Effects of partial mixed rations and supplement amounts on milk production and composition, ruminal fermentation, bacterial communities, and ruminal acidosis

Abstract

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...

Challenges of feeding dairy cows in Australia and New Zealand

“…3). Similarly, Golder et al (2014) identified acidosis risk for a range of diets and showed that PMR diets had significantly lower risks of ruminal acidosis than did diets where wheat was fed in the dairy at a range of intakes (Fig. 4).…”

“…The improved ECM-production responses of PMR were often associated with milk fat concentration not declining to the same extent with an increasing supplement intake, as it did when feeding cereal supplements in the dairy Golder et al 2014). Diet is clearly a major factor in this response (Shingfield et al 2010;Bauman and Griinari 2003).…”

“…Overall, 10 kg DM of total supplement (comprising 70% concentrate and~30% forage) was required for responses of increased DM intake and increased production of energycorrected milk (ECM) for cows consuming cereal/maize-based +/ À canola meal+forage PMR compared with cereal grain fed in the dairy and forage in the paddock Golder et al 2014). Also, milk production reached a maximum at higher amounts of total supplement intake.…”

“…Cows consuming PMR with canola meal compared with a PMR without canola meal increased DM intake from both pasture (lower residuals or post-grazing biomass) and supplement (less refusals) by 0.5-1.9 kg DM/cow.day Golder et al 2014). In these spring and autumn experiments (early lactation and late lactation respectively), cows offered the PMR with canola meal produced more ECM (ranging from 1.7 to 4.0 kg ECM/cow.day) than did cows offered the PMR diet without canola meal Golder et al 2014). These differences occurred when supplement intake was at least 12.0 kg DM supplement/cow.day.…”

“…A good example of this is in the recent research where the formulation of complicated mixes of grain supplements led to increased milk production compared with other dietary treatments of similar ME concentrations (Golder et al 2014).…”