Technical note: utilization of various allotment strategies to evaluate variation and replications required to detect statistical significance in nursery pig research

A total of 720 barrows (line 200 × 400, DNA genetics) were used in two 42-d nursery trials (initially 6.20 ± 0.12 kg and 5.63 ± 0.16 kg, respectively) to evaluate strategies for allotting pigs to pens in randomized controlled trials. At placement, the population was split into three cohorts with similar average weight and standard deviation and randomly assigned to one of the three allotment strategies. Strategy 1 (random) utilized a simple randomization strategy with each pig randomized to pens independent of all other pigs. Strategy 2 (body weight [BW] distribution) sorted each pig within the cohort into one of the five BW groups. One pig from each weight group was then randomly assigned to a pen such that distribution of BW within pen was uniform across pens. Strategy 3 (BW grouping) sorted pigs within the cohort into 3 BW categories: light, medium, and heavy. Within each BW category, pigs were randomized to pen to create pens of pigs from each BW category. Within each experiment, there were 72 pens with five pigs per pen and 24 pens per allotment strategy. For all strategies, once pigs were allotted to pens, pens were allotted to one of the two treatments for a concurrent trial. In experiment 1, environmental enrichment using ropes tied near the pan of the feeder was compared to a control with no enrichment. In experiment 2, treatment diets consisted of basal levels of Zn and Cu from the trace mineral premix for the duration of the study (110 and 17 mg/kg, respectively; control), or diets (supplemented control) with carbadox (50 g/ton; Mecadox, Phibro Animal Health, Teaneck, NJ) fed in phase 1 (days 0 to 22) and 2 (days 22 to 43), pharmacological levels of Zn and Cu (2,414 mg/kg Zn from ZnO; 168 mg/kg Cu from CuSO4) fed in phase 1, and only pharmacological levels of Cu (168 mg/kg Cu from CuSO4) fed in phase 2. These treatment designs were used to determine the impact on coefficient of variation (CV) and to estimate the number of replications required to find significant treatment differences based on allotment strategy. There were no meaningful allotment strategy × treatment interactions for either study. For between-pen CV, pigs allotted using BW distribution and BW grouping strategies had the lowest CV at allotment and final weight in both trials. For overall average daily gain in experiments 1 and 2 in experiment 2, the BW distribution strategy required the fewest replications to detect differences in performance. However, there is no meaningful difference between allotment strategies in replications required to detect significant differences for gain:feed ratio.

Defining the physical properties of corn grown under drought-stressed conditions and the associated energy and nutrient content for swine

Historically high temperatures and low rainfall during the 2012 growing season resulted in drought-stressed conditions in much of the U.S. corn belt. The objective of this experiment was to investigate the impact of these conditions on the composition and energy content in corn and determine if relationships exist among corn quality measurements, chemical composition, and digestibility of energy. Twenty-eight samples of corn from the 2012 drought-stressed crop (DS), plus 2 representative corn samples from the 2011 crop (CNTRL), were collected in Iowa and Illinois using yield as an initial screen for drought impact. Yields ranged from 2.5 to 14.8 t/ha. Each sample was graded by an official of the U.S. grain inspection agency and analyzed for 1,000 kernel weight, kernel density, ether extract, starch, GE, NDF, and CP content. Diets were formulated using each of the 30 corn samples and were fed at 2.6 times the estimated maintenance energy requirement according to the . Sixty individually housed barrows (PIC 359 × C29; 34.2 ± 0.2 kg initial BW) were randomly allotted in an incomplete crossover design to 30 diets across 4 periods. Diet and fecal samples were analyzed to determine DE values. Both ME and NE values were then calculated from DE values using methods developed by and , respectively. Mean DE, ME, and NE values between the CNTRL and DS were not different (3.72 vs. 3.68 Mcal/kg, respectively, 3.66 vs. 3.62 Mcal/kg, respectively, and 2.92 vs. 2.87 Mcal/kg, respectively; > 0.10). Comparing CNTRL with DS, there were no differences ( > 0.10) in ether extract (4.07 vs. 3.96%), CP (8.56 vs. 9.18%), or starch (70.5 vs. 69.5%). However, ADF and NDF were higher in the DS (2.23 and 8.19%, respectively) when compared with CNTRL (1.89 and 6.92%, respectively; < 0.001 and = 0.015, respectively). Small but significant correlations were observed between DE and NDF ( = -0.51, = 0.008), kernel density ( = 0.51, = 0.007), and percent damaged kernels ( = 0.41, = 0.031). No statistically significant correlations were observed between DE and starch or ADF content or between DE and test weight. We can conclude that corn grown in drought-stressed conditions has energy content similar to corn grown under more favorable conditions and, therefore, can be successfully used in swine diets. Furthermore, NDF proved to be superior to fat, starch, and ADF content in explaining the variation in corn energy content.

Disappearance and appearance of an indigestible marker in feces from growing pigs as affected by previous- and current-diet composition

Background

Indigestible markers are commonly utilized in digestion studies, but the complete disappearance or maximum appearance of a marker in feces can be affected by diet composition, feed intake, or an animal’s BW. The objectives of this study were to determine the impact of previous (Phase 1, P1) and current- (Phase 2, P2) diet composition on marker disappearance (Cr) and appearance (Ti) in pigs fed 3 diets differing in NDF content.

Results

When pigs were maintained on the 25.1, 72.5, and 125.0 g/kg NDF diets, it took 5.1, 4.1, and 2.5 d, respectively, for Cr levels to decrease below the limit of quantitation; or 4.6, 3.7, or 2.8 d, respectively, for Ti to be maximized. These effects were not, however, independent of the previous diet as indicated by the interaction between P1 and P2 diets on fecal marker concentrations (P < 0.01). When dietary NDF increased from P1 to P2, it took less time for fecal Cr to decrease or fecal Ti to be maximized (an average of 2.5 d), than if NDF decreased from P1 to P2 where it took longer for fecal Cr to decrease or fecal Ti to be maximized (an average of 3.4 d).

Conclusions

Because of the wide range in excretion times reported in the literature and improved laboratory methods for elemental detection, the data suggests that caution must be taken in considering dietary fiber concentrations of the past and currently fed diets so that no previous dietary marker addition remains in the digestive tract or feces such that a small amount of maker is present to confound subsequent experimental results, and that marker concentration have stabilized when these samples are collected.