effects of dietary crude protein on the performance of

DRMS. 2014. DHIA glossary. IDF. 2015. Bulletin 475/2015. NRC. 2001. National Research Council. Nutrient Requirements of Dairy Cattle. Vol. 7th rev. ed. Natl. Acad. Sci., Washington, D. Olmos-Colmenero and Broderick. 2006. Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows. J.Dairy Sci. 89:1704-1712 Spek et al. 2013. Prediction of urinary nitrogen and urinary urea nitrogen excretion by lactating dairy cattle in northwest Europe and North America: A meta-analysis. J.Dairy Sci. 96:4310-4322.

•  Studies suggested that removal of excess dietary crude protein (CP) has no impact in milk production (Olmos-Colmenero et al. 2006).

•  High dietary CP is usually associated with higher feed cost and loss of excess nitrogen (N) in the urine as urinary urea-N (UUN).

•  Excess UUN excretion represents an environmental concern because urea-N in the manure contributes to ammonia volatilization, nitrate leaching, and nitrous oxide emission.

•  Milk urea nitrogen (MUN) is a monitoring tool to evaluate dietary CP and predict UUN (Spek et al. 2013).

•  Variation in MUN is not fully explained by dietary CP, suggesting individual differences among cows (Spek et al. 2013).

•  The ultimate goal is to formulate diets with the lowest possible dietary CP content to minimize UUN excretion, without penalizing cow performance.

BACKGROUND

•  To evaluate performance and feed conversion efficiency in: •  cows grouped as either high MUN cow (HMUNC) or low MUN

cow (LMUNC; phenotypic basis) but similar parity, days in milk, and milk protein yield, and

•  fed diets with either 16.5 or 14.9% CP (dry matter basis); •  To assess the interaction between dietary CP and cow phenotypic

MUN.

OBJECTIVE

REFERENCES

RESULTS •  All cows were housed in a free-stall pen (Arlington Research Station.) •  Dietary treatments were formulated with differential proportion of

Soyhulls and Soy Plus (Table 2). •  Individual cow dry matter intake (DMI) was recorded continuously

using a roughage intake control e-gates system.

RESULTS

Effectsofdietarycrudeproteinontheperformanceofcowsgroupedbasedonhighorlowphenotypicmilkureanitrogen

Paulina Letelier, Francisco Contreras-Govea, Benito Albarrán-Portillo, Fernanda de Kassia Gomes, and Michel A. Wattiaux

Department of Dairy Science, University of Wisconsin-Madison Contact: letelier@wisc.edu PDPW Business Conference, 2018

Group Item HMUNC1 (n=9) LMUNC1 (n=9) Parity 1.8±0.67 1.8±0.67 DIM 88.4±15.52 83.8±18.00 Milk protein, kg/d 1.4±0.22 1.4±0.21 MUN, mg/dL 15.5±1.48 12.2±1.28

Dietary CP, % of DM Group P-value

Item 16.5 14.9 SEM HMUNC1 LMUNC1 SEM Diet Group Diet x Group

DMI2, kg/d 27.8 27.4 0.93 27.4 27.8 1.27 0.55 0.80 0.50 MY2, kg/d 48.4 47.1 2.22 46.9 48.6 3.09 0.13 0.70 0.78 FPCM2, kg/d 41.4 41.3 2.61 42.2 40.5 2.59 0.99 0.66 0.78 ECM2, kg/d 45.8 45.7 2.09 46.6 44.9 2.85 0.94 0.69 0.79 Milk Composition Fat, % 3.15 3.34 0.19 3.46 3.04 0.22 0.11 0.21 0.45 Protein, % 2.79 2.87 0.05 2.87 2.80 0.06 0.12 0.39 0.56 Lactose, % 4.85 4.94 0.05 4.91 4.88 0.05 0.28 0.68 0.28 SNF, % 8.57 8.76 0.11 8.71 8.62 0.14 0.19 0.53 0.39 MUN, mg/dL 14.14 10.69 0.32 13.43 11.40 0.37 <0.01 <0.01 0.88 Milk components yield Fat, kg/d 1.52 1.55 0.10 1.62 1.44 0.12 0.60 0.32 0.47 Protein, kg/d 1.35 1.35 0.07 1.35 1.36 0.09 0.98 0.93 0.60 Lactose, kg/d 2.36 2.32 0.12 2.30 2.38 0.16 0.56 0.75 0.43 SNF, kg/d 4.16 4.12 0.20 4.08 4.19 0.28 0.69 0.78 0.49 MUN, g/d 6.86 5.00 0.34 6.35 5.51 0.45 <0.01 0.21 0.85 Feed efficiency kg of milk/kg of DMI 1.74 1.71 0.05 1.71 1.75 0.06 0.17 0.66 0.10 kg of FPCM/kg of DMI 1.18 1.14 0.03 1.11 1.20 0.04 0.09 0.16 0.49 kg of ECM/kg of DMI 1.65 1.66 0.04 1.70 1.62 0.05 0.77 0.31 0.59

MATERIAL & METHODS

HMUNC (n=5)

LMUNC

16.5% dietary

CP

MATERIAL & METHODS

Dietary CP, % of DM Item 16.5 14.9 Ingredients1, % of DM CS 35.9 35.9 AS 18.0 18.0 Soyhulls 5.9 9.7 Soy Plus 13.2 8.9 Energy Booster 1.8 2.5 HMC 17.8 17.8 Canola Meal 5.2 5.0 Vitamin & minerals 2.3 2.3 Chemical composition, % of DM CP 16.5 14.9 RUP2 7.6 6.4 RDP2 8.9 8.5 Forage NDF 20.3 20.3 NDF 28.4 30.3 EE 5.6 6.0 Ash 8.7 8.5 Starch3 25.6 25.6

•  Reducing dietary CP from 16.5 to 14.9% decreased MUN without penalizing performance: DMI, milk production, FPCM, ECM, and yields of protein, fat and lactose.

•  Both groups of cows had the same performance but low MUN cows had lower MUN than high MUN cows.

•  Our results suggest that genetic selection could be applied for low MUN (and presumably low UUN excretion) without penalizing milk production and milk protein yield.

CONCLUSIONS Crossover experimental design with 2 periods.

The authors thank USDA AFRI award # 2011-68004-30340 and Wisconsin Alumni Research Foundation for funding, and Dairy Nutrition Plus (DNP) for donation of the SoyPlus used in this study.

ACKNOWLEDGEMENTS

14.9% dietary

CP

1AS: Alfalfa Silage, CS: Corn Silage, DM: Dry Matter, EE: Ether Extract, HMC: High Moisture Corn, NDF: Neutral Detergent Fiber, CP: Crude Protein.

2Predicted according to NRC (2001). 3Predicted according to Spartan.

8

9

10

11

12

13

14

15

16

HMUNC LMUNC

16.5

Table 1. Characteristics of cows grouped by level of MUN (data collected three weeks prior to the initiation of the study).

1HMUNC: High MUN cows, LMUNC: Low MUN cows.

14.9 Dietary CP, % DM

Figure 1. MUN response as influenced by level of dietary CP (P < 0.01) in cows grouped as high MUN cows or low MUN cows (P < 0.01) showing no interaction between group and diet (P = 0.88).

Table 2. Ingredients and chemical composition of the diets.

MU

N (m

g/dL

)

14.9% dietary

CP

16.5% dietary

CP

Period 1 Period 2

LMUNC (n=4)

HMUNC (n=4)

LMUNC (n=5) Group P = 0.88

1HMUNC: High MUN cows, LMUNC: Low MUN cows. 2FPCM: Fat-Protein Corrected Milk (IDF, 2015), ECM: Energy Corrected Milk (DRMS, 2014), DMI: Dry Matter Intake, MY: Milk Yield.

Table 3. Effect of dietary CP content on milk production, milk composition, and feed efficiency