Abstract

The goats raised in the barn are usually fed on fresh grass. As dry forage can be stored for long periods in large amounts, dry forage feeding makes it possible to feed large numbers of goats in barns. This review explains the physiological factors involved in suppressing dry forage intake and the cause of drinking following dry forage feeding. Ruminants consume an enormous amount of dry forage in a short time. Eating rates of dry forage rapidly decreased in the first 40 min of feeding and subsequently declined gradually to low states in the remaining time of the feeding period. Saliva in large-type goats is secreted in large volume during the first hour after the commencement of dry forage feeding. It was elucidated that the marked suppression of dry forage intake during the first hour was caused by a feeding-induced hypovolemia and the loss of NaHCO3 due to excessive salivation during the initial stages of dry forage feeding. On the other hand, it was indicated that the marked decrease in feed intake observed in the second hour of the 2 h feeding period was related to ruminal distension caused by the feed consumed and the copious amount of saliva secreted during dry forage feeding. In addition, results indicate that the marked decreases in dry forage intake after 40 min of feeding are caused by increases in plasma osmolality and subsequent thirst sensations produced by dry forage feeding. After 40 min of the 2 h dry forage feeding period, the feed salt content is absorbed into the rumen and plasma osmolality increases. The combined effects of ruminal distension and increased plasma osmolality accounted for 77.6% of the suppression of dry forage intake 40 min after the start of dry forage feeding. The results indicate that ruminal distension and increased plasma osmolality are the main physiological factors in suppression of dry forage intake in large-type goats. There was very little drinking behavior observed during the first hour of the 2 h feeding period most water consumption occurring in the second hour. The cause of this thirst sensation during the second hour of dry forage feeding period was not hypovolemia brought about by excessive salivation, but rather increases in plasma osmolality due to the ruminal absorption of salt from the consumed feed. This suggests the water intake following dry forage feeding is determined by the level of salt content in the feed.

Highlights

  • Goats raised in barns are usually fed on fresh grass

  • The results indicate that despite the free drinking conditions, increases in saliva secretion during the initial stages of dry forage feeding in large-type goats caused NaHCO3 to be lost from the blood into the rumen which in turn caused a decrease in circulating plasma volume and resulted in activation of the renin-angiotensin system and feeding was suppressed

  • The results indicate that the marked decrease in feed intake observed in the second hour of the 2 h feeding period is related to ruminal distension caused by the feed consumed and the copious amount of saliva secreted during dry forage feeding

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Summary

Introduction

Goats raised in barns are usually fed on fresh grass. When fresh forage is dried, it can be stored for long periods in large amounts. It was clarified that in large-type goats fed on dry forage for 2 h twice daily, increases in ruminal distension, plasma osmolality and subsequent thirst sensations that occurred 40 min after the start of dry forage feeding were the main physiological factors in the marked suppression of feed intake (Thang et al, 2010; 2011a,b; 2012a,b).

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