The Effects of Phytase on Calcium and Phosphorus Digestibility and Bone Composition in Weanling Horses

Summary

Phytate phosphorus is the predominant form of phosphorus in plants and is poorly absorbed by the horse. Phytases are enzymes that break down phytate phosphorus. No research has been reported on the use of phytase in weanling horses.

Situation

The use of horses for sport has a long history. However, over time and with an increase in the cost of equine ownership, the horse is used in competition at earlier ages. Many competitive disciplines have added or expanded their young horse competitions and have added large purses for the winners. Due to the high cost of ownership, people attempt to make a return on their investment in as little time as possible; otherwise the investment quickly becomes a loss. In doing this, horses become very vulnerable to early break downs. The equine skeletal system is not done growing by ages two and three (Lawrence at al, 1994), so it is definitely not suitable or ready for competition. In addition, while the Jockey Club cites that the number of two-year old races has declined over the past few years, the purses have increased. This creates even more motivation to train and compete animals at a younger age. Seventy percent of young racehorses in training are noted to be subject to fatigue fractures of the third metacarpal bone (Nunamaker et al., 1999). Many other disciplines have similar such incentives, such as the Quarter Horse Futurities, and Young Jumper championships, which encourage the use of young horses at high levels of competition. This push towards early use leads to tragic events, such as the breakdown of Ruffian, Barbaro and many racehorses. However, change is not likely to occur anytime soon, especially with the increase in group ownerships of horses. This collective ownership makes horses more affordable to the middle class enthusiast, yet also does not allow for the huge wealth of the more traditional owner to be put into the sport. Therefore, it seems that we must make these horses stronger. By potentially increasing the bone strength of young horses, fractures may become less prevalent. The use of phytase in other species of livestock has shown an increase in bone strength, as well as nutritional efficiency (Tsai et al., 2007; Cromwell et al., 1995; Kim et al., 2005). Therefore, this project was conducted in order to see whether the use of phytase in young horses can increase bone mineral content, and perhaps prevent competitive horses from breaking down early.

Response

Sixteen stock horse type weanlings at an average age of 176 ± 31 days were used in a 2x2 Factorial design experiment in order to study the effects of phytase (Phyzyme(R) XP 5000G, donated courtesy of Danisco Animal Nutrition St.Louis, MO) and differing levels of dietary phosphorous on the bone strength, growth and nutrient digestibility in young horses. The weanlings consisted of 12 colts and 4 fillies. Horses were blocked based on starting weight and sex. Prior to being placed on an experimental diet, the weanlings underwent surgery in order to collect bone samples. A core sample was taken of the third metacarpal (cannon) bone and a portion of the lateral splint bone was removed. The day following surgery, the horses were placed on one of four experimental diets for 120 days: low phosphorous (90% of NRC (1989) requirements), without added phytase; low phosphorous, added phytase (1500 FTU/kg added); adequate phosphorous (110% of NRC (1989) requirements), without added phytase; adequate phosphorous, added phytase (1500 FTU/kg added). Diets were otherwise isocaloric and isonitrogenous. Total feed intake was set at 2.5 % of individual body weight with a concentrate to forage ratio of 70:30 and the horses were reweighed every 14 days in order to adjust intake to growth Each horse was housed in 1.524m x 3.658m stall and left inside 24 hrs during the initial 14 day recovery period. From day 14 through day 120, the horses were turned out for 8 hours per day on dry lot for exercise and kept in stalls the remaining 16 hours. Following day 120, the horses again underwent another surgery on the opposite front limb in order to collect final bone samples. Radiographs were taken of the sampled limbs every 15 days. Fecal grab samples were taken twice per animal during the 120 day period in order to evaluate calcium, phosphorous and energy digestibility. They were collected on day 60 and 120. Calcium, phosphorous and energy digestibility were determined through the fecal samples collected. Blood samples were also taken on days 0, 60 and 120 from the jugular vein, for plasma analysis of calcium and phosphorous content.

Impact

This study was conducted to evaluate the effectiveness of phytase as a way to increase bone mineral content and increase nutrient digestibility. There was no change in bone composition due to the diets or phytase. However, this experiment has shown the difference between the composition of the third metacarpal and the splint bone of the horse. The calcium and phosphorous content between the two bone differs substantially (P< .0001), and thus the splint bone is not a good model for general bone composition in the horse. Plasma minerals were not affected by the different diets or phytase. Digestibility of energy was similar amongst all weanlings, as was expected due to the isocaloric nature of the diets. Phosphorous digestibility was higher in the horses on the low-P diet, and phytase did improve phosphorous digestibility of the adequate phosphorus diet but not the low phosphorus diet. Calcium digestibility did not differ between diet or phytase addition. Phytase did increase bone calcium of the third metacarpal (cannon) bone in the horses on the adequate-P diet from 14.48 to 18.76% of wet weight, yet decreased bone calcium on the low-P diet from 19.17 to 16.23%. There was also a diet by phytase interaction within the adequate-P diet, with the addition of phytase causing P digestibility to increase from 9.48% to 26.04%. These results do not provide any support to the claim that phytase improves bone strength in horses.

State Issue

Other Issue

Details

  • Year: 2008
  • Geographic Scope: College
  • County: Clarke
  • Program Areas:
    • Agriculture & Natural Resources

Author

    Heusner, Gary Lee

Collaborator(s)

CAES Collaborator(s)

  • Azain, Michael J.

Non-CAES Collaborator(s)

  • Liljedahl, Allison
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