Protein metabolism in the rumen of silage-fed steers: effect of fishmeal supplementation

Abstract

1. Ryegrass (Lolium perenne cv. Cropper) silage was given to four Friesian steers (initial live weight (LW) 172 kg) alone or with a fishmeal supplement (150 g fresh weight/kg silage dry matter (DM)) in a balanced twoperiod change-over design. The dietary components were the same as those used in a recent experiment by Gill et a/. (1987). All diets were offered hourly at 24 g DM/kg LW.2. Fishmeal supplementation increased dietary nitrogen intake ( P < 0.01) and significantly increased the flow of total N (P <0.01), non-ammonia N (NAN) (P i 0.01) and amino acids ( P < 0.05) at the duodenum. 4. The efficiency of microbial protein synthesis was significantly increased from 30.8 g N/kg organic matter apparently digested in the rumen (OMADR) to 54.3 g N/kg OMADR by fishmeal supplementation ( P < 001).However, this indicates that relatively high efficiencies can be achieved with unsupplemented high quality silage supplied continuously. Rumen degradable N (RDN) supply was significantly increased by fishmeal supplementation (P < 0.05) but apparent efficiency of capture of RDN by rumen microbes was not significantly increased. 5. Attempts were made to investigate the source of N utilized by the microbes on the two diets by intrarumen infusions of ("NH,),SO, and ~-[4,5-~H]leucine but these were confounded by rumen-mixing problems. Findings obtained suggest that a lower proportion of microbial N may have been derived from rumen ammonia when the silage was supplemented with fishmeal but no differences in the extent of direct incorporation of leucine into microbial protein were observed. This could indicate an increase in microbial peptide uptake on the fishmealsupplemented diet. However, evidence was also obtained suggesting that the improvement in microbial protein synthetic efficiency with supplementary fishmeal was also due to the provision of a more continuous supply of nitrogenous substrates for microbial growth, as a result of hourly feeding.6. The results are related to the increased growth responses attained by fishmeal supplementation of this silage in the experiment of Gill et al. (1987).

Fishmeal supplementation of steers fed on grass silage: effects on rumen function, nutrient flow to and disappearance from the small intestine

“…kg -1 OM to duodenum [3] was applied for the fractionation of the estimated duodenal non-microbial-N into endogenous and undegraded dietary-N [4]. Feed N degradability in the two diets was calculated by difference from the quantity of undegraded dietary N flowing to the duodenum after allowing for microbial and endogenous-N flow [8]. Hence the equations used were:…”

“…The studies conducted by Dawson et al [8] and Beever et al [4] suggested that the responses from steers fed on grass silage with fishmeal may be associated with an increase in the efficiency of utilisation of dietary nitrogen (amino acids).…”

“…The greatest responses to fishmeal have generally been obtained with poor-quality silages, although again the responses are not always clear. This may in part relate to the changes in rumen metabolism or the changes in body tissue metabolism, or a combination of both [8].…”

Forage conservation in round bales or silage bags: effect on ensiling characteristics and animal performance

“…formic-acid-treated grass silage increased daily gains to 0.9 kg d -' when supplemented with fishmeal compared with 0.5 kg d-r for the unsupplemented group, without an increase in silage intake. Steen (1985) found no response in intake or animal performance in one trial, but in a second trial (Steen 1989) Dawson et al (1988) that the extra nonammonia N reaching the duodenum of fishmeal-supplemented steers fed grass silage is retained inefficiently and that the proportion of digestible organic matter intake fermented in the rumen is decreased by fishmeal suppleents suggest that for an explanation of the response to protein supplementation of silage diets we should look elsewhere than at amino acid supply, which presumably is in excess of requirements on such diets (Gill et al 1987 …”

Simulation model for particle dynamics in rumen of cattle fed sugarcane diet

“…Therefore, the addition of higher quantities of soluble nitrogen in diets supplemented with urea will not increase the amino acids in the intestine; neither will a source of rumen undegradable protein as soybean meal. Dawson et al (1988) reported that supplementary protein feeds of inherently low rumen degradability like soybean meal have direct effects on the amount of undegraded dietary protein passing to the duodenum, but can also increase protein flow by stimulating carbohydrate digestion and microbial protein synthesis. In general, if can be said that the new model demonstrated good capability to predict milk production from cows fed sugarcane based diets supplemented with low or high lipid content.…”