Effects of time of maize silage supplementation on herbage intake, milksolids production, nitrogen partitioning and rumen function of lactating dairy cows

Abstract

The effect of the time of maize silage supplementation relative to a short (4-5 hours) herbage meal on herbage dry matter (DM) intake, milksolids (MS) production, nitrogen (N) partitioning and rumen function of lactating dairy cows, was examined in three indoor and one outdoor grazing trial. In the first 2 experiments, cows were fed 3-5 kg DM of maize silage either at 9 (9BH) or 1 (1BH) hour before a short (4 hours) herbage (perennial ryegrass-white clover) meal indoors. Herbage DM intake was similar between 1BH (6.6 kg DM/cow/day) and 9BH (6.7 kg DM/cow/day) in early lactation, but higher for 9BH (11.2 kg DM/cow/day) than 1BH (10.4 kg DM/cow/day) in mid lactation. Milk yield and MS production were higher for 9BH than 1BH in mid lactation (18.8 vs 15.4 and 1.63 vs 1.48 kg/cow/day, respectively), but similar between 9BH and 1BH in early lactation (16.7 vs 16.6 and 1.41 vs 1.33 kg/cow/day, respectively). Feeding 5 kg DM of maize silage at 9 rather than 1 hour before an intensive herbage meal altered the population of the rumen as shown by an 16% increase in the glucogenic precursor supply (propionate). Feeding maize silage at 9 rather than 1 hour before an intensive herbage meal improved utilization of ruminal NH3-N and increased the ratio of purine derivatives to creatinine, suggesting greater microbial protein production. However, these changes were transitory and were not reflected in the proportion of N intake excreted in milk, urine or faeces. Non-esterified fatty acid concentration was higher for 1BH than 9BH in early (0.41 vs 0.27 mmol/l, respectively) and mid (0.084 vs 0.056 mmol/l, respectively) lactation, suggesting that feeding maize silage at 9 rather than 1 hour before short herbage meal reduced mobilization of the cows fat reserve and thereby, the risk of ketosis. In the third experiment, late lactation dairy cows were fed cut herbage (perennial ryegrass-white clover) indoors and offered either no supplement (herbage only, control), or 3 kg DM maize silage at 1 (1BH) or 9 (9BH) hours before the herbage meal. Total DM intake (kg DM/cow/day) was lower for control (13.7) than 1BH (15.09) and 9BH (15.9). The substitution rate (herbage kg DM per kg DM of maize silage) was higher for 1BH (0.56) than 9BH (0.31). However, MS production did not significantly differ between 1BH and 9BH. Faecal N excretion was higher, and the proportion of N intake excreted in urine and the urine to faecal N ratio were lower for supplemented than control cows. The peak concentration of ruminal NH3-N was 20% lower for supplemented than control cows. Nitrogen excreted in faeces and urine was higher for 9BH than 1BH, mainly due to higher N intake (362 vs 342 g N/cow/day, respectively). In the fourth experiment, late lactation dairy cows were offered a herbage (perennial ryegrass-white clover) meal grazed at pasture for 5 hours and fed either no supplement (herbage only, control), or 3 kg of maize silage at 2 (2BH) or 9 (9BH) hours before herbage. Herbage DM intake was higher for control than supplemented cows, and higher for 9BH than 2BH (11.1, 10.1 and 10.9 kg DM/cow/day for control, 2BH and 9BH, respectively). Intake rate (g herbage DM/min) was lower for 2BH (41.5) than 9BH (44.6) and control (45.3). The substitution rate (herbage kg DM per kg DM of maize silage) was higher for 2BH (0.47) than 9BH (0.19). However, MS production was similar between treatments (1.12, 1.2 and 1.26 kg MS/cow/day for control, 2BH and 9BH, respectively). Body weight (BW) loss was less for supplemented than control cows (-0.95, -0.44, -0.58 kg/cow/day for control, 2BH and 9BH, respectively). Faecal N excretion and the purine derivatives to creatinine ratio were higher, and the urine to faecal N ratio was lower for supplemented than control cows, suggesting higher microbial protein production with maize silage supplementation. The N concentration of urine and total urinary N excretion were not affected by supplementation or time of supplementation. Non-esterified fatty acid concentration (mmol/l) was higher for control (0.3) than 2BH (0.15) and 9BH (0.13). Overall, the research showed that under a restricted herbage feed situation where cows had 4-5 hours access to herbage, feeding maize silage at 9 rather than 1 or 2 hours before the herbage meal reduced the substitution rate of herbage, and increased the MS response. Under a restriction herbage feed situation, maize silage supplementation had limited effect on the concentration N and total N excretion in urine due to a small change in N intake being observed. Feeding maize silage at 9 rather than 1 hour before an intensive herbage meal resulted in a small effect on N partitioning to milk, urine, or faeces.