This study investigated the effect of dietary Ca to available P (AvP) ratio and phytase supplementation on bone ash, ileal phytate degradation, and nutrient digestibility in broilers fed corn-based diets. The experimental design was a 4 × 2 factorial arrangement of treatments evaluating 4 Ca:AvP ratios (1.43, 2.14, 2.86, and 3.57) and 2 levels of phytase (0 and 1,000 phytase units/kg of feed). The 4 Ca:AvP ratios were achieved by formulating all diets to a constant AvP level of 0.28% and varying Ca levels (0.4, 0.6, 0.8, and 1.0%). Each treatment was fed to 6 cages of 8 male Ross 308 broilers from 5 to 21 d. At 21 d, digesta from the terminal ileum was collected and analyzed for energy, phytate, P, Ca, and amino acids (AA) to determine digestibility. Digesta pH was measured in each segment (crop, gizzard, duodenum, and ileum) of the digestive tract. Data were analyzed by 2-way analysis of covariance. There was a significant interaction between dietary Ca:AvP ratio and phytase supplementation for weight gain (WG), feed intake (FI), and feed conversion ratio (FCR). In diets with no phytase, Ca:AvP ratio had a greater effect on WG, FI, and FCR compared with those fed diets without phytase. The orthogonal polynomial contrasts showed that the increase in dietary Ca:AvP ratio significantly decreased WG and FI in a quadratic manner, whereas FCR increased (P < 0.05) linearly with higher dietary Ca:AvP ratio. Increasing dietary Ca:AvP ratio led to a significant quadratic decrease in phytate degradation and significant linear decreases in P digestibility and bone ash. Phytase addition increased (P < 0.05) phytate degradation and improved (P < 0.05) energy, AA, and P digestibility at all levels of Ca:AvP with no interaction (P > 0.05) between the main factors. Digestibility of AA was positively correlated (P < 0.05) with the degree of phytate degradation. Increasing dietary Ca:AvP ratio significantly increased gizzard pH in a linear manner. In conclusion, phytase (1,000 phytase units/kg of feed) improved phytate, and P and AA digestibility at all Ca:AvP ratios evaluated in this study.

No abstract

Popping expansion volume (PEV) in popcorn (Zea mays L.) is a distinct heritable character and defined as the ratio of the volume after popping to the volume before popping. PEV is quantitatively inherited and 3-4 genes/quantitative trait loci (QTLs) have been implicated. In the present study, we have dissected the quantitative PEV into two component traits, viz., flake volume (FV) and percent unpopped kernels (UPK), and mapped QTLs using SSR markers for all three traits with 194 F3 families derived from a popcorn (A-1-6) x flint corn (V273) cross. Heritability (broad sense) estimates for PEV, FV and UPK based on F3 mean bases were 0.72, 0.54 and 0.68, respectively. The QTL analyses for the three traits based on combined environment data were performed by composite interval mapping using QTL cartographer. Four QTLs were identified for PEV on chromosomes 1, 3, 8 and 10, which together explained 62% of the phenotypic variance (sigma2p). Four QTLs were found on chromosomes 1, 5, 9 and 10 for FV (explaining 44% of sigma2p) and five QTLs for UPK on chromosomes 1, 3, 4, 5 and 9 (explaining 57% of sigma2p). The relative efficiency estimates of marker-based selection in comparison to phenotypic selection for PEV (1.10), FV (1.22) and UPK (1.11) indicated that marker-based selection could be relatively more efficient. The QTL on chromosome 1S for PEV was found to be most significant, where QTLs for hard endosperm starch concentration had been detected earlier.

Rice±wheat cropping system to which graded levels of NPK fertilizers had been applied for 20 years were compared for yield trends, and changes in response function, soil organic-C and available N, P, K and S status. This study of system in which only chemical fertilizers had been used over a long period enabled long-term yield declines of rice and wheat at dierent levels and combinations of NPK fertilizers to be evaluated. The highest rate of yield decline in both rice and wheat was found when 120 kg ha À1 N was applied alone. The lowest rate of decline was observed when all three nutrients (N, P and K) were applied, at 40, 35 and 33 kg ha À1 for N, P and K, respectively, followed by 120, 35 and 33 kg ha À1 (currently recommended levels). The yield response of rice and wheat to N fertilizer declined over the 20 years, with a higher rate of decline in wheat. In contrast, the response to applied P and K increased with time in both crops, with a higher response rate in wheat. With continuous application of N and P fertilizers, there was a marginal change in available N and K in the soil over time, but an approximately 3-fold increase in available P and an approximately 2-fold increase in available S were obtained by regular dressing of P fertilizer (SSP: 7 % P, 12 % S) over 20 years. The results revealed that balanced, high doses of NPK fertilizers are required to maintain soil fertility and raise grain yields.