The objective of this study was to investigate the effect of an abrupt change from grass hay (81% DM) to grass silage (36% DM) or grass haylage (55% DM), fed at similar DM intakes, and to compare the effects of silage and haylage on the composition and activities of the colon microflora. The forages were from the same swath harvested on the same day. Four adult colon-fistulated geldings were randomly assigned to diets in a crossover design. The study started with a preperiod when all 4 horses received the hay diet, followed by an abrupt feed change to the haylage diet for 2 horses and the silage diet for 2 horses. All 4 horses then had a new second preperiod of hay, followed by an abrupt feed change to the opposite haylage and silage diet. The periods were 21 d long, and the forage-only diets were supplemented with minerals and salt. The abrupt feed changes were made at 0800 h. Colon samples were taken before the abrupt feed change, 4 and 28 h after the feed change, and 8, 15, and 21 d after the feed change, all at 1200 h. Colon bacterial counts, VFA, pH, and DM concentrations were unchanged throughout the first 28 h after the abrupt feed change from hay to haylage and silage. Also, fecal pH and DM concentrations were unchanged during the first 28 h. During the weekly observations, colon lactobacilli counts increased (P = 0.023) in horses receiving the silage diet and were greater than on the haylage diet at 21 d. Streptococci counts decreased (P = 0.046) in horses receiving the haylage diet and were less than on the silage diet at 15 and 21 d. Total VFA concentrations and colon and fecal pH did not differ between diets and were unchanged throughout the weekly observations. The DM concentration of colon digesta and feces decreased (P = 0.030 and 0.049, respectively) on both diets during the weekly observations. The results suggest that in horses fed at the maintenance level of energy intake, an abrupt feed change from grass hay to grass silage or grass haylage from the same crop does not induce any major alterations in the colon ecosystem during the first 28 h. During the subsequent 3-wk period, colon and fecal DM decreased and there were alterations in the lactobacilli and streptococci bacterial counts. The changes in lactobacilli and streptococci counts need further investigation.

The increased urine and probably also evaporative fluid losses suggest that feeding a HP diet will cause an unnecessary challenge for horses during prolonged exercise.

The objective of this study was to investigate the effect of CP intake from 2 grass silage-only diets, differing in CP concentration, fed at similar DMI on the equine colon ecosystem after an abrupt feed change between the diets. Four adult right ventral colon-fistulated geldings were fed one silage-only diet high in CP (HP, 873 g of CP/d) and one diet providing recommended intakes (RP, 615 g of CP/d). An adaptation period of 15 d on either the HP or the RP diet was followed by 2 experimental periods when the diets were fed for 22 d each in a crossover design. Colon samples were taken before and at 4, 12, and 24 h, and at 7, 14, and 22 d after the feed change. During the first 24 h after the abrupt feed change, the concentrations of total anaerobic bacteria and lactobacilli were greater on the HP than the RP diet (7.1 vs. 6.7 log(10) cfu/mL, P = 0.021, 6.0 vs. 5.5 log(10) cfu/mL, P = 0.021, respectively). During the first 24 h post feed change, VFA concentrations did not differ between the diets. From 7 to 22 d, total VFA concentrations were greater on the HP diet than on the RP diet (51.8 vs. 45.1 mmol/L, P = 0.034), and colon pH was lower on the HP diet than on the RP diet (6.9 vs. 7.2, P = 0.035). After an adaptation period of 22 d, N, ammonia, and urea concentrations and osmolality of the colon fluid did not differ between diets. Fecal pH and colon and fecal DM were unchanged throughout the experiment. The results suggest that, in horses fed at the maintenance level of energy intake, a feed change between silages with different CP content may alter the colon bacterial counts within the first 24 h. Moreover, during the subsequent 3 wk, pH decreased slightly and VFA concentrations increased, but no other major alterations occurred in the composition and activities of the colon ecosystem or fecal DM.

Link to this article: http://journals.cambridge.org/abstract_S1478061509342334How to cite this article: S Muhonen, J E Lindberg, J Bertilsson and A Jansson (2008). Effects on uid balance, digestion and exercise response in Standardbred horses fed silage, haylage and hay. AbstractThe objectives were to investigate the effects on fluid balance, digestion and exercise response in Standardbred horses in race training when feeding silage, haylage or hay-only diets. In experiment (exp) 1, five Standardbred geldings were fed forage-only diets: hay (82% dry matter, DM) and silage (45% DM) for 23 days in a crossover design. Total collection of faeces and urine was performed. In exp 2, six Standardbred geldings were fed forage-based diets: haylage (68% DM) and silage (41% DM) for 17 days in a crossover design. On day 17, an incremental interval exercise test was performed on an oval racetrack. In exp 1, horses drank more on the hay than on the silage diet, but total water intake (drinking þ water in feed) was higher and resting values of total plasma protein (TPP) was lower on the silage diet. Total water output per day did not differ and therefore the estimated evaporation was larger on the silage than the hay diet. The apparent digestibility was higher on the silage than the hay diet. In exp 2, heart and respiratory rate, TPP and lactate and blood pH did not differ between the haylage and silage diets during and after the exercise test. In conclusion, feeding silage did not affect faecal water content, but apparent digestibility and estimated evaporative fluid loss were higher on the silage diet compared with the hay diet. The silage did not adversely affect the response to intensive exercise compared with haylage. However, the estimated higher evaporative fluid loss on the silage diet compared with the hay diet might cause an unnecessary challenge during more prolonged exercise.

The treadmill test used in this study to simulate a race resembles the haemodynamic response but not the anaerobic metabolic response observed after a simulated race on a track.