Technical note: A method for quantification of saliva secretion and salivary flux of metabolites in dairy cows1

Abstract

Salivary flow and net jugular flux of metabolites were studied during resting and rumination in 3 lactating dairy cows (BW 548 ± 17.2 kg, days in milk 113 ± 4 d). The method was based on the concentration difference between arterial and jugular blood, and jugular blood flow measured by downstream dilution of p-aminohippuric acid (pAH). Cows were surgically prepared with a permanent arterial catheter in A. intercostales dorsales before the trial. On sampling days, cows were prepared with left and right side jugular, and ear vein catheters for blood sampling and infusion of pAH, respectively. Blood was sampled simultaneously from the 2 jugular veins and artery during periods of rest and rumination. Secretion of saliva was set equal to the net water extraction calculated from the increased hemoglobin concentration in jugular blood compared with arterial blood. Arterial and jugular blood flow summed for both sides of the head doubled (P < 0.001) during rumination (437 ± 19, 424 ± 18 L/h, respectively) compared with resting (210 ± 19, 202 ± 18 L/h, respectively), consequently doubling the saliva secretion (P < 0.001, resting = 7.6 ± 0.8 L/h, rumination = 13.8 ± 0.8 L/h). The extraction of inorganic phosphate (Pi) from arterial blood during resting periods was greater compared with rumination (P = 0.004; resting = 21.7% ± 0.9%; rumination = 15.6% ± 0.9%), resulting in a greater Pi concentration in saliva secreted during resting. The concentrations of Pi in saliva were 4.5 ± 0.3 and 3.7 ± 0.3 times the arterial concentration during resting and rumination (P = 0.09), respectively. The urea concentration in saliva was 0.63 ± 0.04 times the arterial level, showing that urea is less efficiently transferred from blood than water, resulting in a greater numerical urea concentration in jugular compared with arterial blood. The water extraction method presented in the present paper offers an alternative way of estimating saliva secretion without the chewing activity constraints associated with other methods, for example, allowing for determination of saliva flow during rumination.

Factors Affecting Rumen Microbial Protein Synthesis: A Review

“…9 The rumen is usually well buffered, due to the presence of bicarbonates and phosphates founded in the continuous flow of saliva. 19 Rumen, although well buffered by bicarbonate, phosphate, protein and VFA can vary in pH from approximately 7.0 to less than 5 under different dietary condition. 20 Rumen buffering could avert the reduction in pH and could enhance rumen microbial growth, diversity and activity, fermentation end product and microbial protein synthesis.…”

Ruminal microorganism consideration and protein used in the metabolism of the ruminants: A review

“…In the rumen, a redox potential was found (-350 mV, with fluctuations between -250 and -450 mV), with result of a strong ambient environment due to the lack of oxygen. The rumen is usually well buffered, due to the presence of bicarbonates and phosphates founded in continuous flow of saliva (Puggaard et al, 2011;Røjen and Kristensen, 2012;Storm et al, 2014). Saliva production can be high in a cow, reaching over 180 L/day.…”

Impact of corn silage or corn silage plus protein supplementation on the ingestive and rumination behaviours, ruminal fermentation characteristics and efficiency of grazing dairy cows

“…This increase agrees with the findings of Graf et al (2005), who detected an increase in the rumination time of 7.6 min/day/kg DM corn silage. The longer rumination time and greater number of rumination chews suggest the possibility of better buffering for supplemented cows, as quantitatively significant saliva production is related to rumination activity (Storm et al, 2013). Therefore, a higher amount of starch eaten by the supplemented cows could be balanced by a higher amount of bicarbonate entering the rumen.…”