TY  - JOUR
T1  - Influence of Site of Casein Infusion on Voluntary Feed Intake and Digestive Function in Steer Calves Fed a Sudangrass-Based Growing Diet
AU - , E.G. Alvarez AU - , R.A. Zinn 
JO  - Journal of Animal and Veterinary Advances
VL  - 6
IS  - 2
SP  - 249
EP  - 256
PY  - 2007
DA  - 2001/08/19
SN  - 1680-5593
DO  - javaa.2007.249.256
UR  - https://makhillpublications.co/view-article.php?doi=javaa.2007.249.256
KW  - Casein
KW  -infusion
KW  -intake
KW  -metabolism
KW  -cattle
KW  -NDF
AB  - Four medium-frame steer calves (269 kg BW) with cannulas in the rumen, abomasum and proximal duodenum were used in a 4 H 4 Latin square experiment. Steers were allowed ad libitum access to the basal diet, offering  120%  of  the  previous  days  DMI.  Treatments  consisted  of  infusing sodium caseinate (300 g d <SUP>1</SUP>) into: 1) rumen,  via  the  ruminal cannula; 2) abomasum, via ruminal cannula; 3) abomasum, via the abomasal cannula and 4) proximal duodenum, via the duodenal cannula. Dry matter intake averaged 97 g kg<SUP>-1</SUP> BW<SUP>.75</SUP> and was not affected (p&gt;0.20) by treatments. There were no treatment effects (p&gt;0.20) on flow of OM, NDF and ADF to the small intestine. As expected due to the high ruminal degradability of casein (86%), flow of nonammonia N to the small intestine was greater (p&lt;0.01) when casein was infused postruminally then when it was infused ruminally. Casein infusion did not affect (p&gt;0.20) ruminal degradability of dietary N. Observed ruminal degradability of dietary N was in close agreement with expected (49 vs 51%, respectively) based on the National Research Council’s Level 1 model. There were no treatment effects (p&gt;0.20) on ruminal NDF digestion. However, ruminal ADF digestion was greater (5%, p&lt;0.05) when casein was infused postruminally then when it was infused  ruminally.  As  expected,  postruminal casein infusion increased  postruminal digestion of the OM (21%, p&lt;0.05) and N (12%, p&lt;0.01). There were no treatment effects (p&gt;0.20) on total tract digestion of OM, N, ADF, NDF and GE. Casein infusion did not influence (p&gt;0.20) flow of chyme to the small intestine or ruminal turnover.  Flow  of  chyme  to  the small intestine was primarily a function of DMI (chyme, L = 5.3 + 12.1DMI; R<SUP>2</SUP> = 0.50). Postruminal casein infusion increased (75%, p&lt;0.01) the soluble N content of duodenal chyme, but it did not affect (p&gt;0.20) its tonicity, averaging 264 mOsm. The relationship between tonicity and passage rate of chyme from the abomasum was small ( R<SUP>2</SUP> = 0.05 ). Casein infusion did not affect (p&gt;0.20) ruminal DM content or liquid volume, averaging 17.5 g DM kg<SUP>-1</SUP> BW<SUP>.75</SUP> and 471 g  kg<SUP>-1</SUP> BW<SUP>.75</SUP>, respectively. There were no treatment effects (p&gt;0.20) on indigestible NDF intake (averaging 26 g kg<SUP>-1</SUP> BW<SUP>.75</SUP>) or ruminal NDF fill (averaging 41.1 g kg<SUP>-1</SUP> BW<SUP>.75</SUP>). Casein infusion did not affect (p&gt;0.20) ruminal pH, but ruminal acetate:propionate molar ratio was greater (p&lt;0.10) when casein was infused ruminally. Ruminal acetate:propionate molar ratio was also greater (p&lt;0.05) when casein was infused into the abomasum versus the proximal duodenum. We conclude that independently of N status, increasing protein supply to the small intestine will not facilitate an increase in DM intake. Instead, limits to maximal DM intake in cattle fed forage-based diets appears to be largely a function of ruminal NDF fill capacity and rates of passage and digestion of NDF.
ER  -