STAT231: EXPERIMENTAL DESIGN “EFFECTS OF STOCKING DENSITY AND SOURCE OF FORAGE FIBER ON SHORT-TERM...
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Transcript of STAT231: EXPERIMENTAL DESIGN “EFFECTS OF STOCKING DENSITY AND SOURCE OF FORAGE FIBER ON SHORT-TERM...
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
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
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
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
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
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
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
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
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
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