Impact of increasing grain feeding frequency on production of dairy cows grazing pasture

摘要

Pasture is a major component of the diet for dairy cows in Chile. and grain is often used as a supplement to increase milk production. The quantity of grain offered is affected by price and return to the farmer, but 6 kg/day is typical of many situations. However the benefits of feeding grain more frequently than twice daily to cows rotationally grazed on pasture is uncertain. This study was undertaken to measure effects of grain feeding frequency on milk production, intakes and grazing behavior and on blood and urinary metabolites in dairy cows on pasture. The 65 day trial used 28 Black Friesian cows in their second month of lactation. Prior to treatments, milk production averaged 29.7 L/day and mean live-weight was 502 kg. The four treatments included: grazed pasture only (P), pasture plus 6 kg/day of concentrate offered in two equal rations at milking (0600 h, 1500 h) (PC2), grazing plus 6 kg/day of concentrate offered in three equal rations (0600 h. 1200 h, 1500 h) (PC3), and grazing plus 6 kg/day of concentrate offered in four equal rations (0600 h, 1200 h. 1500 h, 2100 h) (PC4). Total feed intakes were determined from controlled-release chromium capsules (CRC) and faecal subsampling and milk composition was analyzed weekly using infrared spectroscopy (Foss 4300 Milko-scan). Milk production was 24.6,28.7: 29.5 and 28.8 L/day for P, PC2, PC3 and PC4 treatments, respectively. Intake of pasture dry matter pasture (DM) (kg/day) decreased from 16.1 (P) to 12.7, 11.9 and 11.1 with increases in grain feeding frequency (P<0.05). Total DM intakes were higher with grain supplementation but tended to decrease with increased frequency, whilst total chewing time (eating and rumination) declined from 1012 (P) to 966 for the PC4 treatment. Grain supplementation increased milk production. but frequency of grain feeding had no effect (P>0.05) on production, milk fat (3.67%), protein (3.20%) or urea (5.68 mmol/L) concentrations. Live-weight and body condition score did not vary (P>0.05) with treatment. Plasma Beta-hydroxybutyrate (BHBA) and plasma urea-nitrogen (PUN) were not affected by grain feeding frequency averaging 0.51 mmol/l and 14.8 mg/dl respectively (P>0.05). Urinary purine derivatives (allantoin + uric acid)/Creati nine (PD/C) ratio was similar in all treatments, so rumen microbial growth did not appear to be affected by grain feeding or frequency. This trial did not indicate any benefits when supplement was given more than twice daily (at milking) and there appeared to be negative impacts when given 4 times daily. We postulate a disturbance in their behavior when offered small supplements frequently, and a possible reduction in feed intake and time spent chewing.