
Δ DMI
(kg)
Δ milk
fat (%)
Δ milk
protein (%)
1 0.64 14.3 5.20 0.10 7.80 5.30
2 0.65 11.6 1.20 0.70 3.93 1.50
3 0.68 9.85 1.10 0.20 2.18 1.10
Exp., experiment; MP, metabolizable protein; MY, milk yield; DMI, dry matter intake
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In conclusion, balancing Lys to Met ratio at low protein diets and partial replacement of SMB with CGM is a mean to improve the MNE and reduce feed costs. 6.1 Conclusion and Recommendations Diets with low MP supply result in high MNE and better utilization with low levels of BUN. Although there was less milk yield in low protein diets but utilizing efficiency was high. Low protein corn-soy-based diets supplemented with rumen protected Met (HMBi) result in increased utilization of protein and low levels of BUN. Partial replacement of SBM with CGM plus urea showed no change in DMI, milk yield. Milk nitrogen efficiency was slightly decreased in CGM diet as compared to SBM diet. Feed cost could be saved by replacing 35% SBM with CGM provided that RDP is balanced by using NPN sources. Diets should be given with possible lowest protein levels having balanced AA particularly Lys and Met, which should be 3:1. High levels of protein could result into increased emission of gases to the environment. Soybean meal replacement with CGM along with some NPN source results in similar outcomes. First strategy is the best out of three currently tested and it can save money. 6.2 Future Perspectives Studies must be conducted to investigate the effects of further lowering the dietary protein levels without affecting milk production in Holstein cows. It will help to improve the dietary N utilization for milk synthesis. The above-mentioned strategies can also be tried simultaneously for improved protein/N utilization in dairy cows. Lysine can also be tried along with Met to balance the low protein corn-soy-based diets. On the basis of RDP and RUP values, other ingredients can also be tried to partially replace SMB.