Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science

Committee Chair

Kolapo Ajuwon

Committee Co-Chair

Layi Adeola

Committee Member 1

Darryl Ragland

Committee Member 2

Cindy Nakatsu

Abstract

Supplementation of pigs with exogenous xylanase, phytase and live yeast (LY) has been shown to enhance pig performance. However, the effect on weanling pig performance is not clear. Therefore, the objective of the series of studies described in this dissertation was to determine the effects of xylanase, phytase and live yeast on growth performance, nutrient digestibility and fecal gut microbial diversity of weanling pigs.

The first experiment was to determine the timing of xylanase supplementation to weanling pigs fed corn-soybean meal based diets and its effect on growth performance, nutrient digestibility and the composition of the gut microbiome. A total of 128 weanling pigs (Duroc × Yorkshire × Landrace); barrows: gilts = 1:1; 6.2 ± 0.6 kg BW; weaning age: 21 d) were randomly assigned to 4 treatments, 8 replicate pens with 4 pigs per pen based on their body weight (BW) at weaning. The 4 treatments were a combination of 2 dietary treatments (with or without xylanase) in 2 time points [phase 1 (day 0-14) and phase 2 (day14-42)]: xylanase/xylanase, xylanase/control, control/xylanase and control/control. Results from this experiment showed that xylanase supplementation to pigs fed corn soy diets within the first two weeks of weaning could lead to reduced growth performance, primarily due to suppressed feed intake. On the other hand, adding xylanase from two weeks post-weaning led to improvement in growth performance up to 6 weeks after weaning. In addition, xylanase addition improved gross energy (GE), nitrogen (N) and phosphorus digestibility at 6 weeks post-weaning, regardless of whether xylanase was added within the first two weeks of weaning or thereafter. However, xylanase supplementation and time of xylanase addition had no effect on fecal microbial community structure at 6 weeks post-weaning.

As a follow-up to the observation that the first two weeks post-weaning was critical when xylanase is added to weanling pig diets, a second study was conducted to determine the effects of xylanase and LY supplementation individually or in combination during first two weeks post weaning on long term growth performance, nutrient digestibility and gut microbiome diversity of pigs. A total of 180 weanling pigs (21 ± 2 d, BW: 6.2 ± 0.16 kg) were assigned to 5 treatments in a randomized complete block design (6 replicate pens, 6 pigs per pen) from weaning to market. The 5 treatments were: control/control, control/xylanase, xylanase/xylanase, LY/xylanase, xylanase+LY/xylanase, where the first diet was fed from weaning to 2 weeks. Thereafter, the second diet was fed from 2 weeks post weaning to d 141 with 6 phases of corn/soybean meal (SBM)/corn distiller's dried grains with solubles (DDGS) diets. Results from this study showed that LY supplementation with or without xylanase increased average daily gain (ADG) at two weeks after weaning (P <0.05) and increased GLUT2 gene expression (P <0.05) on d 15. In addition, xylanase supplementation from week 2 increased apparent total tract digestibility (ATTD) of GE, N and P at the end of day 43 (P <0.05). We also observed a limited effect of xylanase and LY on microbial abundance, whereas a significant effect (P <0.05) of pig age was found on fecal microbial community structure.

A third study was conducted to determine the effect of supplementation of xylanase and LY on long term growth performance and nutrient digestibility of weanling pigs. A total of 128 weanling pigs (21 ± 2 d, BW: 6.24 ± 0.20 kg) were assigned to 4 treatments in a randomized complete block design (8 replicate pens, 4 pigs per pen) from weaning to market. The 4 treatments were as follows for two feeding periods; wean to d 21 and d 21 to d 154; T1) control/control, T2) xylanase/xylanase T3) xylanase +LY/xylanase; T4) xylanase + LY/ xylanase + LY. Pigs were fed a 6-phase feeding program from weaning to market. Pigs were fed a complex diet for 3 weeks from weaning after which they were fed a corn, SBM, corn distillers based diet formulated to meet the pigs’ nutrients requirements (NRC 2012). Xylanase was added at 16,000 BXU/kg and LY was added at 1 g/kg from weaning to d 21, after which if included in the diet, it was reduced to 0.5 g/kg from d 21 to d 156. In contrast to previous studies, diet had no effects on growth performance from weaning to d 21. During the grower phase (d 42-98) pigs fed T3 and T4 had higher (P < 0.05) ADG during the growing phase by 6.7% and 6.1%, respectively, compared with the control with T2 being intermediate. In the finisher period (d98- 156), pigs fed with T4 had higher ADG than T1. At the end of the trial, pigs fed T3 had higher body weight than T1 with T2 and T4 intermediate and not different (P > 0.05) from T1. In addition, the ATTD of N was increased by T2 and T2, T3 and T4 had higher digestibility of P compared with T1 at the end of the nursery phase. The ATTD of dry matter (DM) and GE was increased by T4 and T2 increased ATTD of N at the end grower phase.

The fourth study was conducted to determine the effects of LY supplementation to sows during gestation and lactation and to their offspring after weaning on growth performance and nutrient digestibility of their offspring. A total of 40 sows were assigned to two dietary treatments (control vs. LY) based on parity and expected farrowing date. Birth weight, weaning weight, litter size and mortality were measured. After weaning, 128 mixed-sex piglets (64 from each sow treatment) were selected based on their source litter and initial BW, and randomly assigned to 2 treatments (control or LY) at 4 pigs per pen (total of 32 pigs per treatment) for a 6-week growth performance study. At the end of the growth performance trial, 2 barrows from each pen were moved to metabolism crates for total fecal collection for the digestibility trial. Addition of LY to the sow diets had no effects on birth weight, weaning weight, number of birth and mortality (P > 0.05). Piglets had greater BW on d 21 and 42 postweaning when sows were supplemented with LY, and overall ADG was greater in piglets from sows that received LY (P < 0.05). There were no effects of sow and nursery diets on overall average daily feedintake (ADFI) and gain to feed ratio (G:F) (P > 0.05). Supplementing LY during the nursery phase increased ATTD of DM, GE and P during this phase. The ATTD of GE was also greater in piglets from sows that received LY.

Effects of super dosing phytase on growth performance, nutrient digestibility and serum inositol phosphates of nursery pigs were determined in the last study. A total of 160 barrows were used in a randomized completely block design for a seven-week study. Pigs were assigned to four treatments based on their initial body weight, the four treatments including a positive control diet (PC); negative control diet (NC); NC+500 FTU/kg phytase and NC+2000 FTU/kg phytase. Phytase supplementation increased the BW on d 21, 35 and 49 (P <0.05). ADG, ADFI and feed efficiency were increased by 2000 FTU/kg phytase (P <0.05). Fed blood plasma inositol concentration was higher (P < 0.01) in the 2000 FTU/kg phytase diet. Phytase supplementation increased (P < 0.01) InsP2 and myo-inositol concentration in the duodenal digesta. Similarly, phytase supplementation decreased InsP6 and InsP5 concentrations in the ileal digesta and increased InsP2 and myo-inositol concentration (P < 0.01) in the ileum. Both phytase diets had increased (P < 0.01) InsPs disappearance compared with NC. InsP6 disappearance from the digesta was increased (P < 0.05) by phytase supplementation. Total InsPs disappearance was 93.6% in the 2000 FTU/kg phytase diet and 72.8% in the 500 FTU/kg phytase diet. Longissimus dorsi (LD) muscle plasma membrane GLUT4 concentration was increased (P < 0.01) by 2000 FTU/kg phytase supplementation compared to other treatments.

In summary, xylanase supplementation from weaning until two weeks post weaning had negative effects on growth performance of pigs. However, xylanase supplementation from two weeks post weaning increased growth performance. Supplementation of sows with LY during gestation and lactation increased growth performance of piglets born to those sows. In addition, supplementation of LY from weaning increased nutrient digestibility of piglets. However, age was the only significant factor that affected fecal microbial community diversity in pigs fed with xylanase or LY. Supplementation of super dosed levels of phytase to weaning pigs led to increased growth performance.

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