Pleаse reаd the Experimentаl Treatments and Statistical Analysis sectiоns in Hewett et al. (2025) belоw. What is the experimental unit in this study? Hewett E, Zaragоza L, Lewis C, Houdijk J, Wilson A, Turner S. Exploring the effects of dietary lysine and tryptophan on the social behavior of pigs. J Anim Sci. 2025 Jan 4;103:skaf030. doi: 10.1093/jas/skaf030. Experimental Treatments Pigs were randomly allocated across 6 treatments in a 2 × 3 factorial arrangement in a randomized complete block design (block = wean date and weight), giving 16 replicates of each treatment, 8 per barn, of the following iso-energetic feeding treatments: 1) Standardized ileal digestible (SID) Lys levels: Lys 100 = diets with 100% PIC requirement at the midpoint of the growth phase, vs Lys 80 = diets with 80% PIC requirement at the midpoint of the growth phase; and 2) Trp to Lys ratio (Trp:Lys) of 0.210, 0.185, or 0.160. Full diet compositions, which had a basis of corn, distiller’s dried grains with solubles, and soybean meal, can be found in Appendix 1. Targeted Lys levels were attained through replacing soybean meal and synthetic Lys with corn, and minor modification from synthetic amino acid sources, minerals, and oil to ensure similar ratios of other essential amino acids to Lys at SID level, same levels of net energy, calcium, and standardized total tract digestible phosphorus as per recommendations of the genetic supplier (PIC, 2016) and (NRC, 2012) requirements. Within those Lys levels, targeted levels of Trp were attained by iso-energetic exchange L-tryptophan against a combination of corn and corn oil. The SID Lys levels were derived from a meta-analysis performed by PIC to determine the SID Lys requirements for the average requirement of average daily gain and feed-to-gain ratio for finishing PIC Camborough pigs under commercial conditions (Goncalves et al., 2017). There were a total of 5 feeding phases, pigs were weighed at the end of each feeding phase. Feed delivery was recorded automatically by the feed system and feed remaining in the feeders at the end of the feeding phase was recorded to allow for calculation of feed consumption. Feed samples were taken by the research staff. Statistical Analysis Statistical analyses were carried out using R Software version 4.2.2 (R Core Team, 2021). Models were constructed using the lme4 package (Bates et al., 2015). Pen was the experimental unit. Where appropriate, model residuals were visually inspected to confirm approximation to normality and tested for heteroscedasticity using Levene’s Test. When main effects (Lys or Trp:Lys) or interactions were not significant at P
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