stat231: experimental design “effects of stocking density and source of forage fiber on short-term...
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STAT231: EXPERIMENTAL DESIGN
“EFFECTS OF STOCKING DENSITY AND SOURCE OF FORAGE FIBER ON SHORT-TERM RESPONSES IN RUMINAL FERMENTATION, BEHAVIOR, AND LACTATIONAL
PERFORMANCE OF HOLSTEIN DAIRY COWS”
Mac Campbell
Sam Kriegman
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AIMS & OBJECTIVES Perform a analysis of stocking density/nutritional
interactions on: Ruminal environment (1°) Behavior (2°) Production (2°)
Measuring of this interaction is vital in: Maintaining optimal productive efficiency Well-being of cattle Providing data for nutritional models
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EXPERIMENTAL DESIGN 2 x 2 factorial within a 4 x 4 Latin square design 14-day periods, with first 7 serving as adaptation period Multiparous (n=48) and primiparous (n=20) lactating Holstein cows Focal group of cannulated cows (n=16) Nuisances balanced for:
Days in Milk (190 ± 103)
Milk production (101 ± 18)
Parity (2.2 ± 1.1)
4 pens of cattle (n=17/pen) Experimental unit = pen Observational unit = cow
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DETERMINATION OF TREATMENTSA) 100% Stocking Density, No Straw
B) 100% Stocking Density, Straw
C) 142% Stocking Density, No Straw
D) 142% Stocking Density, Straw
Example of the 2 x 2 Factorial within the 4 x 4 Latin square
PEN 10 PEN 11 PEN 12 PEN 13PERIOD 1 B C A DPERIOD 2 D A B CPERIOD 3 A D C BPERIOD 4 C B D A
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MEASUREMENTS
Mean rumen pH H/d spent below pH 5.8
Continuous monitoring at 1-min intervals on d 12-14 of each period
Dry matter intake Average across d 8-14 of each period
Milk yield Average across d 8-14 of each period
Lying time Continuous monitoring at 10-min
intervals on d 8-10 of each period
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EXPERIMENTAL MODEL (MIXED)
Yijklm = µ + Si + Dj + SDij + Pk + Rl + Eijklm
Where:
Yijkl = dependent variable
µ = overall mean
Si = fixed effect of stocking density
Dj = fixed effect of diet
SDij = fixed effect of the interaction between stocking density and diet
Pk = fixed effect of period
Rl = random effect of pen ~N(0, σ2r)
Eijklm = residual error, ~N(0, σ2e)
i = 1, 2 j = 1, 2 k = 1, 4 l = 1, 4 m = 1, 4
Pre-Planned orthogonal contrasts1. Low vs. High Stocking density2. Straw vs. No Straw Diet3. Interaction of stocking density and diet
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POWER CALCULATIONS
Primary Objectives:
Secondary objectives
1. Krawczel et al. 20122. Yang and Beauchemin, 2007
r = 71 cows/pen r = 25 cows/pen
r = 50 cows/pen r = 33 cows/pen r = 15 cows/pen
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RESULTS 100% 142% P-value
NS S NS S SEM STKD DIETSTKD
x DIET
Mean pH 6.17 6.13 6.09 6.10 0.03 0.07 0.62 0.39
pH < 5.8, h/d 2.29 1.90 4.12 2.77 0.41 <0.01 0.01 0.10
Intake, kg DM/cow
25.4 25.3 25.3 25.2 0.4 0.78 0.69 0.87
Lying Time, min/d 832 827 779 797 11 <0.01 0.56 0.31
Milk, kg/d 41.2 40.4 40.7 40.0 0.7 0.21 0.06 0.79
Significance at P ≤ 0.05Trends at 0.05 < P ≤ 0.10
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LIMITATIONS
Experimental unit forced to be pen rather than individual cow
Loss of data during a single period forces the loss of entire cow from that particular measurement data set
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OUTCOMES
Stocking density negatively affects lying time and ruminal pH
Straw diet counteracted the negative pH effect from higher stocking density with minimal affects on production and behavior