The influence of the screen size used to grind the main cereal of the diet on egg production, gastrointestinal tract (GIT) development, and body measurements was studied in hens from 17 to 49 wk of age. Diets formed a 2 × 5 factorial with 2 main cereals (corn vs. barley) and 5 screen sizes of the cereal (4, 6, 8, 10, and 12 mm). Each treatment was replicated 5 times. No interactions between main cereal and screen size were observed for any of the traits studied. Cereal type and screen size did not affect feed intake, egg production, BW gain, or quality traits of the eggs. Eggs tended to be larger (P = 0.092) in hens fed the barley diet than in hens fed the corn diet. Also, feed conversion ratio tended to increase (P = 0.081) when the cereal of the diet was ground with a 4-mm screen as compared with the average of the other diets. At 49 wk of age, the relative weight (% BW) of the GIT and gizzard was greater (P < 0.05) in hens fed barley than in hens fed corn. An increase in the screen size increased linearly the relative weight of the GIT (P = 0.089), gizzard (P < 0.01), and liver (P = 0.056). None of the other GIT traits or body measurements was affected by the main cereal or the screen size. In summary, barley can substitute up to 45% of the corn in diets for laying hens without any adverse effect on egg production. Therefore, the use of one or other cereal will depend on their relative cost. An increase in screen size improved gizzard development but had little effect on hen productivity. Within the range studied, the size of the screen used for grinding the cereal had little effect on hen productivity, although the use of a 4-mm screen might increase feed conversion ratio and gizzard development.

a b s t r a c tThe effects of the inclusion of raw glycerin (GLYC) and lecithin in the diet on egg production, egg quality and total tract apparent retention (TTAR) of dietary components was studied in brown egg-laying hens from 23 to 51 wk of age. The experimental design was completely randomized with six diets combined as a 2 × 3 factorial with two levels of GLYC (0 vs. 70 g/kg) and three animal fat to lecithin ratios (40:0, 20:20 and 0:40 g/kg). Each treatment was replicated eight times and the experimental unit was a cage with ten hens. Production was recorded by replicate every 28-d period and cumulatively. For the entire experiment, the inclusion of GLYC in the diet hindered feed conversion ratio per kilogram of eggs (2.071 vs. 2.039; P < 0.05) but did not affect any of the other production or egg quality traits studied. The replacement of animal fat by lecithin (40:0, 20:20 and 0:40 g/kg) increased egg weight (60.1, 60.7 and 61.8 g, respectively; P < 0.001) and egg mass production (56.8, 57.5 and 58.8 g/d, respectively; P < 0.01) and improved yolk color as measured by the DSM color fan (9.2, 9.2 and 9.5, respectively; P < 0.001) and feed conversion ratio per kilogram of eggs (2.072, 2.068 and 2.027, respectively; P < 0.05). Feed intake, egg production and body weight gain, however, were not affected. The inclusion of GLYC in the diet did not affect nutrient retention but lecithin inclusion improved TTAR of dry matter (P < 0.05), organic matter (P < 0.05), ether extract (P < 0.001) and gross energy (P < 0.001). In summary, the inclusion of 70 g glycerol/kg diet hindered feed conversion ratio per kilogram of eggs but did not affect any other production or digestibility trait. The replacement of animal fat by lecithin improved egg weight, egg yolk color and nutrient digestibility. Consequently, lecithin can be used as a lipid source in laying hen diets with beneficial effects on egg production.

We studied the influence of particle size of the main cereal of the diet on preference behavior by laying hens. Diets formed a 2 × 5 factorial with 2 main cereals (corn vs. barley) and 5 grinding sizes of the cereal (4, 6, 8, 10, and 12 mm screen). Each treatment was replicated 5 times (10 hens each). After a fasting period of 8 h, hens received their respective experimental diets from 06.00 to 14.00 hours. The geometric mean diameter (GMD) and the geometric standard deviation of the residuals in the feeder were determined every 2 hours. In addition, CP, ash, and Ca contents of the feeds were determined at the start and at the end of the experimental period. The experimental design was completely randomized with data analyzed as repeated measures with particle size and cereal as main effects. The GMD of the original feeds increased with increases in screen size and was greater for the barley than for the corn diets. The difference in GMD between the original diets and the residuals measured at 2 h intervals decreased as the experiment progressed (P < 0.001 for the interaction). Crude protein, ash, and Ca concentrated in the coarse fraction of the original diets and of the uneaten feed, an effect more pronounced for the minerals. Independent of the coarseness of the feed sieve, ash and Ca contents were higher in the uneaten feed at 14.00 h than in the original diets. Hens showed a clear preference for coarse particles irrespective of the concentration of CP, ash, or Ca in the different fractions of the diets. Data showed that birds under-consumed Ca during the morning, a period in which the requirements for mineral deposition are low. In summary, hens showed a significant preference for coarser particles, an effect that was more evident when the cereals were ground coarse. Hens, however, did not show any preference for consuming those feed fractions with greater CP, ash, or Ca contents.

The influence of grinding size of the main cereal of the diet on production and egg quality traits was studied in brown hens from 33 to 65 wk of age. The experiment was completely randomized with 6 treatments arranged as a 3 × 2 factorial with 3 main cereals (barley, corn, and wheat) and 2 grinding size of the cereal (6 and 10 mm screen). Each treatment was replicated 11 times (10 hens/replicate). Diets were isonutritive and contained 2,740 kcal/kg AMEn and 16.8% CP. Egg production, ADFI, egg weight, and feed conversion ratio (FCR) were determined by period (4 wk) and for the entire experiment. Egg quality traits (percentage of undergrades, Haugh units, thickness, strength, color of the shell, and proportion of albumen, yolk, and shell) were measured also by period. No interactions between main cereal and grinding size of the main cereal of the diet were observed for any of the traits studied. Feed intake, egg production, and BW gain were not affected by diet or grinding size. Eggs were heavier (P < 0.01) in hens fed barley than in hens fed corn or wheat, probably because of the higher fat content of the barley diets. Also, FCR tended to improve in hens fed barley compared with hens fed corn or wheat (P = 0.07). Diet did not affect any of the egg quality traits studied. In summary, barley and wheat conveniently supplemented with enzymes, can be used in substitution of corn at levels of up to 55% in diets for laying hens, without any adverse effect on egg production or egg quality traits. Moreover, the substitution of corn by a combination of barley and supplemental fat increased egg size. Consequently, the inclusion of one or other cereal in the diet will depend primarily on their relative cost. Within the range studied, screen size (6 vs. 10 mm) of the cereal had limited effects on hen production.