Nitrogen (N) use efficiency in beef cattle is low (10–20%), resulting in large amounts of N excreted into the environment. The objective of this study was to evaluate the effects of chitosan inclusion and dietary crude protein (CP) level on nutrient intake and digestibility, ruminal fermentation, and N excretion in beef heifers. Eight Belgian Blue × Holstein Friesian cross beef heifers (752 ± 52 kg BW) were used in a 4 × 4 Latin square with a 2 × 2 factorial design. Factors were dietary CP concentration—high CP, 16% (HP) or low CP, 12% (LP)—and chitosan inclusion—0 or 10 g kg−1 dry matter (DM) offered at 50:50 forage concentrate ratio on a dry matter (DM) basis. Apparent total tract digestibility of DM, organic matter (OM), and CP were reduced (p < 0.001) with chitosan inclusion, whereas offering the HP diets increased apparent total tract digestibility of CP (p < 0.001). Offering the HP diets increased urinary N excretion (p < 0.001), while chitosan inclusion increased N excretion in faeces (p < 0.05). Ruminal pH was increased with chitosan inclusion (p < 0.01). There was a CP × chitosan interaction for rumen ammonia (NH3) concentrations (p < 0.05). Including chitosan in the HP diets increased ruminal NH3 concentration while having no effect on the LP diets. Urinary N excretion was increased with increased levels of CP, but chitosan inclusion increased the quantity of N excreted in the faeces.
The synchronous supply of energy and nitrogen (N) substrates to the rumen microbes on grass silage (GS)-based diets can potentially lead to reduced levels of N excreted in the urine. The objective of this study was to evaluate the effect of supplementing GS-based diet with carbohydrate sources differing in rumen fermentation profile on N metabolism of beef heifers. Six Belgian Blue × Holstein Friesian cross beef heifers (487 ± 29 kg BW) were used in a 3 × 3 Latin Square design (n = 6). Dietary treatments were: (RB) GS supplemented with rolled barley; (MM) GS supplemented with maize meal and; (SH) GS supplemented with soya hulls offered at 40:60 forage to concentrate ratio on a dry matter (DM) basis, at maintenance feeding (40 g DM/kg BW0.75). Carbohydrate source had no effect on DM, organic matter, or N intake or total N excretion and the amount of N excreted in the urine (p > 0.05). Animals offered MM excreted a higher percentage of N in the faeces and a lower percentage of N in the urine compared to animals offered RB (p < 0.05). There was a time by interaction for ruminal ammonia (NH3) concentrations (p < 0.01). Ruminal NH3 concentrations peaked at 2 h post-feeding for all treatments. At 3 h post-feeding, ruminal NH3 concentrations for the RB treatment remained higher compared to MM and SH treatments. Molar proportions and total ruminal volatile fatty acids were similar among dietary treatments (p > 0.05). Supplementing GS-based diets with different carbohydrate sources had no impact on the total level of N excreted or the amount of N excreted in the urine. However, there was a higher percentage of N excreted in the faeces and a lower percentage of N excreted in the urine when animals were offered MM compared to those offered RB (p < 0.05).
Chitosan (N-acetyl-D-glucosamine polymer) is a natural biopolymer, which is the second most abundant organic compound on earth, found in lower plants and some arthropods and crustaceans. Studies with ruminants have shown that supplementing with chitosan can alter ruminal fermentation, including higher propionate concentration and lower acetate to propionate ratio, improving the energy efficiency within the rumen though data on nitrogen metabolism is lacking. Therefore, the objective of this study was to evaluate the effects of chitosan with different dietary crude protein (CP) inclusion on rumen fermentation in beef heifers. Eight ruminally cannulated Belgian Blue x Holstein Friesian heifers (752 ± 52Kg BW) were allocated one of four dietary treatments in a 2 x 2 factorial Latin Square design (n = 8). Diets were offered as total mixed ration (TMR) consisting of grass silage plus concentrate. Diets were offered once daily ad libitum. Dietary treatments were as follows: high CP (16%) +/- chitosan (10g kg-1 DMI) supplementation (HP+) or (HP-) and low CP (12%) +/- chitosan supplementation (LP+) or (LP-). Experimental periods were 25d in duration (14 d dietary adaptation and 10 d sampling). Rumen fluid was collected via cannula every 2 h post feeding for analysis of ruminal pH, ammonia (NH3) and volatile fatty acids (VFA) over a 48-hour period. Data was analysed using Proc Mixed procedure in SAS. Significant differences were considered when P < 0.05. Dietary treatment had no effect on ruminal pH (P > 0.05). Chitosan supplementation had no effect on ruminal NH3 and VFA concentrations (P > 0.05), whereas, animals offered 16% CP had higher concentrations of ruminal NH3 (P < 0.001). In conclusion, supplementing a TMR diet fed to beef heifers with chitosan had no effect on rumen fermentation. However, reducing dietary CP concentration fed to beef animals resulted in lower rumen NH3 concentrations.
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