Influence of nutritional strategies on growth performance and digestive tract traits of brown egg laying pullets and subsequent effects on egg production

The thesis contributes to clarify the current knowledge on pullet nutrition, a field with scarce available information. To achieve adequate egg production it is necessary that both pullets and hens are healthy and with a well developed gastrointestinal tract (GIT). The better the uniformity and body development of the pullet is the higher the hen productivity will be. With this in mind, three experiments were conducted with the following objectives: 1) study the effects of feed form and diet composition during the first stages of life on pullet growth and uniformity; 2) study the effects of two different types of fiber at two and levels of inclusion on pullet growth and GIT development for the entire rearing period; 3) analyse the influence of pullet diet during rearing (fiber inclusion) on subsequent egg production and GIT of the hens at the end of the egg cycle. In experiment 1, the effects of fiber inclusion, feed form, and energy concentration of the diet on growth performance of pullets from hatching to 5 wk of age were studied in 2 trials. In trial 1, there was a control diet based on cereals and soybean meal and 6 extra diets that included 2 or 4% of cereal straw (straw), sugar beet pulp (SBP), or sunflower hulls (SFH) at the expense (wt/wt) of the whole control diet. Fiber inclusion increased (P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI), and improved (P < 0.05) energy conversion ratio (ECR; kcal AMEn/g ADG). Body weight (BW) uniformity, however, was not affected by treatment. Pullets fed SFH tended to have higher ADG than pullets fed SBP (P = 0.072) with pullets fed straw being intermediate. Feed conversion ratio (FCR) was better (P < 0.05) with the inclusion of 2% than with the inclusion of 4% fiber. In trial 2, 10 diets were arranged as a 2 x 5 factorial with 2 feed forms (mash vs. crumbles) and 5 levels of AMEn (2,850, 2,900, 2,950, 3,000, and 3,050 kcal/kg). Pullets fed crumbles were heavier and had better FCR than pullets fed mash (P < 0.001). An increase in the energy content of the crumble diets reduced ADFI and improved FCR linearly but no effects were detected with the mash diets (P < 0.01 and P < 0.05 for the interactions). Feeding crumbles tended to improve BW uniformity at 5 wk of age (P = 0.077) but no effects were detected with increases in energy concentration of the diet. Experiment 2 investigated the effects of fiber inclusion in the diet on growth performance and digestive traits in pullets from hatching to 17 wk of age. The control diets of the 3 feeding periods (0 to 5 wk, 5 to 10 wk, and 10 to 17 wk) were based on corn and soybean meal and did not include any additional fiber source. The experimental diets included 2 or 4% of cereal straw or SBP at the expense (wt:wt) of the control diet. From 0 to 5 wk of age, fiber inclusion did not affect pullet performance. From hatch to 17 wk of age, the inclusion of straw had little effect on pullet performance but the inclusion of 4% SBP reduced ADG (P < 0.05) and worsened FCR (P < 0.001). Pullets fed straw had greater ADG (P < 0.05) and better ECR (P < 0.01) than pullets fed SBP. An increase in fiber from 2 to 4% worsened FCR (P < 0.05). Body weight uniformity was not affected by diet. Fiber inclusion increased the relative weight (% BW) of the gizzard at 5 wk (P = 0.056) and 10 wk (P < 0.01) of age but no differences were detected between fiber sources. At same ages, the relative length (cm/kg BW) of the pullets (P = 0.058 and P < 0.01, respectively) and tarsus (P = 0.079 and P < 0.05, respectively) was higher in pullets fed SBP than in pullets fed straw. Fiber inclusion, however, did not affect any of these traits at 17 wk of age. Experiment 3 was designed to study the effects of the treatments used in experiment 2 (type and level of fiber) on egg production, GIT traits, and body measurements of brown egg-laying hens fed diets varying in energy concentration from 17 to 46 wk of age. The experiment was completely randomized with 10 treatments arranged as a 5 x 2 factorial with 5 rearing phase diets and 2 laying phase diets. During the rearing phase, treatments consisted of a control diet based on cereals and soybean meal and 4 extra diets that resulted from including in this diet a combination of 2 fiber sources (cereal straw and SBP) at 2 levels (2 and 4%). During the laying phase, diets differed in energy content (2,650 vs. 2,750 kcal AMEn/kg) but had the same amino acid content per unit of energy. The rearing diet did not affect any production trait except egg production that was lower in birds that were fed SBP than in birds that were fed straw (91.6% and 94.1%, respectively; P < 0.05). Laying hens fed the high energy diet had lower feed intake (P < 0.001), better FCR (P < 0.01), and greater BW gain (P < 0.05) than hens fed the low energy diet but egg production and egg weight were not affected. At 46 wk of age, hen BW was positively related with body length (r = 0.500; P < 0.01), tarsus length (r = 0.758; P < 0.001), and body mass index (r = 0.762; P < 0.001) but no effects of type of diet on these traits were detected. In summary: a) the response of pullets to increases in energy content of the diet depends on feed form with a decrease in feed intake when fed crumbles but no changes when fed mash. The interaction observed could be due to differences in feed wastage, accounted as consumed by the birds, between diets differing in feed form. b) Feeding crumbles might be preferred to feeding mash to pullets from hatching to 5 wk of age. c) The inclusion of moderate amounts of fiber at the expense (wt:wt) of the whole diet improved pullet performance from hatching to 5 wk of age. However, the inclusion of SBP reduced pullet growth at 17 wk of age, with effects being more pronounced at the higher level. Also, an increase in the level of straw from 2 to 4% worsened FCR but did not affect ADG. d) Moreover, the inclusion of up to 4% of a fiber source in the rearing diets did not affect GIT development of the hens but SBP reduced egg production. e) An increase in the energy content of the laying phase diet reduced ADFI and improved feed efficiency but did not affect any of the other traits studied.