Abstract
The objective of this study was to evaluate the effects of four sources of starch on milk production and composition, nutrient digestion and blood metabolites of lactating Holstein cows. Four multiparous Holstein cows (708 ± 70 kg of body weight; 83 ± 9 days in milk) were used in a 4 × 4 Latin square design with 21-d periods. The concentrate portion of the diet contained wheat, barley, maize or potato as the primary source of starch. Intake of dry matter (DM) ranged from 18.7 kg/d to 19 kg/d, and was similar among treatments. Milk production was higher in cows fed the wheat-based diet compared with other diets while the milk fat concentration of the cows fed the maize-based diet was the highest. Milk protein concentration was unaffected by the source of dietary starch. Cows fed the potato-based diet had a lower milk protein, lactose and solid-non-fat yield. Milk yield/kg of DM intake and net energy for lactation (NE L )/NE L intake were higher in cows fed wheat-, barley- or maize-based diets compared with those fed the potato-based diet. Feed nitrogen efficiency was higher in cows fed the maize-based diet compared with the other experimental diets. Total tract apparent digestibility of organic matter, crude protein and ether extract were higher in cows fed the wheat- or maize-based diets compared with those fed barley- or potato-based diets; however, total tract apparent digestibility of neutral detergent fibre and acid detergent fibre were higher in cows fed the wheatbased diet compared with those fed the potato-based diet. These results showed that improved production performance in cows fed the wheat-based diet appeared to be because of greater nutrient digestibility and greater nutrient utilization efficiency. Furthermore, potato starch is not superior to grain starch as a readily available energy source for lactating dairy cows. Keywords: Nutrient digestibility, nutrient efficiency, plasma metabolites, wheat, barley, potato, maize
Highlights
The increase in milk yield of dairy cows that results from their genetic improvement requires the use of large amounts of concentrates that are rich in energy and crude protein (CP) to meet their nutrients requirements (Cabrita et al, 2009)
Fat corrected milk (FCM) and energy corrected milk (ECM) were higher in cows fed wheat, or maize-based diets compared with those fed barley- or potato-based diets (Table 2)
Silveira et al (2007) reported higher 4% FCM in cows fed maize-based diet compared with those fed barley-based diet, but, in a study by Gozho & Mutsvangwa (2008), 3.5% FCM was higher in cows fed barley- and maize-based diets compared with a wheat-based diet
Summary
The increase in milk yield of dairy cows that results from their genetic improvement requires the use of large amounts of concentrates that are rich in energy and crude protein (CP) to meet their nutrients requirements (Cabrita et al, 2009). Non-fibre carbohydrates (NFC) may provide 30 to 45% of the diet on a dry matter (DM) basis (Hall et al, 2010). Root crops such as potato have been used in dairy rations, but have been replaced by grains and maize silage because of labour costs (Eriksson et al, 2004). Starch is the major nutrient providing energy from these cereal grains and potato These cereal grains and potato differ in their starch content, with wheat containing (DM basis) 77% starch, maize 72%, barley 58% (Huntington, 1997) and potato 63% (Wang et al, 2009). Differences exist among these starch sources in their rates
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