Effects of Postrumen Starch Infusion on Milk Production and Energy Metabolism in Dairy Cows

Abstract

Two experiments were conducted to determine effects of postrumen starch infusion on milk production and energy and nitrogen utilization in lactating dairy cows. In experiment 1, four cows in early lactation fed grass silage and concentrates were continuously infused into the duodenum with water or 700, 1400, or 2100 g of purified maize starch daily for 10 to 12 d in a 4 x 4 Latin square design with 2-wk periods. Starch infusion increased milk yield linearly and decreased milk fat concentration in a quadratic manner such that increases in fat-corrected milk and calculated milk energy yield were minimal except at the highest rate of infusion. Changes in milk energy output suggest that even at the highest infusion rate metabolizable energy supplied by infused starch was used for tissue energy or oxidized. In experiment 2 energy and nitrogen balance were measured in four cows in late lactation fed a mixture of dehydrated lucerne, grass silage, and concentrates during the last 6 d of 2-wk abomasal infusions of 1200 g of purified wheat starch daily or water in a balanced switchback design with 5-wk periods. Measurements of fecal starch concentration indicated nearly all the starch infused was digested, but decreased fecal pH and apparent nitrogen digestion suggested an increase in hindgut starch fermentation. Starch infusion decreased urine nitrogen output in part because of increased tissue nitrogen retention but had no effect on milk nitrogen output. In absolute terms, numerical decreases in feed energy intake and energy digestion reduced the recovery of starch energy infused as digestible and metabolizable energy, but in terms of changes in total energy supply with starch infusion, 79% was recovered as metabolizable energy. Starch infusion had no effects on heat or milk energy but increased net energy for lactation due to a numerical increase in tissue energy, implying that in late-lactation cows, starch digested postruminally was used with high efficiency for tissue energy retention as protein and fat.

Post-ruminal or intravenous infusions of carbohydrates or amino acids to dairy cows 1. Early lactation

“…No problem with soft faeces and diarrhoea were observed during starch infusions, and the dosage used here was lower than in other post-ruminal glucose or starch infusion studies (Hurtaud et al, 1998 andReynolds et al, 2001). In a typical Norwegian dairy cow diet, which mainly consists of grass silage and a barley/oats based concentrate mixture when cows are fed 14 to 18 kg DM, abomasal infusion of 257 to 376 g of starch will increase the post-ruminal supply by approximately 100% (Volden, 1999).…”

“…The restriction of the order of the treatments; avoiding two subsequent intravenous infusions, were done across substrates so there should be no systematic order of the substrates. Several studies have demonstrated a positive effect on milk production of infusing nutrients into the gastrointestinal tract or blood (Metcalf et al, 1996;Reynolds et al, 2001;Aikman et al, 2002). However, limited data are available comparing both post-ruminal and intravenous AA and glucose supplementation in the same experiment and animals.…”

“…Small intestinal starch digestion may also provide glucose for absorption and can increase the glucose supply to the mammary gland directly and therefore reduce liver gluconeogenesis. However, it may also allow greater glucose oxidation by peripheral tissues (Reynolds et al, 2001) and thus reduce glucose delivery to the mammary gland. The effects of intestinal glucose or starch supply on milk protein synthesis have proved to be highly variable (Hurtaud et al, 1998 andReynolds et al, 2001) and our understanding of the fate of glucose liberated during starch digestion in the small intestine is rather limiting.…”

“…However, it may also allow greater glucose oxidation by peripheral tissues (Reynolds et al, 2001) and thus reduce glucose delivery to the mammary gland. The effects of intestinal glucose or starch supply on milk protein synthesis have proved to be highly variable (Hurtaud et al, 1998 andReynolds et al, 2001) and our understanding of the fate of glucose liberated during starch digestion in the small intestine is rather limiting. As far as we are aware, no direct comparison of post-ruminal starch and intravenous glucose infusions has been done and our hypothesis is that intravenous glucose supplementation will give similar milk protein response as increased intestinal starch supply.…”

Prediction of nitrogen use in dairy cattle: a multivariate Bayesian approach

“…Of the diet-based strategies for influencing ENU reviewed, reducing diet crude protein (CP) was the only strategy that conclusively improved ENU . Other methods to manipulate the amount, rate, and site of digestion of dietary energy have had variable effects on N utilisation despite popular theories about the effects of energy-protein synchrony and post-ruminal starch digestion (Reynolds et al 1996;Rius et al 2010). Mathematical models of N use and digestion become an important tool to investigate the discrepancy between theory and practice through identification and quantification of dietary and animal factors that influence ENU.…”