JWSS - Journal of Water and Soil Science

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An experiment was carried out on 384 7d old commercial broiler chicks (Lohman) to study the effect of changes in source and level of dietary calcium and limestone particle size on the performance and tibial growth and calcification of broiler chicks. From day 1 to day 7, the chicks were fed with the commercial basal diet. On day 7, the chicks were weighted and randomly assigned to 64 groups, six chicks of similar body weight (82.2±5.4) per group. Each of the eight experimental diets was fed to eight groups of chicks for an experimental period of 49 days. Two calcium sources (oyster shell and limestone), two calcium levels (100% NRC and 85% NRC) and three particle sizes of limestone [ground (less than 0.15 mm), medium (0.6 to 1.18 mm) and coarse (1.18 to 4.75 mm)] were added to diets with the same energy based on a Randomized Complete Design, in which levels of calcium were nested into calcium sources. Particle sizes were nested into calcium sources and levels.

Limestone significantly increased phosphorus retention (in percentage of phosphorus ingestion) at the age of 21 and 56 days and increased tibial length, dry weight and ash weight at 56 days. Calcium level of 85% NRC significantly decreased feed intake and feed conversion, especially during the starter, and increased calcium retention (in percentage of calcium ingestion) at 21 and 42 days. Phosphorus retention and cortical thickness of tibia at 21 and 42 days, tibial dry weight, ash weight and ash percentage at 42 day, were significantly increased with calcium level of 100% NRC. Coarse and medium particle sizes of limestone as compared to ground particle size, significantly improved feed intake and feed conversion, especially during the starter. Medium particle size of limestone with calcium level of 85% NRC and coarse particle size of limestone with calcium level of 100% NRC, significantly improved tibia ossification characteristics and increased calcium and phosphorus retention. By using calcium level of 85% NRC, coarse and medium particle sizes of limestone compared to ground particle size, significantly diminished percentage of leg abnormalities.

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Digestible lysine and sulfur amino acid (SAA) requirements of Ross male broilers were determined during the starter period in two experiments. Broilers were fed a control corn-soy diet (3200 kcal MEn/kg and 23% CP) for 6 days and then randomly assigned to dietary treatments until 16 days of age. The basal diet containing 19% CP was prepared in order to be deficient in lysine for experiment 1 and SAA for experiment 2. Seven graded increment levels of L-lysine HCl or Dl-methionine were added in absences of starch in experiment 1 and 2, respectively. All diets contained 3200 kcal MEn/kg and all essential amino acids, except for the test amino acid, were 10% higher than the NRC (1991) recommendations. The digestible lysine requirements of broilers based on broken-line and exponential models were 1.04 and 1.01%, respectively. The digestible SAA requirements for the mentioned models were 0.846 and 0.841%, respectively.