The Influence of the Physical Form of the Diet on Fluid Dynamics and Mineral Content of Rumen Fluid in Lactating Cows Fed 12 Times Daily

Lactate uptake in the rumen and its contributions to subacute rumen acidosis of goats induced by high-grain diets

Rumen acidosis is the consequence of feeding rapidly fermentable grain diets and it is considered the most common nutritional disorder in intensive feeding ruminants. Due to that mechanism of catabolism and transformation is driven by multi-factors, the role of ruminal lactate and its contribution to subacute rumen acidosis has not been well defined yet. The aim of this study is to evaluate the effects of SARA on the production, absorption, circulation, and transformation of lactate in the rumen. In this study, rumen samples were collected from 12 adult Saanen goats (44.5 ± 4.6 kg BW) equipped with permanent rumen cannula to measure rumen fermentation parameters, organic acids production, microbial profiles, and blood indicators to identify the occurrence of SARA. To further investigate the change in the disappearance rate of ruminal lactate, rumen fluid was collected and a batch culture was performed. The results showed that the clearance rate of ruminal lactate was accelerated by SARA, and the concentration of the ruminal lactate pool was stable. In addition, the rumen liquid dilution rate and the rumen liquid flow rate under the SARA condition of goats were lower than that in normal conditions. The ruminal lactate flow rate had no difference throughout the process of fermentation. However, in vitro data showed that the disappearance of lactate was reduced in SARA. By measuring the conversion of sodium L-[3-¹³C]-lactate in batch culture, it was found that the percentage of lactate converted to propionate was significantly lower in the SARA treatment and 16.13% more lactate converted to butyrate under SARA condition. However, the percentage of lactate transformed into acetate and butyrate was significantly increased in the SARA treatment than that of control. The relative population of total protozoa count in SARA was significantly reduced, while the relative population of Lactobacillus fermentum, Streptococcus bovis, Butyrivibrio fibrisolvens, Megasphaera elsdenii, and Selenomonas ruminantium in the SARA treatment was significantly induced (p < 0.05). It is concluded that the transformation of lactate into butyrate may promote the development of SARA. These findings provide some references to the diet formulation for preventing SARA.

Effect of NDF concentration and physical form of fescue hay on rumen degradability, intake and rumen turn-over of cows

During two experimental periods, eight non-lactating, rumen fistulated Simmental cows were given 2 kg/day of a cereal based concentrate and fescue hay ad libitum. The hay differed in neutral-detergent fibre concentration (LNDF: low; HNDF: high) and physical form (L: long; C: coarsely chopped). The rumen degradability of the dietary ingredients and of an extracted soya-bean meal was studied using the polyester-bag method.

The estimated effective rumen degradability <DG) of dry matter (DM) was significantly higher for LNDF than for HNDF hay (0·490 v. 0·401; P < 0·01). The DM DG of the extracted soya-bean meal and the dietary concentrate were higher when incubated with LNDF than with HNDF diets (0·630 v. 0·581, P < 0·05, and 0·541 v. 0·514, respectively).

Chopping the hay significantly increased the daily DM intake for HNDF diets (from 9·9 to 11·6 kg; P < 0·05), while no statistical differences were found between the other diets (10·2 and 9·6 kg, respectively for L-LNDF and C-LNDF diets). Cows given HNDF hay drank less water (42·4 v. 51·7 I/day) and total water consumption, expressed per unit of DM intake, was lower for the HNDF diets (4·1 v. 5·3 I/kg DM; P < 0·01).

Dietary treatments did not affect the estimated rumen turn-over rate of hay (0·027 per h on average, k1), hay post-rumen turn-over rate (0·069 per h on average, k2) or the estimated rumen liquid turn-over rate (0·100 per h on average, kj. The calculated outflow from the rumen was lower for the HNDF diets (159·4 v. 198·7 I/day). The daily amount of estimated saliva secreted did not differ between treatments, although saliva expressed per kg DM intake was significantly lower for the HNDF diets (10·8 v. 14·8 I/kg DM; P < 0·05).

The HNDF diets gave a lower post-feeding rumen pH (6·29 v. 6·58; P < 0·01), a higher concentration of n-butyrate (9·58 v. 8·32 mmol/l; P < 0·05) and a lower concentration of ammonia nitrogen (NH3-N) (80·5 v. 128·5 mg/l; P < 0·05). Of the C4 and C5 iso-acids, the rumen liquid from cows given HNDF diets had significantly lower concentrations of isobutyrate, isovalerate and n-valerate (P < 0·01). Hay physical form did not affect rumen pH, NH3-N and volatile fatty acid concentrations.