Effects of forage and grain legume-based silages supplemented with faba bean meal or rapeseed expeller on lactational performance, nitrogen utilization and plasma amino acids in dairy cows.

The objective of this experiment was to investigate the effect of forage type [red clover (51%)-grass silage i.e., RCG vs. faba bean (66%)-grass silage i.e., FBG] and concentrate type (faba bean; FB vs. rapeseed expeller; RE) on lactational performance, milk composition and nitrogen (N) utilization in lactating dairy cows. Eight lactating multiparous Nordic Red cows were used in a replicated 4 × 4 Latin Square experiment, with 21-d periods, in a 2 × 2 factorial arrangement of treatments. The experimental treatments were: 1) RCG with RE, 2) RCG with FB, 3) FBG with RE, and 4) FBG with FB. Inclusion rate of rapeseed expeller and FB was isonitrogenous. Crude protein contents of the experimental diets were 16.3, 15.9, 18.1 and 17.9% of dry matter, respectively. All diets included oats and barley and were fed ad libitum as total mixed rations with forage to concentrate ratio at 55:45. Dry matter intake and milk yield were recorded daily, and spot samples of urine, feces and blood were collected at the end of each experimental period. Dry matter intake did not differ across diets averaging 26.7 kg/d. Milk yield averaged 35.6 kg/d and was 1.1 kg/d greater for RCG vs. FBG, and milk urea N concentration was lower for RCG compared with FBG. Milk yield was 2.2 kg/d and milk protein yield 66 g/d lower for FB vs. RE. Nitrogen intake, urinary N, and urinary urea N excretions were lower, and milk N excretion tended to be lower for RCG compared with FBG. The proportion of the dietary N excreted as fecal N was larger in cows fed RCG vs. FBG, and the opposite was true for urinary N. There was an interaction for milk N as % of N intake: it increased with RE compared with FB for RCG-based diet, but only a marginal increase was observed for FBG-based diet. Plasma concentration of His and Lys were lower for RCG vs. FBG, whereas His tended to be greater and Lys lower for FB compared with RE. Further, plasma Met concentration was around 26% lower for FB vs. RE. Of milk fatty acids, saturated fatty acids were decreased by RCG and increased by FB compared with FBG and RE, respectively, whereas monounsaturated fatty acids were increased by RCG vs. FBG, and were lower for FB vs. RE. In particular, 18:1n-9 concentration was lower for FB compared with RE. Polyunsaturated fatty acids such as, 18:2n-6 and 18:3n-3 were greater for RCG vs. FBG, and 18:2n-6 was greater and 18:3n-3 was lower for FB vs. RE. In addition, cis-9,trans-11 conjugated linoleic acid was lower for FB compared with RE. Faba bean whole crop silage and faba bean meal have potential to be used as a part of dairy cow rations, but further research is needed to improve their N-efficiency. Red clover-grass silage from a mixed sward, without inorganic N fertilizer input, combined with RE, resulted in the greatest N-efficiency in the conditions of this experiment.