Open Access
Burley, Heather Kristin
Graduate Program:
Animal Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 09, 2009
Committee Members:
  • Paul H Patterson, Thesis Advisor
  • commercial
  • laying hens
  • crude protein
  • amino acids
  • performance
  • economics
  • ammonia
Recent increases in feed prices for laying hens have renewed interest in reducing costly crude protein (CP) levels in diets and supplementing the lower protein diets with limiting amino acids (AAs) in order to reduce feed costs while maintaining performance. This feeding strategy has the additional benefit of potentially reducing ammonia (NH3) emissions by lowering hen nitrogen (N) excretion. This dietary strategy was investigated under commercial conditions, based on the promising results of previous university scale studies. The objective was to establish if reduced CP, AA supplemented laying hen diets could maintain hen production performance, reduce feed costs, increase farm revenue, lower hen N excretion, and/or decrease NH3 emissions, compared to hens fed typical levels of CP, on a commercial scale. A total of 50,760 Lohmann LSL Lite laying hens were divided into three groups that were each fed diets containing different levels of CP and supplemented with limiting AAs to their required levels. Hens were housed in a high-rise facility with a deep-pit manure storage system. Each diet was fed to two out of the six total cage rows. Diets were corn-soybean meal based and least-cost formulated weekly based on current ingredient prices and nutrient concentrations. Hens were fed these diets ad libitum from 18 to 51 weeks of age (January 20, 2008-September 7, 2008). Diet C was a control diet formulated with the highest level of CP and was meant to represent a typical commercial laying hen diet. Diets B and A were formulated to contain intermediate and low levels of CP, respectively. Weekly diet formulations were examined to establish if diets were formulated to be isocaloric and AA balanced while also achieving the designed CP differences between diets. Monthly replicated data was collected at the front (F), middle (M), and end (E) of the feed trough for each cage row. Monthly samples and data included feed for CP, AA, and particle size analysis, hen body weight, egg weight, albumen height, Haugh units, yolk color, shell strength, shell thickness, and manure percent dry matter (DM), total N, ammonium (NH4+) N, organic N, phosphate (P2O5), potash (K2O), and NH3 flux. Weekly non-replicated production data and egg grade out results by dietary treatment were collected and reported by the producer. Weekly egg income, feed consumption, and feed prices were used to calculate weekly feed cost and egg income minus feed cost, e.g. farmer revenue. A 3 x 3 factorial analysis was performed using the PROC MIXED procedure of SAS© software version 9.1 to detect differences between parameters by diet (A, B, and C), location on the feed trough (F, M, and E), and their interaction. Mean comparisons were made using Tukey’s procedure. Examination of weekly diet formulations revealed that, overall, diets were isocaloric and AA balanced and that diets B and A were formulated at 0.85 and 1.40% less CP than diet C, respectively. Analyzed feed samples collected from within cage rows proved the diets to be AA balanced; however, overall, diets B and A were actually shown to contain 1.53% and 1.98% less CP than diet C, respectively; quite different than formulated CP differences between diets. Feed particle size analysis showed that the high CP diet consistently contained a numerically smaller proportion of large particles (2380-3360 µm) and larger proportion of small particles (840-1190 µm and 420-590 µm) than the lower CP diets throughout the eight month trial, however, these results were not statistically significant. Additionally, feed collected at the M location along the feed trough was made up of a greater proportion of large particles (>2380 µm) than feed collected from the F and/or E locations (P<0.05). Hen body weight and egg weight were numerically lower for the low CP diet versus the two higher CP diets throughout the study, though these differences were not statistically significant. Hen day egg production averaged 87.9, 87.4 and 87.1% for diets A, B, and C, respectively, and albumen height, Haugh units, yolk color, shell strength, and shell thickness did not differ by dietary treatment. Diets A, B, and C consistently had the highest to lowest percentage of large, grade A eggs and lowest to highest percentages of extra-large and jumbo, grade A eggs, respectively, throughout the study. Hen body weights and egg weights were consistently lower at the M location on the feed trough compared to the F and/or E, while shell strength was numerically higher at the M than at the F and/or E throughout the trial, though these findings were not statistically significant. Additionally, overall, albumen height and Haugh units were shown to be significantly higher at the M than at the F and/or E (P<0.05). Yolk color and shell thickness did not differ by location on the feed trough. Mean weekly egg income per hen housed for diet A was $0.0022 and $0.0024 less than for diets B and C, respectively. However, mean weekly feed costs per hen housed for diets A and B were $0.0083 and $0.0070 less than for diet C, respectively. The resulting weekly egg income minus feed costs per hen housed for diets A and B were $0.0059 and $0.0068 higher than for diet C, respectively. Manure percent DM, total N, (NH4+) N, organic N, and P2O5 did not differ by dietary treatment; however, manure K2O was numerically lowest for the low CP diet and highest for the high CP diet consistently for seven out of the eight months of the trial. Additionally, manure percent DM, (NH4+) N, organic N, P2O5, and K2O did not differ by location on the feed trough; however, manure total N tended to be highest at the M and lowest at the F location along the feed trough. Manure ammonia flux increased each sampling period until it peaked at 97.41 mg/cm2/min in May and then decreased until rising again in September; however, ammonia flux did not differ by diet or location on along the feed trough. There were no significant interactions overall between diet and location along the feed trough for any manure components or NH3 flux. This study found that when reduced CP, AA balanced diets were fed to a large scale commercial laying hen flock, it was possible to maintain hen production performance while reducing dietary costs and increasing farm revenue. However, it was also shown that this dietary strategy did not significantly influence ammonia flux or manure composition. These results indicate that although this dietary strategy may not be effective for reducing hen N excretion or NH3 emissions on a large scale basis, it would, however, be economically beneficial for producers to implement in commercial laying operations.