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 TREATMENTS A) 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 10PEN 11PEN 12PEN 13 PERIOD 1BCAD PERIOD 2DABC PERIOD 3ADCB PERIOD 4CBDA

MEASUREMENTS  Mean rumen pH  H/d spent below pH 5.8  Continuous monitoring at 1-min intervals on d 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) Y ijklm = µ + S i + D j + SD ij + P k + R l + E ijklm  Where:  Y ijkl = dependent variable  µ = overall mean  S i = fixed effect of stocking density  D j = fixed effect of diet  SD ij = fixed effect of the interaction between stocking density and diet  P k = fixed effect of period  R l = random effect of pen ~N(0, σ 2 r )  E ijklm = residual error, ~N(0, σ 2 e ) i = 1, 2 j = 1, 2 k = 1, 4 l = 1, 4 m = 1, 4 Pre-Planned orthogonal contrasts 1. Low vs. High Stocking density 2. Straw vs. No Straw Diet 3. Interaction of stocking density and diet

POWER CALCULATIONS  Primary Objectives:  Secondary objectives 1.Krawczel et al Yang and Beauchemin, 2007 r = 71 cows/penr = 25 cows/pen r = 50 cows/pen r = 33 cows/penr = 15 cows/pen

RESULTS 100%142% P-value NSS SSEMSTKDDIET STKD x DIET Mean pH pH < 5.8, h/d < Intake, kg DM/cow Lying Time, min/d < Milk, kg/d Significance at P ≤ 0.05 Trends 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