Changes in the Tissue and Volume of the Stomachs of Calves Following the Removal of Dry Feed or Consumption of Inert Bulk

Abstract

Summary Twelve Holstein heifer calves at 16 and 38 wk. of age were sacrificed after a growth study in which six had voluntarily consumed a high-concentrate diet and six a high-roughage diet. Ratios of hay to concentrate were 9:1 and 1:9. Four bull calves, two fed only milk and two fed milk while consuming shavings, also were studied. The objectives were to observe the effects of continuous consumption of a high-roughage, a high-concentrate, and an inert bulk diet on stomach muscle, mucosa, and volume, and to test the effect on stomach anatomy of reversing 16-wk.-old calves from the above ratios of hay to concentrate back to milk. Rumen papillae disappeared in the calves reversed to milk diets. The rumen collapsed around less fill, but maintained the same potential (water-filled) volume after 18 wk. of milk feeding, as had existed in calves of the same age on dry feed slaughtered at the beginning of the reversal period. This observation was interpreted as indicating a stasis, and not retrogression of reticulo-rumen volume. The amount of muscular tissue (fat-free dry) was less in the reversal calves, but the effect was not statistically significant. A stasis in omasal tissue growth occurred, and the abomasum continued to grow at the same rate as body size. Mucosal and muscular growth were independent. This was evidenced in three ways. (1) Reticulo-rumen mucosa retrogressed at a more rapid rate than muscle. (2) Muscular development was extensive in the absence of mucosal development in the calves consuming shavings. (3) Compared to muscle, well-developed mucosa contained lower nitrogen percentages when expressed on a fat-free dry matter basis (13.3 and 15.1%, respectively). Rumen papillae length was greater in the faster-gaining (high-concentrate) calves. Apparently, both rapid growth and papillary development were due to the higher energy levels consumed by these animals.