The diversity of the equine fecal bacterial community was evaluated using pyrosequencing of 16S rRNA gene amplicons. Fecal samples were obtained from horses fed cool-season grass hay. Fecal bacteria were characterized by amplifying the V4 region of bacterial 16S rRNA gene. Of 5898 mean unique sequences, a mean of 1510 operational taxonomic units were identified in the four fecal samples. Equine fecal bacterial richness was higher than that reported in humans, but lower than that reported in either cattle feces or soil. Bacterial classified sequences were assigned to 16 phyla, of which 10 were present in all samples. The largest number of reads belonged to Firmicutes (43.7% of total bacterial sequences), Verrucomicrobia (4.1%), Proteobacteria (3.8%), and Bacteroidetes (3.7%). The less abundant Actinobacteria, Cyanobacteria, and TM7 phyla presented here have not been previously described in the gut contents or feces of horses. Unclassified sequences represented 38.1% of total bacterial sequences; therefore, the equine fecal microbiome diversity is likely greater than that described. This is the first study to characterize the fecal bacterial community in horses by the use of 16S rRNA gene amplicon pyrosequencing, expanding our knowledge of the fecal microbiota of forage-fed horses.

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Calcium and P balance and mobilization from bone were evaluated through 20 wk of lactation to determine the timing and extent of net resorption of bone mineral and mineral balance in lactating dairy cows. Eighteen Holstein cows were blocked by parity and calving date and randomly assigned to 1 of 3 dietary treatments: high (1.03%, HI), medium (0.78%, MED), or low (0.52%, LOW) dietary Ca. Dietary P was 0.34% in all diets. Cows consumed treatment diets from calving to 140 DIM. Total collection of milk, urine, and feces was conducted 2 wk before expected calving and in wk 2, 5, 8, 11, and 20 of lactation. Blood samples were collected at 14 and 10 d before expected calving and 0, 1, 3, 5, 10, 14, 21, 28, 35, 56, 70, 84, 98, and 140 d after calving. Blood samples were analyzed for Ca, P, and parathyroid hormone concentration. Serum concentrations of osteocalcin (OC), a marker of bone formation, and deoxypyridinoline (DPD), a marker of bone resorption, were measured to assess bone mobilization. Rib bone biopsies were conducted within 10 d postcalving and during wk 11 and 20 of lactation. Dietary Ca concentration affected Ca balance, with cows consuming the HI Ca diet in positive Ca balance for all weeks with the exception of wk 11. Interestingly, all cows across all treatments had a negative Ca balance at wk 11, possibly the result of timed estrous synchronization that occurred during wk 11. At wk 20, Ca balances were 61.2, 29.9, and 8.1 g/d for the HI, MED, and LOW diets, respectively. Phosphorus balances across all treatments and weeks were negative. Bone Ca content on a fat-free ash weight basis was least in cows consuming the MED diet, but bone P was not different. Serum Ca and P were not affected by treatment. Dietary Ca concentration did not affect P balance in the weeks examined, but there was a clear effect of parity on balance, markers of bone metabolism, and bone P. Primiparous cows had greater serum OC and DPD concentrations than multiparous cows. Regardless of dietary treatment, serum OC concentration peaked around d 35 of lactation. Simultaneously, DPD concentration began to decrease, which may indicate a switch from net bone resorption to formation after d 35. However, this was not reflected in balance measures. This information may help refine dietary mineral recommendations for lactating dairy cows and suggests that dietary P requirements are independent of dietary Ca.

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