Nutritional factors affecting animal growth and activity of gut microorganisms

Abstract

Three studies were conducted as part of this graduate program. The first study was to evaluate effects of Nannochloropsis biomass on growth performance, fatty acid profile of leg quarters, and histopathology of skeletal muscle when fed to broiler chicks. Day-old male Ross-708 broiler chicks (n = 576) were separated into 72 battery pens (8 birds/pen). Pens (experimental unit) were blocked by tier location within battery and randomly assigned to 1 of 4 dietary treatments consisting of either 0% (control), 2%, 4%, or 10% algae. All diets, formulated to be isocaloric and isonitrogenous, were fed ab libitum for 18 d. On d 18, pen weights were recorded and 2 birds per pen were sacrificed for fatty acid, histopathology, and toxicology analyses. Data were analyzed using PROC GLIMMIX with fixed effect of treatment, random effects of battery and tier, and pen as the experimental unit. When compared to control, 2% and 4% algae did not impact average daily gain (P = 0.1084) or average daily feed intake (P = 0.9998). However, 10% algae decreased (P = 0.0003) feed efficiency when compared to all other treatments. Fatty acid profile of leg quarters improved with algae supplementation at all levels as demonstrated by linear increases (P < 0.0001) in polyunsaturated and total n-3 fatty acids. There was no impact of treatment on necrosis of muscle fibers (P = 0.3189). Arsenic, cadmium, lead, and thallium were below detectable limits in the liver for all treatments. Supplementation of Nannochloropsis algae to broiler chicks improved fatty acid profile of muscle tissue without negatively affecting growth performance when fed at 2 and 4% of total diet. A second study was conducted to assess impact of various carbohydrates on fermentation by bovine ruminal microorganisms. To do this, ruminal fluid was collected and used to inoculate fermentation bottles containing buffer, forage, and a supplemental carbohydrate source. Bottles contained 5 g of forage (prairie hay, smooth bromegrass hay, or alfalfa) and 0.1 g of supplemental carbohydrate (glucose, fructose, galactose, xylose, mannose, arabinose, rhamnose, lactose, sucrose, melibiose, maltose, isomaltose, trehalose, stachyose, raffinose, raw corn starch, hydrolyzed corn starch, cellulose, sugar cane molasses, or beet molasses). Bottles were equipped with continuous gas pressure monitors and incubated in duplicate for 48 h using the ANKOM RF System (ANKOM Technology, Macedon, NY). Bottles were then opened and terminal pH, in vitro dry matter disappearance (IVDMD), in vitro neutral detergent fiber disappearance (IVNDFD), and volatile fatty acid (VFA) concentrations were measured. Data were analyzed using the PROC GLIMMIX procedure for terminal pH, IVDMD, IVNDFD, and VFA’s with fixed effects of carbohydrate source, forage type, and interaction. Total gas production data were analyzed via NLIN and the MIXED procedure. Total gas production was not affected by carbohydrate source in cultures containing prairie hay or bromegrass (P ≥ 0.06). However, total gas production increased with cellulose, galactose, and hydrolyzed corn starch (P ≤ 0.05) in cultures containing alfalfa. Terminal pH and IVDMD were not affected by carbohydrate source in cultures containing prairie hay, bromegrass, or alfalfa. There was no impact of carbohydrate source on IVNDFD in cultures with prairie hay and alfalfa. However, cultures containing bromegrass had a greater IVNDFD with isomaltose and galactose when compared to control (P = 0.038). Several changes were observed in cultures supplied with prairie hay. Cellulose reduced acetate compared to control (P = 0.003), while the control had a greater A:P ratio when compared to trehalose, sucrose, raffinose, melibiose, mannose, maltose, lactose, glucose, galactose, fructose, and cellulose (P ≤ 0.05). Meanwhile, butyrate concentration was greater (P = 0.010) in cultures containing arabinose, and cellulose led to a greater concentration of valerate (P = 0.007) and caproate (P = 0.003) when compared to control. Control cultures had greater methane production compared to those with cellulose, fructose, and isomaltose (P = 0.001). Finally, total VFA concentration was greater with maltose when compared to the control with prairie hay alone (P = 0.015). In cultures containing bromegrass, a greater A:P ratio was produced in cultures containing arabinose, glucose, isomaltose, lactose, melibiose, molasses, raffinose, rhamnose, sucrose, and trehalose when compared to control (P < 0.0001). In cultures containing alfalfa, there was a difference in A:P ratio between the control and all treatments (P = 0.006). Because most alterations to fermentative parameters were observed with prairie hay, it seems that carbohydrates have most potential to improve digestion of poor-quality forages. In vitro fermentation systems allow researchers to mimic the equine hindgut while providing quick, affordable, and publishable data. In these systems, the substrate:buffer ratio has a profound impact on fermentation parameters. The objective of the third experiment was to evaluate varying substrate levels, thus altering the substrate:buffer ratio for its effect on culture pH, gas production, dry matter disappearance (DMD), neutral detergent fiber disappearance (NDFD), and volatile fatty acid (VFA) concentrations. Cecal fluid was collected from 4 cecally cannulated Quarter horses and used to inoculate fermentation bottles containing buffer and substrate. Substrate consisted of bromegrass or corn included at 0.5, 1, 1.5, 2, 3, or 4 g/flask (as-fed basis) while buffer and inoculant remained constant at 125 and 25 mL/flask, respectively. Flasks were equipped with continuous gas pressure monitors utilizing the ANKOM RF Gas Production System (ANKOM Technology; Macedon, NY) and placed into a shaking incubator for 48 hours at 39°C. Data were analyzed using mixed models with fixed effects of treatment, time, and the treatment x time interaction, repeated measure of time, and random effects of run x horse within run. Differences in total gas production, VFA production, and terminal pH were evident for substrate level and substrate type (P < 0.0001). At 1.5 g or 2.0 g substrate, there appeared to be a shift in slope as the incremental increase in many response variables began to decrease as more substrate was provided. Thus, cultures with > 2 g substrate may have been inhibited by buffer exhaustion or end-product accumulation. The composition of fermentative end products is impacted by substrate concentration, and for cultures containing 125 mL of buffer and 25 mL of cecal inoculum, we would recommend using no more than 2 g of substrate.