Nutritional practices on Manitoba dairy farms

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Abstract
A survey was conducted on 40 randomly selected dairy farms across Manitoba to document nutritional practices and diet compositions, and study relationships between diet composition and milk production. Samples from all feeds, diets, and the bulk milk tank were collected and analyzed. Inclusion rates of feed ingredients were recorded. Production data were obtained from Western Canada Dairy Herd Improvement Services (WCDHIS). Component feeding and total mixed ration (TMR) feeding were used in 37.5 and 62.5% of herds, respectively. Only 24% of TMR-fed herds used two or more TMR. The medians of dietary contents of crude protein (CP), rumen degradable protein (RDP), rumen undegradable protein (RUP), and neutral detergent fibre (NDF), and milk urea nitrogen (MUN) were 18.3% dry matter (DM), 12.2% DM, 5.7% DM, 34.8% DM, and 15.6 mg dL-1, respectively. On average, diets contained 6.2% more net energy for lactation (NEl), 35.9% more RDP, 15.8% less RUP, 74.6% more calcium (Ca), 51.9% more phosphorous (P), 44.9% more potassium (K), 116.1% more magnesium (Mg), and 4.2% more sodium (Na) than the estimated requirements based on the average milk production and estimated DM intake of the cows on each farm. In 25% of TMR-fed herds, TMR was coarser than recommended. Milk yield, and milk fat percentage were affected by breed, but were not affected by feeding practice (TMR or component feeding), diet composition, and physically effective NDF (peNDF) determined as the percent age of feed particles retained by the 8- and 19-mm screens of the Penn State Particle Separator multiplied by dietary NDF. Milk protein percentage was positively correlated to RUP. MUN was positively correlated to RDP, RUP, NDF, and days in milk (DIM). Reductions in dietary CP, RDP, Ca, P, Mg, and K could reduce nutrient excretions to the environment without reducing milk production and health. Increasing dietary RUP content could improve milk production on Manitoba dairy farms. Key words: Dairy cattle, milk production, protein, fibre, minerals, particle size.

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