ABSTRACT:Sixty gravid crossbred gilts were allotted to a 2 x 3 x 2 factorial arrangement of treatments: two Ca sources (sun-cured alfalfa meal and CaC03), three dietary concentrations of Ca (50, 75, and 100% of NRC requirements), and two phases of gestation (55 and 105 d). The objectives were to determine the effect of Ca source, dietary Ca concentration, and gestation phase on bone characteristics (bone breaking strength, bone ash percentage, bone density, and bone ash density in the rib, thoracic, and coccygeal bones), to correlate bone responses to determine relative bone activity, and to determine reliability of the coccygeal bones as indicators of Ca status in the body. At 55 d, rib strength and coccygeal ash content were lower ( P < .01) than at 105 d of gestation. A gestation phase x Ca concentration ( P < .0 5 ) interaction occurred. As Ca concentration increased, thoracic strength and rib ash responded quadratically during each gestation phase, for which at 55 d a minima and at 105 d a maxima was produced a t 75% of NRC. A Ca source x Ca concentration ( P < .05) interaction occurred. Gilts fed alfalfa had the lowest rib bone and ash density when fed 75% of NRC for Ca, whereas gilts fed CaC03 were highest at this level of Ca compared with the other concentrations. Generally, all bones were positively correlated with respect to their response to dietary Ca concentration. Few negative correlations were observed. At this level of physiological maturity, there was no effect of Ca source and little effect of gestation phase on the bone variables measured at the dietary Ca concentrations used in this experiment. The rib and thoracic bones seem to be the most responsive to dietary Ca concentration.
The relationship between fecal, serum or plasma phosphorus (P), and P intake was examined with 10, crossbred, 5-year-old, gestating cows (avg wt 475 kg) in an individual feeding study using 2 orthogonal 5 X 5 Latin squares. All cows received 9.07 kg of meadow grass hay which contained 7.4% crude protein (CP) with an in vitro dry matter digestibility (IVDMD) of 56%, and received .5 kg of 1 of 5 supplements which resulted in P intakes of 10.3,12.4, 14.3,16.1, or 18.4 g/day. Fecal and blood samples were collected for 5 days after a U-day dietary adjustment period. Fecal grab samples were taken twice daily (hour 0880 and 2000). Blood samples were taken at 0800. Statistical analysis included analysis of variance and regression analysis. A linear response to P intake was observed for both plasma and serum P, however, with regression of P intake, the R* for plasma P was .06 and for serum P was JO. Evaluation of morning and evening fecal P levels with regression resulted in different equations. The morning equation (Y = .055 + .212X) had a larger intercept and a smaller slope coefficient than the evening equation (Y =-.781+ .310X). Morning and eveningR* were .69 and .78, respectively. To examine the predictive ability of the P intake equations, a validation trial was conducted with 20 4-to-gyear-old cows individually fed (4/treatment). Daily P intakes were 10.
A study was conducted with gravid gilts to determine the bioavailability of Ca in sun-cured alfalfa meal (AM) and the effect of dietary Ca concentration on bone and blood characteristics during two phases of gestation. Two Ca sources (AM and CaCO3), three dietary concentrations of Ca (50, 75, and 100% of the NRC requirement), and two gestation phases (55 and 105 d) were used in a 2 x 3 x 2 factorial arrangement in a randomized design with five replications (60 gravid gilts). Response criteria were as follows: 1) plasma Ca, P, and alkaline phosphatase (AKP) measured at the onset and at 25-d intervals and 2) metacarpal (MC) and metatarsal (MT) bone breaking strength (kilograms), ash content (percentage), density (grams/cubic centimeter), and ash density (grams of ash/cubic centimeter) at the conclusion of the experiment. Plasma Ca, P, and AKP concentrations were similar between Ca sources. Because the response between Ca sources was similar, the data were pooled among sources. There was a linear decline in plasma P and AKP (P < or = .05) as dietary Ca concentration increased. As gestation progressed from 0 to 100 d, there was a decline (P < .05) in plasma Ca and P. There were no differences in bone breaking strength and ash between Ca sources in either the MC or MT. No differences in bone strength between gestation phases occurred. A gestation phase x dietary Ca concentration interaction (P < .05) was observed for bone ash in both bones.(ABSTRACT TRUNCATED AT 250 WORDS)
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