A study was conducted to monitor changes in cortical bone mineral in the dairy cow in response to demands of lactation and pregnancy using rib bone biopsies in serial sampling. Sixteen Friesian cows from the University dairy herd were used to collect 9 samples during the lactation period and 5 samples during the dry period. The data were analysed using a split-plot design analysis of variance. There were no significant (P > 0.05) differences in cortical bone phosphorus concentrations in rib bone during the lactation period, but calcium concentrations in cortical bone were significantly (P < 0.05) higher at parturition and during the first 30 days of lactation compared to the next 30 days and between 90 and 120 days. Results reported here indicate that the cow resorbs cortical bone during the middle of the lactation period and not during the periparturient period as previously thought. Magnesium concentrations were also significantly (P < 0.05) higher at the beginning of lactation compared to some of the other sampling times, but cortical bone was significantly (P < 0.05) thinner at the beginning of lactation compared to several of the other sampling times. There were no significant (P > 0.05) differences in cortical bone Ca or Mg concentrations during the gestation period. Cortical bone P concentrations significantly (P < 0.05) decreased during the first 180 days, but significantly (P < 0.05) increased at 181-230 days and significantly (P < 0.05) decreased again at 231 days to term. Cortical bone thickness decreased significantly (P < 0.05) from the beginning of gestation to term. There were no significant (P > 0.05) differences in cortical bone thickness or Ca or Mg concentrations in cortical bone during the dry period, but cortical bone P concentrations were significantly (P < 0.05) greater at the end of the dry period compared to the first 30 days of the period. In general, cortical bone Ca and Mg values decreased as milk production increased up to 20 kg/day and cortical bone P values and bone thickness increased. In animals producing over 20 kg/day, however, cortical bone mineral values were greater and cortical bone thickness was lower compared to those animals producing less than 20 kg

A total of 2160 samples of rib bone were used in a split-plot design analysis of variance to show that, on an ash weight basis, P content is not different among the right and left 9th, 10th, 11th, and 12th ribs of cattle above 6 mo of age. Results were similar for Ca on a fresh or dry weight basis. Some differences existed in Mg content among some of the ribs. Location on the rib from which samples were taken was responsible for significant differences in mineral concentrations. Based on results reported herein, ribs 9, 10, 11, and 12 of the right and left side may be used in the serial sampling of bone tissue in the bovine for the purpose of comparing the content of P, Ca, and--to some extent--Mg. Serial sampling makes possible comparison of bovine mineral status based on bone tissue over an extended experimental period that includes eight sampling dates.

Fifteen Friesian oxen between 12 and 18 months of age with a mean body mass of 240.7 kg were randomly assigned to diets containing 0.25 % phosphorus (P) or less, to evaluate the acute effects of an acidiogenic diet of -11.1 meq/100 g of diet dry matter, compared with a basiogenic diet of +25.6 meq/100 g or a control diet of +16.5 meq/100 g of diet dry matter calculated as (Na + K) - (Cl + S), on blood, bone and faecal P, calcium (Ca) and magnesium (Mg) for a period of 9 weeks. Blood, bone and faecal responses to an anionic diet are described. An inverse relationship existed between bone and blood Ca, in which there was resorption from bone with increased blood Ca in response to the anionic diet. The anionic treatment group demonstrated simultaneous increases in bone, blood and faecal P concentrations at various stages of the experiment compared to the cationic and control treatment groups. Results indicate independent absorption and resorption of Ca and P into and out of bone. There was wide variation in the bone Ca:P ratio between 2.02 and 1.51 among animals fed the anionic diet, with the Ca:P ratio following Ca values and not bone P values. Bone and blood P had a linear relationship with dietary cation:anion balance (DCAB), increasing as the diet became more anionic in nature, but faecal P was curvilinear with highest concentrations at -11.1 and +25.6 meq/100 g compared to +16.5 meq/100 g. Concurrent blood, bone and faecal P increases at some stages of the experiment indicate a P-sparing effect of the anionic diet and warrants further research into the long-term effects of anions in the diet, leading to their use as a possible addition to improved licks in P-deficient areas

Thirty-six male and female Holstein and Jersey calves were assigned at weaning to a randomized complete block design in a 2 x 3 factorial arrangement to evaluate the influence of two dietary cation-anion balances (-14 and +39 meq(Na + K)-(Cl + S) per 100 g diet DM) and three amounts of dietary P (.22, .29, and .37%) on performance and P metabolism from 9 to 19 wk of age. Feed intake, average daily gain, and serum inorganic P were higher on the anionic diets and increased with increasing dietary P. Body weights were higher on the .37% P diets by wk 3 and on the anionic diets by wk 6. The interaction of dietary P and cation-anion balance was responsible for significant differences in calf performance; the anionic diet exhibited marked improvement over the cationic diet at the lowest P concentration. Results indicate that the availability of P for young dairy calves may be higher with anionic than cationic diets.

Sixteen Bonsmara calves (4 males, 12 females) between 10 and 18 months of age were blocked according to age and sex and randomly assigned to 2 groups. They were offered licks containing bone meal and salt (50:50 ratio) (control) and bone meal and ammonium sulphate (NH4SO4) at 1.25, 2.5, 5, 10, 15, and 18 % (treatment) to evaluate the effects of dietary anions on bone phosphate (P) concentration. Bone P concentration was significantly (P<0.05) higher in the NH4SO4 group compared with the control group, indicating that NH4SO4 was able to increase the P content of bone at each of the 6 concentrations used in the lick relative to the control animals, thereby improving the P status of the animals. Ammonium sulphate at 15% and 18% in the lick also significantly (P <0.05) increased bone P compared with the lower concentrations of NH4SO4. Bone calcium (Ca) fluctuated as a result of the acidogenic lick. There was absorption of Ca when P was being resorbed and resorption of Ca when P was being absorbed into and out of bone. Bone Ca:P ratio ranged from 3.2 to 6.4 among the control group and 1.6 to 4.3 among the treatment group. Animals receiving the acidogenic lick had a higher percentage ash compared to the control group for most of the experimental period. Bone magnesium (Mg) fluctuated in response to the acidogenic lick, and it was difficult to show a relationship between bone Mg and Ca or P. The overall mean cortical bone thickness was significantly (P < 0.05) greater in treatment (1.60 mm) compared with control (1.43 mm) calves and this was also true at sampling periods 2, 4, 5 and 6. Bone thickness followed bone P and not bone Ca. Results from this research indicate that the addition of ammonium sulphate to a lick had a beneficial effect in improving the P status by increasing bone P and improving the mineral status of bone by increasing the thickness of cortical bone and percentage ash