Intake and performance of dairy cattle on forages in winter

Abstract

The effect of crop type, crop allowance and feeding frequency on DM intake, body condition score (BCS) gain, grazing behaviour and rumen physiology of dairy cattle fed forage crops during winter was examined in three experiments. Experiment 1 examined the effect of wintering dairy cows outdoors on the industry standard allowance of kale (11 kg DM of kale + 3 kg DM of barley straw, K11), with the higher allowance of kale (14 kg DM of kale + 3 kg DM of barley straw, K14) and Italian ryegrass at low allowance (11 kg DM + 3 kg DM of barley straw, G11). BCS gain over the six week winter feeding period was higher for K14 and G11 (0.3 BCS units) than K11 (0.2 BCS units). The % DM utilisation of K11 (96%) and K14 (88%) were higher than G11 (70%), leading to higher DM intake in K14 (12.1 kg DM of kale/cow/day) and K11 (10.5 kg DM of kale/cow/day) than G11 (7.9 kg DM of grass/cow/day). Within 6 hours of being offered a fresh break, cows had consumed over 86% of their apparent daily intake with DM consumptions of 10.4, 10.5 and 7.3 kg DM/cow for the K11, K14 and G11 treatments, respectively. Grazing behaviour was altered by both forage type and allowance. Cows on the K14 treatment grazed for longer over the day than cows in K11 and G11. Rumen ammonia concentrations peaked 7 h after the morning allocation of feed and concentrations ranged from 108 to 212 mg NH3/l for K14, 91 to 306 mg NH3/l for K11 and 57 to 269 mg NH3/l for G11. Rumen pH fell to reach its lowest values of 5.7 for G11, 6.0 for K11 and 6.2 for K14 between 7-10 h after feeding forage in all treatments. However, the rumen pH of K11 and K14 remained high (> 6.0) throughout the day. Further, from bout counts of rumen pH, G11 had more frequent and longer bouts of rumen pH under each threshold except the threshold 6.4 compared with K11 or K14. Hence, there was little evidence of sub-acute rumen acidosis (SARA) in kale-fed cows. Urinary N% was higher for K11 (0.58%) than K14 (0.43%) and G11 (0.52%). Faecal and urine N output per cow was higher for K14 (335 g N/cow/day) and K11 (289 g N/cow/day) than G11 (227 g N/cow/day). Based on stocking density, total faecal and urine N output per hectare was higher for K11 (413 kg N/ha) and K14 (355.9 kg N/ha) than G11 (82.3 g N/cow/day). iii Experiment 2 examined the effect on rumen physiology of feeding cattle either once (1.5 kg DM/day barley straw at 0800 h plus 7 kg DM/day of kale at 0900 h, K1) or twice (0.75 kg DM barley straw 0800 h plus 3.5 kg DM kale 0900 h and 0.75 kg DM barley straw at 1400 h plus 3.5 kg DM of kale at 1500 h, K2) per day over a 7 day period in individual metabolism crates. No significant differences were observed between the two treatment groups in the rumen concentration of acetic acid, propionic acid, butyric acid, ammonia and rumen pH. There was a distinct diurnal pattern of rumen ammonia concentration which was characterized by a peak 2 h post feeding for both K1 and K2. Rumen ammonia concentration ranged from 27.5 mg NH3/l to 170 mg NH3/l for K1 and from 43.7 mg NH3/l to 158 mg NH3/l for K2. Rumen pH remained high (>5.8) on both treatment groups. Experiment 3 examined the effect of wintering dairy cows outdoors on either kale or grass fed in one (11 kg DM kale + 3 kg DM of baled barley straw offered in the morning) or two allocations (5.5 kg DM of kale grazed + 1.5 kg DM barley straw offered morning and afternoon) per day. BCS gain over the six week winter feeding period was higher for grass-fed cows (0.5 BCS units) than kale-fed cows (0.2 BCS units), but unaffected by feeding frequency. % DM utilization was higher for kale-fed (97%) than grass-fed cows (76%) leading to higher apparent DM intake of forage in kale-fed (9.7 kg DM/cow/day) than grass-fed cows (7.7 kg DM/cow/day). % DM utilization and apparent DM intake were not affected by feeding frequency. Prehension bite rate was greater for grass-fed (37.3 bites/min) than kale-fed cows (7.6 bites/min), but more mastication bites were required for kale-fed cows. Cumulative DM intake after 2, 3 and 6 h was greater in cows fed once than twice a day and for kale than grass after 3 and 6 h. Mean eating time was greater on cows offered forage once (477 min) than twice (414 min) per day. Rumen ammonia concentration rose rapidly after the first meal, with all four treatments reaching a peak value within 3 hours of grazing time. From the bout counts, cows which were fed grass recorded the most frequent rumen pH of <5.8 with cows fed grass twice a day recording the most frequent rumen pH of <5.5. Hence, there was no evidence of SARA in kale-fed cows. Overall, the results show BCS gain over the winter feeding period was higher in grass than kale-fed cows when forage was offered at 11 kg DM/cow/day. This was despite % DM utilization and apparent DM intake being lower for grass-fed cows. Increasing kale allowance to 14 kg DM/cow/day increased DM intake and BCS gain. Increasing feeding frequency from once to twice per day decreased the intake rate within the first 6 hours after allocation but did not affect total daily DM intake, % DM utilization or BCS gain. Rumen ammonia concentration for both kale and grass-fed cows peaked 3 h and 7 h after the morning iv allocation, but the concentration stayed within the range of 20-800 mg NH3/l for maximum rumen bacterial growth. Rumen pH remained high (>5.8) for kale-fed cows, hence indicating no evidence of SARA. The calculated faecal and urine N output/ha were higher for kale than grass-fed cows reflecting greater yield of kale leading to increased stocking density.