Late-lactation Holstein cows (n=144) that were offered 15kg dry matter (DM)/cow per day of perennial ryegrass to graze were randomized into 24 groups of 6. Each group contained a fistulated cow and groups were allocated to 1 of 3 feeding strategies: (1) control (10 groups): cows were fed crushed wheat grain twice daily in the milking parlor and ryegrass silage at pasture; (2) partial mixed ration (PMR; 10 groups): PMR that was isoenergetic to the control diet and fed twice daily on a feed pad; (3) PMR+canola (4 groups): a proportion of wheat in the PMR was replaced with canola meal to produce more estimated metabolizable protein than other groups. Supplements were fed to the control and PMR cows at 8, 10, 12, 14, or 16kg of DM/d, and to the PMR+canola cows at 14 or 16kg of DM/d. The PMR-fed cows had a lower incidence of ruminal acidosis compared with controls, and ruminal acidosis increased linearly and quadratically with supplement fed. Yield of milk fat was highest in the PMR+canola cows fed 14 or 16kg of total supplement DM/d, followed by the PMR-fed cows, and was lowest in controls fed at these amounts; a similar trend was observed for milk fat percentage. Milk protein yield was higher in the PMR+canola cows fed 14 or 16kg of total supplement DM/d. Milk yield and milk protein percentage were not affected by feeding strategy. Milk, energy-corrected milk, and milk protein yields increased linearly with supplement fed, whereas milk fat percentage decreased. Ruminal butyrate and d-lactate concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH increased in PMR-fed cows compared with controls for all supplement amounts, whereas propionate and valerate concentrations decreased. Ruminal acetate, butyrate, and ammonia concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH linearly decreased with amounts of supplement fed. Ruminal propionate concentration linearly increased and valerate concentration linearly and quadratically increased with supplement feeding amount. The Bacteroidetes and Firmicutes were the dominant bacterial phyla identified. The Prevotellaceae, Ruminococcaceae, and Lachnospiraceae were the dominant bacterial families, regardless of feeding group, and were influenced by feeding strategy, supplement feeding amount, or both. The Veillonellaceae family decreased in relative abundance in PMR-fed cows compared with controls, and the Streptococcaeae and Lactobacillaceae families were present in only minor relative abundances, regardless of feeding group. Despite large among- and within-group variation in bacterial community composition, distinct bacterial communities occurred among feeding strategies, supplement amounts, and sample times and were associated with ruminal fermentation measures. Control cows fed 16kg of DM of total supplement per day had the most distinct ruminal bacterial community composition. Bacterial community composition was most significantly associated with supplement feeding amount and ammonia, butyrate, valerate, and propi...

There is a growing diversity and complexity of dairy farming systems in Australia. Feeding systems based on the provision of mixed rations to dairy cows grazing perennial pastures (termed partial mixed rations or PMR systems) have emerged and present the dairy industry with opportunities for improved production and feed efficiency, but also with significant challenges. Early research results are beginning to define the situations in which PMR systems are profitable and the mechanisms responsible for the improved milk responses. This review focuses on the role of PMR feeding systems in temperate dairying regions of Australia, highlights initial research findings, and identifies some of the gaps in current knowledge that warrant further research. The key findings were that, when very low allowances of pasture are offered to cows, milk production responses were driven mostly by increases in dry matter (DM) intake, and there appeared to be a minimal contribution to increased energy supply from improved whole tract DM digestibility. Differences in milk responses became apparent when >10 kg of total supplement DM was consumed (0.75 : 0.25 concentrate to forage) as PMR. There was a consistent maintenance of milk fat concentration when increasing amounts of concentrates were consumed as PMR, in contrast with supplements consumed in the dairy. There was also a consistent finding that replacing some wheat in the PMR with canola meal resulted in cows consuming more grazed pasture despite the limitations of very low pasture allowances (10–15 kg DM/cow.day, expressed to ground level). This was accompanied by further increases in energy-corrected milk yield. The potential to improve DM intake was further highlighted when pasture allowance was increased, with intake increasing from 3.6% to 4.5% of liveweight (from 20 to 25 kg DM/day for a 550-kg cow). There was also an indication that ~50% of the milk production benefit from PMR can be captured by providing the concentrate supplement as a grain mix in the dairy. There did not appear to be negative impacts of PMR systems on the social and grazing behaviour or health of cows.

Milk production responses of grazing cows offered supplements in different ways were measured. Holstein-Friesian cows, averaging 45 d in milk, were allocated into 8 groups of 24, with 2 groups randomly assigned to each of 4 feeding strategies. These were control: cows grazed a restricted allowance of perennial ryegrass pasture supplemented with milled wheat grain fed in the milking parlor and alfalfa hay offered in the paddock; FGM: same pasture and allowance as the control supplemented with a formulated grain mix containing wheat grain, corn grain, and canola meal fed in the parlor and alfalfa hay fed in the paddock; PMRL: same pasture and allowance as the control, supplemented with a PMR consisting of the same FGM but mixed with alfalfa hay and presented on a feed pad after each milking; and PMRH: same PMR fed in the same way as PMRL but with a higher pasture allowance. For all strategies, supplements provided the same metabolizable energy and grain:forage ratio [75:25, dry matter (DM) basis]. Each group of 24 cows was further allocated into 4 groups of 6, which were randomly assigned to receive 8, 12, 14, or 16 kg of DM supplement/cow per d. Thus, 2 replicated groups per supplement amount per dietary strategy were used. The experiment had a 14-d adaptation period and a 14-d measurement period. Pasture allowance, measured to ground level, was approximately 14 kg of DM/d for control, FGM, and PMRL cows, and 28 kg of DM/d for the PMRH cows, and was offered in addition to the supplement. Positive linear responses to increasing amounts of supplement were observed for yield of milk, energy-corrected milk, fat, and protein for cows on all 4 supplement feeding strategies. Production of energy-corrected milk was greatest for PMRH cows, intermediate for FGM and PMRL cows, and lowest for control cows. Some of these differences in milk production related to differences in intake of pasture and supplement. Milk fat concentration decreased with increasing amount of supplement for all feeding strategies, but the decline was most marked for the control cows. Milk protein concentration increased for all groups as the amount of supplement increased, but was greater for FGM, PMRL, and PMRH cows than control cows. It is concluded that when supplements are fed to grazing dairy cows, inclusion of corn grain and canola meal can increase milk production even at similar metabolizable energy intakes, and that it does not matter whether these supplements are fed as a PMR or in the parlor and paddock.

Milk production responses were measured in grazing cows offered supplements in different ways. Holstein–Friesian cows averaging 70 days in milk were allocated into 20 groups of eight, each including one rumen-fistulated cow. One of three dietary treatments was then randomly assigned to each of the 20 groups. Treatments were (1) Control (8 groups), where cows were supplemented with rolled wheat grain fed twice daily in the dairy and pasture silage provided in the paddock; (2) partial mixed ration (PMR; 8 groups), where cows were offered a PMR comprising rolled wheat grain, maize grain, maize silage and lucerne hay, which was presented on a feedpad immediately after each milking; the PMR was formulated to provide the same estimated metabolisable energy intake as the Control supplements; and (3) PMR+Canola (4 groups), where cows were fed in the same way as the PMR cows, except that a proportion of the wheat in the PMR was replaced with solvent-extracted canola meal. This ration was formulated to provide the same metabolisable energy as the Control and PMR treatments, but had greater amounts of crude protein. For Control and PMR treatments, supplements were offered at 8, 10, 12 or 14 kg DM/cow.day (2 groups per amount) while for the PMR+Canola treatment supplement was offered at 12 or 14 kg DM/cow.day (2 groups per amount). In addition to their supplements, all groups grazed an allowance of ~14 kg DM/cow.day (measured to ground level) of perennial ryegrass pasture. Yields of energy-corrected milk increased linearly with increasing supplement intake, but there was no difference between Control and PMR cows. When canola meal was added to the PMR, there was an increase in energy-corrected milk at a predicted supplement intake of 13.0 kg DM/cow.day. This was associated with a greater concentration and yield of milk fat in the PMR+Canola cows. Ruminal fluid pH and DM intake from pasture were also greater in PMR+Canola cows. It is concluded that farmers feeding high amounts of supplements to grazing cows could increase milk production by carefully considering the composition and form of the supplement mix, including the inclusion of canola meal.

Human milk oligosaccharides (OS) play an important role in protecting the neonate. In addition to fructo-oligosaccharides and galacto-oligosaccharides, bovine milk OS have great potential to be used in pediatric food products to mimic the functions of human milk OS. Currently, little is known about the accumulation of OS in bovine milk in relation to genetic and environmental factors. A systematic survey on seasonal variation of 14 major OS was thus conducted with 19 cows over the entire milking season using a liquid chromatography-mass spectrometry technique. This study revealed a number of significant correlations between structurally related and structurally nonrelated OS and a substantial individual animal difference for all 14 OS. Most of the 14 OS displayed a remarkable seasonal variation in abundance (up to 10-fold change), with the highest abundance observed in April and May (i.e., autumn) for the majority of the 19 cows.