A. Klop

Effect of maize starch concentration in the diet on starch and cell wall digestion in the dairy cow

An in vivo experiment was performed to determine the effect of level of maize starch in the diet on digestion and site of digestion of organic matter, starch and neutral detergent fibre (NDF). In a repeated change-over design experiment, three cows fitted with a rumen cannula and T-piece cannulae in duodenum and ileum received a low-starch (12% of ration dry matter) and a high-starch (33% of ration dry matter) diet. Starch level was increased by exchanging dried sugar beet pulp by ground maize. After a 2-week adaptation period, feed intake, rumen fermentation parameters (in vivo and in situ), intestinal flows, faecal excretion of organic matter, starch and NDF were estimated. When the high-starch diet was fed, dry matter intake was higher (19.0 kg/day vs. 17.8 kg/day), and total tract digestibility of organic matter, starch and NDF was lower when the low-starch diet was fed. Maize starch concentration had no significant effect on rumen pH and volatile fatty acid concentration nor on the site of digestion of organic matter and starch and rate of passage of ytterbium-labelled forage. On the high-starch diet, an extra 1.3 kg of maize starch was supplied at the duodenum in relation to the low-starch diet, but only an extra 0.3 kg of starch was digested in the small intestine. Digestion of NDF was only apparent in the rumen and was lower on the high-starch diet than on the low-starch diet, mainly attributed to the reduction in sugar beet pulp in the high-starch diet. It was concluded that without the correction for the reduction in NDF digestion in the rumen, the extra supply of glucogenic (glucose and propionic acid) and ketogenic nutrients (acetic and butyric acid) by supplemented starch will be overestimated. The mechanisms responsible for these effects need to be addressed in feed evaluation.

Influence of DGAT1 polymorphism on response of dairy cows to ruminal supplementation of linseed oil

The DGAT1 gene encodes for the diacylglycerol acyltransferase enzyme which catalyzes the final step in triacylglycerol synthesis. Various polymorphisms have been reported for DGAT1. One of them, the K232A DGAT1 polymorphism in which lysine as the 232nd amino acid is replaces by alanine, is associated with increased milk yield, lower fat and protein concentrations (Grisart et al., 2001) and altered milk fatty acid (FA) composition (Schennink et al.,2007). Milk FA composition is, on the other hand, also affected by nutritional factors including dietary FA composition (Sterk et al., 2011). Until now, no literature data could be retrieved to establish whether the response in milk FA composition of dairy cows to changes in dietary FA composition is influenced by DGAT1 polymorphism. Therefore, a study was performed with 8 rumen-cannulated dairy cows in mid-lactation with different DGAT1 polymorphism, receiving either palm fat or linseed oil.