PS4-4. Effects of Age on Gastrointestinal Morphology, Morphometrics, and Digesta Changes in High-forage, Rotationally Grazed, Mineral-supplemented, Late-weaned Ruminants with Low Reproductive Performance

This study used 5 spring culled Spanish Kiko (n = 3; 2-3 years old & n = 2; 6-7 years old) does’ gastrointestinal tracts (GIT) as model ruminant systems (MRS) to evaluate the effects of age on GIT development in mineral supplemented yet low reproductive performance late weaned, rotationally grazed, high forage fed ruminants. Morphology, morphometrics and sequential changes in digesta DM, NDF, ADF & ash were determined. Macromorphological differences were not observed, but micromorphological differences were indicated by the morphometric data. Rumen (668.05 vs 644.23g & 16440.00 vs 14828.33cm3), reticulum (115. 75 vs 100.53g & 505.00 vs 426.66cm3) and omasum (160.75 vs 121.36g & 1745.00 vs 1621.67cm3) were heavier and more voluminous in older (OMRS) versus younger MRS (YMRS), respectively. Contrastingly, YMRS had heavier (246.26 vs 236.95g) but less voluminous (2712.33 vs 2955.00cm3) abomasum. Similarly, cecum (91.73 vs 79.60cm), colon and rectum (712.53 vs 663.76cm) but not small intestines (2220.71 vs 2297.60cm) were longer in OMRS. Small intestine (566.10 vs 510.85g) and cecum (160.03 vs 143.05g) but not colon and rectum (305.33 vs 592.55g) weights were heavier in YMRS. Reticulorumen digesta DM was higher (17.45 vs 13.94%), declined to lower percentage initially in the omasum (10.89 vs 14.98%) and remained lower in OMRS versus YMRS until the rectum (27.13 vs 26.78%), respectively. Digesta DM (14.09%) remained relatively unchanged throughout the forestomach, declined in the abomasum (10.10%) and continually increased throughout the small intestines (14.67%), cecum (15.52%), colon (22.55%), and rectum (26.78%) in YMRS. Digesta NDF was similar throughout the reticulorumen (51.12%), declined initially in the omasum (38.63%) and subsequently in the small intestine (27.70%) before continuously rising throughout the large intestine (54.84%) in OMRS. Contrastingly, whereas NDF was also similar throughout the reticulorumen (51.94%), initial decline occurred in the small intestine (29.05%) and an observed continuous rise throughout the large intestine was lower (46.65 vs 54.84%) in YMRS versus OMRS. Digesta ADF was higher throughout the GIT (47.20 vs 37.76%), except in the reticulum (34.60 vs 41.93%) of YMRS versus OMRS, respectively. Notably, ash percentages were lower throughout the GIT (12.41 vs13.57%), except in the reticulum (16.41 vs 14.59%), abomasum (10.95 vs 11.24%), cecum (13.34 vs 14.05%) and rectum (12.88 vs 12.26%) in YMRS versus ORMS, respectively. Effects of age on GIT morphology, morphometrics, andsequential changes in digesta nutrient profile of mineral supplemented low reproductive performance late weaned, rotationally grazed, high forage fed ruminants were apparent in the model ruminant systems evaluated in this study.