Effects of forage source and extruded linseed supplementation on XXXX emissions from growing dairy @entity291 of differing body weights.

@entity1568 @entity2829 @entity1735 @entity39000 @entity577 @entity62 @entity291
Changes in diet @entity1735 amount and type (i.e., starch vs. fiber) and dietary oil supplements can affect ruminant @entity577 emissions. Our objectives were to measure @entity577 emissions, whole-tract digestibility, and energy and @entity1568 utilization from growing dairy @entity291 at 2 body weight (BW) ranges, fed diets containing either high @entity2829 silage (MS) or high grass silage (GS), without or with supplemental oil from extruded linseed (ELS). Four Holstein-Friesian heifers aged 13 mo (BW range from start to finish of 382 to 526 kg) were used in experiment 1, whereas 4 lighter heifers aged 12 mo (BW range from start to finish of 292 to 419 kg) were used in experiment 2. Diets were fed as total mixed rations with forage @entity62 ( @entity62 ) containing high MS or high GS and concentrates in proportions (forage:concentrate, @entity62 basis) of either 75:25 (experiment 1) or 60:40 (experiment 2), respectively. Diets were supplemented without or with ELS (Lintec, BOCM Pauls Ltd., Wherstead, UK; 260 g of oil/kg of @entity62 ) at 6% of ration @entity62 . Each experiment was a 4 * 4 Latin square design with 33-d periods, with measurements during d 29 to 33 while animals were housed in respiration chambers. Heifers fed MS at a heavier BW (experiment 1) emitted 20% less @entity577 per unit of @entity62 intake (yield) compared with GS (21.4 vs. 26.6, respectively). However, when repeated with heifers of a lower BW (experiment 2), @entity577 yield did not differ between the 2 diets (26.6g/kg of @entity62 intake). Differences in heifer BW had no overall effect on @entity577 emissions, except when expressed as grams per kilogram of digestible organic matter ( @entity39000 ) intake (32.4 vs. 36.6, heavy vs. light heifers). Heavier heifers fed MS in experiment 1 had a greater @entity62 intake (9.4kg/d) and lower @entity39000 (755 g/kg), but no difference in N utilization (31% of N intake) compared with heifers fed GS (7.9 kg/d and 799 g/kg, respectively). Tissue energy retention was nearly double for heifers fed MS compared with GS in experiment 1 (15 vs. 8% of energy intake, respectively). Heifers fed MS in experiment 2 had similar @entity62 intake (7.2 kg/d) and retention of energy (5% of intake energy) and N (28% of N intake), compared with GS-fed heifers, but @entity39000 was lower (741 vs. 765 g/kg, respectively). No effect of ELS was noted on any of the variables measured, irrespective of animal BW, and this was likely due to the relatively low amount of supplemental oil provided. Differences in heifer BW did not markedly influence dietary effects on @entity577 emissions. Differences in @entity577 yield were attributable to differences in dietary starch and fiber composition associated with forage type and source.
