Effects of feeding grass or red clover silage cut at two maturity stages in dairy cows. 1. Nitrogen metabolism and supply of amino acids

Abstract

This study investigated the effects of plant species (red clover vs. timothy-meadow fescue) and forage maturity at primary harvest (early vs. late cut silage) on rumen fermentation, nutrient digestion, and nitrogen metabolism including omasal canal AA flow and plasma AA concentration in lactating cows. Five dairy cows equipped with rumen cannulas were used in a study designed as a 5 x 5 Latin square with 21-d periods. The diets consisted of early-cut and late-cut grass and red clover silage, respectively, and a mixture of late-cut grass and early-cut red clover silages given ad libitum with 9 kg/d of a standard concentrate. Grass silage dry matter intake tended to decrease but that of red clover silages tended to increase with advancing maturity. Milk yields were unchanged among treatments, milk protein and fat concentrations being lower for red clover than for grass silage diets. Rumen fluid pH was unchanged but volatile fatty acid and ammonia concentrations were higher for red clover than for grass silage diets. Intake of N, and omasal canal flows of total nonammonia N (NAN), microbial NAN, and dietary NAN were higher for red clover than for grass silage diets but were not affected by forage maturity. However, microbial NAN flow and amount of N excreted in the feces decreased with advancing maturity for grass diets but increased for red clover diets. Apparent ruminal N degradability of the diets was unchanged, but true ruminal N degradability decreased and efficiency of microbial synthesis increased with red clover diets compared with grass silage diets. Omasal canal flows of AA, except those for Met and Cys, were on average 20% higher for red clover than grass silage diets. Omasal canal digesta concentrations of Leu, Phe, branched-chain, and essential AA were higher but those of Met lower for red clover than for grass silage diets. Plasma AA concentrations, except for His (unchanged) and Met (lower), were higher for red clover than for grass diets. However, none of these AA-related variables were affected by forage maturity. Total digestibility of N and excretion of N in the urine were higher for red clover than for grass diets and decreased with advancing maturity. It was concluded that despite the higher total AA supply of cows fed red clover versus grass silage diets, further milk production responses on red clover diets were compromised by an inadequate supply of Met as evidenced by lower Met concentration in the AA profile of omasal digesta and plasma.

The effect of high polyphenol oxidase grass silage on metabolism of polyunsaturated fatty acids and nitrogen across the rumen of beef steers1

“…These findings agree with previous red clover versus grass silage comparisons Merry et al, 2006;Vanhatalo et al, 2009). Greater NMN with RC is reported to result from a lower N degradability in the rumen Merry et al, 2006;Vanhatalo et al, 2009) and has been attributed to the PPO activity inherent in red clover protecting dietary protein (Lee et al, 2004;Merry et al, 2006;Halmemies-Beauchet-Filleau et al, 2014). However, in the current study, no difference was observed between treatments when the flow of NMN was reported as a percentage of N intake (62.5%), which coincidentally is also greater than previously reported for forage silage diets (33.8%; Merry et al, 2006), further indicating a likely overestimation of duodenal flow in the current study.…”

“…Greater total N flows entering the duodenum with RC than with either PR or CO were in agreement with previous results comparing red clover with grass Merry et al, 2006;Vanhatalo et al, 2009) and in part can be attributed to the greater N content of the RC. The greater total N flow with the RC diet was composed mainly of NMN (dietary, endogenous, and ammonia N).…”

“…Thus, the contribution of microbial N to the total N flow was lower (P < 0.05) with red clover (37%) than with PR (48%) and CO (45%). These findings agree with previous red clover versus grass silage comparisons Merry et al, 2006;Vanhatalo et al, 2009). Greater NMN with RC is reported to result from a lower N degradability in the rumen Merry et al, 2006;Vanhatalo et al, 2009) and has been attributed to the PPO activity inherent in red clover protecting dietary protein (Lee et al, 2004;Merry et al, 2006;Halmemies-Beauchet-Filleau et al, 2014).…”

“…Although values for apparent and true OM digestibility across the rumen on all forage diets are scarce in the literature, a meta-analysis of typical North American and European ruminant diets performed by Huhtanen et al (2010) predicted values of 42 and 74% for apparent and true ruminal OM digestibilities compared with 37 and 56%, respectively, in the current study, evidencing a potential overestimation of duodenal flow. Vanhatalo et al (2009) reported significantly greater EMPS with red clover than grass silage when offered with a dairy concentrate ration (60:40 forage:concentrate) although numerically similar to the values reported in the current study where there were no differences between RC and PR.…”

“…The greater levels of ammonia-N in CO may be related to a reduced protein complexing through PPO or a combination of an extended wilt and the greater pH of the silage resulting in greater protease activity increasing proteolysis. The latter explanation would explain the greater ammonia-N (% total N) for silages in the current study than typical reported values for red clover (3%; Vanhatalo et al, 2009), perennial ryegrass (6%), and cocksfoot (6%; Aufrère et al, 2003). The use of a formic acid silage inoculant by Vanhatalo et al (2009) and Aufrère et al (2003) as opposed to live culture in the current study may also have influenced ammonia-N.…”