The impact of dietary protein levels on nutrient digestibility and water and nitrogen balances in eventing horses1

Abstract

This study was performed to evaluate the impact of dietary protein levels on nutrient digestibility and water and nitrogen balances in conditioning eventing horses. Twenty-four Brazilian Sport Horses, male and female (8.0 to 15.0 yr; 488 ± 32 kg BW), were used in a randomized design with 4 levels of CP diets: 7.5%, 9.0%, 11.0%, and 13.0%. A digestion assay was performed with partial feces collection over 4 d, followed by 1 d of total urine collection. Data were submitted to regression analysis and adjusted to linear and quadratic models (P < 0.05). No differences were observed in the intake of DM, OM, EE, ADF, and NDF as a function of dietary protein levels. Dry matter intake average was 1.7% of BW. CP and N intake showed a linear increase as a function of increasing protein level in diets. A quadratic response (P < 0.05) was observed on the CP and NDF digestibility coefficients, with the maximum estimated level of digestibility at 11.6% and 11.4% CP in the diet, respectively. There was a linear effect on ADF digestibility coefficients, digestible DM and protein intake, and CP/DE ratio according to dietary protein levels. There was no impact of dietary protein levels on daily water intake, total water intake, or fecal water excretion. Urinary excretion values showed a linear increase in response to increased dietary protein levels, but no impact was observed on water balance, with an average of 8.4 L/d. Nitrogen intake (NI), N absorption (NA), and urinary N increased linearly as a function of increasing dietary protein levels. There was no impact of dietary protein levels on N retention (NR), with an average of 7.5 g N/d. Nitrogen retention as a percentage of NI or NA showed no significant changes in the function of dietary protein levels. There was an impact of dietary protein levels on the digestibility coefficient of CP, NDF, ADF, and digestible protein intake on conditioning eventing horses. The 11.6% CP level in the diet provided an intake of 2.25 g CP/kg BW and 0.37 g N/kg BW, and this intake was the most appropriate for the conditioning of intensely exercised horses, considering the responses related to NI, NA, and the estimated NR to NA ratio. The NDF and ADF responses indicated that dietary fiber was more digested with an increased amount of N in the digestive tract.

Protein Source and Intake Effects on Diet Digestibility and N Excretion in Horses—A Risk of Environmental N Load of Horses

“…In this study, soya groat-supplementation produced less faecal N, but not less urinary N, than in the other supplementations. Oliveira et al [ 59 ] found that soya digested well, but extra N was excreted in urine. Many studies reported elevated N lost in urine when the CP content in the feeds and CP intake was increased [ 41 , 58 , 59 , 60 ].…”

“…Oliveira et al [ 59 ] found that soya digested well, but extra N was excreted in urine. Many studies reported elevated N lost in urine when the CP content in the feeds and CP intake was increased [ 41 , 58 , 59 , 60 ].…”

Comparison of Feed Digestibility between Ponies, Standardbreds and Andalusian Horses Fed Three Different Diets

“…However, providing pelleted or steam-flaked barley instead of ground barley appeared to limit the negative impact of starch on fibre digestibility [35,39], and gradually increasing the amount of grain fed will have facilitated adaptation, enabling more pre-caecal starch digestion. Protein levels in the two high-energy diets were similar, and also greater than the control diet, and this may have been a factor contributing to the improved digestibility of NDF [40].…”

“…Animals on the hypercaloric diets showed significantly greater apparent digestibility of gross energy and crude protein, which may have been a consequence of the calories rather than other factors. However, the increased amount of protein-rich soya hulls and lucerne chaff in those diet groups might have contributed also, because increased dietary protein levels have been suggested to improve the digestibility of crude protein, NDF and ADF in sport horses [40].…”

Effect of Varying Dietary Crude Protein Level on Milk Production, Nutrient Digestibility, and Serum Metabolites by Lactating Donkeys

“…Aguerre et al [ 39 ] and Lee et al [ 40 ] did not find an effect of diets ranging from 15.3% to 16.6% and 14.8% to 16.7% CP on DMI in dairy cows, respectively. Oliveira et al [ 41 ] also reported that DMI was unaffected by dietary CP levels in horses. In the present study, we observed no difference in DMI between the dietary protein levels, which might be caused by the isoenergetic diets.…”