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Degradability and utilization of dietary nitrogen sources commonly fed to dairy cows

University of British Columbia

Various forages commonly provided to dairy cattle were fed to cannulated steers in order to study dietary nitrogen breakdown and utilization. Feed intake and apparent digestibility of dry matter, fibre and nitrogen were monitored as well as microbial nitrogen production in the rumen. Two Holstein and two Ayrshire steers, each fitted with a re-entrant duodenal cannula were used. Two of the steers were also used before the cannulae were fitted. Five different forages were investigated: low quality grass hay (1.7%N), alfalfa cubes (2.3%N), high quality grass hay (2.7%N), Italian ryegrass (1.7%N) and orchard grass (2.1%N). For each forage, each steer was allowed a two-week adaptation period followed by a four-day digestiblity collection period. Fecal samples were obtained daily, and digesta samples were collected at the duodenum three times daily. Unfortunately, due to illnesses, only one steer was able to complete all of the digestibility trials with all of the forages. When low quality hay and alfalfa cubes were given, cannulation had no effect (p>.05) on feed intake or apparent digestibility of fibre and nitrogen. Only apparent digestiblity of dry matter was higher (p<.05) for the intact steers. Feed intake, and apparent digestibility of dry matter and nitrogen were greater (p<.05) for the higher nitrogen (alfalfa cube) diet. Forage type had no effect (p>.05) on feed intake, and apparent digestibility of dry matter and fibre when any of the forages were given to cannulated steers. Nitrogen apparent digestibility was greater (p<.05) for the higher nitrogen forages. The amount of feed offered (maintenance or ad libitum) had no effect (p>.05) on feed intake, dry matter, fibre and nitrogen digestibilities. In respect to apparent digestibilities and quantities of microbial nitrogen obtained at the duodenum, forage type had a significant effect on all parameters. The proportion of apparent digestibility of dry matter and fibre occurring in the rumen were greater (p<.05) for the lower nitrogen forages. The proportion of nitrogen digestibility occurring in the rumen was greater (p<.05) for the higher nitrogen forages. The ratio of microbial nitrogen: total nitrogen was greater (p<.05) for the lower nitrogen forages. The particular day of the digestibility trial or time of duodenal sample collection had no effect (p>.05) on apparent digestibilities or total microbial nitrogen. Feeding level had a significant effect on some of the parameters at the duodenum. Apparent digestibility of fibre and nitrogen and total microbial nitrogen were higher (p<.05) when the forage was fed ad libitum. The quantity of bypass nitrogen measured at the duodenum, and the apparent digestibility of the bypass nitrogen was much lower for the lower nitrogen forages.

Text

2010-04-22

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http://hdl.handle.net/2429/24037

Animal Science

University of British Columbia

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