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The objective of this study was to investigate the effect of perennial ryegrass (Lolium perenne L.; PRG) ploidy and white clover (Trifolium repens L.) inclusion on milk production, dry matter intake (DMI), and milk production efficiencies. Four separate grazing treatments were evaluated: tetraploid PRG only, diploid PRG only, tetraploid PRG with white clover, and diploid PRG with white clover. Individual DMI was estimated 8 times during the study (3 times in 2015, 2 times in 2016, and 3 times in 2017) using the n -alkane technique. Cows were, on average, 64, 110, and 189 d in milk during the DMI measurement period, corresponding to spring, summer, and autumn, respectively. Measures of milk production efficiency were total DMI/100 kg of body weight (BW), milk solids (kg of fat + protein; MSo)/100 kg of BW, solids-corrected milk/100 kg of BW, and MSo/kg of total DMI. Perennial ryegrass ploidy had no effect on DMI; however, a significant increase in DMI (+0.5 kg/cow per day) was observed from cows grazing PRG-white clover swards compared with PRG-only swards. Sward white clover content influenced DMI as there was no increase in DMI in spring (9% sward white cover content), whereas DMI was greater in summer and autumn for cows grazing PRG-white clover swards (+0.8 kg/cow per day) compared with PRG-only swards (14 and 23% sward white clover content, respectively). The greater DMI of cows grazing PRG-white clover swards led to increased milk (+1.3 kg/cow per day) and MSo (+0.10 kg/cow per day) yields. Cows grazing PRG-white clover swards were also more efficient for total DMI/100 kg of BW, solids-corrected milk/100 kg of BW, and MSo/100 kg of BW compared with cows grazing PRG-only swards due to their similar BW but higher milk and MSo yields. The results highlight the potential of PRG-white clover swards to increase DMI at grazing and to improve milk production efficiency in pasture-based systems. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine whether the intake of fresh highly digestible ryegrass could be limited by the total amount of energy absorbed. Moreover, it investigated whether the limitation was more specific to energy absorbed as volatile fatty acids in the rumen compared with energy absorbed in the lower gastrointestinal tract. Four treatments were compared: infusion of 1.25 kg of glucose into the rumen (R1.25), infusion of 2.5 kg of glucose into the rumen (R2.5), infusion of 1.5 kg of glucose into the duodenum (D1.5), and a control treatment consisting of water and salts. Treatments R2.5 and D1.5 were assumed to supply about 16.5 MJ of net energy for lactation. All treatments consisted of 2 infusions, one into the rumen and the other into the duodenum, with one of these infusions being a control. All infused solutions were iso-osmotic with osmolarities around 340 and 330 mmol/L for rumen and duodenum, respectively. Treatments were compared using 4 dairy cows in mid lactation according to a 4 x 4 Latin square design replicated twice during 8 periods of 7 d each. Cows were housed in tie stalls and fed ad libitum with fresh perennial ryegrass cut every morning during the spring at 28 d of regrowth. Intake and feeding behavior were measured, as well as concentrations of ruminal fermentation products and some blood metabolites. The pepsin-cellulase organic matter digestibility of the offered herbage averaged 0.76 ± 0.011. The average dry matter intake of herbage was 15.5 ± 0.52 kg/d. The glucose infusions decreased dry matter intake by 0.95 kg/d compared with the control, but had the same satiating effect regardless of site or dose of infusion. The average concentration of volatile fatty acids in rumen fluid was 97.9 ± 2.03 mmol/L and the molar proportion of propionate was 21.6 ± 0.19 mmol/100 mmol. Glucose infusions into the rumen led to a decrease in the molar proportions of acetate from 64.4 on the control treatment to 60.9 mmol/100 mmol on R2.5 and increased the molar proportions of butyrate from 10.2 (control) to 13.5 mmol/100 mmol on R2.5, and minor acids (valerate and caproate), from 1.27 (control) to 2.54 mmol/100 mmol on R2.5, proportionally to the dose infused. These results suggested that energy nutrients can limit intake in dairy cows fed high-digestibility ryegrass and that butyrate and minor acids would have a limited satiating effect compared with propionate. [ABSTRACT FROM AUTHOR]