ABSTRACT
Choline has been demonstrated to partially substitute methionine in broiler chicken diets due to their interconnected biosynthesis pathways. Yet, research on the impacts of dietary choline supplementation on modern strains of high-yielding broilers is limited. The objective was to evaluate the effect of increasing additions of choline chloride on the performance and carcass characteristics of broilers fed reduced methionine diets and reared under summer environmental conditions. Ross 708 x Yield Plus male broilers were reared for 41 days on used litter in floor pens (n = 2232; 31 birds per pen). Birds were fed one of six corn and soybean meal-based, reduced methionine diets containing 0, 400, 800, 1200, 1600, or 2000 mg of added choline chloride per kg of feed. Diets were provided in three phases. On day 43, 10 birds per pen were processed. Increasing dietary choline resulted in similar body weight gain, reduced feed intake, and improved feed efficiency. Choline chloride supplementation linearly increased both breast and carcass yields while concomitantly increasing the incidence and severity of wooden-breast-affected fillets. These results indicate that supplementing reduced-methionine broiler diets with choline chloride during high environmental temperatures may improve feed efficiency and increase carcass and breast yields but may also increase wooden breast.
ABSTRACT
In vitro procedures are commonly used to estimate rumen protein degradability and protein digestibility of feed ingredients. However, it is unclear how well these assays correlate to in vivo data. The objectives of this work were to compare postruminal protein availability estimates from one in vitro procedure and one in situ/in vitro procedure with in vivo observations for blood meal (BM), feather meal (FM), and a rumen-protected lysine prototype (RP-Lys). The FM and BM used for this experiment were subsamples of material assessed in vivo by an isotope-based method and the RP-Lys subsamples were of a prototype tested in two in vivo trials: a lactation trial and by plasma appearance. Subsamples of the BM (n = 14) and the FM (n = 22) were sent to each of three different laboratories for in vitro or in situ/in vitro analysis of crude protein (CP) and determination of rumen undegraded protein (RUP) and digested RUP (dRUP). Subsamples of the RP-Lys (n = 5) were sent to one laboratory for in vitro analysis of CP, RUP, and dRUP. Two diets containing BM or FM were assessed using the Cornell Net Carbohydrate and Protein System (CNCPS) v6.55 with ingredient inputs derived from either the CNCPS feed library, the isotope dilution method, or an average of the in vitro results from the three laboratories to determine how much the differences among estimates affected ingredient values. In vitro dRUP estimates for BM from one laboratory closely matched those determined in vivo (66.7% vs. 61.2%, respectively), but no in vitro estimates for FM matched the in vivo values. Surprisingly, there were significant differences in protein digestibility estimates from the modified three-step procedure across the two laboratories for BM (P < 0.0001) and for FM (P < 0.0001) indicating significant variation among laboratories in application of the method. Within all laboratories, BM estimates were reported in a narrow range (CV values of 2.6 or less). However, when testing multiple samples of FM or the RP-Lys prototype, CV values within a laboratory ranged up to 11 and 34, respectively. For the RP-Lys, dRUP estimates from the in vitro method were roughly half of that determined by the in vivo methods suggesting poor concordance between the in vitro and in vivo procedures for this ingredient. The inconsistencies within and among laboratories accompanied with dissimilarities to in vivo data is problematic for application in nutrition models. Additional refinement to the in vitro techniques is warranted.
ABSTRACT
The objective of this study was to adapt existing in vitro methodologies to determine the extent of intestinal digestion of corn oil (CO), canola oil (CA), and beef tallow (BT) via manipulation of incubation length and concentrations of lipase, bile, and calcium within a buffer solution. Unless otherwise stated, 0.5 g of each lipid source were incubated separately and in triplicate, with triplicate batch culture runs for each treatment in 40 mL of 0.5 M KH2PO4 (pH = 7.6) for 24 h with pancreatin (8 g/L), bovine bile (2.5 g/L), and CaCl2 (10 mM). Individually, concentrations of pancreatin, bile, and CaCl2, as well as incubation length were tested. To examine the use of this assay to estimate in vitro total tract digestion, a KH2PO4 solution with concentrated amounts to reach the same final concentrations of pancreatin, bile, and Ca were used as the third step in a three-step total tract digestibility procedure. Free glycerol and free fatty acid (FFA) concentrations were measured using colorimetric assays as indicators of digestion. Data wereanalyzed as a completely randomized block design (block = run), using the Glimmix procedure of SAS. For each lipid source, free glycerol increased with increasing pancreatin; however, FFA was lowest at 0 g/L pancreatin but was similar at 6, 8, and 10 g/L. Both glycerol and FFA were greater for 2.5 and 5 g/L of bile than for 0 g/L for each lipid source. Calcium concentration did not affect glycerol or FFA for either CO or CA; however, glycerol and FFA for BT were greater when calcium was included at 5 and 10 mM than at 0 mM. For all fat sources, free glycerol and FFA increased after 1 h until 12 h, but did not increase from 12 to 24 h. When a concentrated mixture was used following fermentation and acidification steps, digestibility using FFA concentration increased as compared to just adding buffer; however, free glycerol concentration was indeterminable. Thus, free glycerol and FFA can be used as indicators of lipid digestion when a lipid source is incubated for at least 12 h in a buffer solution containing 8 g/L pancreatin, 2.5 g/L bile, and 5 mM Ca when only estimating in vitro intestinal digestion; however, when utilizing this assay in a three-step in vitro total tract digestibility procedure, only FFA can be used.
