Effect of Parotid Saliva Secretion on Dry Forage Intake in Goats

Abstract

Research was carried out to clarify whether a suppression of dry forage intake during the early stages of feeding in ruminants is caused by feeding induced hypovolemia which is produced by the accelerated secretion of parotid saliva. Goats with a parotid fistula were fed roughly crushed alfalfa hay cubes, commercial ground concentrate feed and NaHCO 3 twice daily (10:00-12:00, 16:00-18:00). The animals were free access to drinking water all day prior to, during and after experiments. The animals were intraruminally infused every day prior to the morning feeding period with parotid saliva collected from the parotid fistula over a 24 h period. The present experiment consisted of two treatments, non-infusion (RNI) and intraruminal infusion of parotid saliva (RSF). In the RSF treatment, 4-5 kg of parotid saliva (280-290 mOsm/l) collected over a 24 h period was intraruminally infused 1 h prior to the commencement of the morning feeding. During feeding, eating and parotid saliva secretion rates were measured. Blood samples were also periodically collected from the jugular vein. During and after 2 h feeding, water intakes were measured, respectively. These measurements were used to define thirst levels. It is thought that rumen fill in the RSF treatment was higher than the RNI treatment. Plasma osmolality in the RSF treatment increased in the first half of the 2 h feeding period due to the intraruminal infusion of parotid saliva. Therefore, parotid saliva secretion rates in the RSF treatment were lower than the RNI treatment for 30 min period from 30 to 60 min after the commencement of feeding. On the other hand, plasma total protein concentration and hematocrit in the RSF treatment decreased by 3.2 and 3.3% prior to the commencement of feeding due to the intraruminal infusion of parotid saliva. In the first half of the 2 h feeding period, plasma total protein concentration and hematocrit in the RSF treatment showed a tendency to decrease compared to the RNI treatment. Thirst level in the RSF treatment during feeding was approximately 31.3% less than the RNI treatment. Upon the completion of the 2 h feeding period, cumulative feed intake in the RSF treatment was significantly larger (19.7%) than the RNI treatment. The results suggest that a suppression of dry forage intake during the early stages of feeding in goats is partly caused by feeding induced hypovolemia, which is produced by the accelerated secretion of parotid saliva.

The Physiological Suppressing Factors of Dry Forage Intake and the Cause of Water Intake Following Dry Forage Feeding in Goats — A Review

“…In countries such as Japan where ruminants are raised in barns, most farmers feed their livestock a diet of dry forage twice a day. In NFC when goats were fed on dry forage for 2 h twice daily, irrespective of whether drinking water was supplied ( Nagamine et al, 2003 ; Sunagawa et al, 2003 ; 2008 ) or withheld ( Sunagawa et al, 2002 ; 2007 ) during feeding, eating rates rapidly decreased in the first 30 or 40 min of feeding and were subsequently reduced to very low rates for the reminder of the 2 h feeding period. The low eating rates mean that dry forage intake significantly decreased.…”

“…The low eating rates mean that dry forage intake significantly decreased. Sunagawa et al (2002 ; 2003 ; 2007) reported that a suppression of dry forage intake during the early stages of feeding was partly caused by feeding-induced hypovolemia, which was produced by the accelerated secretion of parotid saliva. Under NFC, ruminal distension, ruminal fluid osmolality, plasma osmolality and thirst levels all increased at the same time during the second hour of the 2 h dry forage feeding period.…”

“…Saliva in ruminants is secreted in large volumes during dry forage feeding ( Sato, 1975 ; Sunagawa et al, 2003 ). Ruminant saliva is mainly composed of fluid, mucin and NaHCO 3 .…”

“…Saliva is produced using plasma components. Therefore, sheep and large-type goats eating dry forage secrete large quantities (3,998±327.27 g/2 h, Thang et al, 2011a ) of saliva ( Stacy and Warner, 1966 ; Sunagawa et al, 2003 ), which decreases plasma volume (a fall of 15%) during initial stages of dry forage feeding ( Blair-West and Brook, 1969 ). During dry forage feeding, plasma HCO 3 − as well as pH also remarkably decreases due to loss of NaHCO 3 from the blood via the saliva into the rumen ( Sasaki et al, 1974 ).…”

An intravenous replenishment of salivary components decrease water intake and increases feed intake in freely drinking large-type goats fed on dry forage

“…When ruminants commence feeding on dry forage they secrete copious volumes of parotid saliva (Sato 1975;Sunagawa et al 2002Sunagawa et al , 2003, and large amounts of fluid and NaHCO 3 move from the circulating blood into the rumen in the form of saliva. Blair-West and Brook (1969) found that sheep fed lucerne chaff once a day showed a marked reduction in plasma volume within 15 min of the commencement of feeding.…”