tThe effects of a shortage of dietary N and of a rumen protected CLA (rpCLA) supplementon DMI, rumination, rumen fluid characteristics, milk yield (MY), and milk N/N intake ratio(ENU) were studied in mid-late lactating cows. Twenty cows housed in 4 pens in groups of5, homogeneous for parity, days in milk (DIM) and MY, were fed on 4 different diets: with150 g (CP15) or 123 g (CP12) of CP/kg DM, with or without an rpCLA supplement (containing6.34 g/d of C18:2c9,t11 and 6.14 g/d of C18:2t10,c12). A 4 × 4 Latin Square experimentaldesign was used with periods of 3 wks, although the sequence of the 4 treatments (CP15or CP12, with or without rpCLA) was such that each group received CP15 or CP12 for 6consecutive wks. The CP12 diet was formulated from CP15 by replacing soybean meal withbarley grain to maintain similar energy, fiber content and feed particle size. Ruminationactivity, DMI, and MY were recorded daily. Rumen fluid was analyzed for VFA and ammoniaN content, and milk for quality traits. Nutrient digestibility was estimated using Lignin(sa)as a marker. Period, treatment and group (random) were included as sources of variationin the statistical analysis. Dietary CP restriction tended to reduce DMI (−7.7%; P = 0.09) anddigestibility, but increased time spent in rumination (+10%; P = 0.009), decreased rumenfluid ammonia N (−36%; P < 0.001), and reduced MY (−4.8%; P = 0.047) and milk proteincontent (−4.7%, P = 0.026); it had no influence on the ratio between energy-corrected milkyield and DMI. CP restriction reduced N intake by 122 g/d and N in milk by 14 g/d, didnot influence N in feces, but increased ENU from 0.31 to 0.36 (P < 0.01). A low marginalresponse of 115 g milk N/kg to the increased N intake from soybean meal was found. Theaddition of rpCLA tended to reduce DMI (−8.1%; P = 0.07) and decreased milk fat content(−15%; P = 0.002), but decreased N in milk only when added to CP12 (CP × rpCLA interaction,P = 0.016). A shortage of N supply increases ENU without apparent alteration of BW, BCSand blood metabolites. Long-term investigations to clarify the role of body N reserves andof a shortage of CP supplies on N partitioning are needed.
Influence of N shortage and conjugated linoleic acid supplementation on some productive, digestive, and metabolic parameters of lactating cows
SCHIAVON, STEFANO;CESARO, GIACOMO;TAGLIAPIETRA, FRANCO;GALLO, LUIGI;BITTANTE, GIOVANNI
2015
Abstract
tThe effects of a shortage of dietary N and of a rumen protected CLA (rpCLA) supplementon DMI, rumination, rumen fluid characteristics, milk yield (MY), and milk N/N intake ratio(ENU) were studied in mid-late lactating cows. Twenty cows housed in 4 pens in groups of5, homogeneous for parity, days in milk (DIM) and MY, were fed on 4 different diets: with150 g (CP15) or 123 g (CP12) of CP/kg DM, with or without an rpCLA supplement (containing6.34 g/d of C18:2c9,t11 and 6.14 g/d of C18:2t10,c12). A 4 × 4 Latin Square experimentaldesign was used with periods of 3 wks, although the sequence of the 4 treatments (CP15or CP12, with or without rpCLA) was such that each group received CP15 or CP12 for 6consecutive wks. The CP12 diet was formulated from CP15 by replacing soybean meal withbarley grain to maintain similar energy, fiber content and feed particle size. Ruminationactivity, DMI, and MY were recorded daily. Rumen fluid was analyzed for VFA and ammoniaN content, and milk for quality traits. Nutrient digestibility was estimated using Lignin(sa)as a marker. Period, treatment and group (random) were included as sources of variationin the statistical analysis. Dietary CP restriction tended to reduce DMI (−7.7%; P = 0.09) anddigestibility, but increased time spent in rumination (+10%; P = 0.009), decreased rumenfluid ammonia N (−36%; P < 0.001), and reduced MY (−4.8%; P = 0.047) and milk proteincontent (−4.7%, P = 0.026); it had no influence on the ratio between energy-corrected milkyield and DMI. CP restriction reduced N intake by 122 g/d and N in milk by 14 g/d, didnot influence N in feces, but increased ENU from 0.31 to 0.36 (P < 0.01). A low marginalresponse of 115 g milk N/kg to the increased N intake from soybean meal was found. Theaddition of rpCLA tended to reduce DMI (−8.1%; P = 0.07) and decreased milk fat content(−15%; P = 0.002), but decreased N in milk only when added to CP12 (CP × rpCLA interaction,P = 0.016). A shortage of N supply increases ENU without apparent alteration of BW, BCSand blood metabolites. Long-term investigations to clarify the role of body N reserves andof a shortage of CP supplies on N partitioning are needed.
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