Paper-Lecture21 - Influence of Carbohydrate Source and...

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Unformatted text preview: Influence of Carbohydrate Source and Buffer on Rumen Fermentation Characteristics, Milk Yield, and Milk Composition in Early-Lactation Holstein Cows J. J. KENNELLY, B. ROBINSON, 1 and G. R. KHORASANI Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5 ABSTRACT The effects of concentrate to forage ratio and sodium bicarbonate (buffer) supplementation on intake, rumi- nal fermentation characteristics, digestibility coeffi- cients, milk yield, and milk composition were examined in 4 cannulated Holstein cows (100 20 d in milk). A 4 4 Latin square design with 2 2 factorial arrange- ment of treatments was implemented for 3-wk experi- mental periods. The 4 treatments were a 50:50 concen- trate to forage ratio with 1.2% of dry matter (DM) and without added buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. The forage component of the ration was a 50:50 mixture of alfalfa and barley and triticale silage, and diets were fed ad libitum as a total mixed ration. Although feed intake was not influenced by treatments, substantial treatment differences were observed for milk yield and milk composition. Cows fed high-concentrate diet had lower ruminal pH, ruminal acetate, and butyrate con- centrations, whereas propionate concentrations were significantly elevated. The addition of buffer, at both levels of concentrate inclusion, resulted in elevated to- tal volatile fatty acids and acetate concentrations. We concluded that altering the forage concentrate ratio in the diet of lactation cows influenced milk yield and milk composition, but the addition of buffer to the diet prevented the elevation in trans-C 18:1 fatty acids in milk fat, and related milk fat depression, associated with feeding high-concentrate diets. ( Key words: lactating cows performance, forage per- centage, buffer, rumen digestion) Abbreviation key: BCS = body condition score, FA = fatty acid, HCNB = concentrate to forage 75:25 without buffer, HCWB = concentrate to forage 75:25 with buffer, MCNB = concentrate to forage 50:50 without buffer, MCWB = concentrate to forage 50:50 with buffer. INTRODUCTION High-concentrate diets influence milk composition, especially milk fat content (36). The relative propor- Received November 17, 1998. Accepted May 28, 1999. 1 Present address: Great Northern Livestock Consulting Ltd., Box 1479, Westlock, AB, Canada T0G 2L0. 1999 J Dairy Sci 82:24862496 2486 tions of fatty acids ( FA ) in milk fat will also vary with the amount of grain fed (12). Grummer (14) suggested that diets that cause milk fat depression also change the concentration of specific FA in milk fat. For example, concentrations of long-chain FA ( 18 carbons) increase relative to concentration of short-chain FA because de novo FA synthesis in mammary tissue is reduced (16, 36). Gaynor et al. (11) and Selner and Schultz (31) proposed that the decline in percentage of milk fat, with a diet high in concentrate, may result partly from...
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Paper-Lecture21 - Influence of Carbohydrate Source and...

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