Energy and protein allowances and requirements in stallions during the breeding season comparing different nutritional systems

This study was conducted to estimate the nutritional value of diets given to stallions of different breeds during the reproductive season, and comparing allowances with requirements. The systems compared were the French INRA, the 1989 NRC, and the 2007 NRC. Data on reproductive activity, daily exercise, BW, BCS, feed intake, and feed composition during 4 mo (from March to June) were recorded on 12 stallions used for commercial AI programs. Stallions belonged to 3 different breeds: Italian Haflinger (IH, n = 4), Holstein (HOL, n = 4), and Italian Heavy Draft horse (IHDH, n = 4). Data recorded were used to estimate the actual energy and protein intakes and theoretical requirements of the stallions using the aforementioned systems. A deviation index [DI = (intake − requirement)/intake × −1] was calculated to allow a comparison among methods as a proportion of under- or overestimates of theoretical requirements. All data were statistically analyzed with a mixed model for repeated measurements. The reproductive activity of the stallions was affected by month (less in March and greater in subsequent months; P < 0.05). Daily exercise was generally low during the middle breeding season, and the intensity and kinds of exercise differed according to the breeds. Changes of BW and BCS of the stallions were not statistically significant (P = 0.69 and P = 0.17, respectively) during the experimental period, and therefore diets could be considered balanced to support all animal needs. However, the energy and protein allowances were not always consistent with the theoretical requirements considering all 3 nutritional systems. Energy and protein INRA recommendations showed, on average, +0.90 and +0.27 greater DI than actual intakes, respectively, for IH and HOL stallions, whereas the theoretical requirements were much closer to allowances for the IHDH stallions (DI close to 0). The 1989 NRC energy and protein recommendations, respectively, were +0.67 and +0.87 greater than intake for IH, +0.28 and +0.43 greater for HOL, and only +0.06 and +0.17 greater for IHDH stallions. The 2007 NRC energy and protein recommendations, respectively, were +0.70 and +0.52 greater for IH, +0.33 and +0.17 greater for HOL, and +0.52 and +0.49 greater for IHDH than actual intakes. Therefore, all systems overestimated the requirements of the stallion, particularly in lighter breeds. Further studies to validate requirements for breeding stallions of different sizes are recommended.